[Ndv]

Hi everyone

Could my vibration/shudder on acceleration be due to slightly bent input shaft ?

A few months ago I wrecked the standard clutch on my 2 litre coupe on a track day in Brands Hatch. Two of the three metal strips that connect the pressure plate to the diaphragm broke. It was quite a bang, but managed to get car back to pits in limp mode as it was in the last corner...

I then decided to replace with an uprated performance clutch and new flywheel.

This all works fine, but I have/don't the following symptoms:
-Upon acceleration in 2nd, 3rd, or 4th gear, the clutch/gearbox noticeably vibrates/shudders in the rev range of about 2000 to 3500
-This only happens when the clutch is fully engaged, that is, it is not some kind of clutch shudder upon engagement from a contaminated friction plate etc
-If I rev the engine with clutch disengaged, it is smooth enough (that is, no miss-balance of crank vs new flywheel/clutch assembly)
-Also, gearbox has undergone recent rebuilt, so I assume its not the input shaft bearing that is worn

This leaves me to think that possibly:
-When the standard clutch broke, it gave a significant knock to the friction disc/input shaft
-The input shaft is now slightly bent/out of kilter, which causes the symptoms described above

Curious if anyone has experienced this in the past, and if there is a way to confirm the hypothesis without taking the gearbox apart ? Any other suggestions welcome.

Thanks
Niels

 

[Alfamale 62]

Not on same car but I switched to a performance clutch and it vibrated horribly I took it back and fitted another same thing, so went back to a new OEM and it was fine.
Your going to have to split the box from the engine so easy enough to put a dial test indicator on the gearbox input shaft, if that's good and the brass bush in the crank is in spec I'd try an OEM clutch and pressure plate if you can loan one

 

[bellagt]

The other parts around the shaft (bearing, aluminum case) are more likely to yield, bend or break before the input shaft would.

 

[Andrew]

I had a slightly bent input shaft on an MGA Twin Cam but it gave no symptoms. Vibration is rpm-related, not road-speed-related? There are many possibilities. Try to eliminate one at a time.
I have heard of out-of-balance clutches but I've never run into it, especially at such a low rpm. Did you remove the flywheel? Exhaust is hanging happily? Did you change the trans mount? Change the driveshaft at all?
Andrew

 

[r-mm]

Every time I've brought a rotating assembly to my highly capable machinist he has commented that he never needs to do more than kiss a crank, flywheel but that pressure plates are horrible offenders. He welded a big honker of a patch on my alfa and had to do some surgery to my porsche. all nice factory sachs stuff, you think they'd be good but no.

 

[IanB]

You're going to need to drop the trans and check for run-out.
Check the flywheel, the input shaft, and for the heck of it - the clutch disc itself.

All need to be in-spec.
IF they are in spec, then you are onto the driveshaft, quibo, u-joints - something further back....
Vibration is something spinning out of spec. - IMHO