Pronounced knocking on front end.........W123
 

I will spare you the details and try to get to the point...I have been chasing down a front suspension knocking noise for 6 months...the noise occurs in vicinity of hubs, both front wheels, but more pronounced on right. I have now completed a complete rebuild of front end, including:

Upper control arms (UCA)
Lower control arm (LCA) bushings
tie rods
drag link
ball joints
guide rod mounts (at foot wells)
guide rod mounts (at LCA)
rebuilt brake calipers
new rotors
new wheel bearings & grease seals

The noise I hear is a definite pronounced bump, bump, bump that happens when I drive over "washboard surface" from 10 to about 35 mph (dirt roads, railroad tracks, road patch, etc.)...sounds kind of like a bad ball joint.

I always thought the noise was suspension related, and not brake related, so only recently did I drive over washboard surface with brakes applied and not applied, and the noise does not happen when brakes are applied. When brakes are applied, the suspension sounds as tight as a new ferrari (almost), and when brakes are not applied, bam, bam, bam, bam.

I applied brake pad sticky stuff to the backs of the pads the other night, and this had absolutely no effect. Can anyone suggest what the noise might be.


Here is everything under the sun that I can think of:

1. Brake pads knocking? (not likely since sticky stuff had no effect, but maybe the old brake pad springs I have are weak...I will try putting in new brake pad springs...the brake pad pins are fine and tight, so it cant be them)
2. Brake caliper pistons knocking inside of caliper housing ?(If they were that loose, wouldn't they leak? I did rebuilt them, pistons are held in place by rubber o-ring and rubber seal...maybe the rebuild kit I used had squishy o-rings...not likely)
3. Loose wheel bearings (bearings are new, adjusted just right, no play. In fact earlier this summer I tried overtightening the right wheel bearing and that had no impact on the noise...in fact I drove it too long like that and ruined the new bearing and had to replace it again!)
4. Rotors loose? (I checked...also, I have done this job several times, and no way these rotors are loose...there are 5 or 6 bolts that attach rotors to hubs.)
5. Maybe its this: When noise doesnt occur when braking, the weight of the car while braking is thrown forward compressing the guide rod mounts, preventing them from knocking. (there is no way the noise is due to guide rod mounts, these are new, and the noise is definitely at the wheel/hub..down low way in front, and not at the foot wells)
6. Cracked steering knuckles? (just not possible)
7. Funky brake pads (they seem just fine, nice snug fit into caliper. There is very little play between the ends of the brake pads and the calipers where the pads slide into the calipers)


Can anyone think of anything else...I did order new brake pad springs...these are called "anti knock springs" so maybe this is the obvious solution...I can't wait till they arrive (but I really doubt this is the solution...if the pads are knocking, the noise would have been affected by applying the sticky pad coating). But I will try bending the existing springs to apply more tension and see if that effects the noise.

Thanks in advance for any help.

Mark

Horrible isn't it. Ive been chasing the same thing on my drivers side of the 126. The only thing i haven't replaced is the guide rod mount (to the frame, that big weird thing on both sides of the 126) but it still looks good.

Sometimes it can sound like the sound is up front when its actually in the rear. Have you checked your sway bar links on the rear? They will make a distinct "clunking" sound that will resonate through the whole car when they're worn out. I'd check those out.

Could be your driveshaft too.

Jimmy, where are you on the comments with this one? note the denoting on the models...

ok, have you had someone else drive the car while you sit back and listen carefully for the noise?
I would pull the back seat out and also empty everything out of the rear and give it a try.
I am guessing that since this is a wagon, you have replaced the accumulators... "it's always the accumulators"

If the accumulators are bad, it would be like riding a bull in a rodeo at the back end. Should not cause noise.

Driveshaft would cause vibration.

I think the key is that the noise stops when he brakes - which tells me its got something to do with a brake component.

Whats the front and rear rotors looks like? Any grooves?
Can one of the calipers be loose?
How about rear axles? Hows the boots look like?
Can you jack up the rear, turn, wiggle the wheels and observe?
Can you jack up the front, turn, wiggle the wheels and observe?

My 2 cents.

Maybe an upper shock bushing? Just a guess. You can feel the vibration through the body and it can sound/feels like a ball joint or something that's loose lower in the suspension. When you jack the car up, you load the bushing, so it's hard to detect. You might be able to feel it if you put your hand on the top of the shock and have someone lift the fender up and down as hard as they can.

Have you checked your sway bar bushings? They anchor the brake torque.

Have you tried searching for other non-suspension related items that could be loose and shift?

Thanks...
 

Thanks a lot...But I dont think those suggestions cant be the cause...this is a vibrating clunk when the front wheels go over "washboard" road surface. I have replaced flex disks and center bearing on the driveshaft, and also the rear swaybar links and bushings (sway bar to frame). Your comment about the rear wheels, though, made me think of how best to describe the noise I am experiencing....it is very much like what you would hear from the rear when the little ball joints on the rear sway bar links (sway bar to wheel carrier) have gone bad.....a type of vibrating clunk as the wheel vibrates over a rough road surface. However, the noise I am experiencing is absolutely from the front end, not the rear (although I do appreciate your comments about this because I have certainly had situations where you think the noise is coming from one location only to find out its from somewhere completely different). In my current case, I hear the first bump a the front wheels when the front wheel first hits, say, a patch in the road, or a man-hole cover, while the rear wheel is still on smooth pavement. Definitely front wheel noise, and the noise is eliminated when I apply the brakes while driving over washboard surface.

Thanks,

Mark

Don't think so, but thanks...
 

I have detached both shocks (recent bilstein comfort) to make sure upper rubber bushings are in place, and to make sure lower bushing is tight....everything is tight. Noise is definitely at wheel and not from upper shock towers.

Thanks,

Mark

Not yet...But
 

But, I have had sway bar bushing go bad in my previous 300D, and that usually results in the crunch sound from just forward of the dash firewall where they are located (sway bar to frame). The noise I am experiencing is not from the firewall area. Also, I did replace upper control arms, and at that time also put new bushings where sway bar attaches to UCA. So it can't be this...plus the noise is different.

The noise I am experiencing sounds like the wheel bearing is loose, or if all lug nuts were slightly loose. But I checked these things...not them.

Thanks,

Mark

Done that...
 

Accumulators are new...plus noise is definitely from front.

Thanks,

Mark

Mark - I mean your FRONT sway bar bushings behind the battery and booster.

I will look into it...
 

I am 100 percent sure noise is from front end.....HOWEVER....I am actually going nuts over this so I will try anything...I will check out rear brake components. Cant be rear swaybar links because they would still bump while braking....Yes, the key is the relationship to braking. Calipers are all tight.

This weekend, though, I will remove calipers, look things over and such, then put it all back together, proper torque etc....I will also detach and re-attach the other things that are attached to steering knuckle, and will see if that has any effect on the noise.

I really want to get my hands on the anti-knock caliper/pad springs...if the new ones don't arrive today, I will bend the existing ones to add more tension, and hope for the best.

Thanks,

Going ape sh-t in Massachusetts..

Mark