MarkM

Great, if you've found the problem. Until your last post, I would have suspected the track rod bushings. When applying the brakes, the lower control arm is driven backwards into the chassis through the track rod, if the bushing is failing, all of the play is then taken out, and the noise goes away. Release the brakes, drive over a washboard road, and the noise returns. My buddy had similar symptoms on his '83 SD, replacing the track rod bushing solved it.

Perplexed
'77 300D

I think he tried that but I havent. Ive been planning to do this

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1981 300SD 512k OM603

Thanks for the input....I don't think this is it (but I may be proven wrong!)...the track rod bushings (AKA guide rod, or braking rod, bushings) are new (1 year ago), and don't seem to be loose....when I recently replaced LCA bushings, and had the springs compressed, I couldnt get any play from the track rod bushings by moving the wheel assembly back and forth (I couldn't get any play out of ball joints either). The main reason I don't think its the track rod bushings is that when the bumping noise happens, I don't hear any noise from the foot wells...when track rod bushings are bad, my experience is that bumping noise will usually very clearly be coming from the footwell locations where they are attached, and the noise would be a deeper thump, and you would hear is when braking....you would not need "washboard" road surface. the noise I hear seems so clearly from the wheels (out to the corners down and low), and is a much higher frequency....very much like if I loosened a brake caliper, or the spindle nut (but these possible causes have already been eliminated).

At this point, I am making arrangements for replacing the ball joints (which were replaced in April!!). But, before I do these, I need to think of another way to conclusively eliminate (or verify) track rod bushings as the possible cause. Maybe just buy a new one and put it in (but I just returned the rented spring compressor from when I just did the LCA bushings)....I think this can be done without spring compressor, but its not as easy.

Note that having the bumping noise disappear when braking is also consistent with ball joints being the cause, for the same reason you describe above...braking preloads the suspension, pushing the wheel assembly back...this means that the lower part of the ball joint housing seated in the steering knuckle is pushed back while the upper part of the ball joint (spindle and ball) is held forward by the track rod/LCA..thus taking up any play.

I'll keep you posted.

Thanks again,

Mark

Thanks

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

Dont replace them if there no play. Thats just a huge waste of money.

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1981 300SD 512k OM603

I replaced the ball joints (Lemforders) yesterday, and the bumping noise is still there!

Now I am thinking it has to be the guide rod mounts....I know there have been several posts suggesting this, but I disagreed because these are fairly new...I looked back in my records....they were replace in April 2005...the bumping noise began in spring of this year...about 50,000 miles since they were replaced....the metal is still shiny on them!

The bumping noise is so closely related to wheel bouncing, and it does go away with braking, so with the benefit of having conclusively eliminated ball joint/calipers/LCA/rotor/wheel bearing, all indications point to these guide rod bushings!

I just did quite a bit of searching on this forum re: guiderod bushings, and it seems that several posts over the years have described the symptoms I have exactly....bumping over washboard road surface at low speed, and a front end shake at 60 mph (which I have but I assumed were due to bad front tires)....and have said these symptoms are indicative of bad guide rod mounts.

So I guess I will continue with my process of elimination to correct this bumping noise....it does get expensive and time consuming to re-do things that have recently been done! Especially since I cannot detect any play in the guide rod mounts with the car up off the ground....I am coming to realize that this is typical of suspension-related problems....that you can only hear the noise when driving, but can't replicate the noise with the car up on jack stands.

Regards,

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

Mark,

This might of been mentioned previously, as for I didn't look for it, but you might want to check to make sure you Motor Mounts are bolted down securely especially from the center bolt. I had a knocking noise and it was because the center bolt connecting to the mount arm was not seated fully even though it was tight. It ended up being cross threaded. New arm later and problem solved.

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1983 123.133 California
- GreaseCar Veg System

i believe my problem is the ball joint thing for the guide rod at the foot well. Im ordering a new one

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1981 300SD 512k OM603

Hmm, how about my clunk. I hear it near the pass. footwell on a washboard surface but only when the temp. outside is less than 50 degrees. Loose caliper maybe? The entire front suspension and all rubber is new.

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1980 240d
1999 SL500

Well, after chasing this for six months with much anguish, I can now begin the mental recovery process, as I replaced the guide rod mounts (the big bushings at the foot wells) this morning, and I knew I found the problem when the bad mounts were removed, and I could feel play in the shaft/ball of the mounts. Thanks for all of your help, and kudos to some of you who correctly diagnosed the problem (I insisted that this couldn't be the problem since they were essentially new...18 months!....and were a reputable brand...Febi/Bilstein. Also, I swore I heard knocking from the wheels/hubs and not at the foot wells.)

Anyway, a few key points for the benefit of everyone on this site.

1. If you are going to replace shocks, certainly get Febi/Bilstein. HOWEVER, for all other suspension-related parts (ball joints, upper control arms, guide rod mounts), steer clear of Febi!! The Febi ball joints I installed in April '08 were crap, and the Febi guide rod mounts I installed in Nov. '06 were crap. Go with Lemfoerder or Meyle....I just put in Meyle guide rod mounts. I bought the Febi mounts here at Fastlane....nothing against Phil or against Fastlane...I just want to provide good information here....I will call Phil on Monday and discuss with him in person...He is very interested in this type of feedback, and he is a very helpful great guy, and Fastlane is still terrific (its just that Febi suspension parts suck!). Note that All Parts Express (also linked to this site) has Lemfoerder and Meyle...so I encourage all of you to go to this site as well as Fastlane.

2. The key symptoms of the bad guide rod mounts...and I mean not the major clunking of totally failed mounts, but the initial klunking of the mount that is beginning to fail and developed a little play, are.....1. Knocking at low speeds..(10 to 25 mph) when driving on "washboard" road surface. At higher speeds the knocking does not happen because the guide rod mount is pre-loaded with the suspension pushed back by road friction/wind resistance, and 2. Knocking goes away with braking...same reason, pre-loading the guide rod mount. Note that these very specific symptoms were reported by others on this site...I had done a very detailed search of the archives, sorting through the comments that were unclear or irrelevant to my situation, and there were about a half dozen individuals who reported these specific symptoms of early guide rod mount failure...thanks to those individuals.

3) When guide rod mounts have totally failed, with lots of play, you can detect a major klunk by repeatedly applying and letting off the brakes...this is the standard diagnosis of failed guide rod mounts. But when there is only a little play like mine had, there is not enough play to hear knocking by applying and letting off the brakes. But when the wheel is bouncing up and down when driving over washboard rod surface at low speeds, the guide rod mount is not pre-loaded, and the rapid knocking is very pronounced!

Final note....I did change the guide rod mounts without compressing the main springs...pretty simple....I did follow advice of others at this site and used a come along....Loosen the lower control arm eccentric bolts, upper shock connection (don't disconnect these, just loosen!), and guide rod attachment at the LCA (this last thing gives you enough play to move the guide rod around to line it up with the new guide rod. Quite a bit of force is required to pull the suspension forward to provide clearance to remove the guide rod mount, so you want to make sure you don't pull your car off the jack stands....I parked my car with front bumper up against a tree and attached the come along to my wife's car...to the towing eyelet. Very simple...took about 3 hours to do both guide rod mounts.


Again, thanks to all for your help,

Mark

P.S. The front suspension is now completely rebuilt, and is so tight it drives like a Ferrari...well not quite that good! I am scheduled for an alignment Monday, and will put new snows on Monday night...I will be driving to New Jersey and back this next Wednesday (12 hrs. round trip) and will very much enjoy my ride!!

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

I tried to replace my mounts today but couldn't. I hooked the come along to another car and tried to pull the LCA forward but I was afriad I would pull it off the jackstand. I got it forwward quite a bit but was afriad to go any further. I just put it back together and I plan to remove the spring and spring perch then just pull the whole rod out.

I don't have any trees to use

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

motor mount ,,,,??

My car has been making this noise since at least 2005 or 6. I replaced both of the guide rod mounts also, along with the rest of the front suspension bushings ball joints shocks etc. The metal is still shiny. The car still makes the noise. Sounds like a low pitch rattle at low speed on uneven pavement, cobblestones, etc. Right front only. Sounds a bit like a loose battery, but it is not loose and the rattle is a bit too rapid for that. Drives fine but makes noise.

I guess I will replace the guide rod mount again on the right.

One thing is it still seems to eat the inner corner of the left front tire very quickly, even after alignment was redone. I drive a very curvy road to work and back and I think the right wheel is tracking in a different direction than the left when in a left hand sweeper, when the right front tire is loaded hard the effective toe must change relative to the left front wheel, so the left wheel being unloaded slides to match the track of the right.

Talk about an irritatingly persistently refractory problem!

I am no mechanic, but I try. I JUST bought a 1991 300se. It has the same type of noise you describe when driving on a washboard dirt road. My thinking was the same as yours.....suspension. Until I remembered that the seller told me it needed new motor mounts. Could this be the problem? I have new mounts ready to install, I will update afterwards.
PS hello everyone, new to this forum

After replacing my motor mounts the noise was gone