Unexplained Clutch Fork Wobble - Can Anyone Shed Some Light?

[garthalgar]

Right, so my MK3 Carlton Estate needed a new clutch (well, didnt need, but as i'm driving it to rome I decided a new clutch may be a good idea). I bought a replacement 3 piece clutch to fit and spent a saturday casually working away to fit it.

Started the car up and the vibrations coming from the clutch pedal were awful. Quick look underneath showed the clutch fork vibrating quite badly. After a few ideas and realising that the bearing was quite loose in the posts, I bought a new LUK thrust bearing to fit. The length of the flats were 1mm shorter than the previous bearing (and felt much better quality), so this fit snugly inside the posts. I figured this would fix it, as I thought that the bearing being loose could let the arm move. Well despite the new thrust bearing being a perfect fit in the arm, it still wobbles. It does it all through the rev range, but gets really bad between 1500 and 2100 rpm.

If you push lightly onto the pedal it goes away. I cant think what else it could be? The fingers on the diaphragm all appear to be flat, none poking up. The clutch is aligned correctly, and in fact, feels fantastic, as a new clutch should. It doesnt slip at all either. Its just the fork vibrates when you let off the pedal. It is definitely correctly adjusted, so that it sits in line, maybe slight further forward than the brake pedal. 

Could someone shed some light or have an idea? I drove it around today and did about 80 miles to see if it would die down, but its still there. don't want to end up destroying a bearing/fork/clutch. And anything that doesnt involve removing the gearbox for the third time would be fantastic! Starting to lose the plot haha.

Heres a video from showing the fork wobbling...

[820]

It could be wear to the gearbox sleeve the bearing sits on, was there much muck on it when you removed the old bearing.
How is the clutch arm mounted in the bellhousing? is it on a ball, is there a spring missing or not sitting correctly.
You could try adding a little freeplay to the cable so the bearing can clear the clutch pressure plate to prevent it continually spinning with the engine. If the cable was adjusted previously to bring up the pedal on the old clutch you might find you have to slacken it for the new clutch.

[v8ian]

I was going to ask if there is a spring missing??? Is the cable adjusted correctly, I used to back the arm off so there was about 3mm of free play at the arm so the bearing is off the clutch,

[garthalgar]

May 9, 2015 21:03:59 GMT 820 said:

It could be wear to the gearbox sleeve the bearing sits on, was there much muck on it when you removed the old bearing.
How is the clutch arm mounted in the bellhousing? is it on a ball, is there a spring missing or not sitting correctly.
You could try adding a little freeplay to the cable so the bearing can clear the clutch pressure plate to prevent it continually spinning with the engine. If the cable was adjusted previously to bring up the pedal on the old clutch you might find you have to slacken it for the new clutch.

don't think its the sleeve. The sleeve is plastic anyway so cant imagine they would use a plastic sleeve if it were to wear. There werent any ridges at all signifying that it had worn. Was hardly any much at all.

The clutch arm is mounted on a ball on the farside of the bearing and the bearing sits in the middle. The ball isnt worn at all and the prongs that hold it onto the ball are tight. It has now been apart twice so definitely no spring/bolt etc missing!

If you add freeplay to the cable it vibrates even worse, which makes me think more that its an adjustment issue. The bearing is there to spin on the fingers anyway isnt it? The clutch cable is probably original and well stretched over the 126000 miles its done anyway.

May 9, 2015 21:43:17 GMT v8ian said:

I was going to ask if there is a spring missing??? Is the cable adjusted correctly, I used to back the arm off so there was about 3mm of free play at the arm so the bearing is off the clutch,

Definitely no spring missing...

When you wind the adjuster all the way in, the wobbling stops, but the clutch pedal sits to high (the only adjuster for this is on the fork itself). I think, due to the original being well stretched, that if I replace the clutch cable, I can put the same amount of tension on the arm with a fewer amount of threads, therefore taking the pedal down to where it should sit and fixing the issue?

I hope that makes sense.... I want to try that anyway before I take the gearbox out again because i'm convinced that is all correct. The clutch genuinely feels perfect. It only wobbles when you let off the clutch, where i think it may be 'bouncing' off the diaphragm. 

[v8ian]

I think the Idea of changing the cable is probably a good idea, 2 reasons, the cable will let you down when you don't expect it, and as you said its well stretched.....

[garthalgar]

Cable replaced. No dice. So investimigated again...

Pulled the arm away from the diaphragm then slowly let it return. You could hear where some fingers, almost a side of them, hit the bearing. As you let the bearing rest on the diaphragm it starts juddering and wobbling.

So, pulled gearbox back off again to look at the fingers in detail. Stuck it on the bench and checked the height with a vernier. 4 or 5 fingers on one side are 0.5mm shorter than the rest. I think this would be enough, when spinning at engine speeds, to cause the fork to do its wibbly wobbly thing. Ive replaced the bearing, cable and made sure everything was correctly done up. It wasnt doing it before so this has to be the issue by process of elimination!

Ah well, i'll be speaking to the seller I bought the clutch from and hopefully getting a refund as its clearly faulty. Time for a second new clutch. Deary me.

You can just about see the gaps in these photos...