engine vibration

Need some advice

My car an 83 sc with 77k miles runs fine in all respects except for a noticable engine vibration when accelerating hard. I have only recently noticed this and it appears to get worse as the rpm rise, paticuarly above 3000rpm. The clutch is nearing the end of its life with plenty of juddering on take up, could it be due to the clutch ? I am assuming that its not the main bearings as the vibration is not present at low rpm. I baught the car some time ago and this is definatly a recent problem, approx last 500 miles, Oh and the oil pressure is good at 4 bar

whats going on guys ?

Bruce

Does it vibrate when revved in neutral? If not, it sounds like drivetrain. (CV joint, motor mounts etc.) If it does vibrate in neutral, I'd guess either an exploding rubber centered clutch disc or if it was updated, broken/missing damper springs in the clutch disc.

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Tyson Schmidt
72 911 Cabriolet

That's right. Engine vibration is really FAST, and rare. A slower, more shuddering vibration is often a CV joint or something. Think simple.

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'83 SC

when was the last time you inspected your cv joints and half shafts? i just finally cured the same prob on my '85 after checking EVERYTHING else. the splines on one of the ends of my half shafts were heavily worn and i also had some pretty significant pitting in 3 of 4 of my joints... caused the exact same symptoms you are describing. fwiw...

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Adam Nitti
ajnitti@mindspring.com
www.adamnitti.com
'85 911 Carrera Coupe

thanks for the advice, I am about to go and do the checks as you all suggested. Post results later

Bruce

I have just driven the car with the following results:-

There is no vibration at idle or when revved in neutral

The vibration is very noticable in first and second gear and to lesser extent in third.

It is definatly gets worse the harder you accellerate

If you lift of the vibration stops

It appears to be related to wheel speed not engine speed

Its surprising how rough the car feels now I know its there, I just guess these thing must be really gradual in nature not helped by the weekend low mileage use only.

So what the final diagnosis, cv joints?
if so are there any ways to check on the car?

Thanks


Bruce

I am most suspicious of the CV joints. Grab the drive shafts and twist them, and also push-pull them up and down. As I said, there should be NO play axially.

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'83 SC

Boots broken or torn? If so, may have been a loss of grease or contamination causing CV joints to go bad. If they're okay, could still be bad joints, though. Any funny sounds when you go around a corner, such as clanking? Suspect CV joints here.
regards,
jlex.

i would think that if you had a cv prob you'd feel it to some extent in all gears under hard acceleration.

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Adam Nitti
ajnitti@mindspring.com
www.adamnitti.com
'85 911 Carrera Coupe

well I just tried to check the cv's, by turning the gearbox output flange by hand with the car on the ground and wheels locked by the hand brake (very awkward and long reach). The flange can can be turned 1/8" or so. It feels quite rough and notchy with most slack apparent on the inner cv joint. The drive shafts are quite free to float axially between the inner and outer cv,s.

Is this conclusive of the cv's being worn or am I not checking them correctly?

Bruce

You may have found your problem. With everything free (gearbox in neutral, handbrake off) see if you can twist the drive shaft relative to the tranny drive flange. If you can, this is your problem. This also makes sense to me because inner CV joints tend to shudder when worn.

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'83 SC

Adam Nitti is the newest expert on changing out the bearings... I'm sure he'll sacrifice a weekend to help out if you don't want to get dirty.
regards,
jlex.