020 Gearbox Troubles - Clues?

[HuH]

Hi,

The gearbox is an ACD close ratio five-speed gearbox which is not in the best shape, but it was working fine before I took it out and had new carrier bearings put in.

It's now back in the car but it has an intermittent issue when engaging first or reverse from a stop. Basically something doesn't engage until the clutch pedal is almost completely out and then it clunks into gear quite fiercely. It does not happen every time.

It's been suggested that the linkages are to blame and that it's not completely selecting first so the synchros are just spinning up and then the dogs are eventually engaging and causing the big clunk.

I noticed another weird symptom. The car was on a slight downwards slope, handbrake on and foot off the brake, I select first, keep the clutch in and release the handbrake, but the car does not start rolling. I slowly release the clutch pedal and build up a few revs but the gearbox was not engaging. To avoid the big clunk I clutch in and shift to neutral. Only then the weight of the car starts it rolling on the slope.

Something in the box was holding the car on the slope despite the clutch being disengaged.

Can anyone suggest possible causes? Ways I can try to fix it? I do recall one of the linkages being mildly bent when I took the gearbox out. I will have another look and see if I can straighten it just in case that is part of the problem.

Thanks.

[roccodingo]

possibly a lot of things mate.

Was the bearing swap done by a reputable workshop with intrinsic VW knowledge ??

From you description of the car being unable to roll downhill ( how steep) with the clutch in and handbrake off it sounds like there is too much preload on the diff carrier bearings. or could be a load of other problems.

The carrier bearing replacement needs to be done and the diff centre checked for rolling resistance. Its not just a swap them bearings over and put it back together excersise unfortunately. Bearings even tho there made to tight tolerances still have an individual variation. Installing new ones means the precise parts need to have a certain amount of resistance to rotate in operation so careful measuring and then adjustment by shims is critical for correct set up. The right set up will give you a quiet and long service life for those components.

Check with whoever you used as to if and how they adjusted the bearings. maybe it is the shift linkage, but I have never heard of the shift linkages causing partial engagement, usually it either does or it doesnt...

Check out my friend Brians rebuild page for more info.. Welcome to BrokeVW.com

Post up what you find. good luck.

[gldgti]

possibly a lot of things mate.

Was the bearing swap done by a reputable workshop with intrinsic VW knowledge ??

From you description of the car being unable to roll downhill ( how steep) with the clutch in and handbrake off it sounds like there is too much preload on the diff carrier bearings. or could be a load of other problems.

The carrier bearing replacement needs to be done and the diff centre checked for rolling resistance. Its not just a swap them bearings over and put it back together excersise unfortunately. Bearings even tho there made to tight tolerances still have an individual variation. Installing new ones means the precise parts need to have a certain amount of resistance to rotate in operation so careful measuring and then adjustment by shims is critical for correct set up. The right set up will give you a quiet and long service life for those components.

Check with whoever you used as to if and how they adjusted the bearings. maybe it is the shift linkage, but I have never heard of the shift linkages causing partial engagement, usually it either does or it doesnt...

Check out my friend Brians rebuild page for more info.. Welcome to BrokeVW.com

Post up what you find. good luck.

I agree - thats exactly what I was thinking. Seems like maybe the differential is holding everyhting still, so when the car is not moving it makes engagement of 1st and reverse difficult.

[Dub Toffee]

Don't know if you know Julian but, he's a go to man for anything VW especially Gearboxs.
based in Sydney 0405 808 488

[mk1turbo79]

I don't know Julian, but there would have to be something wrong to send a box out with enough diff preload to stop the car rolling. At a guess you would need about 0.5mm or more to actually stop a car rolling.

so when the car is not moving it makes engagement of 1st and reverse difficult.

If that was the case every time you have your foot on the brakes it would be hard to get gears?

[gldgti]

If that was the case every time you have your foot on the brakes it would be hard to get gears?

not exactly what I was trying to say, but dont forget there's 2 cv joints on each side between the brakes and the differential that allow some rotation before they take up.... its often only a matter of a tooth width.

[CPITUNING]

Check out my friend Brians rebuild page for more info.. Welcome to BrokeVW.com

+1 - this site has a wealth of information. I diagnosed and fixed my gearbox by using this site.. brilliant!

[HuH]

Thanks a lot for the responses. Really helpful stuff. I've driven the car a little more and I'm less sure about what the problem is now, but the theory about diff preload seems very plausible. It's really hard to diagnose as it's not a consistent problem. Surely if it was preload it would be an issue all the time?

Holding the clutch in at a set of lights with first engaged is pretty much guaranteed to cause a problem when you take off, but shifting to neutral and leaving the clutch out while waiting then clutching in and selecting first when you're ready to take off gives perfect results more or less every time. When you want to get reverse things get tricky, and shifting from reverse to first in one movement with the clutch in is a problem as well. Reverse to neutral (clutch out) then into first is usually fine however.

Sadly I may not find out the answer as I'll be selling the car on to a buyer who knows about the issue and is going to investigate/solve it. I'll try and find out what he discovers.

The bearing swap was done by a very well known gearbox and diff shop here in Sydney. They knew about the preloaded diff setup before they opened it as well. I did put pressure on them to get the gearbox done as I was leaving to go overseas, so it's possible they Friday afternooned it in a bit of a hurry.

[gldgti]

Hey mate,

The other thing I could think of is that the clutch disk might not be running true and thus, dragging. That can make selecting 1st and reverse very hard.

I had a similar problem once with my mk3. I found a bit of metal swarf was caught under one of the diaphragm spring fingers in the pressure plate which was causing the issue.