Gearbox problems

Drivetrain problems

Moderators: theelanman, dapinky, Specky, Dave Eds, DaveT, Elanlover, Nige, muley, Enright, Sy V, algirdas, nitroman, clemo, GeoffSmith

Re: Gearbox problems

Postby John_W » Fri 05.10.2018, 12:43

It was good to talk to you last night. I've sent you an email with lots of pictures and dimensions and an Isuzu part no from Chris Brown (your name came up in conversation!).
User avatar
Posts: 3780
Joined: Mon 21.04.2003, 12:31
Location: Aberdeen

Re: Gearbox problems

Postby John_W » Sun 04.11.2018, 21:54

I am happy to report that my Elan is now back on the road following the gearbox problems I had on the way to Hethel. I fixed it myself and learned a lot, so I thought I’d write it up for the benefit of the next person. Stand by for a post to rival dapinky’s best - and by best I mean longest! :lol:

You probably won’t want to read all of this unless you can’t sleep, like horror stories or think you have this problem and want to fix it. However, you should read the Summary and Conclusions as this problem is going to happen to somebody else in the future.

The “Stuck in 5th gear” Syndrome

  • Summary
  • Introduction
  • Symptoms / Conditions when experienced
  • Cause of the problem
  • Procedure to fix:
    ⁃ a) check your nuts
    ⁃ b) if no significant damage
    ⁃ c) if further damage (in my case there was)
  • Conclusions
  • References


Fixing the “stuck in 5th” problem is an easy DIY job which shouldn’t even need any new parts (apart from two new 32mm nuts), but if a gear gets damaged as mine did then finding replacement parts is the problem. I could not find them new, and was lucky enough to be helped by Brit-Car-Nut who kindly supplied a second-hand gear set from a GEO Storm. This syndrome has affected at least nine LEC members and it is going to happen to somebody else - guaranteed! There is a reason why Gerald at GST has developed expertise in fixing it.

There are different levels of this problem, and how much work you have to do depends on how long it has been going on for, how bad it has got and how lucky you are. It might be that you only have to re-torque a nut, or you might additionally have to remove and press back together the 5th output gear, or you may have to replace damaged parts. Even should new 5th gear wheels be required, it does not require the gearbox to be removed or even molested in other than a minor way. If you can change the gearbox oil, you can perform this repair. If you have the parts it should be easily accomplished in a day.

Refer to the attached gearbox diagrams.

The syndrome is caused by the 32mm nut that secures the 5th input gear onto the primary shaft coming loose, thus allowing the 5th input gear to move out under load and start forcing apart the two-part 5th output gear. This eventually prevents the 5th gear synchro ring from disengaging, effectively jamming the gearbox in 5th. This takes place over hundreds or thousands of miles of use, and it is unlikely that you will be aware of the problem until you find that you cannot shift out of 5th gear. This means that you will have to remove the 5th output gear and have it pressed it back together before re-assembling everything using two new 32mm nuts. It is probably best not to drive too far once you become aware of the problem; it feels really nasty, so you won’t want to anyway.

If you hear a slight “whirring” sound from the engine at tick-over, place a stethoscope against the gearbox rear end cover and you might be able to convince yourself that you can hear the loosened nut and input gear grinding away at the output gear and oil gutter bolts. However the only sure way to tell if the nut has come loose before the “stuck in 5th” syndrome manifests itself is to remove the gearbox rear end cover to check. This is a simple job and will only cost you a new gasket (or a bit of liquid gasket) and 100ml of oil to replace what spills. I believe that it is well worth performing this inspection the next time you check or change your gear oil, and that this should be added to the routine maintenance schedule.


Having polished the car especially for the Lotus 70th event, I set off happily on the 500-mile drive to Hethel, however I only made it as far as Stirling (125 miles) before I lost all gears except 5th (and 1st if I cut the ignition while stationary) and had to limp back home. When this happens to somebody else (and it will), I recommend that you call a breakdown lorry unless you are very close to home to minimise the risk of damage.

When I posted my predicament on LEC, both Pinky and Brit-Car-Nut correctly identified the problem and pointed me to this thread. My thanks to both of them, and especially to Brit-Car-Nut for his role in getting my car back on the road by providing the “getting rare” parts I required.

Several LEC people have experienced the problem of being stuck in 5th gear: Andrew Ennis, Davey_B (probably), valimar, rip, Specky, owentec, jimjams, Dean, and now me. Additionally, rip reports that Gerald at GST has fixed this problem on several Elans (new and old) over the years. Having taken my 5th gear apart and fixed it, I see no reason why the same problem could not occur on any Elan. Other owners have had a mechanic fix it for them, however I found that it is an easy DIY job.

This thread (Reference 1) was very useful in helping me identify and fix the problem, but beware! This thread should be looked on as an LEC thought process for arriving at the solution, which means that not everything in it is correct or relevant. In addition to the invaluable information from rip, valimar, Specky and owentec, it contains a few blind alleys and the inevitable misunderstandings of second-hand information from a mechanic, as well as a bit of speculation and deviation. In doing the job myself I gained a deeper understanding of the problem and was able to understand how some of the misconceptions came about. I have tried to find out not just what is happening, but why it is happening. I also found out how to fix it. But not how to ensure that it won’t happen again.

There are three levels of this problem, and how much work you have to do depends on how long it has been going on for, how bad it has got and how lucky you are.
  1. If the input shaft nut has just loosened, you will only have to put on a new nut, torque it up and peen (stake) it to the shaft. (However, it is unlikely that you will be aware that the nut has come loose.)
  2. If the input gear has started to prise apart the output gear set, you will have to remove the output gear and press it back together before refitting with new nuts. (You will eventually notice this by being stuck in 5th.)
  3. If there has been damage caused to the 5th gears, you will have to replace one or both of them. In the worst case, there will also be internal damage to the gearbox and you will need to rebuild or replace it. It depends on your luck.
It’s a fairly easy job to dismantle the 5th gear set, and you do not have to disturb the main gearbox to do it. The 5th gear components aren’t really ‘in’ the gearbox, more like enclosed in their own separate compartment at the end of it. It’s as though 5th gear was added after the gearbox had been designed!

Note that it is also possible to be stuck in 5th gear owing to a fault within the selector housing that sits on top of the gearbox and is operated by the gear cables. One of the components within the housing is a small cam which prevents you going from 5th straight into reverse by accident. This cam can break or become poorly adjusted such that it locks the selector box in 5th. A quick trawl through LEC posts shows that this has been experienced by G UK, dapinky and BigErch. (References 2, 3 & 4).

It should be easy to tell which of these two problems you have:
  • The selector housing problem will lock you in a gear.
  • The loose nut problem will allow you to come out of 5th gear using some force on the gear lever, but you will be unable to select other gears on the move; by switching off the engine, you should be able to select gears. However, on the move again it will feel terrible, as described by valimar, because you are almost in the position of having two gears selected at once. The car will lurch as the 5th gear synchro ring slips and grabs. If it is ignored, I guess there is a danger of having two gears selected at the same time, which will either stall the engine or break the gearbox.
This note refers to the “loose nut” problem, and the selector housing problem will not be mentioned again.

Symptoms / Conditions when experienced:

The problem usually occurs after a long run in 5th gear. When you come to change down from 5th you find that you can’t, then by applying brute force to the gear lever it does come out of 5th but won’t go into any other gear. If you stop and cut the engine, you can select other gears, but on starting the engine it feels like you shouldn’t have - it is very lurchy and grabby, because as well as being in your chosen gear, the 5th gear synchro ring is being pinched onto the 5th gear synchro cone and is trying to select 5th at the same time.

Descriptions by rip and valimar capture what it feels like (mine felt the same):
  • rip : “When I engage the clutch this happens with a lurch forward as something internal appears to move. I can then find my way through the gears up to 5th (but it is a little crunchy).”
  • valimar : “after driving hard (190km) for about one hour, the gear lever got stuck in 5th gear! I had to stop the engine a few times, to be able to change gears, and with some difficulties I could reach home. Putting the car in the garage backwards I had also problems: it was just like the wheels were blocking causing some resistance, not willing to go backwards. I suspect some synchromesh must be jammed.“
The car’s age or mileage would seem to be irrelevant: Andrew Ennis had his problem years ago on a low-mileage S2, my problems occurred at 96,000 miles and rip reports “Gerald told me that he remembers this being a more common fault when the cars were newer”.

So how can you tell if you have this problem and are there any advance warning signs? Yes, but they are easy to miss, and the first you are likely to know about it is being stuck in 5th. It is unlikely that you will be aware the nut has come loose. If you are very in-tune with your car you might detect a “whirring” sound at idle. With the benefit of hindsight, I believe that the slight “whirring” sound coming from my engine was probably the input gear contacting the output gear dog-ring and oil gutter bolt heads. Unbelievably for what was happening, the sound was very subtle and could not be heard on the move, but it definitely sounded “wrong”. I thought it was a CAS bearing as that was where the sound was loudest and changed the CAS, however the sound did not go away. The CAS was probably only conducting the sound and amplifying it inside the CAS cover. I wondered if it was associated with the cam-belt tensioner or water pump, however I never tried putting a screwdriver or stethoscope against the gearbox rear end cover; if I had, I’m sure I would have heard the source of the noise. Now that the 5th gear set has been replaced, the sound has disappeared (and I can hear all the other engine noises more clearly).

Cause of the problem:

The “Stuck in 5th gear” syndrome is caused by a chain of events that leads to the two pressed-together parts of the 5th output gear (the helical gear and the “dog” gear) separating, thus preventing the 5th gear synchro ring from disengaging and effectively jamming the gearbox in 5th. This process occurs gradually, and it may be thousands of miles before the effects are obvious. By the nature of its cause, the final jamming in 5th gear will occur after a period cruising in 5th gear.

Key to understanding the cause are four points (refer to the gearbox diagrams 1 to 4):
  • The 5th output gear is made up of two parts, pressed together on splines (see photo 15): one part is the helical gear which is permanently meshed with the input gear, and the other part is the dog-gear ring and conical mating surface onto which the yellow-metal synchro ring presses when the 5th selector gear assembly is moved to engage 5th gear. (This output gear is the one that has to be pressed back together as part of the repair technique often quoted from Gerald at GST.)
  • It is the selector assembly which is permanently fixed to the output shaft (by a splined drive and a 32mm nut torqued to 94 lb-ft with loctite), not the output gear. The output gear is completely free to move (both rotationally and laterally on the output shaft) and is only locked in position by the 5th gear selector assembly when 5th gear is engaged. (see photo 7)
  • When 5th gear is not engaged, there is sufficient space between the selector gear assembly and the output gear for the synchro ring to disengage from the conical mating surface of the dog gear and move freely.
  • When 5th gear is engaged, forces are channeled through the helical teeth of the input and output gears. The direction of rotation is such that the output gear is forced inwards on its shaft against a bearing and the input gear is forced outwards on its shaft against its lock-nut.
The 5th input gear is fixed to the primary shaft by splines and is retained by a 32mm nut (torqued to 94 lb-ft); the clutch is attached at the other end of the primary shaft. The 5th output gear is mounted on a needle roller bearing and spins freely (its helical gear permanently in mesh with - and permanently driven by - the input gear). At the end of the output shaft is the 5th synchro gear, which is permanently mounted on splines at the end of the output shaft and is also retained by a 32mm nut torqued to 94 lb-ft (see photo 4). It is only when the synchro gear is pushed inwards by the selector fork onto the dog gear part of the output gear (with the yellow-metal synchro ring sandwiched between the two ensuring crunch-free changes) that significant forces and drive are transmitted to the output gear. When drive is transmitted through 5th gear, the helical part of the output gear gear is forced inwards by the rotation of the input gear which (by Newton’s third law of action-and-reaction) forces itself outwards against its lock-nut. If the nut has loosened, the input gear forces itself outwards to meet (and lever off) the output dog gear set and to grind the heads off the bolts holding the oil gutter in place.

The initiation of the process through which the two parts of the 5th output gear become prised apart sufficiently to permanently engage 5th gear is the loosening (for unknown reasons) of the nut holding the 5th drive gear onto the primary (input) shaft. This nut eventually loosens enough that the only thing keeping it on the shaft is the mounting plate for the internal gearbox oil gutter which starts to be scored (see photo 2). Candles has posted “I find it hard to imagine how the input shaft nut works loose” and I agree. The rotation of the input shaft is certainly in the right direction to unwind the nut, however the nut has very small mass and it is hard to see how it could be unwound by inertia as it is torqued to 94 lb-ft, loctited in place and peened into grooves in the input shaft in two places. Nevertheless, it does unwind itself, perhaps through vibration or through small rotational movements of the gear on the splines eventually loosening the nut. Perhaps a very thin washer would help.

With no nut holding it in place, every time 5th gear is selected the drive forces applied through the helical input and output gears cause the 5th input drive gear to move outwards on its shaft, while forcing the helical part of the 5th output gear inwards on its shaft. When the unsecured 5th input drive gear moves outwards it meets two sets of obstructions: the “dog gear” wheel of the pressed-together 5th output gear and also the three bolts holding the internal gearbox oil drain gutter in place. The 5th input gear then proceeds to grind away at the three bolt heads (which are softer than it; see photo 3), thus allowing it to move out further, applying more force to lever the output dog gear set off the output helical gear. The dog gears of the 5th output gear are as hard as the 5th input gear and score the input gear (see photo 18). With the helical part of the pressed-together 5th output gear being forced inwards by the input gear and the dog gear being forced outwards, the composite 5th output gear begins to be levered apart (see photo 17). As the 5th input gear levers the output gear apart more and more, so it moves further outboard and grinds even more off the heads of the oil gutter bolts, allowing it to force the 5th output gear apart even more. Meanwhile the 32mm nut on the output shaft is still torqued up tight and is holding the 5th output gear assembly tightly in place. Critically, this nut is not holding the output gear itself in place (this gear is free to move on a needle-roller bearing), rather it is holding the 5th synchro gear and selector fork assembly in place (see photo 7). What this means that there is becoming less and less room for the 5th gear yellow-metal synchro ring (sandwiched between the synchro assembly and the output gear dog-ring) to disengage from the cone on the 5th output dog gear. Once the output gear has separated by 3mm all the space for the yellow-metal synchro ring to move has gone, and the synchro ring is permanently touching the cone of the dog gear - you are permanently in 5th gear.

Procedure to fix:

Refer also to Section FF of the Elan Service Notes (reference 5) and Specky’s write-up on this thread (reference 6).

Procedure part “a” - check your nuts:
  • Jack the front left of the car as high as you can, chock the rear right wheel securely and place an axle stand under the car. I also left the trolley jack in place.
  • Remove the left front wheel to gain access to the gearbox rear end cover (see photo 1) and place a drip tray under the cover to catch spillage.
  • Remove the air pipe from the wing to the throttle body, to gain access to the speedometer cable drive for oil filling and to the 5th gear set to remove the roll pins in the selector fork. (If you feel the need, move the coolant header tank, but it’s not necessary.)
  • Refer to Lotus Service Notes Section FF “Transmission”.
  • Thoroughly clean the area around where the speedo drive enters the gearbox and loosen the nut on the speedo drive locating plate, rotate the plate out of the way and remove the speedo drive from the gearbox oil-fill hole (reference 7). Find a suitable hose and funnel to allow you to top up or replace the oil.
  • Remove the seven bolts from the gearbox rear end cover. Note that they are different lengths, so ensure you know where they came from. The front one cannot be removed in situ owing to lack of clearance. A blow from a rubber mallet on the side of the cover should break the gasket seal and a small amount of oil will escape.
  • Remove the cover and check if the 32mm nut on the end of the input shaft (the one towards the front of the car) is still in place. It should be easy to see if its two peened-in markings still align with the grooves in the hollow input shaft, or if it has unwound past the end of the shaft (see photo 5). Also check if the two parts of the output gear (the one towards the rear of the car) are still pressed together or if a gap has opened (see photo 16). Check that the nuts on the input and output shafts are still torqued to 94 lb-ft (but don’t move them unless necessary or you will break the loctite seal). Check with a magnet for any metal particles in the cover, in the spilled oil or elsewhere. If all is well and you are only here to inspect things to allay your paranoia, breathe a sigh of relief, clean what you can get at (including the oil gutters in the cover plate) and put everything back together. You can even curse me for having induced the paranoia in the first place. If you’re here because you’re stuck in 5th gear, read on …
Procedure part “b” - if no significant damage is found:
  • If the input gear and its nut are loose, check inside the end cover you have removed for scoring of the oil gutter plate and for damage to the heads of the oil gutter mounting bolts (see photo 3). Check the face of the input gear for score marks (see photo 13). Check if a gap has opened between the two parts of the output gear (see photo 16). If you find any or all of these things, you have found your problem, and you will probably find metal particles in the oil, oil gutters and casing.
  • Remove the two concentric roll pins which hold the 5th gear selector fork on its selector shaft. I used a suitable punch/drift from below (approx 4mm diameter and as long as you can get). To allow the punch straight access to the roll pins the car must not be in 5th gear, and if the 5th input gear has moved outwards on its shaft you will have to move it back into its correct position (by putting the car in gear and tightening the nut as far as you can). Push, wiggle and persuade the 5th gear selector assembly inwards on its two shafts (the selector shaft and the output shaft) to select 5th gear as well as the other gear already selected using the gear lever (see photo 7). (It is not necessary to remove detent bolts, springs or balls.) You will probably have difficulty moving the selector assembly as the reason you are here is that the assembly has jammed up. The gearbox is now locked.
  • Un-peen the two 32mm nuts from input and output shafts (good luck with that) and unscrew the nuts. Pull/wiggle the entire selector off its two shafts as a complete assembly while holding it together (or bits will fall out) - see photo 8. Remove the output and input gears (and the yellow-metal synchro ring which will probably be wedged onto the output gear cone). Take everything to the bench for inspection.
  • The manual has specifications for clearances and tolerances should you want to check these. However you are really looking for something much more obvious (see photos 3 , 6 & 10). Look for a gap between the helical teeth and the dog teeth parts of the output gear, any broken or damaged gear teeth, or a worn yellow-metal synchro ring.
  • The output gear should have almost no gap between the helical teeth and the dog teeth (see photo 16) - if a gap exists (and there is no other damage), get it pressed back together by a garage or engineering works. If that’s all you find, count yourself lucky, clean everything up carefully looking for metal particles (including oil gutters and inside the hollow input & output shafts - check with a magnet) and put everything back together. You will probably find damage to the heads of the bolts holding the oil gutter inside the end cover if the input gear has ground these away. Use your judgement as to whether these need to be replaced (use green loctite) or just carefully filed. If you have found damaged metal, drain the gearbox oil, flush everything through (I used paraffin), check again for metal particles and when you are happy re-assemble everything and refill with oil. If you found more damage, read on …
Procedure part “c” ⁃ if further damage is found (in my case there was):
  • On the bench I found that my 5th output gear had separated such that a gap of 3mm existed between the helical gear and the dog gear (see photo 16), sufficient to prevent the yellow-metal synchro ring disengaging. As a consequence, the synchro cone showed minor signs of bluing (friction). Worse, a large piece of one helical tooth had broken off the output gear. Inspection of the gearbox bearing retainer plate inside the 5th gear compartment showed gouges consistent with something being caught behind the 5th input gear and carried into the 5th output gear teeth (see photo 12). The gouges are the traces of the broken-off piece of lock-nut being dragged on its quarter-turn journey to oblivion between the input and output gears. The gouge marks are most pronounced at the point where the output gear tooth unfortunately broke off, after which they stop abruptly. However, it could have been much worse: by a stroke of luck, the broken tooth became lodged in an oil gutter and did not get into the main gearbox to cause further destruction (see photo 11).
  • The problem then became one of finding spare parts. The 5th output gear is A100F6239S. Lotus have none (annoyingly they were on the 2016 Aftersales List at £36.73 instead of £186.42). Neither SJ not SW Lotus have them; I did not phone individual dealers. I called Lotus and spoke to Chris Brown who was very helpful. Lotus never had many of the 5th output gears in the first place and the last one was sold to Stratton in May 2017 to put on a customer’s car. He gave me an Isuzu equivalent number (8-97071745-0) which Brit-Car-Nut cross referenced (as 8970717450) to be the replacement for GM's 94139577 which is in the 1991 GEO Storm Single Cam engine. (Robie-the-robot lists gear ratios for various GEO Storm and Lotus Elan gearboxes (reference 8 ). Only the 5th gear is consistently similar, however Brit-Car-Nut has stated that only the Single Cam GEO Storm engine has compatible parts, and that is what he supplied to me.)
  • For the record, the parts are as follows:
    Output gear (the broken one): A100F6239S
    ⁃ 34 teeth
    ⁃ Outside diameter 74 mm
    ⁃ Inside diameter 41 mm
    ⁃ total gear wheel thickness 30 mm (2 parts pressed together) ; 33mm (if the 2 parts have been levered apart)
    Input gear: AlOOF62OOS
    ⁃ 41 teeth
    ⁃ Outside diameter 88 mm
    ⁃ Inside diameter max 26.8 mm between bases of splines; min 24.5 mm between tips of splines.
    ⁃ total gear wheel thickness 25.3 mm
    Fixing nuts:
    ⁃ Input shaft AlOOF6201S; output shaft AlOOF6245S (but both are identical)
    ⁃ 32mm AF
    Synchro ring, yellow metal: AlOOF6155S.
  • On finding such damage I took apart and cleaned the synchro assembly, carefully cleaned any metal debris that I could find from the cover, oil gutters and inside the hollow shafts. I drained the gearbox oil and flushed everything through twice with paraffin then once with oil, checking the drained fluids for metal particles (I used a magnet and also put fluids through a filter paper). Note that there is no magnet in the drain plug; there is a magnet inside the gearbox at the clutch end, however it is not easily accessible. After cleaning, I was happy that almost all of the metal debris had remained in the 5th gear compartment and not migrated to the main gearbox. It could have been a lot worse.
  • I fitted the replacement GEO Storm gears as a pair with their yellow metal synchro ring. I also replaced the three damaged bolts holding the oil gutter inside the cover plate, and proceeded as follows:
  • Fit the input gear onto the splines on the input shaft.
  • Lubricate the needle-roller bearing on the output shaft and fit the output gear to mesh with the input gear. Fit the yellow metal synchro ring onto the output gear synchro cone.
  • Reassemble the synchro assembly according to the Service Notes diagram and locate the selector fork in its groove. Punch/press the two concentric roll pins partly into the top hole in the selector fork to seat them securely (it will save swearing later). Fit the selector fork and synchro assembly onto their respective shafts at the same time. Once fitted, ensure that the selector mechanism locates correctly with the lugs on the yellow-metal synchro ring and can slide on its splines over the synchro ring and onto the dog teeth of the output gear. This was by far my most favourite part of the whole job. I enjoyed it so much I did it four or five times, sometimes pausing to find the little “hub inserts” that Specky refers to, which had pinged out. Push the selector inwards on its shaft to select 5th gear as well as another gear selected using the gear lever, thus locking the gearbox.
  • Thoroughly clean the threads at the ends of the input and output shafts with solvent to get rid of all oil, and apply the strongest Loctite you can find before fixing on a new 32mm lock nut on each and torqueing to 94 lb-ft.
  • Pull the selector fork outwards to its correct position and drive the two concentric roll-pins home.
  • Peen in the collars of the lock-nuts into the two grooves on each shaft. (Use a suitable punch and rotate the shafts using a socket on the nuts to afford the best access for your hammer & punch.)
  • Lubricate everything you can see with gear oil (see photo 19) .
  • Verify that you can select gears with the engine off.
  • Refit the gearbox rear end cover using a new gasket or liquid gasket. Torque the end cover bolts to 14 lb-ft (and apply liquid gasket to threads of topmost bolt as per Service Notes). Remember to place the front bolt in its hole in the cover before offering up the cover (space restrictions).
  • Refit the drain plug and torque to 29 lb-ft. Fill the gearbox (through the speedo drive hole) with 1.9 litres of Castrol Syntrans 75W-90. (This is a 75W-90 GL-4 fully synthetic gear oil. Do not use an oil classed as GL-5 as these contains additives which are corrosive to yellow metals such as synchro rings and bushings. Note that the Wiki wrongly recommends GL-5 oil. The gearbox oil originally specified by Lotus in the manuals and handbook was Mobil 1 RTS 9775 fully synthetic SAE 5W/30. When this was discontinued Lotus recommended Castrol TAF-X 75W-90, however this is no longer available and was replaced by Castrol Syntrans 75W-90 (Syntrax 75w-90 in the US).)
  • Refit the speedo cable, rotate the retaining plate back into place and tighten the bolt. Do not over-tighten - Lotus specify only 4-5 lb-ft.
    Remove axle stand, replace wheel and replace the throttle body intake hose.
  • Verify that you can select gears with the engine running. Test drive.


A common cause of being stuck in 5th gear is the 5th input gear becoming loose on the primary shaft and forcing apart the two pieces of the 5th output gear, eventually preventing the synchro ring from disengaging and jamming the gearbox in 5th. The nut retaining the 5th input gear is highly torqued and located using Loctite and peened in two places, so how it becomes loose is a mystery. One of the most remarkable things is that in most cases there can be so little damage caused by such a major components becoming loose and grinding and scoring the internals of the gearbox over thousands of miles!

It is a relatively simple DIY job to repair this problem. However, replacement parts are becoming scarce, even second-hand.

Although I suffered a broken gear wheel, I was lucky. If I haven’t fed your paranoia enough yet, having seen what a broken-off piece of soft metal locking nut did to my fifth gear set, just imagine what your gearbox would look like if a hardened steel broken gear-tooth got into it. Listen out for “whirring” sounds at idle, and remove the gearbox rear-end cover to check your nuts the next time you check or change your gear oil or whenever paranoia strikes.

  1. LEC thread “Gearbox Problems”: viewtopic.php?f=48&t=14484
  2. Selector Housing problem post by G UK » 20 Sep 2008 22:33 in thread “Unable to select a gear”: viewtopic.php?f=48&t=13347&p=174704&hilit=5th+Gear+problems#p174704
  3. Selector Housing problem LEC thread “No Reverse but gear cables look fine” by BigErch 23 Jun 2014 21:21 : viewtopic.php?f=48&t=23426&p=307145&hilit=reverse+spring+has+broken#p307145
  4. Selector Housing problem post by dapinky » 27 May 2015 22:00 “No Reverse but gear cables look fine”. viewtopic.php?f=48&t=23426&p=307153&hilit=selector+in+neutral#p307153
  5. Lotus Service Notes Section FF “Transmission”
  6. Procedure to fix “stuck in 5th” post by Specky » 14 Apr 2009 22:31 on this “Gearbox problems” thread: viewtopic.php?f=48&t=14484&p=194835#p194835
  7. - how to replace gearbox oil
  8. gear ratios table ... ission.htm

1) Gearbox diag1 Image

2) Gearbox diag2 Image

3) Gearbox diag3 Image

4) Gearbox diag4 Image

Photo captions:
  1. Gearbox end casing covering 5th gears.
  2. Inside of 5th gear compartment cover. The loose input gear wheel has chewed up the bolt heads holding on the lubrication channel and the nut has ground into the channel mounting plate. Image
  3. Chewed up bolt heads and mounting plate. Image
  4. The nut on the input shaft on the left (ie towards the front of the car) had broken its peened-in collar and loosened by several turns, allowing the gear wheel to move out towards the end of the shaft. Image
  5. The nut was completely loose, such that I could turn it by hand (compare the length of shaft protruding past the nut on the RHS shaft with the length of nut sticking beyond the end of the LHS shaft). Image
  6. The culprit. Broken peened collar of nut. Part of peening mark still visible. Image
  7. 5th selector fork moved in by hand to engage 5th gear.Image
  8. 5th selector fork assembly. Image
  9. Roller bearing for output gear, and drive teeth for synchro gear. Image
  10. Broken tooth on helical gear of 5th output gear. Image
  11. The missing tooth from 5th output gear was in the oil lubrication gutter in the 5th gear compartment. So I didn't have to take the gearbox apart to find it! Lucky! Image
  12. Marking on gearbox bearing retainer plate inside 5th gear compartment. Image
  13. Replacement GEO Storm 5th drive gear (input) on left cf. scored original on right. Image
  14. Replacement Geo Storm 5th output gear on left cf. damaged original on right. Note blueing heat damage to synchro cone. Image
  15. Replacement Geo Storm 5th output gear on left cf. damaged original on right. Note that the dog tooth/synchro cone part of the gear sticks out further on the original gear owing to separation of its two parts. Image
  16. Replacement Geo Storm 5th output gear on left cf. damaged original on right. Note that the dog tooth/synchro cone part of the old gear has separated from the helical tooth part of the gear by 3mm. Image
  17. Original input gear (left) and output gear (right) showing how the input gear has levered the output gear apart. Image
  18. Original input gear (left) and output gear (right) showing the input gear has been scored by the backs of the dog-teeth as it levered the output gear apart. Image
  19. Replacement gears in position, loctited and nuts peened into grooves. Image
Last edited by John_W on Mon 05.11.2018, 02:07, edited 3 times in total.
User avatar
Posts: 3780
Joined: Mon 21.04.2003, 12:31
Location: Aberdeen

Re: Gearbox problems

Postby Rambo » Sun 04.11.2018, 21:59

Well done John :bowdown:

Make sure the powers that be get that into WikiLEC alongside Alan Head's gearbox problems

PS I haven't read it all as it's way over my head, but the photo's are excellent :smt023
Last edited by Rambo on Sun 04.11.2018, 22:02, edited 1 time in total.
User avatar
Don't push me
Posts: 7647
Joined: Wed 24.12.2003, 00:37
Location: Kelso

Re: Gearbox problems

Postby John_W » Sun 04.11.2018, 22:02

Alan Head's already done a write-up!!! :banghead: :banghead: :bonk: :bonk:
User avatar
Posts: 3780
Joined: Mon 21.04.2003, 12:31
Location: Aberdeen

Re: Gearbox problems

Postby Brit-Car-Nut » Sun 04.11.2018, 22:11

Well written and well done!

Alan's write-up seems to be the gearbox removal process for jobs like a clutch replacement or changing to a non-slip diff kind of project (or a good clean of the engine area).

Planning some gearbox maintenance over winter.
Please contact me via eMail, not by PM
Lotus Manuals
Posts: 4698
Joined: Tue 03.07.2007, 17:07
Location: Charlotte, NC USA

Re: Gearbox problems

Postby dapinky » Sun 04.11.2018, 23:38

It's never a bad thing to have an updated 'how I did it' guide to refer to - nobody has the only way to achieve a result, and we all modify such procedures as we see fit (and then claim them to be the only way to do it!).

Rest assured, this will be published in a suitable repository :wink:

Just the one now, but this one's mine! - and it will be finished eventually.....

go on - click this link - you know you want to!
User avatar
LEC Administrator
Posts: 8713
Joined: Sun 15.10.2006, 12:54
Location: As far west as you can get in West Wales before you become Irish (Pembroke Dock).

Re: Gearbox problems

Postby Steve A » Mon 05.11.2018, 00:18

That's one epic posting John :clap: and very comprehensive :bowdown:
"If everything is under control, you are going too slow."
User avatar
Steve A
Posts: 2273
Joined: Tue 18.09.2007, 12:44
Location: South East Essex

Re: Gearbox problems

Postby JusNoGood » Tue 06.11.2018, 21:22

Incredible John :clap:

I'm the paranoid type. So I'll start to hear a whirring noise now :bonk: ....feeling very tempted to open her up to take a look now!
User avatar
Posts: 370
Joined: Fri 12.01.2018, 09:20
Location: Reigate, Surrey

Re: Gearbox problems

Postby John_W » Tue 06.11.2018, 21:37

Just try the stethoscope/screwdriver on the gearbox end-casing for starters.
User avatar
Posts: 3780
Joined: Mon 21.04.2003, 12:31
Location: Aberdeen

Re: Gearbox problems

Postby par » Fri 22.05.2020, 13:06

Maybe a bit of a long shot but does anyone know of alternatives for the 32mm nuts for 5th gear A100F6201S mentioned in this thread or any possible sources?

The only place I could find them listed online was at the Elise Shop however a few days after placing the order they cancelled it and issued a refund!

Is a similar sized driveshaft hub nut likely to up to the job?
User avatar
Posts: 452
Joined: Thu 19.02.2015, 23:22
Location: Fife

Re: Gearbox problems

Postby Brit-Car-Nut » Fri 22.05.2020, 15:16

The hub nut is much thicker and will scrape the cover.

A100F6201S is ALSO GM # 94124014.

There are several listed on eBay UK, but shipping costs are high.

Try your local Vauxhall dealer to see if they can still get one.

I have a bunch (14) but timely postage to the UK is stupid expensive and everything I have posted recently has missed the target delivery date by more than I liked.

The nuts are $14.00 each (the price has gone up since they became hard to find) and Priority postage is $45.00 (2 to 5 business days delivery).
I hope you can find one at a GM dealer in the UK.

When John Wham ordered the gear and gaskets, he ordered TWO (2) nuts. Maybe he will be willing to sell you his spare?
Please contact me via eMail, not by PM
Lotus Manuals
Posts: 4698
Joined: Tue 03.07.2007, 17:07
Location: Charlotte, NC USA

Re: Gearbox problems

Postby par » Fri 22.05.2020, 23:28

Thanks BCN!

Gives me another option to search for :)
User avatar
Posts: 452
Joined: Thu 19.02.2015, 23:22
Location: Fife


Return to Transmission, and Clutch

Who is online

Users browsing this forum: No registered users and 2 guests