Need Expert help - Tough time finding vibration...

[talltorontoguy]

I'm getting really frustrated and as Bruno says "I want to love my car again!"

I have the shimmy / vibration - 1992 535 std transmission

History:

I've replaced the thrust arms (w/750 bushings), lower control arms, swaybar links, shocks and springs. Three different sets of tires / wheels have been balanced and installed with same results. All in last 30 days.

I have not recently replaced Rotors. I have not replaced steering links or wheel bearings.

Description:

1. Originally the shimmy was present only at about 90-100km/hr or around 55mph. There was a sort of 'band' it was present in, any speed above or below that band the shimmy would go away.

2. Various part replacements didn't seem to affect the shimmy much (thrust arms helped) until the most recent addition of lower control arms, after which the shimmy seemed to change.

3. Now at speed below 55 there is no shimmy. But above 55 the shimmy appears and then stays on through higher speeds. I'm thinking that the old control arm bushings were absorbing some of the vibration and now its more apparent.

Diagnosis: (HELP)

1. Rotors??? The shimmy is more pronounced when braking at highway speeds, which points me to rotors. However the runout on the rotors was measured to be minimal (wasn't zero though).

2. Wheel Bearings??? I was also thinking it could be wheel bearings. However there is no obvious play in the wheels and there is no noise from the bearings on turns etc (as you would normally expect from a failing wheel bearing).

Anything else anyone can think of?

Rod

[MicahO]

Were the rotors checked for runout while they were mounted on the car, or when they were off the car? It's possible that there is some crud on the hub face or on the rotor face that is putting the wheels (or the rotors and the wheels) off of true. You may want to take the rotors off and scrub down the hub face as well as the mounting face on the rotor. It takes surprisingly little accumulation to make an issue there.

I've been in a similar situation, though my vibration was in the seat of the pants and at different speeds, not front end related. I know how frustrating this can be. Good luck with it!

[talltorontoguy]

Thanks...

Good tip. The rotors were checked while on the car so any crud would have been taken into account for the measurement.

Would even a very small runout cause a vibration both while braking and while driving at highway speeds?

R

[MicahO]

Thanks...

Good tip. The rotors were checked while on the car so any crud would have been taken into account for the measurement.

Would even a very small runout cause a vibration both while braking and while driving at highway speeds?

R

Frankly, the vibration at that speed when not braking says wheel balance to me, but you've been down that road. Of course, there is the slim possibility that all 3 sets were improperly balanced, either on the same machine with a problem, or perhaps all were balanced to zeros but only done statically (weights on one plane) rather than dynamically (weights on the inside and the outside). Static-balanced wheels on these cars won't cut it, I've been there, and had the argument with the technicians.

The vibration while braking says thrust arms, but you've been there too.

So the commonaility may be the rotating mass of the brake rotors, either a bit crooked, or 'naturally' unbalanced.

You also mentioned that the tie rods were not new - replacing those, plus the idler arm, plus an alignment may take some slop out of the nose, which might be enough to compensate for any natural imbalances.

[talltorontoguy]

Thanks for your reply.

Only one of the three sets of wheels were statically balanced, the others were dynamically balanced so odds are low that this is the problem (but still not out of the question).

I'm thinking its got to be the rotors, there's just no other explanation that makes sense to me.

Too bad I don't have a 4th set of brand new wheels with brand new tires with brand new balancing to be able to eliminate the tires as a problem. Ah well... just when you thought three was enough. :-\

Anyone else have any suggestions?

[grease]

just wondering, are you riding on BMW wheels or some aftermarket wheels. Also are they low profile tires. Only reason I ask is because if they are aftermarket wheels they may not be hub centric causing a wicked vibration. Does the car vibrate at lower speeds then 55mph or does it seem to come on at that speed?

[talltorontoguy]

Thanks for your response, geez... I sound like a customer service rep.

The vibration comes on at about 55 mph. If I am doing say 70mph and brake the vibration will be pretty rough while decelerating through the 55mph range. Then its fine until stopped.

One thing of note is that the brakes feel like they're grabbing ever so slightly when decelerating from about 10mph to 0. By grabbing I mean they seem to get tighter and looser a little as the wheel rotates (as if the rotor were out of round). Doesn't pull either way. This is VERY minor though and most people wouldn't even notice... I'm just hyper sensitive to it - but... maybe indicator of a problem? (All brake calipers rebuilt and system bled 60 days ago)

All three sets of wheels are BMW.

1st - Style 5's (e39) with hubcentric rings. I was suspicious for the same reasons you mention hence the reason for change #1.

2nd - Stock 15" basketweaves w/all season MXV's

3rd - Steel 15" winter wheels w/winter tires artic alpin pilots

Still stumped...

Rod

[Jeff N.]

Couple things to consider / try:

1 - the rotor and or rim faces might have corrosion on them. This will cause a perfect balanced wheel to be off balance on the car. A good alignment shop can resurface wheel faces. You should be able to check the rotor face for run out.

2 - checked your brake carrier mounting bolts lately?

3 - did you correctly torque up the thrust arm bushings and control arm bushings? You have to load up the front end before you torque them up.

Jeff

[winfred]

things we do when trying to kill the shimmey, rotors and thrust arm bushings (i prefer m5 to 750 bushings but ether will do if new) first, replace any suspension/steering component that has any play, grab the center link on the idler arm side and see if you can move it up or down, if so the idler arm bushing's dead, if you can twist the center link it's dead. if it's still grooven and mooven it's on to struts

[talltorontoguy]

Hey guys, thanks for jumping in.

Carrier bolts are recent.
New struts / springs
No obvious play in components.
New thrust arms with 750 bushings, torqued under load (on ground)
New lower control arms
New sway bar links

I will check the corrosion factor, but I think its pretty clean.

Groan... this is starting to ^$&% me off big time.

Rod