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Front Suspension Knock

Posted by eb 
October 05, 2012 11:46AM
So, I overhauled the struts on my E30 about a month ago, which hadn't been done since the car was new. New Bilstein HDs, new soft parts (upper/lower spring pads/shims, strut mounts/guide support assemblies), and new hardware, and keeping the stock springs for a variety of reasons. I hadn't done this job before but I am very handy, very careful, and had researched the topic extensively over a couple of months while I was figuring out my parts list. Other than some minor glitches (a broken brake caliper bolt and having to spend a day finding a better ball joint separator), everything went according to spec and to plan.

The immediate outcome was great. Cornering improved significantly, tire bounce going over road seams on the freeway was eliminated as was rocking when stopping abruptly, and the previously aggressive front-end shimmy when braking at speed is entirely gone. So far, so good.

The problem is this: The right side knocks badly when going over a road patch, pothole, or the curb lip into a driveway, although not on going over speed bumps more slowly or those plastic reflective lane markers. So, higher-acceleration bumps. I re-inspected externally and everything is seated properly, the mount nuts and ball joint lock nuts are torqued to spec, and the gland nut (the collar nut retaining the shock in the strut housing) also is tight.

The question is, what's up? Before I spend a weekend taking the strut assembly back apart, I thought I'd see if anyone had any thoughts about what I should be looking for. I'm guessing the shock may be loose inside the strut housing perhaps, or that the shock itself may be bad (although I wouldn't know how to determine that). Alternatively, some other suspension component may be involved that I am not thinking about. Of course, the real problem may be user error by a newbie. Any thoughts would be greatly appreciated.

**Problem aside, one lesson learned on the project: I highly recommend the Harbor Freight universal ball joint separator for removing the control arm and tie rod ball joints. A pickle fork will almost certainly shred the rubber boots, besides being a chore to use. Once I finally got the tool, I had all four joints off in less than ten minutes. Pelican also has a somewhat similar tool but it is more than twice the price ($46 cf. $19.99) and may not be versatile enough to work on the control arm joints.
October 05, 2012 09:23PM
Since you say that the shocks were original, it could be that the control arms are also original. That knocking could be the ball joint on the control arm. I had a similar noise on my cabrio and it was cured by new control arms. I also replace the rubber bushings on the rear end of the control arms. Those were difficult to do without a press. I broke my small bench vise on them. Had to go to Pep Boys and have them finish pressing them together.

If you suspect a loose shock strut, bouncing one front side of the car should be able to make it clunk. You could also jack it up and take a look at the retainer to be sure it is tight. You can likely reach inbetween the spring coils to try and move the retainer. My guess is unless the control arms have been replaced, it is likely one of them.


Bob in Everett
October 07, 2012 10:29AM
Along with Bob's suggestions; also check the sway bar rubber bushes. Do this with the car on the ground. Just grab the sway bar near the bushes and yank on it to see if there is any play.
When these are worn, they can cause the situation you have described.
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