Z3 Shake at High Speed - Real Challange with no Solutions

[OrestK]

I have a 1997 BMW Z3 2.8 that has a shake between 65-70mph. You get above that and it goes away pretty much. You can accelerate/decelerate right through the range and not feel the shake. But if you slowly accelerate/decelerate into, or better yet hold a speed in that range, you hit a sweet spot and can feel the vibration. Some times its stronger than other times. Some history..... I hit a huge pot hole on the driver side years ago that bent both front and rear rims and to the best of my recollection this was the start of the problems. I did some basic repair as listed below. I drive the car only in the summer so I just learned to live with the high speed shake. REPAIRS: (1) I had the rims straightened. It helped but did not eliminate the problem. (2) I came across a cheap set of after market rims and bought Them (big mistake). Had them high speed balanced, car still had vibration. (3) Put the original rims back on the car and had BMW check and re-straighten the bent rims again to their spec professionally. Helped allot but still had some vibration. (5) bought 1 new OEM Z3 Rim because I could not find 2 new ones, and it helped a bit more. (4) Finally bought a set of 4 new BEYERN Rims with C7 Pirelli all season radials from BAVAUTO this month. They came pre-mounted and balanced. Got much better, but still did not get rid of the sweet spot vibration. (5) Had drive shaft checked for balance and preload - no issues. Car brakes smoothly mvat all speeds - assume rotors good. Do not hear any squeaking/chirping/grinding - assume bearings are good. Difficult to say if shake is being generated in rear or front as I feel the shake in my seat and in the column. After 4-5 years of this stuff I am at wits end. Can anyone provide me with some feedback or experience on other possible sources of vibration that could cause the 65-70 vibration? I assume it has to be a rotating part because it is speed sensitive. Any help would be tremendously appreciated. I do not want to start just replacing parts.

[Terry F.]

Hi OrestK,

I would advise you to correct or strip out the coding to make it easier to read.

Thanks,
Terry

[OrestK]

Post edited per your suggestion.

[Itsablurr]

How many miles and what is the service history of your suspension wear items such as bushings and ball joints?

[PbFut]

Given it seems to change with load on acceleration, my guess is motor or trans mounts. It sounds like you may be getting the vibrations from a couple sources which you seem to have identified. Wheels always a major issue. Wheel alignment can also present as you describe. Kind of wondering if a tie rod end is giving up. Tough one. Good luck.

[OrestK]

Car has 58,696 miles. Front lower control arm bushings and rear sway bar links replaced @ 50,000 miles.

- - - Updated - - -

Thanks for the feedback and sugestions.

[cleanerPA]

Maybe your steering column bushing? Tie rod ends loose? Ball joints?

It you get vibration from the engine, it will be rpm dependent. Trans mounts, possible.

[Lyall]

I've got the same thing at ~55mph, but I'm pretty sure it's a wheel balancing issue. The last time I bought tyres they said they balanced them but they didn't do a nearly half good job. Consistent same vibration when I'm in that speed area.

I know you've investigated in more detail, but wanted to add anyway. Had a place work for ages trying to fix it with no results then turned back to the wheel balancing and solved it all.

[PbFut]

It you get vibration from the engine, it will be rpm dependent. Trans mounts, possible.

Yes agree, Good point!

[mschrenk]

May not be the cause but I had a high speed vibration that was cured with hub centric wheel rings.

[z3aficionado]

Can you replicate the shake with the car on a lift and hit that sweet spot 65mph? Or does it need to have contact on the road for the shake to happen?

[deni2s]

Sounds like some resonance thing. Do you have still attached those heavy things under rear bumper cover which were supposed to eliminate resonance? Just brainstorming...

[z3forlife]

Check the inside edge of your rims and look for bends/flat spots. Stock rims can be bent rather easily just going over railroad tracks too hard

[OrestK]

Thanks to all for your feedback. I do not believe wheels are an issue. I have now gone through three sets of rims (original straightened, cheap after market with new tires, and now Beyern with Pirelli). Have had them balanced at different shops including BMW. Still has shake.......so rims and tires I would say not.

my question is this. If the shake is speed sensitive, would that not mean a rotating part? How do stationary components like bushings, rods, control arms, cause speed sensitive vibration?

i feel it in the seat and you can see it in the whole car like the glove box shakes, the passenger seat, anything that is loose in the car.

[PbFut]

Loose or soft bushing will allow a wheel to pull out of alignment spec. The associated wheel vibrates and a sweet spot so to speak is at your particular speed.
Put the car on stands or safer, a lift, and run it up to speed. Do you still have the shake? If no, likely in front. Remove the rear wheels. Still shake? Put front wheels on rear. Shake return? If it shakes with wheels off, then it's in the driveline. You get the idea. Do a methodical process to try and ID the location. You can do this on stands in the garage. Just be careful. FrankenCoupe gets run up on stands before every event. Good luck.

[Dadnabbit]

Just a suggestion based on a one time fix of another car. I had never changed a CV half shaft for any reason other than a ripped boot/dried out total failure case. This car had a vibe at 62 that was not related to wheels (swapped out with mine) and if the two owners were in the car with me (No it wasn't a Z3 : ) The vibration was reduced by half compared to driving alone- more weight produced a slightly different angle of the half shaft. Upon inspection, the shaft"s ball and cage area of the inner joints were dry of grease and worn after 140K of use.