Bumpiness at 35mph (94 540i)

[maximXL]

I've searched these forums thoroughly but have unable to find info about my issue. I drive a 350Z but my wife has a 1994 540i with 88k miles which we love to death.

We've had it for a while now. It's in flawless shape and we've had 2 different mechanics look it over and fix minor things. However, 1 issue remains....

On colder days the car gets bumpy around 35mph. It feels like the wheels become oval at that specific speed. You don't feel it in the steering wheel at all...it's just a general vibration (drive shaft?) that feels like the tires are lop-sided. Prior and after 35mph it's smooth as glass though.

We've recently replaced the tires, alligned them, and have been told that our rims are not damaged.

On warmer days this issue is less likely to appear although it usually shows up every day.

Anyone hear of this? I don't think it's BMW-specific but we've had it checked out and nobody knows what it is.

Thoughts? Suggestions of things we should check out?

Thanks!

[uscharalph]

I've searched these forums thoroughly but have unable to find info about my issue. I drive a 350Z but my wife has a 1994 540i with 88k miles which we love to death.

We've had it for a while now. It's in flawless shape and we've had 2 different mechanics look it over and fix minor things. However, 1 issue remains....

On colder days the car gets bumpy around 35mph. It feels like the wheels become oval at that specific speed. You don't feel it in the steering wheel at all...it's just a general vibration (drive shaft?) that feels like the tires are lop-sided. Prior and after 35mph it's smooth as glass though.

We've recently replaced the tires, alligned them, and have been told that our rims are not damaged.

On warmer days this issue is less likely to appear although it usually shows up every day.

Anyone hear of this? I don't think it's BMW-specific but we've had it checked out and nobody knows what it is.

Thoughts? Suggestions of things we should check out?

Thanks!
What kind of tires do you have mounted?

[uberhahn]

i have similar simptoms (ok, the car does). My vibration had multiple sources. Started with tires. Got better. Checked and replaced guibo (no difference).

Most of my vibration came from my engine fan (actually fan clutch). Experimented by taking it off an driving without. Vibes totally gone. In the process now of installing an new unit.

I thought that my vibes were speed dependent, but I could induce them at zero speed (with or without clutch)

uberhahn

'94 530i 5-speed.

[632 Regal]

LMAO!

this is what they call flatspotting, perfectly normal and usually aquired with new tires till they break in. If you have them balanced without running the tire true youll experience even worse probs. Flatspotting is a normal part of new tire break in with the new compounds these days and isnt anything to worry about unless it persists over about 5-10k miles.

thats my nickel on this subject.

[maximXL]

Thanks for the feedback.

This issue was happening with the OLD tires so we had the tires replaced thinking it might help. No change. It happened on really old tires AND brand new ones.

The tires we got are Falken's (same exact size as the stock tires it replaced).

I'll take a look at the fan next.

[ryan roopnarine]

if changing tires did not help, i'd say that if it feels like a vibration only felt in the bottom of your seat, and it makes a little "growl" when it does it, its likely the flexdisc on the driveshaft, and/or the center bearing. check the flexdisc to make sure there are no cracks in it, no chunks missing, all 6 bolts going through it, et cetera.