Vibrations - only at full throttle in lower gears?

[Effjay]

Hi guys,

I have a bit of an issue with my Grande Punto - recently completed a fairly significant big turbo conversion including forged internals, new cams etc.

When accelerating with heavy/full throttle in gears 1-3 there is a vibration coming through the car, it's fairly significant, more than an exhaust vibrating against bodywork for example. It feels like clutch judder, but it only happens at full (or near enough full) throttle and continues all the way through the revs - whenever I've experienced clutch judder before it's only been at lower revs?

It's not an engine misfire - the engine revs cleanly, there's just vibration along with it; it definitely feels drive train related.

Going full throttle in fourth gear the vibrations don't appear, the car accelerates vibration free all the way to redline. The vibrations also don't appear if you take the revs up at part throttle in any gear.

Only thing I can think it may be is a contaminated clutch plate. I had a leak from the sump on the clutch side due to missing a bit with the sump sealant, and I'm wondering if some of the engine oil has worked it's way on to the clutch somehow, although realistically I'm not sure how likely this is.

Before I start tearing things apart, I just wondered if anybody had experienced anything similar? Or had any ideas what this is likely to be?

Thanks.

[GreenV8S]

Clutch torque would be broadly similar in every gear and if anything slightly greater in the higher gears, so the symptoms don't suggest a clutch slip issue.

From the symptoms my first guess would be that peak prop shaft torque in the lower gears is flexing the engine / gearbox mounts far enough for something to foul.

[Little Pete]

It is unlikely to be oil on the drive plate causing the problem. Once the clutch is fully engaged the only problem you would get would be clutch slip. I would think it is something worn on the drive train causing the vibration under load. Check for any up and down movement in the driveshaft inner joints where they come out of the gearbox. This would indicate worn differential bearings. If the offside shaft has a support bearing in a housing mounted to the engine, check for play here too. Is there any noise on acceleration or deceleration or is there a noise accompanying the vibration or is it something you can feel rather than hear?
I would also drain the gearbox oil into a clean container and look for evidence of bearing failure in the oil.

[stevieturbo]

Nothing you describe suggests anything clutch related.

The fact you say it does it in some gears and not others, pretty much suggests a gearbox related problem

Are there only 4 gears ?

[Effjay]

Thanks for the responses so far.

Little Pete said:

It is unlikely to be oil on the drive plate causing the problem. Once the clutch is fully engaged the only problem you would get would be clutch slip. I would think it is something worn on the drive train causing the vibration under load. Check for any up and down movement in the driveshaft inner joints where they come out of the gearbox. This would indicate worn differential bearings. If the offside shaft has a support bearing in a housing mounted to the engine, check for play here too. Is there any noise on acceleration or deceleration or is there a noise accompanying the vibration or is it something you can feel rather than hear?
I would also drain the gearbox oil into a clean container and look for evidence of bearing failure in the oil.

Thanks, will give all of these a thorough check over at the weekend.

No noise that I could tell, however the exhaust that's on the car at the minute is fairly loud so may have been masking something; again, will check this out at the weekend.

stevieturbo said:

Nothing you describe suggests anything clutch related.

The fact you say it does it in some gears and not others, pretty much suggests a gearbox related problem

Are there only 4 gears ?

Car has 5 gears. When I said fourth, I really meant fourth and higher.

Edited by Effjay on Tuesday 3rd January 17:45

[AER]

Could be engine mounts or, perhaps more likely, driveshaft/CV joints failing.

[VYT]

AER said:

Could be engine mounts or, perhaps more likely, driveshaft/CV joints failing.

I'd go with this as a first check.

Op says "Fairly significant turbo conversion". More torque causing the engine to flex more on the mounts. Only happens in lower gears when drive line torque is higher.

[imagineifyeswill]

Puntos are prone to the differential bearings collapsing but normally noisy enough that you would know about it.