Technical Gearbox Problem

[Berger]

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.

 

[Berger]

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.

 

[Berger]

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.

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:

 

[Berger]

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.

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.

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!

 

[Berger]

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.

 

[Berger]

Thanks, I just wanted another opinion on things before i started down the wrong path.

Plan for this week is:
Monday, refit clutch and gearbox.

Tuesday: Rebuild car to a working state, fill box with oil etc.

Wednesday: Test gearbox and car. Cry or Woop that ive sorted/not sorted it.

Thursday: Remove gearbox from car.

Friday: Pop open gearboxes and start to remove bearings from them both.

Saturday/Sunday: Put my old AP clutch on the car (provided the gearbox works, will test in the week with the brand new clutch to avoid introducing more variables) and then refit newly built coupe turbo gearbox. Im not junking a £180 clutch kit if i dont have to! The other can sit on a shelf as a spare for when i need it.

 

[Berger]

Got the gearbox on the car (twice, forgot the clutch release bearing first time!) then rebuilt it to a state so its on wheels now.

Just needs filling with oil, the boost hoses popping on and the battery connecting up tomorrow.

So i should know tomorrow night if its the flywheel or the gearbox at fault!

Can remove and refit the gearbox quicker than the book time working on my drive now ive done it that many times! (3 1/2 hours)

 

[Berger]

Got it all back together and working today.

Used my old friction plate, pressure plate and flywheel. So i have a spare brand new MGR clutch.

Fitted the Type B diff into the coupe gearset/casing which i tested as a complete gearbox before i even opened it in the week.

Put it all together.

Works perfectly now.

Guessing it was broken gear selector mechanism / selector forks or syncros. For what it would have taken taking it all apart, all the syncros off the shafts etc to find out it seemed like way too much hassle, just changed the gearset out for a known working one.