How the Gearbox Selectors and Detents Work

For the benefit of those who suffer gear selection or jumping issues, this is a quick post with some photos of the selector mechanisms.

The gear stick sits in a pivot level with the gearbox tunnel cover. The stick extends a little further through this ball, where it sits in a row of three steel cups. Each of these cups is attached to a selector shaft. Because the nature of the movement of the bottom end of the gearstick below the pivot ball is the opposite to the top of the stick, the right hand selector shaft is for reverse, the middle for 1st and 2nd gear, and the left for 3rd and 4th. The shafts slide fore and aft, but in the opposite sense too, so the reverse shaft will slide rearwards to engage, as will 1st and 3rd, while 2nd and 4th require their respective shafts to slide forwards.  These shafts have forks attached, which slide locking members into the gears to prevent the selected gear from free-wheeling on the main shaft (the reverse gear actually slides across to engage, unlike the others which maintain their position always) .

To hold the selector shafts in their neutral or in-gear positions, they have detents. These are grooves machined in the sides of the shafts, with spring loaded ball bearings that sit into these grooves when the shaft is in the required position. The detents also serve a second function: they prevent simultaneous selection of multiple gears. By using a length of steel rod with rounded ends, like an elongated ball bearing, between each shaft, a cunning extra set of grooves on the shafts and a sliding pin in the middle shaft, it’s impossible to have less than two shafts in the neutral position at any time.

With all the shafts in neutral, each shaft’s detent ball will be sitting in the middle of the shafts’ outboard grooves (top grooves on middle shaft). Each of the shafts will also have their inboard (both sides on middle shaft) grooves aligned with the detent bars.

As a gear is selected, the outer detent will sit in a new outer groove, but the inhibitor bar will have no inner groove in which to sit – it is forced into the groove of the adjacent shaft, locking it in its neutral position. If the left or right shaft moves into a gear selection, the inhibitor bar in contact with the selected shaft will press the pin in the middle shaft against the other inhibitor bar, locking the furthest shaft too.

The reverse gear itself has no detents, just that on the selector shaft.  The same is true for the in-gear positions on 3rd and 4th, though their synchro unit does have three detent springs to hold the neural position when selected.  The 1st/2nd gear synchor hub has a set of thee springs and ball bearings that work in a similar fashion in the sliding member of the hub as to those on the shafts.  Failure of the springs on the synchro units requires gearbox stripping, but a problem with the selectors can be worked on with the gearbox still in place.

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  1. steve cooper says:

    coo. i have similar problems with selection on a ’71 series 3.
    i am scared to take the box top off as i have a theory that any assembly with springs is to be avoided, and springs and ball bearings is a no no.
    question. what diameter are these balls? my local place didnt stock them and said they didnt as any balls work. what should i do?
    will that vertical spring shoot a ball into the box as soon as the cover is released?

  2. It’s not as worrying as you think. None of the springs are under so much pressure that they’ll shoot out when released.

    You need to remove the brass top plug for the 1st/2nd detent, and both steel “L” plates (two bolts each), and then remove the springs under each. You will notice that the reverse detent spring (comes out from under the right side plate) is shorter and more tightly wound than the other two, which are identical to each other.

    Once the springs are out (and you have recovered the rubber rings from the side springs), you can use a magnetic screw driver to remove the ball bearings in a controlled manner, but it’s not really necessary. All you really have to do is remove the gear stick bracket from the top of the box, remove the nuts and studs securing the middle of the top panel and remove the two horizontal bolts that hold the rear of the panel to the transfer box housing.

    You can then lift the top clear, tapping it with a soft faced mallet if required. As long as the LR is not parked on much of a slope, the ball bearings shouldn’t move far from their positions, and will be easily recovered. If they do fall into the box, then draining the oil will recover them.

    Just remember to loosen the bolts that hold the selector shaft seal retaining plates (front of the panel) to allow a bigger gap before refitting, and then re-tighten them afterwards.

  3. steve cooper says:

    i am taking the seats out now, stand by, stand by!
    sorry for delay but had to delve the bowels of the computer to find you!

  4. steve cooper says:

    many thanks have replaced springs and can report that the gearbox is……………………………………………almost exactly as before,
    never mind.

  5. steve cooper says:

    the replacement gearbox fitted 3 years ago is now making horrid noises……

  6. Sorry to hear that, Steve. Was it second hand or recon, and how much did you pay for it if it was recon? The reason I ask is that I have found, through several recon transmissions and engines, that there tends to be much more con and not a lot of re in the business. That’s why I always try to advise people to refurbish their own units personally.

    If you could expand a little on all the symptoms with as much detail as possible, including mileage, oil type and consumption, engine fit and type of driving use, then I might be able to make some educated guesses as to what’s wrong. Hopefully we can find something simpe and cheap.


  7. Rob Ling says:

    Hi there,

    Thanks for sharing this, it will come in extremely useful for my 81 swb. Bought it last week, test drove, all gear selections working fine. We put the vehicle in neutral and left in 2wd and towed back 60miles using an A frame. A test drive yesterday – the first since getting the vehicle back and shunting on the drive – and no gears apart from 1st and reverse. Gear lever appears to go into neutral ok but cant move the selectors back and forth enough to engage any other gears.

    Having lifted the tunnel off there appears to be very little travel at all. I can feel the notches on 2nd and 4th but it’s as if the notch for 3rd gear isn’t there and i’m pushing the lever against something solid. I’m going to lift the top cover off and have a look at the selectors themselves later on.

    Any ideas? any help would be amazing.

    Many thanks,

  8. Hi Rob. Thanks for the feedback.

    Take a close look at the lever’s movement before you remove it – quite often the tapered screw in the right hand side of the pivot block wears and allows the lever to rotate about its vertical axis. If this occurs, you can try turning the screw 90 degrees as a temporary fix while you get a new screw (Dunsfokd Land Rover will stock them and they’re pretty cheap).

    If that’s not the problem, then you’ll have to open the top of the box to make sure the selector inhibitors and detents, is all those balls and rounds rods, are clean and free from corrosion. Pay close attention to the sliding pin in the 1st/2nd shaft as it will hold an inhibitor in place if jammed.

    The other thing that can prevent selection of 3rd and 4th is Tue shattering of the leaf springs on the 3rd/4th synchro unit as happened to me again recently (have a look in the transmission section of the blog). Draining the oil will tell you if this has happened, though you will also be able to see through the open gear box top.


  9. Rob Ling says:

    Hi Nick,

    Sorry it’s taken a while, had some problems getting the seatbox off and ordering tools of correct sizes to undo everything – finding there is a rare mix of imperial af, whitworth and metric used on my landie. I eventually got into the gearbox and drained the oil, there were some tell tale bits of bronze that came out with it i identified as bits of the 3rd/4th synchro cage. There was very little oil that came out, maybe a cup full which was slightly alarming and slightly more from the transfer case. I got the gearbox off and on the bench last night and confirmed the diagnosis – catastrophic failure of the syncro cage.

    Still not entirely sure what caused the failure although there does seem to be quite a bit of play on some of the gears and now most of the broken pieces removed the all shafts rotate as they should. Could this be due to it running dry or maybe something seized whilst it was stood?

    I’m almost ready to get the bell housing off so i can have a proper look inside but been struggling to get the layshaft retaining bolt off – it’s very tight and i’m yet to find a way to stop the mainshaft turning so i can apply torque to undo the bolt. I made the mistake of separating the main and transfer boxes after lifting the assembly so i could get them into my shed to work on…didnt read the section in the workshop manual which states lock up the hand brake mechanism before undoing layshaft retaining bolt. I’ve also taken the selectors off.

    Thanks for your help, learning a lot as i go along, this will be my first gearbox rebuild and so far things are going very well (apart from all my tools and me being coated in EP90 which isnt great as i work in an office) at least with the bellhousing off i’ll be able to start cleaning everything.


  10. Hi Rob.

    A cupful of oil is very low indeed – there should be about three pints in there and five in the transfer box. That will almost certainly be the cause for the play you mention. You’ll need a full set of bearings and bushes, plus the synchro unit, for certain.

    To undo the lat shaft bolt, remove the detents and interlocks between the selector shafts and then engage reverse gear and fourth at the same time. That’ll lock the gear shafts up so you can undo the bolt with plenty of torque. Use the same method on reassembly to set the bolt torque with a torque wrench, and use a low to medium strength thread lock (blue) when you do that.

    The worst job is removing the snap ring from inside the third gear. I use a few small screw drivers down the shaft splines to spread the ring and another to pry it up the shaft bit by bit, but if you can find the special pliers to spread it, then it’ll save you considerable time and patience.


  11. Andreas says:

    Hello, Great site and thanks for the info on such things! I would like to ask you something about my car, maybe your experience will save me a lot of trouble. I have a Lightweight (which is basically a series 2 chassis with a lightweight body) fitted with a 2.5 N/A engine. The car when I bought it was giving me trouble with 2nd & 4th gears (spitting them out when the engine was resting on them (downhill). I took it to my mechanic and told him and he said it probably needed gear lever adjustment and he also fixed the wobbly gear lever. After that the car now has no problem with 2nd & 4th gears but gives me the exact same problem with Reverse, 1st & 3rd so I believe it has something to do with adjusting the gear lever rather than the synchromesh that is so common. Any advice or ideas on this?

  12. Hi Andreas,

    I’m quite familiar with the 2.5na diesel (12J) and the Lightweight – have a poke around on here and you’ll find I have had both.

    There is no adjustment on the gear lever as such. There is a pointed nosed grub screw on the right hand side of the pivot base which engaged into a slot cut in the lever’s pivot ball to stop it rotating in the socket, as it wants to do when you apply the linear motions to the top of the lever because of how it is cranked; only a dead straight lever wouldn’t try to rotate about its own axis. If the grub screw wears, the rotation of the lever makes gear selection more difficult, but it has no effect of gear holding or jumping.

    There is adjustment on the selector mechanism. This would be by the repositioning of the forks on their shafts, and this would involve removing the top of the gear box to gain access. Furthermore, SII gearboxes have an adjustable stop bolt on the casing behind the reverse gear shaft to prevent over-selection of that gear, but this was deleted on the SIII.

    With that many gears jumping out, I’d suggest you either have the very common loosening of the castellated nut ob the back of the main shaft inside the transfer box) or worn bearinngs. Either would allow excess end float on the main shaft, forcing the gears to jump out. This incliludes the possibility of a worn spigot bush in the engine’s crank shaft allowing the gear box input pinion to move laterally, though in my experience this only affects fourth gear.

    Start with the castellated but, and if that is right, give the shaft a pry fore and aft via the inspection cover on the top of the transfer box. If you get any longitudinal or lateral movement at all (not rotational), then your bearings are worn out and the unit needs a rebuild

    Hope that helps.


  13. Andreas says:

    The amount of knowledge awes me! Thanks for that (its funny how from forums and sites like these I can go to my mechanics and tell them what to do) but since I do not have the in depth mechanical skills myself and that sounds like its quite of a fuss, I think I’ll just leave it as it is for now. I thought it would be something like worn bushes on the gear lever end rather than something that the gearbox would need to be opened up.

    Thank you so much for you reply though

  14. Flattery will get you everywhere! Thank you for your compliments. I hope you have the opportunity to get it fixed or replaced soon. I do have a guide on how to rebuild the gear box which just helps a give an idea before you take the job on and highlights some of the bits in the manual (which you really do need for the job). The Haynes manual is good enough. The hardest part of the job is getting the transmission in and out of the vehicle – the gear box work isn’t too bad.

  15. Andreas says:

    Hi Nick,
    Finally got some time to spent on the Landy today. I discovered that when the car is engaged in Low Gears 4WD the gears won’t jump out (although I tested this on a downhill asphalt road and not off road!) I also took a small video of the gear selectors which somehow seems to me they are a bit to loose (?) How does this seem to you?

    Hope the link works.


  16. That is a pretty worn gear stick and won’t help with quick or easy gear selection, but won’t be the cause if the jumping. Its worth replacing, though.

    While I can’t see any logical reason why transmission wind up between the front and rear axles should affect gear box operation, it does seem to. Wind up tends to jam the gear box in gear, as you are finding, and in extreme cases you can feel the engine struggling against the transmission, almost like the brakes coming on.

    Of the main shaft end but is tight, then jumping gears can only be due to worn bearings or shafts allowing incorrect movements. The synchro hubs do not hold themselves in gear – their springs are to apply pressure against the bailk rings to synchronise the rpm of the parts before dog teeth engagement. The gears are only held in selection by the detent srubhs and ball bearings in the top of the box. If the springs are weak, the grooves in the shafts worn or any dirt or defect is preventing the ball bearings sitting fully into the shaft grooves, then weak gear holding would be the result.

    I think you should replace the three springs with genuine new springs and take a close look at the selector shafts and the detent spring/ball channels for free movement of the balls.


  17. Hi Nick,

    I have a series three lightweight diesel

    It sometimes gets stuck in reverse it does come out but only with a lot of wiggling about, it’s not a strength thing but takes ages to come out sometimes, and is very embarrassing.

    Any ideas

  18. Hi David,

    I’d suspect the groove for the detent ball is a bit deep or the ball is jamming or worn too small. I’d remove the top cover and check for any dirt or corrosion that could jam the ball and replace the ball and spring just in case they are out of specification. I’d also check the sliding interlock pin in the 1st.2nd rod for free movement as this could be preventing the rounded bar between the reverse and 1st/2nd rods from moving out of the interlocked position.


  19. Aladin.Bob. says:

    I have a question , Whats the reason for reverse gear jumps, or makes noise while reversing on landrover sr ll sr lll A
    as mention above regarding springs and balls , those issues are solved, But the problem is always on these gearboxes.

  20. Jumping out of reverse can be caused by the gear’s inner bush wearing a taper on the idler shaft, so the torque prides a thrust force on the idler gear. Later SIII units has a needle bearing to try to stop this, but the SIII Suffix A box and all SII boxes had the bronze phosphor bush and would suffer this issue at high milage. Another possible cause is a maladjusted stop bolt preventing reverse from fully engaging so the detent ball doesn’t sit fully down into the selector shaft groove, or a weak detent spring.

    As for the noise, they can crunch on selection if the vehicle is moving at all or if the clutch drags as they have no synchromesh. They also tend to be noisy when reversing much faster than idle because the teeth are straight cut rather than helical. Any fault with the bush or idler shaft will exacerbate the noise, but even in perfect order, reverse is noisy.


  21. I have a ’74 gas 109 ex-mil in Norway that har a new civilian gearbox installed 20,000km ago. It had a bit of a clicking sound in forward gears at low rpm since I purchased. Recently it started making a really loud clicking/clunking sound while reversing. It still works, but worried about ruining the rest of the trans. I just drained the fluid and there are a couple small chunks of metal, as well as some general metal in the oil. The pieces are 2-3mm of unknown origin. Obviously the best thing to do is to pull the trans and tear it apart but it’s in use every day while we move houses…no time right now…just hope it doesn’t go boom….any ideas?

  22. Without seeing the pieces that came out, I can’t tell what has broken. The noise could just be a bit of backlash (play in the gear mesh and splines), or it could indicate a fault. Do you have any pictures or can you give a detailed description? It’s not uncommon to get small flakes like glitter, but lumps are not normal.

  23. hi nick please can you help, my series 2A now goes straight into reverse without any resistance making it difficult to avoid when driving, what could cause this
    thanks very much

  24. Hi Luke,

    That’ll be a fault on the inhibit flap. If you remove the tunnel cover, you’ll see a hinged flap that covers the reverse selector shaft “bucket”. That flap is spring loaded and provides the resistance on the lateral motion of the gear lever. If the flap hinge has broken (as has happened a couple of times to me) or both of the springs have snapped (happened to me too), then the flap will not be able to resist the gear lever.

    The springs just hook in place on the flap and its mounting, and the whole assembly is attached to the selector rod by two bolts. The hardest thing in the repair will be removing and refitting the tunnel cover as the floor plates need to come out, and that is a pain on the driver’s side because the pedals and hand brake lever get in the way.

  25. Hi Nick,

    Just finished rebuilding a series 2 gearbox, just started on rebuilding the transfer box. I have replaced all bearings and oil seals but refitted the original 3rd 4th Syncro unit (no obvious signs of wear and the three springs were in place) When I tested it on the bench 3rd and 4th were difficult to engage but is this just because there’s no gear lever fitted yet? Is it false economy not to renew?
    Thanks in advance, Steve

  26. If the splines on the outside of the hub are thick enough, and the baulk rings (bronze bits) are in good order (they can be easily distorted, but should be fine if not dropped, levered or bashed, and the fine ridges that provide the friction to act as a clutch and scynchronise the gears wear down with age), then there is no reason to replace the unit. It is, however, prudent to replace the three steel strip leaf springs between its hub and notched “pillars” as these wear on their middle hump where they engage the slots in the pillars and eventually shatter, usually jamming the hub in the process and locking out 3rd and 4th gear.

    The tightness you mention on the bench is probably due to slight misalignment of the gear teeth, which won’t be an issue when they’re spinning, or a dry main shaft, which won’t be an issue once oil has been splashed about. I doubt there is a fault with the synchro unit.

  27. That’s great, many thanks, I’ll strip it out and renew the springs as suggested

  28. thanks very much nick you were absolutely right, both springs were broken on the inhibit flap
    much appreciated

  29. He shoots…. He scores! ;).

    Glad to be of help, Luke. Remote diagnosis can be a bit hit and miss, so I’m glad it was something recognisable and simple to fix.

  30. Hi Nick,
    I’ve got 2nd gear selection problems in my 68 series 2a truck. All other gears are fine but second selector wont move. I guess from what I’ve read here I start with the location screw in the base of the gearchange? I’ve got the floorboards out, so the next thing would be the springs and balls in the detent. Where abouts is the sliding interlock pin found , is it also located with the springs and balls or do I need to take the front part of the lid/cover off.
    When anything happens with the gearbox I just groan, having had it out twice in the 20 years I’ve had this truck, one time with a broken lay shaft, another with a broken gear in the overdrive. It’s probably due to come out again to do seals as it’s leaking from wherever a shaft protrudes. Is it possible to do these from underneath or do I need to grit my teeth and get into it. The problem is at my age I’m running out of friends who are prepared to risk their backs helping to get the thing out of the cab. Someone suggested cutting the cross member then bolting it back, with lugs welded on, after. You obviously know Landys very well, so thanks for such a helpful site. Alistair

  31. Hi Alistair,

    If it’s any consolation, my gearbox has developed a reluctance to engage second gear since I moved away, so my wife has been struggling with it. I think it’s just a bit of dirt from the gear box getting into the selector mechanism, from the symptoms described, and I suspect yours is too.

    The interlock pin is in the 1st/2nd selector shaft, where the side detent grooves are. It’ll be obvious when you see the shaft removed from the box. I think you just need to remove your selector shafts and parts for a good clean and reassemble to regain second gear. To do that, remove the gear stick assembly, then the steel “L” plates with the two 7/16″ bolts, recovering the springs and rubber seals held by the plates, and the bronze plug between them and the spring underneath. It is also prudent to slacken the four 7/16″ bolts that hold the selector shaft seal retainer plates in place at the front end of the top cover, so that you can get the o-rings in behind the plates on assembly more easily.

    Once you have the springs removed, undo the two 9/16″ nuts and the two 1/2″ bolts through the vertical rear section to remove the top cover. It’s likely to need a tap with a rubber or wooden mallet (or heavy hammer with a wooden block to avoid metal to metal hammering). As the top cover is lifted away, recover the three detent ball bearings (may drop to the floor if parked on a side slope, so an old white bed sheet folded over and placed underneath to catch the balls is a good idea). If a ball drops inside the box, don’t worry – drain the oil and you’ll find it in the drain plug.

    Remove the selector shafts and the two interlock rods (same diameter as the ball bearings) from between the shafts, and then clean everything scrupulously. Make sure there is no corrosion and that the sliding pin in the 1st/2nd shaft is free to slide. Once clean, spray with WD40 or use light oil for lubrication and reassemble, leaving the ball bearings, springs and their retainers until last. Make sure that the heavy one of the three springs is used on the right hand side for reverse gear detent; many people mistakenly put it in the middle under the bronze plug.

    You can replace the transfer box output seals and the gear box main shaft rear seal in situ. You need to remove the prop shafts and their drive flanges and the hand brake assembly, but it’s not too hard. The gear box main shaft seal needs the transfer box input gear to be removed, and you have to remove the rear bearing carrier/overdrive/PTO and top inspection panel to do that. The genuine seals are steel with a rubber lip and are a pig to fit because their outer steel edge picks up on the edge of the hole they fit in, buckling and distorting. I found that lightly bevelling the seal edge with a file and RTV sealant as a lubricant on the outer circumference helped, but buy a couple just in case, as you’ll be stranded otherwise. The input pinion from the clutch has a seal inside the the cast front cover inside the bell housing, so the unit has to be removed to replace that. It might be worth doing an oil change and adding a bottle of seal reconditioner before you tackle the gear box seals, though periodic replacement of the transfer box seals isn’t a bad idea ad they get dirty and worn from off road use.

    Military vehicles had bolt-on cross members like you are pondering. My new chassis was built to that spec, but Marsland galvanised the chassis with the cross member bolted in place, subsequently welding the cross member and its bolts in place. I was less than pleased about that. It does allow the transmission to be lowered out of the vehicle, saving you from removing the seat base, which is quite a big job.

    I have in the past removed and refitted the transmission in sections, separating the transfer box from the gear box and then the gear box from the engine, when I didn’t have access to an engine crane, and managed to do it with the seat base in place, but it was still a struggle, especially lifting the transfer box in from underneath while laying on the ground. I wouldn’t recommend it, and now I have my own engine crane, I do it the standard way through the door.

    I hope that is of use. Good luck!


  32. David Pearce says:

    Hi Nick,
    I have a 1989 Defender 90 and have building up the courage to tackle a source of muttering from the young lady. Firstly, it can be a challenge to downshift from 3rd to 2nd and from 2nd to 1st. Secondly, finding 1st rather than 3rd is often a matter of luck (with finding reverse on occasions) – 1st & 3rd seem to be rather close together with 5th a good distance away. What should I be looking for?

  33. Hi David

    The LT77 and R380 are very different from the gear box in this article, but I have worked a little on the selector of my Range Rover’s R380.

    The lateral stick movement is centralised by two springs under a steel cover box at the base of the gear stick. You need to remove the rubber gaiter and gasket, then this steel cover to access the springs and their retainers. Then select third or fouth gear and slacken the spring retainers to allow twhir mounting plate to settle with equal spring pressure with the stick in the middle of its lateral range (hence 3 or 4). Then tighent the screws. It is possible that the retaining plate has snapped a lug, so the springs aren’t applying the force they should on the stick, so check for sheared or bent lugs that the spring ends hook or press against.

  34. Hi Nick,

    Fingers crossed you can help!

    I have just rebuilt my gearbox as per the green bible (1964 88 Petrol) due to a very noisy and well shot input shaft bearing.

    Whilst in there I replaced the big main shaft bush which had broken in two and all the other bearings as I was in there.

    All turned over on the bench ok selecting all the gears, so put it back in.

    Starts her up and all that nasty bearing whine is gone and the selection feels nice and crisp given all new detent springs and balls.

    Off down the road and fine until under load in second third and top when you can hear an intermittent clacking kind of sound as if a gear is trying to mesh and being spat out again.

    I measured up everything again and again and really don’t see what I could have got so wrong?

    The only thing I can think is if I some how the reverse idler gear is wandering up and down its shaft or selector fork location as there is a fair bit of slop between the shaft and the selector fork pinch bolts?

    I really hope I don’t have to take the cursed thing out again.

    Any ideas gratefully received.

    Many Thanks


  35. The reverse idler is actually a pretty good suspect – it’s very easy to install the fork and selector shaft with the prongs missing the groove on the idler gear, which would allow the gear to slide about by itself rather than be firmly held in the neutral position. The fact that it does it in all gears except first, though. makes me suspect that there might be excess end float on the first gear wheel, the gear being held firm against either thrust washer when torque is applied to it but able to vibrate fore and aft when torque is removed by selecting other gears. Did you replace its inner bush (splined inside, spiral grove outside)? If so, did you set the gear end float by filing/turning the end oft he bush down?

  36. Hi from Africa, your advice will be greatly appreciated. I have a 1978 landy with a chev 4.1 motor and a overdrive gearbox(says superdrive on leaver). When in 1st gear there is a tick tick noise when you drive. 2nd to 4th has no problem. When you engage reverse the gearbox totally locks up, feels like its selected forward and reverse gear together. I also cant get the gear leaver to move out of the reverse position unless i jack one of the rear wheels off the ground, it will rotate a tiny bit as though diff wind up and then i will be able to take it out of reverse.
    im hoping you can give me some guidance as I think its a selector problem as the box isnt making any noise and feels the same as always when I drive it using 2nd to 4th only and avoiding 1st and reverse.

  37. Hi Rich,

    Selecting first or second moves the outer ring of the synchro hub aft or forward respectively so that its internal splines lock the hub inner member to the gear wheel’s dog teeth; the gears themselves are in permanent mesh and don’t slide along the shafts. Reverse gear is engaged by sliding an idler gear on a separate shaft forward into mesh with a gear on the layshaft and another on the outer circumference of the 1st/2nd synchro sleeve while it is in neutral. If the reverse gear stop bolt or fork position is mis-set, or the fork is not engaged correctly in the idler gear’s slot, then the idler gear could be jamming against the teeth of first gear, causing both issues.

    Earlier boxes have a plain bush inside the reverse gear which does eventually wear out. They also suffer wear on the idler shaft, which becomes tapered. I believe it ormally manifests itself as jumping out of reverse gear, but these could also be an issue, but I think the fork/shaft mis-setting is more likely.


  38. Hi. I have a series three gearbox suffix D gearbox. I have just replaced the main shaft and the lay shaft. I’ve also replaced; the reverse idler gear, idler gear shaft and syncromesh unit. After rebuilding the gearbox, reverse gear keeps jumping out of mesh. After taking the top cover off, it appears that the reverse selector shaft does not line up perfectly with the indent and the ball. What could be the problem?

  39. Hi Matthew

    There are a few things for you to check. Firstly, make sure that the inhibit flap/reverse light trigger assembly on the front end of the selector rod is in good order; the hinge or springs can fail and block the movement of the shaft. Next, make sure that the fork is correctly engaged in the groove of the reverse idler gear. You’ll need to remove the top cover to do this. If that is OK, then remove the fork and shaft to check for any wear ridges or other damage that could cause binding or locking between the shaft and the casing. On reassembly, make sure that the detent ball springs are fitted in the correct locations – it is very common for people to thing the heavy gauge spring goes under the brass cap retaining the 1st/2nd detent, but that is wrong – it’s for reverse gear and should be under the right hand side “L-plate”, the left and centre springs being the two identical softer springs.

    If that doesn’t sort it out, then you may be looking at a gear box rebuild. The B suffix and later units had a much improved reverse gear idler and shaft with needle bearings replacing the earlier plain bronze phosphor bush, but they can still suffer wear, especially if oil changes and top ups are neglected, resulting in a taper on the idler shaft that could restrict the sliding motion of the gear and also causes a thrust force that throws the gear out under engine torque.

    Fingers crossed for a cheap and quick solution. My money is on the detent springs being in the wrong holes.

    Happy new year.


  40. DAVID GOODSON says:

    Howdy Nick,

    Presenting problem: Dragging Clutch. I recently had my LT 76 professionally rebuilt for my ’67 109 LHD. I successfully replaced the clutchplate/flexplate/pilot bushing last year when I rebuilt the engine. Upon reinstalling the gearbox, I had no problems sliding back into place but the clutch is dragging. I pulled out the box again inspected the clutch and gave the pilot bushing a good polishing and checked it for grabbing/alignment. Reinstalled box with no problem. Clutch still drags. Hydraulics worked fine before rebuild and seem to work fine now. System is fully bled. My question is the shop manual says one possible fault could be “incorrect adjustment of control levers.” However, other than reverse, I cannot see any way to adjust them. Thanks for any advise.

  41. I would take that comment about the levers to refer to the clutch levers, not gear box selector forks and shafts. I have never worked on a SII clutch, but from what I have seen, the slave cylinder operates an arm that turns a torque rod that runs into the bell housing to operate the release fork. If there is any maladjustment on that shaft or any play on any part attached to it, then you will get a dragging clutch. I have often heard of worn cross-pins on the shaft, so that’s where I’d look first.

    Other causes could be a defective clutch plate (I’ve heard of pattern parts being too thick) or a seizing spigot bush. I think the latter was the cause of a dragging clutch on our Lightweight that only manifested when the transmission and engine were well warmed up.

  42. Mark Arthur says:

    Hi Nick – (I have a 1975 SWD petrol Series 3) I had the gearbox replaced three years ago with a recon from a company now gone out of business. it gets very light occasional use. I have two problems:

    1) I have had difficulty getting low range selector lever to stay in the rear 4WD position for sometime, but as I hardly ever need to use it have not gone further than removing the rubber boot and doing the occasional 20 yds on a byeway holding it in place to see if use frees it up. It sits in the rear position momentarily but just pops forward. any suggestion?

    2) second and by far more urgent problem starting this morning is that I have lost 2nd gear (its as though it is not there, no noise no nothing, just like pushing against a wall almost all the time. It does goe go in, quietly, occasionally.
    Also 3rd has starting grinding and popping out.

    I have had no previous symptoms leading up to this point. Everything apart from the low range problem has been great with this box until this morning. I limped home and went out again at lunchtime, same problem with 2nd and 3rd seems to be even worse. help!?

  43. Hi Mark

    Sorry to hear that you’re having problems.

    Jumping out of the transfer box gears is usually the rubber boot pushing on the lever, but if you have already removed it for elimination, then I’d suggest first removing the steel cover next to the selector shaft to see if the inside of the two cylinders are packed with dirt – it can get inside them and prevent free and full movement of the shafts. I would also check the detent ball and spring are moving freely in their bore under the brass plug in front of the lower rectangular top plate, and just check that the shaft hasn’t rotated so the detent grooves are sloping instead of horizontal, as that would reduce the hold the detent ball has on the grooves.

    Any time someone has problems selecting gear, especially second, the best advice is to check the main shaft rear but (castellated but that is behind the input gear under the upper cover plate of the transfer box) is tight; the lock washer tabs can unfold or rear off, allowing the nut to loosen, which then let’s the shaft slide for and aft in its bearings. Selecting second would move the whole shaft forwards instead of just the synchro unit, preventing gear selection. It has no effect on selecting first gear, but all gears except fourth become clanky on throttle movement. It could affect third gear, but I’m not sure how. It is possible that if the main shaft has been running forward of its proper position, third gear would have been pressing on the synchro cage and either worn the baulk ring or perhaps even causing one or more of the synchro hub leaf springs to fail, which would then prevent the synchro unit from synchronising the splines on third gear during selection. If the springs have failed, you should find pieces of them when you drain the oil (drain it through a sieve to catch any bits).

    Checking and tightening the nut can be done easily in situ, but replacing any broken bearings, gears or the third/fourth synchro unit requires the box to be removed for rebuilding.

    Let me know what you find.


  44. Ken May says:

    Advice please.
    Have a 1972 Series 3.
    Jammed in 2nd gear.
    Have taken off the top of the gearbox and removed the selectors. At the rear the nut on the main shaft had wound itself back and jammed against the rear housing as the lock washer had failed.
    Freed everything off, wear looks minimal for a 45 year vehicle. Oil looked OK, no debris came out on draining.
    Back to the selectors, 3/4 gear selectors look OK, but 1/2 solid.
    Suspect that 3/4 gears have moved back along the shaft.
    Is it gearbox out or can I drift the gears back into position?

  45. Hi Ken

    If the rear nut was loose enough, then you could have the shaft and everything on it move forward inside the box. This would tend to force a change into 1st or jumping out of second, rather than jamming it in second.

    Which part of the mechanism seems stuck? The selector shaft or the synchro unit itself? Have you tried selecting neutral on the 3rd and 4th and removing the elongated detent balls between the shafts to see if the 1st/2nd will move? Could also be the reverse gear stuck forward, preventing the synchro hub moving aft from 2nd position to neutral.

    Please get back to me with which parts you have tried moving and the exact parts that are stuck.


  46. Ken May says:

    Many thanks Nick,
    Have got all the detent balls out, 3/4 moves OK.
    Yes the reverse is stuck which as you say is probably preventing 2nd gear from going into neutral.
    How do I free of the reverse?

  47. If the shaft is solid, give it a light tap with a wooden block or a rubber mallet. Don’t belt it or you could break internals.

    If that doesn’t work, try lifting the shaft up to make sure it isn’t corroded to the case. If it comes up easily, then the reverse idler may have siezed on its shaft, which will require a complete strip down to replace the shaft and gear, cutting the shaft to do so. I really hope it’s not the last, and I’ve not heard of it ever happening, but it is possible.

  48. Chris Sanger-Davies says:

    Trying to get to the bottom of a gearbox or at least assume its a gearbox issue on a 1999 defender 110

    This happens randomly and seems to happen when the vehicle is cold rather than hot but not completely then! It has happened when pulling away from a junction and also when changing down gear to go up a hill you just get rev’s of the engine and the gear is not engaged could it be the throttle sense.. because u can feel it in gear! Just no power to pull away almost like the couch has given way but clutch seems fine.

    Local landcover guy drove it and could not find a fault of course it did not do it when he drove it. (his comment which was not very helpful was drive it till it breaks down!) But when you pull out of a junction and then it drops out of gear but its not very safe! it does then go back in and drive fine for 100’s of miles then randomly does it again.

    Would it be a gearbox issue or could it be something else? Any help would be greatly appreciated.

  49. Hi Chris

    I suspect the clutch, probably a seizing release bearing sleeve holding the pressure on the pressure plate after the pedal has been released. A faulty pressure plate or drive plate could also have some misaligned part that is preventing the plates closing back up under spring pressure.

    The other alternative, but less likely and less susceptible to temperature, is a damaged selector fork failing to fully engage the gears when the lever is in correct position.

  50. Paul Bulpit says:

    Dear Nick,

    I am basically new to Series but have just bought a bitzer to play with in my retirement, as I had a IIA forty years ago, jib in the back!

    First issue is it jumps out of first on take-up so here I am finding you. (i) Tightening the screw in the pivot block immediately improved things, you say above Dunsfold stock them, but not easy to identify “screw” on their site – does it have a name or part number? (ii) on removal, the screw doesn’t appear worn unevenly, however, so maybe the lever ball groove itself…. there are two levers on fleabay (L-R Parts), FRC2046 & BR3072, which do I need? Both look the same. It’s an all synchro box, may be from a later vehicle.

    Yet to investigate the detents, but intend to – where can a set/kit be obtained? Thanks.

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