Technical Gearbox Problem

Berger

Berger

Berger

Soldato
Joined
22 May 2003
Posts
10,856
Location
Wigan
Back in November i removed the gearbox from my turbo, and fitted a rebuilt 620Ti gearbox with LSD. Managed about 2000 miles on it, got it back from MOT then within 50 miles it became increasingly hard to get it into 1st and 5th gear, mainly 5th, and they all started to get slightly crunchy.

Took it off the road and stuck it on a SORN then set about trying to find the fault. Here is where i have got to so far and im running out of ideas or easy fixes!

When the car is cold it goes into all gears fine, but as it warms up it gets increasingly difficult to select 1st, once you have rammed it in 1st and keep the clutch depressed it will select all gears nicely.

The box is filled correctly to the right level, drained to confirm.

The gear selector UJ/Yoke is good, not effort here.

The clutch bracket isnt flexing or broken.

The clutch cable is brand new.

Thought the clutch could have been at fault, Picture of old clutch, looks slightly unevenly worn but not bad by any means, plenty of meat left on it. removed it and fitted a brand new OEM MGR friction plate, pressure plate and clutch release bearing.

Rebuilt the gearbox into a new casing and replaced the selector rod, couldnt see any problems, but im not a professional but ive built 3 other boxes and all work fine....

Im thinking perhaps its blown a syncro or something internally in the gearbox which isnt easily identifyed, gets driven hard but has been well maintained.

Otherwise ive no idea, its been suggested the flywheel could be at fault but i cant see how this would impact on gearbox selection, i would expect it to just slip, ive never had a problem with the clutch slipping before. Could get this skimmed locally, what should I expect to be paying, £25 or so? Cant hurt when the gearbox is off, but then if i go replacing two things at once ill not know what the problem is.

But then its not exactly a 5 minute job to take the gearbox off and put it back on and rebuild it to a usable state. Day and a half probably working on the drive. Maybe a long day at best.
 
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A syncro would only affect the one gear so I wouldn't have thought it's that. If it's affecting all gears you'd have to look towards either something in the selector mechanism or the clutch not disengaging fully (Which is where the flywheel diagnosis comes in.)
 
My (Amandas) 206 does this. It's the gear linkages. Quoted £70 inc labour to sort out.
 
Its not the gear linkages, these are fine.

Its a hot/cold problem, works fine when cold, but when heated and obviously something expands then the problem occurs.
 
Sounds like the synchro like Kaiowas mentioned. Unfortunately I've never worked out how synchro actually works so I can't comment on what might be worn out, but the synchro looks like a set of tapered rings and gubbins inline with the gears inside the gearbox. If it's worn out it will crunch the gears and they will be hard to select, hot oil is thinner so will bypass the synchro faster and it will crunch more. :p
 
Berger said:
Its not the gear linkages, these are fine.

Its a hot/cold problem, works fine when cold, but when heated and obviously something expands then the problem occurs.
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That nearly always points to a clutch problem. A dragging clutch will make it very hard to engage gears. Check the flexy hydraulic pipe between master and slave cylinder and make sure it's not swelling up under pressure when hot. Have you flushed the system through with new fluid and thoroughly bled it?
 
First thing's first, who rebuilt it in the first place and how many miles had it done before rebuild and were the synchros replaced? Also can you describe in more detail what you mean by 'increasingly hard to get it into 1st and 5th gear, mainly 5th'.

What kind of oil do you have in it and have you tried a different oil? This is the first thing that i would try.

I would rule out a problem with the clutch if you've replaced it and the flywheel will only need skimming if the clutch judders when you slip it. If the biting point of the clutch is no where near the top of the pedal travel then it should be ok.

What car is it? Is 5th top gear as some people drive with their hand on the gear lever which puts pressure on the selector fork and creates excessive wear?
 
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Dogbreath said:
That nearly always points to a clutch problem. A dragging clutch will make it very hard to engage gears. Check the flexy hydraulic pipe between master and slave cylinder and make sure it's not swelling up under pressure when hot. Have you flushed the system through with new fluid and thoroughly bled it?
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He said it's cable operated.
 
Dogbreath said:
Good point. In which case he need to check the surface of the flywheel for any run out, ensure all the fingers on the pressure plate are at the same height, and check that the release bearing is perfectly square to the pressure plate.
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You cant have the release bearing not square to the pressure plate, you put it on the forks for the clutch release on the gearbox input shaft before you put it onto the car.

The gearbox had done ~70k miles, when i say rebuilt, i removed it, opened the gearbox up, checked for excessive wear in the gearbox and replaced all the bearings and seals. All the gearbox rebuilders and the bearing supplier i used said dont bother to reshim the box as it wont need it. Took their advice, and it ran perfectly for 2000 miles as i said, then within 50 miles went pete tong.

When cold you can put it in gear fine, perhaps a little less smooth than ideal but it goes in fine, as the car comes up to temperature it gets more difficult to select the gears.

1st is the hardest, but none of them are as they should be. As you push the gearstick over, then when you go to push it forward, which would pull the selector inside the gearbox and the gears downwards you meet resistance. It physically wont go into gear no matter how hard you try.

Im using MTF94 which is the only recommended oil for use in Rover/Honda PG1 gearboxes.

I had the problems with a 12k mile AP uprated clutch, fitted a brand new OEM MGR clutch as i thought i may have bent the fingers fitting the box the first time by hand. Refitted the box using my engine crane taking lots of care, went on perfect. So its not a clutch problem.

Removed the gearbox/clutch after work tonight, took a photograph of the flywheel:

16052008132sm8.jpg
 
Berger said:
You cant have the release bearing not square to the pressure plate
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I'm not particularly familiar with the PG1 but the release bearing usually slides along a sleeve which runs over the gearbox input shaft. If this sleeve is bent or damaged in any way it's entirely possible for the release bearing to not run square to the fingers. Also if the bell-housing does not bolt up perfectly square to the engine due to e.g. a damaged dowel or bruised surface this will cause the same problem.

Removed the gearbox/clutch after work tonight, took a photograph of the flywheel:
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It looks as though the flywheel has seen some pretty high temperatures with those surface cracks. Are the "splodges" greasy finger prints or discoloured areas of metal? If it's the later, that's another sign of overheating. It's quite possible the flywheel has been distorted by excess heat which could cause your problems. I certainly wouldn't re-assemble without at least resurfacing that flywheel. If it's been really toasted you probably won't be able to remove the discoloured areas (assuming not greasy finger prints!) by skimming, a new or good s/h flywheel would be needed.
 
Berger said:
When cold you can put it in gear fine, perhaps a little less smooth than ideal but it goes in fine, as the car comes up to temperature it gets more difficult to select the gears.

1st is the hardest, but none of them are as they should be. As you push the gearstick over, then when you go to push it forward, which would pull the selector inside the gearbox and the gears downwards you meet resistance. It physically wont go into gear no matter how hard you try.
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That flywheel does look like it's had a hard life but I don't think it's the root of your problem. As long as the clutch is disengaging properly when the pedal is depressed then it can't cause an issue with gear shift.

First make sure that you haven't got too much free play in the pedal so that you get enough pull on the clutch to lift the pressure plate. If the biting point is near the floor (too much free play) then it may drag and give you shift problems.

Then what you need to do is get it all hot so that it becomes difficult to shift, then stop the car and try to run through the gears. If it's ok then that would point to a problem with the synchros. If it's still a problem then I would be looking for an issue with selector movement.

Considering it's in all gears that you have this problem, then I would be more inclined to say that you have an issue with the selector movement.

Hope this helps.
 
wolvers69 said:
That flywheel does look like it's had a hard life but I don't think it's the root of your problem. As long as the clutch is disengaging properly when the pedal is depressed then it can't cause an issue with gear shift.

Then what you need to do is get it all hot so that it becomes difficult to shift, then stop the car and try to run through the gears. If it's ok then that would point to a problem with the synchros. If it's still a problem then I would be looking for an issue with selector movement.

Considering it's in all gears that you have this problem, then I would be more inclined to say that you have an issue with the selector movement.

Hope this helps.
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I got it to the point where it was warm and would give me issues on the drive before i took it apart. My mate found a BMW bulletin for the same problem, which recommended warming it up, holding at the point of resistance and turning the car off.

Possible causes inside of the transmission:
- - Faulty synchronization.
- - Internal gear shift linkage binding.
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Held it at the point of resistance in 1st, turned it off and it was still tough to engage first, pointing at the gearbox.

Flywheel could probably be replaced/skimmed but it doesnt look much different to the others ive seen... They could all be cooked mind!
 
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wolvers69 said:
Then what you need to do is get it all hot so that it becomes difficult to shift, then stop the car and try to run through the gears. If it's ok then that would point to a problem with the synchros.
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To go a bit further, if it's very stiff when hot with the engine turned off, this would point to a gearbox fault. If it changes ok when hot and engine off, then it points to a clutch issue.
 
No its still stiff with the engine off when hot.

Have a spare gearbox which i bought from a rover forum member that i can put on.

This one came from a scrappers last year but it wouldnt suprise me if its blown since then when it was on my car.

Thinking ill fit the other gearbox to the car, see if it works, if so then remove it from the car and fit the differential from the faulty gearbox as its the later type B. Ill junk the shafts/mechanism if they are likely to be no good. Not spending hours troubleshooting and replacing parts when they are 10 a penny, the only parts of worth are the casing and the torSen differential.

The coupe box has a type A which are known to fail. One side sheers off resulting in it throwing the driveshaft out and losing all drive.

Provided the weather is good i can have it rebuilt in a couple of hours to a state when i can test it. Probably a weeks worth of 90 min shifts after work to get it on the car, off and back on again.
 
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