Fairey Overdrive Fitting
Thursday, March 15th, 2007
Having rebuilt the Fairey overdrive, this post shows how to fit the overdrive to a standard transmission. It shows the whole procedure except for the installation of the selector lever and bracket, but I’ll try to explain that further on. This guide is applicable to refitting an overdrive or fitting one to a vehicle for the first time.
Start by chocking the wheels and cleaning the outside of the gearbox and transfer case. It doesn’t have to be spotless, but you don’t want any debris falling in while it’s open, so scrape of all the loose rubbish, degrease with “Gunk” (or similar) and a stiff brush, and give it a thorough rinse with a hose.
The standard transfer box has a dished circular plate at the rear which holds a bearing for the rear end of the gear box’s main shaft, secured by six studs and nuts. The nuts on my unit were 15mm, but I suspect most units have 9/16″ nuts. There are two inspection covers on the top of the transfer case, each secured with four studs and 1/2″ nuts. The rear bearing carrier and upper (left hand) inspection plate need to be removed.
With these two panels removed, the rear end of the gearbox main shaft and the transfer box input gear (on the main shaft) are visible. The gear is retained by a castellated nut, which in turn is secured with a tab washer. With the gear box and transfer box in neutral, rotate the main shaft until the one tab engaged in the nut. Once this tab is at the 12o’clock position, select 1st gear to lock the main shaft in place.
Use a hammer and drift to lever up the tab and then undo the castellated nut. This nut has a standard right hand thread but is on very tightly. LR have a special tool to fit the nut, but a hammer and drift (large flat screwdriver) work equally well through the top inspection aperture. Remove the nut, the tab washer, the spacer washer and the gear. Retain these with the bearing carrier.
Inspect the main shaft for wear – look at the splines and the rear bearing surface. It’s unlikely that there will be any major faults here, but it’s always worth checking. Also make sure that the condition of the “clutch sleeve”, which is the overdrive’s replacement for the input gear, is in good order – the fine outer splines are prone to wear. If more than 25% worn, I’d strongly recommend replacement. If you have a new tab washer for the overdrive, make sure you use this on assembly, as the standard tab washer’s tabs are too long and foul the inside of the overdrive’s shafts. If you do not have a dedicated overdrive tab washer and can only source a standard type, file 1mm off each tab end.
Thoroughly grease the overdrive’s clutch sleeve with LM grease internally and externally, or better still (if you can find it), Rocol Anti-Scuff Paste. Make sure that the exterior bearing is well packed as it will get little lubrication once the overdrive is installed. Fit the clutch sleeve with the outer splined end towards the rear of the vehicle, followed by the spacer washer, special tab washer and castellated nut. With the gear box still in 1st gear, use the special tool or hammer and drift to tighten the castle nut as much as possible and then tap in the tab which aligns (you may need to select neutral and rotate the main shaft again to find the aligned tab/slot, and even tap the castle nut slightly tighter or looser to get the alignment perfect).
Once the tab is engaged in the castle nut’s slot, refit the top inspection panel with a thick smear of grease on each side of the gasket. Fitting this panel now will help prevent foreign objects falling into the transfer case.
Now prepare for the overdrive fitting. The overdrive main shaft (input shaft), recessed inside the larger output shaft, must have a generous application of LM grease or ASP in the gearbox main shaft bearing (the perforated plastic surface as far in as possible) and around the splined areas where it engages on the clutch sleeve. Fit the gasket, again with a heavy smear of grease on each side, to the transfer case studs. Make sure the six nuts and lock washers are easily to hand. Ensure that the gear box and transfer box are in neutral.
Lift the overdrive into position from below the vehicle, carefully feeding the geared output shaft through the aperture. It should push most of the way in with little resistance, but may stop short. If this hang up occurs, it’s because either the output shaft gears have not meshed with the transfer box intermediate gear cluster or the overdrive’s main shaft and the clutch sleeve splines are not meshing. Either way, rotating the casing of the overdrive back and forth while easing it forward should cure the problem. If this is not possible because the casing is already on the studs, flicking the starter motor with 1st gear will do the trick. If it hangs up with about 1/2″ to go, then this is the castle nut tab washer catching on the main shaft – remember the standard tabs are too long.
With the overdrive butted up against the transfer case, fit the top pair of lock washer and nuts, only turning the nuts on a couple of turns to prevent any possibility of the overdrive falling out. Then slide the overdrive out against the nuts. The reason for doing this is that two of the studs have sections of overdrive casing behind them, and it’s impossible to get the nuts onto their studs with the overdrive fully seated. Once these two washers and nuts are fitted, wind them on, reseat the overdrive and fit all the washers and nuts, tightening them up in an “opposite pairs” sequence.
Fitting the lever is relatively simple with the box and floor in situ. Fit the bracket to the back of the gearbox upper housing with the two existing bolts. Drill a pilot hole at a point 108mm above the foot well floor and 54 mm(4cyl engines) or 41mm (6cyl engines) forward from the floor’s rear corner (not the back end of the tunnel as the seat base slopes) through the tunnel cover and just into the bracket.
Remove the bracket and measure where the drill mark is in relation to the bolt hole. Transfer these measurements onto the tunnel cover and these will be the pivot hole centre. Use a tank cutter to cut a 2″ hole at this point.
Accessories, FAQ, Transmission
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March 10th, 2008 at 16:48
The nuts for the rear bearing housing are 3/8″ BSF which is approximately 19/32″AF spanner size in the absence of BSW/BSF spanners.
May 3rd, 2008 at 17:33
What are the tubing arrangements onto the cover plates – is it some system for auto-oiling?
May 3rd, 2008 at 18:12
Hi Paul,
They’re just for a remote breather, as I felt that the existing small hole would allow easy dirt and water ingress. the silicone pipe joins a gearbox breather and runs up into the engine bay.
June 21st, 2008 at 13:28
Hi!
Are the overdrives available on any site for a Series 3 LWB 109 & a DEfender 110 station wagan?
June 21st, 2008 at 15:40
Hi Prithvi,
The Fairey design OD for Series Land Rovers is now produced by Rovers Down South in New Orleans, USA. The UK distributor for the unit or parts is http://www.johncraddock.com . For a only slightly more money, you can also get the Rocky Mountain “Roverdrive” (SX model for Series), which is quieter and tougher, though slightly harder to engage. Their website is http://www.roverdrives.com , and includes contacts for ordering. The Toro model (similar to the Fairey) is obsolete, and very hard to get parts for.
For Defenders, you have two choices – the GKN overdrive, which is a solenoid actuated unit (a switch is added to the main gear stick, with no extra lever), or the Rocky Mountain DX, which is very similar to their SX model, and is lever actuated.
I now use the RM Roverdrive SX, having sold this Fairey unit, as the older model would not cope for long with the torque of the Tdi engine in my 109. So far, I’m very pleased with it – it’s quieter, and doesn’t need weekly topping up with oil.
Nick.
February 27th, 2009 at 10:52
Nick,
Just to thank you for all your work in providing the info on overhauling and fitting a series 3 O/D.
Am just about to start on mine, and your info will be most useful.
March 29th, 2009 at 15:37
We have just reviewed your page on fitting an overdrive, and have come across the problem where we 1/2″ to go (As detailed in one of the paragraphs), but have tried what you have suggested. Is there anything else that could cause this this?
March 30th, 2009 at 09:15
Hi Simon,
First of all, see if it’s just the splines on the input shaft and clutch sleeve misaligned. Try engaging first gear (so the engine will hold the clutch sleeve splines in their position), high range and overdrive “engaged” or”disengaged” – anything but neutral. Then rotate the transfer box gears (by rolling the vehicle a foot or so, or by jacking up and turning a wheel) while gently pressing the overdrive housing forward. This should align the splines and allow the unit to slide forward against the transfer case.
At that 1/2″ gap, the other likely culprit is the locking tab washer between the conical castellated nut and the clutch sleeve *the input piece of the overdrive that replaces the transfer box input gear). It’s probably one or more of the un-bent tabs fouling the inside of the overdrive’s input shaft. Fairey (and subsequent licence builders) used a special tab washer that was identical to the standard LR supplied one except for having shorter tabs. I would suggest you either remove the current tab washer and file the tabs down a little, or use a vacuum cleaner while filing to catch the particles as you file it in situ (the former would be the preferred method).
The only other cause that I can think of is that one or more of the mounting studs has unwound when the nut was removed, and is now sticking out of the transfer casing more than it should and is pressing against part of the overdrive casing. It’d just need winding back in with pliers.
Good luck – let me know if you still have any trouble.
Nick.
May 17th, 2009 at 07:33
thanks mate this is a great resource. it has made the task of fitting an overdrive to my ex army series 3 109 not such a daunting task.
July 22nd, 2009 at 18:40
First, thanks very much indeed for the information: I had literally no idea of what is involved in getting the overdrive installed. I’d had it done ‘professionally’ with the previous two gearboxes (!); hence installing the third gearbox myself…
Second, are there any tricks involved in getting the overdrive OFF the old gearbox? I’ve undone all the nuts and it seems to be glued in place.
Cheers,
Roger
July 23rd, 2009 at 14:22
There are no real “tricks” as such Roger – it’s all relatively simple.
Chock the vehicle and put the hand brake on. Drain the overdrive. I put the gear box, overdrive and transfer box in nuetral so that the helical gears can freely rotate while the unit is withdrawn. Then disconnect the selector rod and shaft by remoing the split pin and clevis pin.
When you undo the overdrive retaining nuts, you’ll find that some of them hit the overhanging parts of the casing before they’re fully off. Don’t worry about that – undo all the nuts as far as possible, and you will then be able to shunt the overdrive partially away from the transfer box to finish off the last few turns on the awkward nuts.
Thye unit should pull straight off, but a lot of people use sealant on the gasket, so you may need to tap it off with a soft mallet. I use grease on gaskets – it seals just as well, but doesn’t stick or make a mess.
To undo the nut retaining the clutch sleeve on the main shaft, rotate the main shaft by hand until you can see the locking tab which has engages the castle nut, then engage 1st gear. Use a hammer and small chisel (or cheap screw driver) to bend back the tab, then undo the nut. If the shaft rotates as you try to undo the nut, then the engine is turning over. Using a flywheel locking tool will solve that problem (a scrap R380 reverse light switch works well). If the clutch is slipping, then you’ll have to remove the the gear box top cover to try to jam the gears with a sutable tool. The clutch will also need attention.
I hope that helps.
September 6th, 2009 at 13:41
Hi,
Fitted my overdrive yeasterday and all is working well. Thanks for the instructions. I was more than ready for the job after reading them.
Sisky
May 14th, 2010 at 10:57
Hello Nick.
Was wondering if you can help me with my Axle Rebuild on my swb series 2a landrover. im at the stage of fitting the diff bearing and i know for sure that there should be 1 x shim fitted onto the shaft before fitting the bearing. The problem is i have got 2 shims which look identical but cannot remember where it come from.Is there a chance the 2 x shims were just stuck together or should the other shim go on after the bearing?
May 17th, 2010 at 16:52
Hi Kevin,
I assume that it’s a Rover diff, being a SIIA and also an 88″. There are shims against each bearing on the pinion. The “inner” end has the bearing fitted first, followed by the shim, and the “outer” end (with the pinion fitted to the diff casing) has the shim followed by the bearing, followed in turn by a spacer (539745) of similar diameter but thicker than the shims, a larger washer (FRC4586) and then the pinion flange. The only other shims in the diff are on the planet gears which accept the half shafts, set to mesh correctly on the non-shimmed pin axis planet gears. The diff carrier position and end float are set by adjustment of the big castellated nuts that press against the carrier bearings.
It’s possible that the shims you have were added together to meet the required distance of one single shim of a thickness that was unavailable, or it may be that they were erroneously put together on one side of the bearings. The only way of telling is to assemble it the way you think it came apart and testing the mesh and backlash of the pinion and crown wheel. Sorry I can’t be more specific.
May 17th, 2010 at 23:04
Hi Nick,
I came to this page as I am about to remove and refit my Fairey overdrive – many thanks for the commentary, I first fitted it about 25 years ago and no longer have the instructions.
Re Kevin’s comments on the diff bearing (presumably the pinion bearing) I am not sure about what you replied.
I have just finished my axle rebuilds and replaced the oil seals on both Rover diffs. On one diff there were four shims behind the outer bearing and two thin ones had broken because they had been incorrectly assembled with the thin shims against the bearing race. The LR manual on setting pinion preload requires two of the thicker shims (about 30thou each) and then smaller ones in between – as required to set the pinion preload to 7-12 lbs. This is measured by fitting the pinion nut to 85ft-lbs and then measuring the force required to turn the pinion.
On one diff I needed two 6thou shims and 1 on the other to get the preload right. In each case this was in addition to the 30thou ones.
May 18th, 2010 at 17:38
Thanks, Steve – I was working from the LR Parts Catalogue, not having done a diff rebuild myself.
June 11th, 2010 at 21:12
hi nick. am so glad i have found the info on fitting and overdrive unit. i have an eagle rv fibre galss shell on a range rover classic chassis. i have a 4spd manual and also a spare 4 spd manual ( with overdrive) ready to take off the donor gear box and fit, firstly the truck is in ibiza and i fly out in 5 weeks time. i plan to remove and fit in 1 day and then tinker (on other bits of the truck ready for the trip)for another day then drive it back to the uk to finally finish it (thinking of a wade ro34 supercharger etc). (the truck had been out there for my summer hols for 5 yrs)
what would you reccomend i replace when removing from the donor one and installing on the truck one. ie gaskets ,bearings, the appropriate tap washer etc etc.will not have time to overhaul the over drive unit though ! also while i am in that area i would like to service the gearbox. oil filter (if one ?) and overdrive seperate oil ?(or is it shared ??
so in a nut shell. is it do-able in the i day i have and any info or experience on the gearbox and overdrive i have would be great. i dont know what make it is. it just has a lever as you have explained to be pushed back and forward to be engaged etc. it was taken from a v reg range rover 4 spf 3.5 v8. i also have the exact engine and box in my truck but minus the overdrive. so i just want to put it in.
thanks shaun
June 13th, 2010 at 18:22
Hi Shaun,
Unfortunately, the RRC has a very different transmission to the type featured in this blog, and though the Fairey Overdrive for the RRC is broadly similar in design to this one, I don’t know what differences it has. I would expect it to suffer spline wear on the clutch sleeve in the same way as the series unit, so that could be a useful spare to take with you. Other than that, it’s impossible to predict what servicing it needs without testing and inspecting it. Good luck, though!
Nick.
June 15th, 2010 at 20:05
thanks for the advise nick , will look into it further and see if i can find someone who knows that type well
July 9th, 2010 at 14:06
Great work Nick. Quick question if I may. Have just bought a 2nd Hand Overdrive to repair aling with an empty casting.
Both look the same but only the empty casting has the Fairy name details on the case.
Any idea who made the case with no name?
Regards
Pete
July 11th, 2010 at 09:36
Hi Pete
My guess would be that your casing was made by Superwinch – my Superwinch overdrive had no markings and I believe they were the only licence holders for the design after Fairey disappeared except for the current holder, Rovers Down South (of New Orleans), who mark their casings with the raised letters “RDS”.
The casings and innards should be interchangeable, needing only the variation of the shims used at the back of the main shaft to account for production tolerances, but it’s not something I have ever tried. RDS still manufacture all parts for the overdrives, so can supply any parts you need.
Nick.
July 20th, 2010 at 12:08
Thanks for your Prompt response Nick!
Regards
Pete
December 28th, 2010 at 18:04
Hi Nick, just found puddle of oil under my overdrive. Had closer look and overdrive unit covered in oil. Took off top plate and unit half full of oil, to top of dipstick. Assume oil seal (part no RTC7173) has failed causing oil to migrate from transfer box and escape through the breather hole on top plate of overdrive unit. Would you agree, and if so is it much of a job to replace this seal assuming I can still get hold of one.
December 29th, 2010 at 19:37
Hi Huw,
A failed oil seal will normally allow oil to migrate from the overdrive into the transfer box, not the other way, because the transfer box oil level should be significantly lower than the overdrive’s. However, I’ll wager that your main gear box oil has migrated back to the transfer box, as is extremely common, overfilling the transfer box and back filling the overdrive until it loses oil through its top cover.
There are several things you can do to deal with this, and all have been covered in the transmission section of this blog.
1) Use a remote breather system on the three gear boxes, using silicone tube and ideally some steel unions (brake bleed nipples would work well);
2) Regularly check the oil levels of the three units, draining down the over-full transfer box and topping up the other two as necessary (made easier if you fit the military type gearbox top-filling cap and tunnel cover and fit Rocky mountain dipsticks to the gear box and transfer box);
3) Replace the gear box’s main shaft rear seal and ensure the rear bearing carrier is fitted into the gear box casing with Locktite bearing seat compound (similar but not quite the same as thread lock) – it is this joint that causes most of the oil migration from gear box to transfer box, not a faulty seal, and it is common for the bearing carrier to spin in the casing, wearing it further and creating swarf in the transfer box, main shaft play and excess end-float, eventually causing gear box issues like jumping gears or difficult selection in addition to a worsening oil migration problem. This can only be undertaken with the gear box removed and stripped down, though, so you’d best live with 1&2 until a rebuild is required. Be warned – almost all recon units, including LR factory units, have omitted bearing seat compound and will require stripping again to rectify, so you’re better off getting the manuals and tools or an experienced friend and doing it yourself. This was covered in the most recent post about rebuilding the gear box(early 2009).
Good luck.
January 4th, 2011 at 19:13
Many thanks for you reply Nick. I shall do what you suggest and will get the gearbox out ASAP and treat it to an overhaul. Regards, Huw.
January 5th, 2011 at 09:28
You’re welcome, Huw, but before you do go to the trouble of removing the transmission and overhauling it, do check the three oil levels – I’d put money on the cause of your trouble being the main gear box oil moving aft, but it could be something else. If you find the main box low and the transfer box over-filled, it’ll confirm the diagnosis.
April 28th, 2011 at 14:05
Hi Nick,
Ive had my S3 SWB for 15yrs now (1st n only vehicle), it came with an OD unit and is a Fairey OD type. About 3yrs ago the lever inside the cab for the OD started to rattle quite loudly whereas before it didnt. It moves freely back n forth about an 1.5inches when the vehicle is parked, never used to.Driveing at 50mph this becomes v v noisy, engaging it into any gears at any time is not a problem and it doesnt pop out of gear at all. As I dont use it much the above isnt a problem as I dont use it for around town (30-40mph). The noise only happens when engaged.Im guessing something has worn or a spring inside the unit has broken not keeping the lever taught ?!?! not sure. Any ideas Nick?
May 18th, 2011 at 15:25
Lever rattles are usually down just to wear in the lever links and pivots and result from a harmonic frequency being matched by the engine or other sources of vibration. The two clevis pins in the bent link shaft from the OD’s selector shaft to the lever pivot should have a plastic strip folded around on itself acting as noise reducing washers or shims, but these are frequently missing. I used the lid of a Tupperware box to make up washers to fit between the linkage parts to stop the rattle after the original strips wore out.
Another likely issue is worn selector fork pads, which should be easy and cheap to replace – you’ll need to remove the top cover, rear end of the linkage and the fork’s pinch bolt, , the detent ball and spring and the stop grub screw, slide the selector shaft out the back of the unit and then lift the fork out. The pads are a loose fit in the fork, so try not to drop the old ones inside the unit as the fork comes out.
Nick.
June 22nd, 2011 at 19:49
Hi Nick. fitted a second hand overdrive to my land rover.Ifound your guide very helpfull thanks.
On testing with the overdrive off there is no drive however in the on position every thing works fine.just a slight whine.before fitting i drained the oil and no foreign bodys were found. took the inspection cover off and all looked good.Wonder if you have any ideas to the problem. Once again many thanks. John.
June 22nd, 2011 at 20:15
Hi John, and thanks for your interest in the blog. I’m glad you have found it useful so far.
It sounds as if the unit might not be selecting the disengaged position properly, but before you start stripping anything down, you are pulling the selector lever all the way back, aren’t you? The overdrive has a neutral stick position, not just engaged and disengaged. It stumped the AA once when Helena wanted to use the 109 and I was away – they diagnosed a complete clutch failure but the overdrive was just selected in neutral!
If you are moving the lever to its limit, then something may be restricting its movement. As memory serves, the top of the lever should move about 8″ or so, with a detent for neutral right in the middle of the arc. Things that could restrict it are the lever’s (cranked type) rotational adjustment kinking it too far aft, in which case the top will hit the seat base, middle seat or cubby box and it just needs the bottom locknut slackening to rotate the lever to lean sideways rather than aft, then tightening the locknut.
Another issue could be the selector fork not being the right way around or its pads running forward of the slot in the synchro hub. Another cause could be a problem with the selector shaft detent or the lock grub screw underneath it (which could be a little too tight and binding on the shaft), or something stuck between the casing and the bend in the connecting rod between the selector shaft and lever.
If the selector mechanism is all correct, then the fault must be stripped teeth on the front end of the synchro hub or back end of the output shaft. I’d be surprised at that, though. My bet is on the selector mechanism not travelling through its full range.
June 22nd, 2011 at 20:50
Thanks for the info Nick.
I will try and sort it tmz and let you know the cause.
beer time now try and get my head in gear.ha.
Thanks John.
June 23rd, 2011 at 15:45
Hi Nick.
your advice on none selection of drive with overdrive not selected worked a treat
Had a good look at the selector fork; and guess wot; no brass shoes or guides left. [not sure of there technicle name].so as you suggested the selector would not move the requred distance to select.
Bad mechanics; but learnt my lesson not to trust sellers that a second hand unit is fine.
On the plus side; new guides fitted; And it works as it should.
Hope this comment may help other land rover owners in the future.
Once again many thanks Nick. John.
June 26th, 2011 at 17:49
Glad to hear you have it sorted out, John. Sadly, my experience of second hand or even professional reconditioning matches your experience with this overdrive making me very distrustful of second hand or rebuilt assemblies. In fact, the only reconditioners I trust apart from the original manufacturers (like buying engines or transmissions directly from LR or PAS steering boxes from Adwest) are Turner Engineering. I learnt a long time ago to treat all second hand units as suspect and always strip them prior to use, reconditioning them myself, just like the Tdi engine and the new axles for the 109.
July 16th, 2011 at 12:19
Hi,
Great blog, very helpful and well presented. I have a Fairey o/d unit but no levers. Can anyone tell me the lengths of the operating rods so can make up a set?
Ian
July 16th, 2011 at 13:05
I don’t have the Fairey unit any more, so can’t help with dimensions, but I think making up the levers is a bit unrealistic – the bracket and lever itself would be simple enough, but making the pivot assembly and accurately machining the connecting rod’s slots and clevis pen holes is not a DIY proposition unless you have high-precision equipment. Craddocks sell the parts, and Rocky Mountain can help with some of them too.