131 drivetrain vibration query

[keith m 131]

Hi all,

Hope can someone help with this query.

I had bad vibraton under torque ie driving hard through the gears. I had the prop balanced and it improved slightly. I then changed the guibo on the gearbox and again had slight improvement.

Now the vibration under torque is minimal but the car will sit at 55 mph with no vibration at all however when I accelerate to 65 ish I get a loud drone with some vibration. When I back off the throttle and let the car slow back to 55 the noise and vibration disappears. 

I bought a replacement engine without a flywheel and fitted a flywheel I had spare to it and also fitted a new clutch aswell. Do you think that the flywheel or clutch could be causing the problem.

I thought that once a flywheel is balanced then it should be suitable for any 2ltr engine. Surely it is a disc that is balanced to run thru on any crankshaft. Am I being silly thinking that?

If this is the problem then is it expensive to have balanced and where can I get it done.

Could the clutch be causing the problem. I centred the clutch prior to fitting the gearbox.

All theories would be appreciated.

Cheers

Keith 
 
 
 

[djape1977]

i don't think it has anything to do with the clutch.
what about propshaft mount? did you change it? u joints? wheel bearings?

[keith m 131]

changed the centre bearing when I had the prop balanced. New UJ's fitted, new front wheel bearings but not changed rear bearings because the vibration appears to be coming through the gear lever so dont think it would be wheel bearings cos the vibration is intermittent.

What do you think about the possibility of the flywheel? Although if the flywheel was out of balance then would it not vibrate constantly. Am I right in thinking that it is the flywheel itself that is balanced and it is not balanced to a specific engine?

Thanks for the reply

[djape1977]

you're welcome. that's why we're here

as far as my experience on rwd fiats goes, clutch/flywheel combo will vibrate on start and not at high speed. in theory, flywheel should be balanced to a specific crankshaft, but just in theory. i never heard of anyone doing it unless preparing a race engine.

there's one more thing that makes such  vibrations and it has nothing to do with drivetrain. wheels! bent or wobbly wheelrims or damaged tyres will vibrate on some particular speed, and not in at any other. usually it's between 80 and 100km/h (aprox. 50-60mph) below or above that speed nothing happens. the easyest way to determine if wheels/tyres are faulty is to swap them temporary for other set and test the car. other way is to put the wheels one by one on the balancing machine and spin them by hand at low rpm. just look for a wobble or up/down motion. usual balancing won't show bent rims and weights won't correct it. damaged tyres also. wheel might be ok, but the tyre might show some up/down or side motion. it's easyly visible by naked eye. and before you ask, the vibrations are not felt just thru steerin wheel. sometimes steering wheel will not vibrate at all, while the whole car might.
usual way this kind of damage occurs is hitting a pothole or climbigh a curb. alloy wheels are prone to such damage.
one more thing that could be the cause is the faulty engine/gearbox mount. the way to tes those is to get under the car with a crowbar and try to lift the engine or gearbox. if they're not ok, you'll see...

sorry for my bad english, it ain't my native language

[keith m 131]

Thanks djape and steve, well I am really pleased to hear that the problem is nothing to do with balancing of the flywheel. Although if all else fails I will remove the bell housing and check that the flywheel is aligned correctly as pointed out by steve.

The car has been standing on new tyres and alloy wheels for 2 years or so whilst other projects took priorty, the car was moved and driven from time to time. The wheels have never even hit a pot hole.

I recently had the wheels checked and balanced, they are directional tyres, one of the rear wheels was 95 gramms out (quite alot) and the other three were all about 15-20 gramms out and these were factory balanced, hmmmm.
All balanced to zero now however do you still think that the tyres could be causing the problem ie. flat spots on tyres. Would flat spots on tyres not have shown up on the balancing machine. I have no vibration coming through the steering.

I dont have the car with me until next week so I cant carry out the elimination process on wheels as described by djape.

Have checked both engine and gearbox mounts and they look ok but it is hard to know what they behave like whilst under torque. I looked at the mounts for splitting and cracks etc, is that right if not what else sould I be looking for???

I fitted a brand new genuine Fiat clutch, by way of a pressure plate, disc and thrust bearing. So that should be ok.

If anything else pops into your heads then  please throw all ideas my way.

Regards

Keith

 

[jasonh131]

you should have had the whole prop balenced  includind the spidider out of the gearbox , when spliting the guido i allways mark it and put it back as it came out ,
 i foundto my annoyice on a alfa 75 with 3 guidos ,1 out of sink
jason

[keith m 131]

Thanks Jason, very good point I will keep what you say in mind.

Regards

keith