Fairey Overdrive Overhaul

Annoyingly, the overdrive sprung a leak somewhere, dumping its oil into the transfer box. I suspect it was the smaller seal between the input and output shafts – I didn’t know where to locate it within the output shaft on the initial rebuild at the start of the 109 project as there is no obvious shoulder for it to sit against. This time I drifted it down firmly as far as it would go and found a firm seat, so it should work better.

I have taken a great deal of photos to document the whole strip and rebuild to create this as a “how to” feature – there are a lot of people buying up second hand overdrives from forums, shows and e-bay, so hopefully this will help them refurbish their units cheaply and effectively. It assumes the overdrive is already off the vehicle.


overdrive top cover off The first task is to remove the top panel by removing the four 1/2″ bolts. The panel may be stuck on its cork gasket, so have a replacement ready. Next, remove the selector fork and shaft by taking out the 1/2″ pinch bolt in the fork and undoing the selector shaft detent and retaining grub screws almost entirely. The shaft can be tapped out of the rear of the casing, allowing the fork to be removed. Retain the fork’s brass pads – they’re unlikely to need replacement. The selector shaft front opening’s plate can be removed for O-ring replacement by removing the two small bolts.
Overdrive rear cover off With the fork removed, undo the four 1/2″ nuts on the rear cover. The cover should come off with careful prying. Be careful not to damage the mating faces of the cover or main casing. There is a large O-ring around the rear cover that should be replaced on rebuild. Keep the cover’s nuts and spring washers in the cover during the work.

Now the back end of the input shaft is visible. Use circlip pliers to remove the small circlip. Put this to one side, followed by the washer beneath it. This exposes a second circlip, which must also be removed. Then may follow one or more shims, followed by a three-piece thrust bearing set. Place all these parts in order in a container or tray.input shaft circlips and bearing

With these clips and bearings removed, the input shaft can be removed from the unit. This is the the shaft that can be seen by looking inside the geared output shaft on the front of the overdrive. It can be pushed out from the back. Once the front end emerges from the output shaft, withdraw it completely and put it to one side. There may be a thrust bearing set comprising of a thick washer (with a bevel on the inside edge), a thin washer and the needle roller race near the thick end. Retain these on the shaft. This bearing may have stayed inside the output shaft, in which case you should remove them Input shaft bearings and tubesnow. There will also be a pair of tubular spacers and a roller bearing in the rear gear of the overdrive – remove these and place in the same container as the other input shaft parts.

Next, to get the output shaft and rear units out, you have to free the layshaft (its teeth will interfere on the mainshaft gears’ synchros, causing damage if you try to force them out with the layshaft in place). To do this, lever the rear end of the layshaft out with a screwdriver until there is enough exposed to grab hold with a pair of grips. It can be resistant as a vacuum ban develop in the forward case’s shaft withdrawing layshaftrecess. Rotating as you pull may help. Withdraw it completely and allow the layshaft gear cluster to drop into the corner of the overdrive sump.

Use a soft faced mallet to tap the output shaft aft, drifting out the rear gear and bearing set. It’s very unlikely that the outer ball race bearing will need replacement, so don’t be tempted to remove the big criclip holdin the rear gear in its bearing. Inside the front of the gear you will find a thrust bearing and roller bearing set. remove them and lay soft mallet drifting rear gear outthem in sequence with a container for the whole rear gear assembly.

As you remove the rear gear unit, the synchro hub is likely to drop. This is not a problem, but make sure you retain the spacer ring that sits between the rear gear and the synchro hub with the rear gear. Remove the synchro hub complete with brass rings, and then withdraw the output shaft from the front of the casing. There is a further thrust bearing set between the front face of the synchro hub and the output shaft. Keep these together. Note that the outer part of the synchro and the two brass rings are synchro and adjacent bearingssymmetrical, but the inner hub is not – the nosed side is to the rear, while the flat side for the thrust bearing faces the front on reassembly.

Next, withdraw the output shaft through the front of the casing. If the complete thrust bearing kits came out with the inner input gear and the synchro hub in the earlier stages, there will be no more metal parts on the output gear – the only remaining attached part will be the blue rubber seal inside the front end (quite far in), which should be removed and binned. Make a careful check on the thrust bearing faces at the rear gear bearingsback end and deep inside the front (inside of where the seal was) for thrust bearing washers – you really don’t want to loose those and they do tend to stick with oil vacuum.

Remove the layshaft cluster. There will be two roller bearings and a tubular spacer inside, and a thrust bearing pack for each end (probably still in the casing). These thrust bearings are likely to have matching shims to set the layshaft cluster endfloat. In this case, one shim can be seen next to each output shaftthrush bearing kit.

This should leave the casing with only the front bearing and seal. Lever the seal out, ensuring that the casing is not damage in the process. Clean and inspect the casing and bearing. Again, it’s unlikely that the bearing will need replacement, but if it does, it should be drifter out from behind and a replacement squarely and gently pressed or drifted in from the front. A new seal should be fitted at this point.

INSPECTIONcasing and front bearing

Check each component for wear or damage. Some wear to the splines on the shafts and synchro unit will be evident, and is unserviceable if more than 1mm has been eroded. The bearings are usually OK, but if there is evidence of any scoring, pitting or corrosion, renew them. Polishing of the bearing tracks is acceptable as long as there is no wear ridge.

Close attention should be paid to the condition of the clutch sleeve (the spline part that replaces the gear on the vehicle’s gearbox main shaft and the input shaft – the fine spline wear, and if they wear too much thy’ll strip, leaving the vehicle witlayshaft partshout drive regardless of overdrive or gear selections.

The plastic mesh bush inside the input shaft supports the end of the gearbox mainshaft, substituting the bearing in the standard aluminium housing on the back of the transfer box. If it is damaged, it will cause rapid wear of the gearbox mainshaft’s bearing surface. Damage or wear to the splines or bush require replacement of the complete part.

All seals, O-rings and circlips should be replaced as a matter of course, and are sold in kits. Shim packs are available cheaply. The bigger components are more input shaft splinesexpensive, and some of the bearings are specific to the unit and could be difficult to obtain, but Rovers Down South are now manufacturing the overdrive new and can supply parts direct in the US or via John Craddock in Europe.


In Haynes’ finest tradition, reassembly is the reverse of stripping.

Start with the replacement of the front main bearing if required, and the front main seal. The selector shaft’s frclutch sleeveont O-ring sited inside the lozenge shaped cover on the right hand side of the casing should be renewed now too.

Also fit new O-rings to the rear cover, layshaft and rear end of the selector shaft. Use the input shaft as a drift to set the new inner oil seal in its correct position inside the output shaft.

If the synchro unit came apart during the strip down, or if you find missing or worn out detents, here’s how to rebuild it. First, If you’re going to open it up, lay it on top of a towel, and lay a heavy cloth over it. this will stop the ball bearing shooting across synchro partsthe room and into oblivion as it comes apart. Lift the outer ring and sharply tap the inner hub down. The two should separate, allowing you you with draw the three springs for check or replacement.

all fitted and hub loweredtwo down, one to gofitting ball bearingsleeve and hub

To reassemble the synchro, lay the outer ring flat and hold the inner hub up inside it. Fit the springs and square doughnuts (making sure the curve of the doughnuts matches the curvature of the hub) and allow the inner hub to sink so that it’s sitting on them. Fit the ball bearing to one spring and press it in, forcing the doughnut down as the balls presses in. Push the doloose layshaftughnut down as far as possible so that the ball bearing is retained by the outer sleeve. Repeat for the other two detent balls, then sink the inner hub down fully into the outer sleeve.

Next is to set the end float on the layshaft. Oil and fit the bearings and spacer inside the layshaft gear cluster. Using LM grease, assemble the front end layshaft thrust bearing kit and any shims that were present with it on strip down. Use just enough grease that parts stick together. With the overdrive casing sitting rear end up, fit the front bearing/shim pack to their seat in the casing, then install the cluster. Next assemble the rear thrust bearing/shim pack like the front, and slide them into position. Be very careful to ensure the shims are fitted on the casing side of each bearing pack. Then use a long handled tool down the layshaft aperture to “stir” thlayshaft front thrust bearing e bearing packs and cluster in to alignment and insert the layshaft. The complete layshaft should have a very small amount of endfloat, only just perceptible by hand. If it’s obvious, it excessive and more shims must be inserted. If there is no endfloat, remove a shim (very unlikely). Once the endfloat has been correctly set, remove the layshaft and fit a long narrow tube, bar or screw driver that will allow the cluster to move laterally while holding the bearing packs roughly in place.

inserting input shaftoutput shaft fittedNow fit the output shaft through the front of the casing, oiling the seal and seal land first. Oil the input shaft all over and ensure its thrust bearing (against its wide section) is set the correct way around – thick washer against the shaft’s “cup” end (bevelled edge against the shaft’s radius corner), needle race, then thin washer – and insert it it carefully through the output shaft. Be very careful not to damage the inner seal. Stop with the input shaft’s rear end just protruding from the back of the output shaft by 1/2″.

rear bearing fittedsynchro fittedOil the synchro’s thrust bearing and refit to the rear of the output shaft before fitting the synchro unit, complete with brass rings, behind the output shaft. Next fit the rear gear spacer ring on the synchro hub’s nose, then fit the rear gear unit, complete with its internal thrust and roller bearings, through the rear of the casing. The rear bearing can be tapped into place with a mallet or pressed in using the rear cover as necessary.

alignedstirringNext, “stir” the layshaft cluster and bearing packs again to align them for layshaft insertion. If you have a pool of oil in the bottom of the layshaft aperture, try to remove it by inverting the overdrive or wicking it out with a cloth. This is to make the shaft insertion easier – with the shaft’s locating hole full of oil, the shaft is difficult to press down fully and springs back out. If you can’t get all the oil out and the shaft’s tail is protruding excessively, don’t worry – the next step of fitting the rear cover (after installing the new O-ring on the cover) will draw the shaft down into its proper position. the oil in the aperture will be slowly forced out of the way. Just close down the rear cover squarely and slowly, turning each nut an equal amount in sequence, using a short handled 1/4″ drive socket only – air tools will draw the cover down too quickly, forcing the shaft down faster than the oil can dissipate, likely causing hydraulic cracking of the overdrive casing.

selectror shaft top grub screwselector shaft detent (lower) grubscrewFinish by inserting the selector shaft (with its new O-ring) through from the back of the casing so its end is just showing in side the top hole. Fit the fork and feed the selector shaft through it. Make sure the elector shaft is rotated so that the detent grooves face downwards, the long slot up, parallel to the head of the grub screw, and tap it through until the slot for the fork’s pinch bolt lines up with the fork’s bolt holes. Insert the bolt, but don’t full tighten yet. Titghten the top and bottom grub screws fully and back of 1/2 turn a dab of thread lock is useful). Fit the top cover with a new cork gasket and loosely fit the four corner bolts.

overdrive with lik rodThe final tightening of the fork pinch bolt has to be done once the overdrive is fitted in order to allow the selector shaft to rotate to align with the selector lever link rod – if the pinch bolt has been tightened and the alignment is slightly out, the link rod’s clevis pin will not fit through the hole on the front end of the selector shaft. Once the selector rod and shaft and rod are connected, the overdrive should be selected to neutral. with the shaft held in neutral by the detents, carefully hold the synchro hub in exact centre so that an equal amount of the brass teeth an be seen each side, and tighten the pinch bolt. Smear both sides of the cork gasket heavily in LM grease and fit the top cover tightly. Fill the overdrive unit with the correct amount of EP 90.

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  1. Bob Cairns says:

    Excellent information. I have just purchased a second hand unit and may need some parts. Can you recommend a supplier of the seals and clutch sleeve


  2. Hi Bob.

    All parts are available from Rovers Down South, based in New Orleans, I think. They bought the licences to the Fairey design from Superwinch, and manufacture them new.

    If you’re in the UK, you can get all their parts through John Craddock, but they’re not cheap. A more limited supply of parts at lower prices are available from LEGS or directly from Superwinch (Tavistock, Devon).

    The seal kits are about £30, and include both shaft seals, the selector rod O-rings and large rear cover O-ring.  A new clutch sleeve is about £45.

  3. I check the oil in my toro overdrive through the top panel – the normal fill hole has been damaged so I can’t even get it off. Works great.

    Also, the breather tube is top importance. I have a breather line running from the rear diff, teed at the OD, then running up to a socket on the schnorkel. Also works great.

  4. Hi Nick,

    Great this information you share!
    I’ve bought a second hand overdrive, and via this information it’s easier to strip it down.

    My first inpression of the status of my overdrive is that it’s in a good shape. The only thing i have to change is the “input gear”(RTC7187)and ofcourse seals.

    If anyone has a good input gear, let me know.

    Greetz from Holland

  5. Hi Nick,

    I fitted my Series 1 with an overdrive some time ago and it is fairly noisy, as in it whines loud enough to be clearly heard above the rest of the racket and be annoying. Before I rebuild it, any likely culprits that spring to mind to give specific attention to?


  6. Hi Nick

    Thanks a million for all the info. I stripped mine down before I found your website. I’m so glad I did find it as you saved me a good few hours of playing Overdrive Tetris…

    Keep up the good work!

    From the small fishing Village at the Southern Tip of Africa called Cape Town, Thanks again.

    1965 IIA 88″ 2.25 Diesel

  7. Hi Ian,

    My overdrive whined from new, and continued to do so throughout my ownership of it,including after its rebuild. I found it to be the noisiest part of the transmission, and was clearly audible at almost all speeds when engaged. I don’t think its whine signifies any fault – they have a reputation for their noise. They are still very worthwhile, because they are still much quieter than the engine when exceeding 50mph without an overdrive


  8. John Knott says:

    Thanks Nick. Another very well put together and illustrated article. Well done!

  9. rob jenkins says:

    excellently put together, thanks for putting so much effort into producing this literature

  10. Gerrit Gärtner says:

    Hi Nick,
    Thanks for your great work, it´s really encouraging.

    I have a question about an overdrive I bought; it seems to be a Santana GLR 120A, bigger than the Faireys, containing nearly 1,8 l of oil.
    Mounted to the car (no problem with your descriptions) he´s screaming, that seems to be quite normally, but afer a couple of miles at about 60 miles he gets really hot – nearly impossible to touch it – so I took it off again.
    The main geaerbox got hot too, but less than the overdrive.

    What do you think about?

    Greetings from Austria
    Series III 109 – 1974

  11. Hi Gerrit,

    Overdrives always run very hot, regardless of which type you have. I now use a “Roverdrive” with epicyclic gears instead of conventional main shaft and lay shaft configuration (like the Fairey and Toro designs, the latter of which is what I suspect you have). The Roverdrives share oil with the transfer box (they are not sealed), and come with a replacementtransfer box bottom plate with cooling fins. Roverdrive also recommend the use of semi-synthetic oils to resist the heat.

    Even without an overdrive, the transfer box becomes far too hot to touch – unlike the main gear box, which has a locked main shaft in 4th so does no work in top gear, the transfer box has no direct drive output, all of the energy going through the gears. That produces a lot of heat, whether it be a Series unit or the later LT230s from Range Rovers, Defenders and Discoverys.

    I’d recommend using 75W90 synthetic or semi-synthetic oil in the transfer box and overdrive, but apart from that, I wouldn’t worry. Fairey and Toro overdrives usually are noisy from new, especially when engaged. If the oil has no coarse particles in it when drained and you have no selection problems or heavy clanks and bangs, it’s probably fine.


  12. martin says:

    Hi Nick

    Thanks for taking the time to post up all this information I am sure that it will be useful as I think I will need to strip my newly acquired overdrive that although looks in good condition both inside and out will not rotate freely, just waiting to clear the mess of my bench and get the spanner out!!

    Thanks again


  13. Hi Nick,

    Thanks for your post and pictures. very helpfull. I just acquired a Fairey OD for my 109SW SIIA. Just one question, as my landy is a LHD, does left support bracket and link rod exist ? If not, can it be modified to be fitted on the left instead of right ?
    Many thanks from France,

    Thanks again,

  14. Hi Cedric,

    I’m glad these blog entries are useful to people.

    There would probably be a way of modifying the selector lever and linkage to sit on the left side of the transmission – the steel bracket would just be inverted and the pivot and lever fitted as before but in reverse. The problem would be the linkage from the lever to the selector shaft, as it wouldn’t reach around the back of the overdrive from the left side. You could make up a link, but you may find that it flexes too much because of the long lateral distance between the selector shaft and the axis of the linkage.

    If you look at the selector lever itself, you should see a kink or bend near one end, very close to the threaded section. That bend is deliberate – it is used on the pivot end, not the handle end, to lean the lever towards the driver, whichever side he sits on. The lock nut is used to hold the lever firmly in whichever position it is screwed into. If your lever is straight (some early levers were, and some levers have been replaced with threaded bar), then remove it, heat with an acetylene torch until red hot and bend in a vice. The bend should be just next to the end of the threaded section and should be about 10 degrees, but you can increase or decrease that as suits you. Bend it too much and you won’t be able to screw the lever into the pivot as it will hit the transmission tunnel as you turn it, but that’s the only limitation.

    Good luck,


  15. Cedric says:

    many thanks for your input. I’ll work on the first option, reverse the linkage.


  16. Before you do anything permanent, check the amount of space between the left side of the gear box and the tunnel cover – it’s much tighter than on the right hand side and might not be wide enough to accept the linkages without modifying the tunnel cover, floor panel and seat base.

  17. It looks it will not fit. 1/ my tunnel cover already has a big hole on the left side for the gear box oil tapping, 2/ yes it’s quite tight 3/ my linkage has a slight angle, by reversing it, it will not fit. I abandon this option and will go the easy way by bending the lever as you suggested.
    Many thanks for your advices.
    A very last and small question : I quite like the green knob. Not sure it’s genuine, but with the yellow and red, I find this quite fun. At present, I only found supplier in the US, but they don’t want to shipp … Any idea in the UK ?
    Have a good week-end. Cédric

  18. I thought it might be too tight to squeeze the linkage down the left side. At least by keeping it standard, replacement parts will not be too hard to find.

    Some Fairey units and PTO levers were green, but I think most were black. Some were spherical, like the late gear lever knobs, while some were flattened like the red and yellow lever knobs, so you may find all sorts at auto-jumbles and the second hand sales at the big shows. However, I rather suspect that the Roverdrive lever shares the same thread, being Canadian and still having a preference for Imperial threads and fittings (the unit itself has a mix of Imperial and Metric fixings), so its green knob may well fit. It does have the name “Roverdrive” engraved in white, along with the engaged and disengaged lettering, though. Martin Hogan of RockyMountainspares.co.uk may well be able to supply one for you – he is an unusually friendly and helpful chap.

  19. Many thanks !!!

  20. Oliver says:

    I am currently puzzled with the overhaul of my fairey.
    I have disassambled the unit and have replacec all worn parts.
    Especially the input gear has been worn and needed replacement.
    Now I fit the unit back in the vehicle but have problems egaging the OD. With the top cover open and the bolt of the fork loosen, I even can not egage it using a hadle/srew driver. The synchro just won’t slip over the input gear teeth. Are there different part specs under the same part number ???
    I can not imagine any assembly bug – Any ideas ?
    Your support is kindly appreciated.



  21. Hi Oliver,

    I’m not aware of any parts variations that are incompatible, but there have been a few changes over the years – the design was available as a factory option on the SI, so has been around for a considerable time. As far as I know, the changes have been the bearings (same measurements but different numbers and thicknesses of needles or balls), details in seals and fixings, and variations in the selector lever and knob. Nothing that should prevent full operation. remember though that I am just another enthusiast – I’m not a professional mechanic and have only ever worked on this one Fairey unit that I had on my 109.

    I suspect your problem is due to one of three things:
    1) The selector shaft is mis-set and needs adjustment of its rotational position or the grub screws need adjustment;
    2) The synchro unit detents have a fault, either a broken spring or one of the square tabs inserted with its camber set the wrong way around, or;
    3) The teeth inside the sliding synchro section are directly aligned with the teeth on the baulk ring and gear rather than slightly offset, needind as small rotational movement of the gears to allow the parts to engage.

    Try slackening the grub screw under the selector shaft detent half a turn, leaving the fork pinch bolt loose, to determine if it’s scenario 1. Try idling the engine with the transfer box in neutral and the main box in first gear and then selecting overdrive engaged and disengaged 9with the pinch bolt tight) to test scenario 3. If neither of those tests is successful, I think you’ll have to strip it down again to take a close look at the synchro hub assembly.

    Good luck,


  22. oliver says:

    thanks a lot for your fast and comprehensive response.
    I think I can eliminate 1, since even if I seperate the funktion of the selector shaft and fork by taking out the bolt completely and trying the synchro to engage with the input gear synchro teeth with a srew drive I do not succeed.
    2 can be probabely disqualified, too since I have had the OD assembled and working with the synchro assemply before deciding to change the input gear.
    3) even when aligning the synchro teeth manually engaging OD is not possible.

    I strongly suspect the synchro teeth of the new input gear to be out of spec and will take the OD apart for further inspection.
    I will post new findings as soon as available.



  23. I think we need to clarify a few issues. You say you have replaced some parts, including the input gear. Please list all the parts you have replaced and clarify what you mean by input gear – the input gear is the gear at the very back of the main shaft, just behind the synchro unit and its baulk ring and just ahead of the rear main bearing, but many people refer to the clutch sleeve (the splined boss which is fitted to the gear box main shaft in place of the transfer box input gear as the overdrive input gear).

    We also need to clarify which direction of selection is blocked – engaged, disengaged or both; I understand you have the synchro in neutral and get the impression you can’t select it to the “engaged” position, which is where the synchro’s outer sleeve moves aft towards the rear cover, but we need to clarify that.

    If you did replace the input gear as I defined it, and it is the “engaged” position that is troublesome but “disengaged” (synchro sliding forward) is OK, then I suspect a problem with the new input gear. In that case, you could start by counting the number of synchro teeth on the new and old gears (put a blob of paint on one to use as a datum) and compare the teeth to those on the baulk ring (they should have similar positions, widths and diameters). The fact that the problem only appeared after replacing the input gear supports this potential diagnosis.

    Get back to me when you can – we should be able to get to the bottom of this, and these sorts of problems are invariably something very simple.


  24. oliver says:

    yes, we are on the same page. With “input gear” I refere to RTC 7187.
    I have replaced this part and I am experiencing a problem with this part. Engaging the OD – moving the synchrounit sleve over the input gear teeth backwards- is not possible. As you mentioned, I suspect the synchro teeth at the new input gear to be the problem. This is why I have asked if there are different types of RTC 7187 in the market.
    I will disassemble the unit and make respective measurements. I had difficulties to get this part since all dealers in GB and even in Australia are out of stock. I finally suceeded getting it in Austria. So I expect, that I have to rework RTC7187 if feasable.
    I give feeback after disassembly.
    If you send an email to o_moll@hotmail.com, I can reply and share pictures ….



  25. Ian from Leeds says:


    Thanks for sharing this page! With the info above and some other webpages, I’ve begun to rebuild my overdrive 🙂 It was working fine but whined (screamed actually) at high speed which i gather is likely to be down to worn needles. How did you assess the condition of the needle bearings? I am thinking of replacing them all whilst it is stripped but some may be okay and not need replacing! How can I tell which bearings to replace and which ones are okay?


  26. Hi Ian,

    Those needle rollers are hard to find, so visit a bearing specialist and get replacements before you bin them. Fairey overdrives do whine when engaged, and that’s just a standard characteristic – mine was brand new when fitted and whined from day one. It actually sounded like a turbo charger while accelerating. If the unit’s noise is uncomfortable, then it does need attention, but it’s not necessarily the bearings that are failing; it could be the gears.

    Look very closely at the bearings, and check all of them, not just the needle bearings. Remember that the needle bearings are just thrust bearings – they only carry loads because of the helical nature of the gears and as such their loadings are not very great – it’s the roller and ball bearings which take the tangential or radial loads and carry most of the forces. Look for any roughness, pitting and discolouration. A bearing that is failing will feel rough or make grinding noises when turned with a little pressure, though a good bearing can do the same when completely dry. test them with just a little WD40 on them but no heavy oil or grease and this will quickly reveal any bad bearings.

    However, don’t aim for a silent overdrive – it shouldn’t be noticeable when “disengaged”, but a conspicuous whine when “engaged” is simply “what they do” and nothing to worry about. You will hear people telling you that it’s faulty and should be silent in all conditions, but in my experience those sorts of individual either have hearing damage or so many other loud defects on their vehicles that the overdrive’s whine is masked.


  27. Ian from Leeds says:

    Hi Nick,

    Thanks for your reply. I meant the cylindrical roller bearings but will check all as you say. It was definately a scream when at cruising speed (of the ear-damaging type) hence the strip down. I will be happy with a whine when finished.


  28. Ian from Leeds says:

    Hi Nick,

    I’ve checked all the bearings and now have a shopping list as long as my arm! The endfloat appears okay at the moment but I’m concerned that it will need shims when the new bearings go in – was this your experience? You say the shims (RTC7189) are available cheaply but I can only find them at Craddocks for £17


  29. Hi Ian,

    I did need to add some shims on my rebuild, but I didn’t replace any bearings. I got my shims from Superwinch at their Tavistock office – they had some old “new stock” parts in their stores and sent them to me for a very reasonable price. I find that Craddock tend to be quite expensive for most things, though I never bought any overdrive parts from them because I rebuilt my unit before they were appointed RDS’ main UK distributor.

    When you set the end float, make sure you leave a small amount to allow the oil to get through the bearings and to allow for thermal expansion of the bearings or casing. The manuals don’t have any figures, but a bout 0.2mm seemed to work well for me and is similar to the settings in the main gear box.


  30. Hi Nick,

    Great resource. Gave me the confidence to have a go at the overdrive.

    Anyway, I wondered what the “blue” seal was that you mentioned in the 6th paragraph of the strip down section. I just stripped my overdrive and I neither found a blue seal ar any seal in the location you mentioned.

    For clarity, this is inside the main output shaft and is a seal between the output and input shafts?

    Even if it is missing, what seal kit do I need to order to get a replacement?



  31. Andy from NZ says:

    Hey Nick,

    Thanks for the excellent info. I managed to fit my secondhand Fairey overdrive after I gave it a clean and new oil.

    It runs quietly but gets really hot. By hot I mean at least 80 degrees and I am to afraid to drive it any further. When people mention overdrives get hot is more than 100 degrees ok?

    I put some molybond hi load grease in there hoping that the molybdenum disulfide would help. It all runs smoothly and quietly but still gets just as hot. I reckon if I had a plastic breather like you do it would melt.

    The molybond hi load has a max temperature rating of 180 degrees. I could start a grass fire! On the plus side I could cook eggs.

    The transfer case I would guess gets to about 50 degrees.

    I have two theories, 1) someone overheated the previous oil and now its all carbonated and stuck to the bearings and gears causing heat. 2) is that since it didn’t have a breather, dirt got in there and its about to blow up.

    Another final slightly different question. Somewhere I read that you shouldn’t put different lubricants into the transfer case because it will go through and affect one of the clutches. But I put LM grease / molybond on the main gear when I installed it as recommended. Which advice is correct?

    Kind Regards

  32. Hi Tom,

    It’s all a while ago now, so some of the details are a little fuzzy, but as I recall, the seal between the main shaft and output shaft was the blue one, and it sat on the wider end of the mainshaft, forward of the thrust bearing. As this was the same on the old seals in my unit, I had assumed that this was normal. You may be able to get an “old new-stock” seal kit from Superwinch in Tavistock, Devon, or from Rovers Down South via Craddocks, though I gather RDS spares support is getting more difficult. Any seal specialist should be able to help you if you can give them the numbers normally printed (typically raised) on the face of the seal.

    Sorry I can’t be more helpful.


  33. Hi Andy,

    Overdrives and transfer boxes get very hot – too hot to touch without getting burnt after a long run. This is true of not only Series vehicles but LT230s on Defenders and Discoverys too – the main gear box doesn’t work all that hard on a Series vehicle because it spends most of its time in 4th gear, which just locks the input pinion and main shaft together, but the transfer box has the full torque going through the gear train at all times, so high speed driving really works it hard, especially behind a Tdi or V8. The same can be said for any kind of overdrive, whether it be a Fairey/Toro/Roverdrive type bolted to the back of the Series transfer box, a GKN or Roverdrive behind an LT230, or the overdriving 5th gear in an LT77/R380 (Defender, Discovery and RRC main gear box), where engaging the overdrive directs the motive effort through the gear train instead of just locking the input and output components together.

    So, I’d be surprised if your transfer case only reaches 50oC – I’d expect both transfer case and overdrive to reach well over that. Keep an eye on the oil colour when you drain it. It will pick up some greyishness and slight glitter, but shouldn’t be too grey if replaced on schedule (12,000 miles) – you should still be able to make out the main “dirt-free” colour. If that base colour is similar to the original straw-yellow, then all is well. If it’s a burnt caramel colour, then it’s cooking. Synthetic W75 transmission oil should deal better with heat issues, but excessive heat in the transmission can only be caused by one thing (assuming the engine isn’t a monstrously tuned Tdi or V8); friction in the bearings. If the units are quiet, bearing faults are unlikely (though far from impossible). It’s important than bearing pre-loads and end floats are set correctly – they should be tight enough to prevent excess movement but free enough to allow unrestricted rotation.

    Using different lubricants in different parts of the transmission is no problem if the seals and breather are all working correctly – a Defender with a GKN overdrive will have a different lubricant in each unit (MTF94 on the gear box, either EP90 or W75 synthetic in the LT230 (depending on vehicle age), and ATF in the GKN (Roverdrives use whatever is in the transfer box as they share the oil)). Contamination of Series transmissions’ EP90 with some grease will not harm anything. I just use mineral EP90 in all of my transmission behind a Tdi, with occasional additions of Slick 50 transmission additive and have had no trouble, even though the casings are too hot to touch after a decent drive. If you know the bearing pre-loads in the overdrive and transfer box are correct and are still worried, you could fit a Rocky Mountain transfer box bottom plate, which has cooling fins like a motorbike engine and is also stiff enough to reduce weeping.

    Hope that is of some reassurance.


  34. Chris B says:

    I have just completed a full strip and rebuild of my Fairy Overdrive with no bits left over , and replaced all , repeat all , bearings and thrust washers . The teeth all look in very good order with no noticible wear . Endfloats are shimmed to 2 thou’ ( maybe 3 tops ).
    However , whilst the unit no longer screams on overdrive overrun , it is as noisy as ever under acceleration – 4th.gear being particularly noticable .
    Perfectly quiet though when only 1:1 straight thru’ is engaged .

    Any good ideas please ?

    It sounds to me just like a back axel with the backlash incorrctly adjusted , though these are normally only noticible on over-run .
    I wonder if it could be the case that there is something wrong with the setting between the layshaft gear and the output shaft gear .
    When shimming the layshaft I did it at the rear of the layshaft because it was easier to get at and , in the absence of any specific instructions , it seemed best to shim the shaft towards the drive surfaces .

    I am trying to avoid having to take the unit in and out on a trial and error basis – and would much appreciate any advice .

    I should mention that I recently did a full job on the main gearbox , and it purrs .

  35. Fairey overdrives howl. It’s as simple as that. Some people claim that they only howl when badly worn and that their Fairey is quiet. I suspect their either deaf or have such a cacophony of other noises in their LR that they can’t hear it. As long as the bearings on the lay shaft are OK, and the bearings between the main shaft and output shaft are good, then any whine will be from the gears meshing, and there is nothing you can do about that. My (Superwinch built) Fairey howled like a banshee from new, especially when accelerating – it sounded a lot like a turbo charger. You mainly notice the noise accelerating in 3rd or 4th because the overdrive innards are turning faster than in 1st or 2nd and because when accelerating the gears and bearings are under the greatest load. Any slight movement of the lay shaft gears from relocation or alteration of the shims could change the gear mesh ever so slightly, which could increase howling, but that will polish itself off within 500 miles of engaged use.

    Just drive it as it is for a running in period and then drain and replace the oil. I really doubt you have any problems – Faireys all whine loudly, and that is not just a dismissal of problems but experience of brand new, old and freshly rebuilt units.

    I hope that puts your mind at ease.


  36. Thank you very much , Nick , for your advice . I’ll play it as you say and hope it beds in a little .

    At least it’s running cool .

    regards , Chris B

  37. Nick , you were absolutely right . After a couple of hundred miles it has become noticably quieter – obviously bedding-in .
    I still remain absolutely staggered that a British engineering company of good reputation could put this product on the market with it’s name on .
    Wailing and moaning from new .
    Though thinking back , I grew up in the Midlands in the sixties , and remember exactly what the engineering standards and attitudes were like .
    It took the Japanese and the Germans to drag us out of the Fred Dibnah age .
    An apocryphal story came out of Longbridge at the time of their first collaboration with the Japanese . They queried a Japanese engineering drawing , sent to them , saying there were no tolerances on it . The Jap’s said ” No , we have given you the size . That is the size you make it ”

    Anyway , thanks to you for your help . C

  38. Firstly, thank you for providing useful guidance and illustrations. I often recommend your web site to others.
    Secondly, I have found it impossible to obtain all of the replacement parts nowadays, and so I embarked on identifying all of the bearings, and if necessary arranging manufacture of other parts. Please do not consider this to be an advertisement, but if helpful, I can assist where others may fail.
    Shop4Autoparts.net are also a useful source. I list some items via eBay, but I may also be contacted directly.
    Thank you,

  39. Ian, could you please send me contact details that can be displayed on here for others’ benefit?

  40. See “Fairey Overdrive” bearings, gasket kits, seal kits and installation kits listed on eBay for information (Manchester). Use eBay questions/messaging in the first instance.
    Thank you,

  41. Howard L says:

    I have started to rebuild a Fairey overdrive that I bought in bits a few years ago. When I bought it I inspected all the parts and bought all the parts necessary to rebuild it, but never quite got round to doing it. The laygear (RTC7192) had a chipped tooth on it so I sourced a good second hand one from eBay. The problem that I have is that the needle bearings and spacer (RTC7193) are a good/easy fit in the old laygear but the needle bearings won’t fit in the “new” one (the spacer fits) – the internal diameter is about 1mm less (35mm v 36mm). I tried pressing one of the needle bearings in but broke it. Should the needle bearings need to be pressed in (the “new” one doesn’t have the same wear marks internally) or have I somehow picked up a dud one ? Are Range Rover ones similar? I have counted the gear teeth and they are the same. Do I just need to be a bit more careful “pressing” them in ?

    Thanks in advance for help.

  42. It sounds like you have an incompatible part, either from an overdrive from a different licence owner (Superwinch or Rovers Down South), or from a different design spec, but I’ve never heard of different evolutions of the Fairey unit – I was under the impression that they didn’t change throughout their production history. It could be from a Toro overdrive, made by Bearmach, or from a Range Rover overdrive, both of which were similar but not identical to the Fairey unit. A fault in the manufacture of the new part is also not impossible, especially if it was a pattern part, which is likely using ebay, and this was a problem that affected another reader of this blog, who’s pattern replacement gear didn’t have the same number of synchro teeth.

    Whatever the cause, bearings should never be tight as they will seize; only bearing races (the circular tracks) should be tight on a shaft or seat, but the bearings themselves should be free to move easily. Chips in teeth are very subjective, and while replacement is the ideal, the damage is sometimes small enough that it shouldn’t cause any trouble – if the chip is small, dress it so that the edges are smoothed and there are no protrusions to damage the teeth on the meshing gear and just re-use the original shaft. If you can email me a photo, I’d be happy to give you my opinion (remember I’m not a gearbox specialist, though).


  43. Howard L says:


    Thanks for your reply. You are right. I found that the replacement laygear had ‘Ribas’ stamped on it in very small letters and looking on the web, this seems to be an “improved” version of the Fairey overdrive used by Santana. Anyway I sourced a brand new lay gear from John Richards Surplus and have moved on to my next problem…I’ll post again if I can’t resolve it ‘;-)


  44. Howard L says:


    Thanks for all the info on the website, I couldn’t have done it without you since my overdrive arrived as a box of bits. It is all back together now and is looking good.


  45. I’m glad to hear that you have managed to complete tue rebuild, Howard, and am very pleased that the blog was helpful – it makes writing it worthwhile to know that people find it useful.

    Thanks for keeping in touch and letting me know of your success.


  46. davidh says:

    I have just rebuilt my newly aquired overdrive using your excellent guide as I had a problem with 2mm endfloat of the output shaft. I thought it may be a collapsed bearing inside the overdrive however I have found that with the rear endcap off, the rear bearing moves in the aluminium casing when the output shaft is pushed in from the front.

    I am thinking of using some Loctite 641 Bearing retainer compound medium strength to stop the bearing moving, however I am a bit concerned that this may inhibit removing the bearing in future rebuilds. Also, this compound has a max operating temp of 150″C and the overdrive will get hot!

    Is my proposed fix viable ?

    I would welcome any advice on how to proceed.

    Many thanks


  47. Hi David,

    Check the bearing closely for any wear as it controls the end float on the two concentric shafts. Check for axial as well as radial play, and try to twist the races out of parallel. Any movement other than rotational indicates the bearing has failed.

    If it’s OK, then fitting it with the seating compound is a good idea. It will make removal more difficult in the future, but not especially so – you could just warm the casing and bearing outer race with a blow torch to cassette compound to release. I have used this compound on a few bearings on my vehicles to good effect, most notably the gear box main shaft rear bearing and carrier, stopping them spinning at their seats (making swarf and noise) and stopping the usual oil loss into the transfer box.

    Good luck.


  48. Mike Cramb says:

    Hi Nick,
    I recently bought a Fairey o/d on Ebay it was supposed to be reconditioned but it wasn’t. Its going into my 1958 Series 1 109 inch ute.
    I have all the bearings and seals and a new input shaft but cant find a Lay gear anywhere they are out of production i’m told . I sourced most of the parts here in Australia and the rest from Craddocks UK. Any help locating a lay gear Part # RTC7192 would be much appreciated.

  49. Hi Mike,

    There were three manufacturers: Fairey, long since gone, Superwinch of Tavistock (Devon) and Rovers Down South (New Orleans). Finding Fairey stock is unlikely, but I got the parts for my overhaul from Superwinch’s old stock – they had been out of production a while, but still had some stock of parts. RDS also stopped making overdrives a while ago, but if you can track them down, they may have old stock. Craddocks were the UK supplier for RDS, while Rovers North (somewhere on the US East Coast) did a lot of work with them. Dunsfold Land Rover have stocks of all sorts of old bits and pieces, so would be worth a try. Other than that, all you can do is trawl forums and ebay for another overdrive to rob of its shaft, but that is financially risky as you have already learned the hard way. Good luck!

  50. Mike Cramb says:

    Thanks Nick
    I will let you know how I get on.. I gather from the Forums that I have googled up that I am not the only one looking for this part.

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