Suspension Issues/Questions

[hdaemon]

Car: '90 535i 5spd, 205k Miles

Issue #1: Moderate vibration at 65-80mph.

At highway speeds, I get a moderate amount of vibration in the vehicle. I feel it mostly through the seat rather than the steering wheel, and it's visibly noticeable through the gearshift lever. The vibration has been there for a while, and exists independantly of the set of wheels/tires that are on the car. Above about 80mph or so the vibration settles down and smooths out.

My initial presumption is that it may be a bad set of upper control arms, either the bushings of the arms themselves. The PO had the bushings replaced several years ago with the 750i bushings, but kept the old arms. I'm not sure on the exact number but I think probably ~5yrs and 50-60k or more ago. How long do the 750i bushings last? Or might it just be that the ball joints are going bad?

If I replace the arms myself, is an alignment needed after reassembly?


Issue #2 - Soft rear end

An issue that has arisen in the last couple of months is that the rear end has started to feel really soft, particularly on the left side. It feels almost as though the rear left tire is low on pressure, even when it isn't. The left side of the rear seems to be sitting about 1/4-1/2" lower than the right. Also, when driving on concrete (ie- into/out of the parking garage at work), that the rear left tire squeals at every opportunity.

Having had the dogbones replaced <10k ago, and a new set of Bilstein HDs ~25k ago, I'm guessing that I might need a new set of subframe mounts?

If that's a likely possibility, how difficult a job am I looking at? I'm reasonably decent with a wrench, and have easy access to workspace and most any tools I'll need. My primary concern is the bushing puller. Is this a case where only the genuine BMW tool will work appropriately, or are their acceptable substitutes, and if so, what are they? This is a situation where I would be able to work all weekend on the problem, but would need the car back together for monday.

[nyc525iTe34]

Issue #1 ...If it's not the bushings then I would look at the 1) drive shaft/line or the 2) hand-brake. Often the CV joints on the driveshaft/line will deteriorate and cause a vibration/noise from under the center of the car. Also, the hand-brake mechanism sometimes deteriorates causing a noise as well. I would lean more towards the drive shaft/line as the real issue (if it's not the bushings).

[632 Regal]

ill pitch a guess, check the tires for out of round first, if round then they may need a rebalance. Out of round tires rear their ugly heads at about 70mph.

as for the sag, check that the springs have both been seated against the stops when assembled.

[hdaemon]

Issue #1 ...If it's not the bushings then I would look at the 1) drive shaft/line or the 2) hand-brake. Often the CV joints on the driveshaft/line will deteriorate and cause a vibration/noise from under the center of the car. Also, the hand-brake mechanism sometimes deteriorates causing a noise as well. I would lean more towards the drive shaft/line as the real issue (if it's not the bushings).

What's the best way to check the driveshaft? I replace the flex-disc and center bearing about 20k ago. All I did at the time to the rear CV joint was to repack it with grease when putting everything back together.

Is there some way that I can check things without completely dropping the driveshaft again?

[hdaemon]

ill pitch a guess, check the tires for out of round first, if round then they may need a rebalance. Out of round tires rear their ugly heads at about 70mph.

as for the sag, check that the springs have both been seated against the stops when assembled.

Out of round/out of balance wheels was my first guess, but the vibration is there with two completely different sets of rims/tires.

I'll check the springs when I get a chance to get under the car this weekend.

[632 Regal]

do your rims or the other set require hubcentric rings?

When you did the center bearing did you preload it?

[nyc525iTe34]

To check the CV joints simply hoist the car in neutral and put it on a lift. Try rotating the front axel and then back axel first. Then try manually rotating the drive shaft. If you hear any clicking sound then you know there's an issue with the CV joint.

Alternatively, perhaps when you put everything back together and packed the CV joint with grease you didn't fit everything as tightly as possible. Even if the CV joint or driveshaft are just a little off it can cause noise issues - banging against the heat shield cover.

Hope that helps...

[hdaemon]

do your rims or the other set require hubcentric rings?

When you did the center bearing did you preload it?

I'm not sure if they do or not. One set is the original 15" basketweaves that came with the car, the other is a set of aftermarket rims. Both sets sit up on the hubs with no discernible difference in the amount of play (which isn't much if any to begin with).

And yes, when doing the center bearing, I did make sure to preload it, per the Bentley manual.