E30 Zone

hi all

i've had this problem since i bought the car and have finally decided to fix it if i can. when accelerating (moderatly and hard) a vibration comes from the back of the car at around 3800rpm but stops at 5500rpm.
im guessing its got something to do with the driveshaft, diff or the mounting brakets somewhere.
can anybody help???

Mitchell

These can be tricky to pin down.
First off you need to decide whether it is related to

1. engine speed
or
2. road speed

After the drive leaves the gearbox, all bits are only affected by road speed. The wheels, wheel bearings, driveshafts, diff, propshafts and centre bearing are all road-speed sensitive.

The engine, clutch and input shaft of the gearbox are affected by engine revs.

well it would have to be road speed then cause the clutch n gearbox r still pretty new
cheers fo the response

OK, so you might have a genuine balance issue (particularly if you have had work done and the propshaft mating surfaces have been put back 90 or 180 or 270 degrees to the original - some propshaft assemblies are balanced after assembly and therefore are only ever truely balanced when assembled that way.

The propshaft center bearing is a favourite, also any of the Universal Joint spider bearings, and all other bearings - although some can just create noise.

Wheel centering (apline reps?) balance, tyre condition (no bulges / flats) can also affect this. If you've got the energy and there is not obvious play anywhere in the system when you are underneath it trying to shake bits of the drive train then I guess I'd look for oil leaks from the diff/wheel hubs as these can indicate worn bearings (as the seals cannot take the movement/heat and still seal).

Also check the bolts holding things in like the diff etc are tight - maybe take it to an MOT place and get someone to determine play in any suspension bushes or shot dampers - which can all contribute.

trying not to sound stupid lol, but whats a MOT place? lol .. dont think we have these here in aussie
as for the wheels, they r genuine bbs split rims and where balanced when i had new tyres fitted, but will check all bits of the drive train tomoro when its light
thanks

Sorry - didn't realize you were not in the UK!

MOT -> Motor Order Test (or similar) - they have ramps and levers - the test looks for loose/worn suspension components, and is fairly cheap.