Car shakes at freeway speeds - solved
copied from Bimmerboard, in case someone has this problem:
Was driving on freeway at 65 mph for half an hour with no problem. Alignment and tire pressures OK. Then whole car started to shake, like there was an earthquake outside. Lane change didn't help. Within a minute I had the car slowed down to 50 mph and the shake subsided. Subsequently on city streets car droven normally. What should I check? I had suspected drive shaft, but I didn't hear the characteristic knocking under the seat accelerating from a traffic light.
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Last June I began to notice that the 750 shook badly when taken up to 65 mph. I didn't drive too often afterwards and last Thursday I forgot about the problem and took the car to the freeway again. Not surprisingly, the problem didn't go away by itself.Engine runs well. I examined the front tires. The right tire looks normal. Outer edge around the left tire has worn out. Looking through the spring, the strut boot has collapsed. I used the old boot when I switched to Bilstein touring ten+ years ago. I plan on disassembling the front left to see what goes wrong. Does it look like the strut insert fails? or the thrust arm or lower control arm?
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Replaced front calipers yesterday
Following up from a problem first surfaced last June. I drove the 750 only a few times during these ten months, including a trip to CA smog check station (and passed!).
I tried to sink my mind into the front suspension to figure out what was causing the dragging and bouncing that occurred two times at freeway speeds. Both occurred right after I stepped on the brake because of traffic ahead. Eventually that led me to believe that binding of the left front brake should be the cause. Once that idea is in my head I know I have to replace the brake components before looking for other culprits. Some fourteen years ago I rebuilt the original calipers, and probably didn't do it right. This time I just go with rebuilt calipers from O'Reilly, $94 for both sides.
http://www.bimmerboard.com/members/c...%20caliper.jpg
As shown in photo, a one-inch section of the rubber boot around the old piston was ripped. That could be the reason why the piston was dragging. I went on to remove the old piston and inspect, and found no rust spots. Still, the misplacing of rubber can be enough to interfere with piston movement.
The only problem during reassembly was that the brake hose refused to detach from the pipe at the wheel well. Craftsman flare wrench, penetration spray, vise grip, etc, only rounded the 11 mm nut on the pipe side (circled in red in photo). I had to give up but the remaining problem is that the hose is now twisted, not by much, perhaps by some 45 degrees. But that twist is enough to keep the hose from forming a natural arch when the wheel is on the ground. That may cause future problems.
http://www.bimmerboard.com/members/c...ake%20hose.jpg
As for the strut and strut mount, a fellow at O'Reilly told me the boot is not absolutely necessary. For now I just spray some silicone lubricant on the shaft and not to do anything to the strut. Last night I drove around town and car behaved perfectly. This afternoon I'll take the car to the freeway and see if problem goes away.
Patrick C 88 E32 750 172K
