Severe transmission failure

[vlad.tudose]

Hello,
I own 2 polos and this is my first post.

Yesterday I removed the gearbox from my 9n 1.2l manual. This is for diagnosis after a major failure in the road few weeks ago due to an attempted downshift where I accidentally dropped into 2nd instead of 4th.

Felt like something broke and the engine spins freely with very little power transmission (baby crawling pace in 1st gear clutch fully up 5k rpm). Furthermore, lifting the clutch at idle in 1st gear does not result in a stall but the car trembles. In terms of the clutch, the pedal felt exactly the same as before. On the other hand, no problems getting into any of the gears.

Nevertheless, I suspect it to be the gearbox. However some people have told me its the clutch. I would like to hear some other thoughts.

Also while I've got everything out the car is there anything else worth replacing, other than clutch of course? I wish to elmimiate a clunking noise which would present itself on every use of the clutch.

This weekend might take gearbox apart will keep updated.
Many thanks.

[RUM4MO]

Have you taken the clutch assembly apart, I'd hope that you have ripped/damaged the clutch plate's centre hub - the part that the gearbox input shaft engages into.
Have you tried, with the gearbox out of the car, engaging gears and turning either the gearbox input shaft or the drive shaft stubs?
If you have the gearbox out, why not buy a complete "clutch assembly" which should be driving plate, clutch cover and release assembly.

[vlad.tudose]

I really do hope it is just damage to the clutch. I have ordered a clutch assembly which I'll fit this weekend.

I didn't get the chance to remove clutch yet, getting the gearbox out was so temperamental without a lift or ramps.

I didn't try engaging the gears with the box out the car, as I removed the gear selector but I guess I still could have tried by fitting it back on.

I recall the input shaft being sturdy with no play and I believe it did have smooth motion. The driveshafts also were smoothly rotating. However maybe it is worth noting that the washer was broken on both driveshaft stubs which I removed -

Broken Component on both driveshaft stubs

s-l400.jpg (14.23 KiB) Viewed 2020 times

- and that the bell housing had a collection of what looked like dust + shavings?

[Adam_013]

I really do hope it is just damage to the clutch. I have ordered a clutch assembly which I'll fit this weekend.

I didn't get the chance to remove clutch yet, getting the gearbox out was so temperamental without a lift or ramps.

I didn't try engaging the gears with the box out the car, as I removed the gear selector but I guess I still could have tried by fitting it back on.

I recall the input shaft being sturdy with no play and I believe it did have smooth motion. The driveshafts also were smoothly rotating. However maybe it is worth noting that the washer was broken on both driveshaft stubs which I removed - s-l400.jpg - and that the bell housing had a collection of what looked like dust + shavings?

So thats what that is... When I changed the clutch in my 9n3 TDi this had split into 3 pieces, I carefully popped them back in and slapped it all back together and never caused an issue.
Maybe it's just luck, or that is simply doesn't do a lot.

[RUM4MO]

I recall the input shaft being sturdy with no play and I believe it did have smooth motion. The driveshafts also were smoothly rotating. However maybe it is worth noting that the washer was broken on both driveshaft stubs which I removed - and that the bell housing had a collection of what looked like dust + shavings?

I'm lucky enough not to have found that part broken, though the dust in the bellhousing is to be expected as that will be clutch plate dust etc.

[vlad.tudose]

So I had some time today to replace the clutch assembly. The replacement kit arrived pretty fast.

I found that the splines on the clutch disk were completely intact, but the disk itself was extremely worn. It also looked like it endured alot of heat, judging by the discoloration on the metallic part.

Using the gear selector which I fitted back on temporarily, I went through all gears and saw that the driveshaft stubs moved as I rotated input shaft, as expected.

Is it safe to say, then, that the gearbox is completely intact and that it was the clutch that caused the failure?
I know gearboxes are meant to be quite sturdy as long as they have the right amount of transmission oil.

Perhaps the clutch got so worn that it was slipping badly while the engine was spinning almost freely. I will admit that my driving style does involve alot of pressure on the clutch, some bad habits I will have to adapt.

Would this explain the sudden failure though? It definitely explains the excessive shavings in bell housing, engine spinning almost freely when reved and not stalling with clutch pedal fully lifted.

I guess all I need to do now is refit the gearbox after making sure the clutch disk is properly aligned (forgot about alignment tool). I just want to be certain so that I don't whack it back just to realise I'm still having problems.

I'm also considerng replacing the slave cylinder just for good measure. As for the clunking noise I mentioned earlier, I'm hoping the new throwout bearing and grease in the right places will take care of that.

Cheers

*EDIT*

After a bit of thought and looking at the photos more, I realise that the clutch disk wasn't just worn alot. It was literally worn to the bone.

The old disk still had friction material engine side, but transmission side aka the side that contacts pressure plate was bare metal. All the friction material had come off and it was literally scraping, with circular dowels leaving a ring scored into the pressure plate. When I compared with new clutch disk I foolishly assumed that the old disk was meant to have a bare metal side and the new disk was just better. Damn im stupid

Think I've cracked it though. Feel like a successful detective. And thankfully don't have to take apart gearbox.

[RUM4MO]

Thinking out loud, (not always a good idea), I was trying to work out why only one side of a cutch plate would get worn down to the metal, and one thing that would allow that to happen, ie only the engine side to get worn down, would be if the clutch plate was not free to move along the splines on the gearbox input shaft - make sure that you clean up the gearbox input splines and check that the clutch plate can move all the way along the splines.

I'm happy/willing to be corrected though.

Edit:- actually it is more likely that the unfortunate changing down into the wrong gear caused the flywheel side friction material to get ripped off - and after that the rivets would have cut into the flywheel.

Another Edit:- above is a bit wrong as it is the clutch cover side that lost it friction material, same reason though.

[alexperkins]

I really do hope it is just damage to the clutch. I have ordered a clutch assembly which I'll fit this weekend.

I didn't get the chance to remove clutch yet, getting the gearbox out was so temperamental without a lift or ramps.

I didn't try engaging the gears with the box out the car, as I removed the gear selector but I guess I still could have tried by fitting it back on.

I recall the input shaft being sturdy with no play and I believe it did have smooth motion. The driveshafts also were smoothly rotating. However maybe it is worth noting that the washer was broken on both driveshaft stubs which I removed - s-l400.jpg - and that the bell housing had a collection of what looked like dust + shavings?

These brass rings often break up, but they can go back in providing they havent been disturbed. They dont stay in one piece for very long

[RUM4MO]

I edited my last posting to correct it!

[vlad.tudose]

Thinking out loud, (not always a good idea), I was trying to work out why only one side of a cutch plate would get worn down to the metal, and one thing that would allow that to happen, ie only the engine side to get worn down, would be if the clutch plate was not free to move along the splines on the gearbox input shaft - make sure that you clean up the gearbox input splines and check that the clutch plate can move all the way along the splines.

I'm happy/willing to be corrected though.

Edit:- actually it is more likely that the unfortunate changing down into the wrong gear caused the flywheel side friction material to get ripped off - and after that the rivets would have cut into the flywheel.

Another Edit:- above is a bit wrong as it is the clutch cover side that lost it friction material, same reason though.

The flywheel side of the clutch disk was nearing the end of its life too. I am lucky that it was the gearbox side of friction material that went first otherwise I would have to replace the flywheel, which fortunately is still in good condition. Would much rather damage the pressure plate. Maybe clutch disks are made that way intentionally for this reason to protect the flywheel?

Im not sure how smooth the motion along the splines would have been with all the dust in there, but I do agree that the aggressive downshift is probably what tore up the last bit of the clutch disk on the gearbox side, which turned into the large bits of shavings. Ill make sure to clean and grease the splines properly though.

I hope you can see why I thought it was the gearbox though, due to the sudden breaking coincidentally happening at the same time as a nasty downshift.

This has all caused me to learn more about transmission and I'm glad it was just the clutch.

These brass rings often break up, but they can go back in providing they havent been disturbed. They dont stay in one piece for very long

Well too late now... I spent £20 for the bloody replacements! And this was cheaper on ebay than VW as they quoted me £17 each when I called them up... For a little brass ring!