HELP Required! Mystery vibration

[steveww]

My S4 has a vibration, especially when under hard acceleration. The vibration intensity changes with speed. It is present in all gears.

I have checked front and rear UJ on the prop. Diff mounts, engine mounts, gearbox mounts. I have turned the wheels, diff etc over by hand and there is only a little bit of backlash in the diff.

Everything in the drive line appears OK. Sure turning by hand does not put the strain on the components that rear world use does.

The engine is fine, revs up and runs sweat no nasty noises so I am pretty sure that it is a drive line problem.

Any suggestions?

[1964 S1]

If it were my car I'd ;
Check the front u-joint through the access panel, reach in and wiggle and jiggle, there should be no play.
If it's not that then I'd jack up the rear and check rotoflexes, or solid axle joints with the axles drooping and free to turn.
If it's not that then I'd jack up the motor a little bit and double check that a motor mount hasn't torn.
From you description it's probably not a motor mount... does the whole car vibrate, does the shift lever feel "normal" when the vibration occurs?
Good Luck, Eric

...here's a weird one that just came to mind, loose bellhousing to engine block bolts..

A sage here in Cincy, Rallye Ralph Crawford, for decades, has advised British Sports Car Owners to go from one end of their cars to the other, once every few years, and tighten every nut, bolt, and screw. Good Advice.

[paddy]

Does the frequency of the vibration change with road speed or engine speed? Also, does it happen at all on overrun?

I just resolved a mystery vibration which was caused by the oil cooler take-off (fitted between oil pump and filter) touching the steering column, passing engine vibrations to the column and through to the dash. It started to happen when one of the engine mounts started to sag, and only happened with the engine in a particular orientation; with power on it would be touching, but not on overrun. A similar thing has happened to me previously with the airbox touching the footwell roof (wrong engine mount).

As well as the things others have listed I'd also check the gearbox output shaft bearing.

Paddy

[alexblack13]

Hi Steve,

You might want to carefully check the tyres. If it alters with road speed etc. I chased red herrings around for a while then discovered a goosed tyre. It had a fair bulge in it. Felt like world war 3...


Alex B....

[steveww]

Hmm interesting. The problem is intermittent - don't you just love those

At the moment it has disappeared but before it when it was there between 35 - 55 mph in any gear, more pronounced with harder acceleration.

I have been over everything in the drive line: all UJ, tyres, prop shaft, engine mounts......

Aarrgghh!

[alexblack13]

If you slipped the car into neutral when it was producing the vibe at say 50 mph ish. Engine on tickover, what happens? Still there?

Wouldn't simply be wheel balance would it?

Keep us posted
Don't screeeeem just yet. You will find it
Alex B....

[steveww]

Wheel balance would not change will acceleration.

I guess I just need to keep driving it until the condition becomes chronic then the failure should be obvious.

[Roy Gillett]

I had a very worn lower trunion that put a vibration into the steering that felt for all the world like wheel balance but would come and go. Turning a few corners enthusiastically usually brought it on and long straight cruises made it go away.

Roy

[types26/36]

[quote="steveww"] more pronounced with harder acceleration.
I have been over everything in the drive line: all UJ, tyres, prop shaft, engine mounts......quote]


How about the crankshaft spigot bearing failing ......just a thought

[oldelanman]

Hi Steve,
Have you checked the driveline hardware is tight ? ... loose diff flange or driveshaft bolts could be the cause.

Regards,

[alaric]

Hi. Hub bearings worn and not running true? If worn then changing the load under acceleration may change the direction of the angular momentum vector relative to the angular rotation vector - sorry - bit of physics speak slipped out there - I mean, is the balance of the wheel changing due to a worn bearing.

If you have wheel nuts and not spinners, have you fitted locking wheel nuts recently, that put the whole wheel assembly out of balance?

All the best.

Sean.

[johnsimister]

My car has this vibration under acceleration sometimes. I think the wheels are out of balance, too, and I also think the two things are connected. At speed the vibration is sometimes worse than at other times, and I think it's because the out-of balance wheels are either cancelling each other out to a degree or exacerbating each other's effect, depending on their relative rotational positions at the time.

I think out of balance wheels could make a worse vibration under acceleration because the extra turning energy would exaggerate the impact of a heavy spot hitting the road. The physicists among you could probably explain that better unless I'm talking nonsense, but that's how it feels. Let's just say that when the wheel balance vibration is at its worst, the extra acceleration vibration also gets worse. I shall get my wheels rebalanced forthwith and see what it's like then.

I had plenty of time to think about this today during a highly entertaining zoom from Dorset back home to Herts, avoiding motorways as much as possible. I was in a convoy with two friends, Peter in his red S4 and Chris in his BDG-powered Caterham 7. The pic below is during a pause to find out exactly where we were. We were soon joined by a gentleman who had an Elan many years ago but it went up in smoke. I really must fit my fire extinguisher.

John

[david.g.chapman]

Steve,

Could one of your spark plugs be playing up under load? 3 and a half cylinder running may not be obvious in the rev range you describe.

Might be also worth checking your stromberg diaphrams just in case.

Dave Chapman.

[robertverhey]

I had a resonance at 2000rpm that drove me mad for months, until I finally found it. Broken alternator tightening strap. Had snapped near the timing cover

Robert

[johnsimister]

Or, continuing the wheel imbalance idea, the wheels are out of true. They are quite fragile and easily bent on a typical modern disintegrating road. New steel wheels appear currently unobtainable. I called Susan Miller about them, as she showed them on her website, but they've now all gone.

John