Vibration

[mickl]

The car vibrates when moving along, worst maybe at about 60kmph. The vibration is not in the steering as the steering wheel is quite smooth, it seems to be coming from the floor and i feel it through my seat. i am thinking maybe the tailshaft is not properly balanced?
Any ideas or tests I can do, or should it go in to a specialist??
Cheers
Mickl

[colcol]

If it has started to vibrate, you have most likely lost a balance weight off your prop shaft, or picked up a rag or plastic bag that has wrapped itself around the shaft, or you could have lost the clamp bolts off it and it has gone out of balance, get under the car safely and see if there is anything that looks dodgy, turn the shaft and see if it is running out, [ not turning a true circle], or if there are any welded on weights missing, sometimes you can clobber a speed hump or pick up a rag that wraps itself round tha tailshaft for a few minutes and causes it to go out of wack, if nothing is obvious, you may have to go to a tailshaft balancing comnpany, Colin.

[colcol]

And it was interesting watching the company balance the tailshaft on the VL Commodore, they put it up on a hoist, put a sensor on the gearbox put a timing light type gun on the tailshaft and the timing light flashed at the heavy spot then they marked the heavy spot, put some weighted hose clamps on the tailshaft until they got the right weight and position, they removed the weighted hose clamps, then spot welded the weights on the tailshaft, it worked like a dream, then drove car home and all was good, not an uncommon problem driveshafts going out a whack so it seems, Colin.

[mickl]

Thanks for the tips........The vibration peaks at about 3000rpm when stationary, which is a bit of a nuisance as most travelling is at about those revs.
I have had a good look under the car and there doesn`t appear to be any obvious cause...no caught-up plastic, no weights missing nor can I detect any bending in the shaft. However, the bearing between the front and rear shafts does not seem centered in its housing and i can move the whole shaft here about 5mm up to bring it central with the housing. Could this be an issue?
Mickl

[colcol]

No, i think the bearing should be central in the housing, either the bearing is loose in the housing, or the housing has become out of shape and won't hold the bearing properly, or the bearing is worn out and is a allowing the shaft to flop around and pulling the bearing out of the housing, Colin.

[aggie57]

You posted this on the 105 section so we are talking 105 series? 

[mickl]

Yep, car is 75 berlina.
I will put up with the vibs for another couple of weeks and will book it in to Monaco Performance for Geoff to have a look at it. Thanks to all for assistance once again.
Mickl

[aggie57]

Yep, car is 75 berlina.
I will put up with the vibs for another couple of weeks and will book it in to Monaco Performance for Geoff to have a look at it. Thanks to all for assistance once again.
Mickl

Ok - so when the car is stationary the tailshaft will be as well.  Unless the rear wheels off the ground, both in your case as there should be a LSD fitted.

Which implies that the problem comes from somewhere forward of the tailshaft.

[mickl]

I put the car on stands with it in gear when seeing where the vibration was worst. It peaked at 3000 rpm when on the stands but when on the road it is probably worse at 2500 rpm.....especially on a trailing throttle when the accelerator pedal is released.
Mickl

[aggie57]

With the rear wheels turning as well then?  If so then try the same thing with the car in neutral and the handbrake on, so the tailshaft and rear wheels are not moving.  That will start to isolate the source to a specific part of the drive train.  All you're doing otherwise is replicating the same conditions as normal driving.

By way of comment as well, personally I would be extremely reluctant to get under a car on stands with the engine running particularly if you know it already has a vibration.  Stands are OK for static work but you really should have it on a 4-point hoist. 

[mickl]

Thanks for the response Alister. With the car in neutral and the tailshaft and rear wheels stationary there is still some vibration but perhaps not quite so bad as when on the road. I am taking the car around to Monaco Performance in Newcastle in a week or two so Geoff can retorque the head after getting a new head gasket late last year, so I will get Geoff to see if he can track the vibration down.
I agree with your comments about supporting the car. I try for 3 methods whenever i raise it: I put stands under the rails, I leave the trolley jack under whatever lift point i am on and I also put large 12 inch wood cube blocks under the rails or strong part of the floor too as the fail safe backup. A bit over the top maybe but it only takes an extra minute or two.
Regards
Mickl

[aggie57]

Great Mickl - better safe than sorry.  Don't we all wish we had room for a hoist at home.  Mind you, that may not be popular with some people I could think of!

[mickl]

Vibration pretty well sorted now. Replaced the do-nut like bearing on the shaft and also a couple of worn universal joints.
The uni joints are rather stupidly 0.1mm different in size and were a little hard to source.
Mickl

[colcol]

The reason manufacturers make parts odd sizes is so you have to go genuine, and they have a captive market, for years oil filter threads were 3/4 inch, then car makers changed it to 20mm, [hello Alfa Romeo 156 JTS!], Colin.