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Front end noise is driving me NUTS!

2K views 21 replies 9 participants last post by  Ianwright40 
#1 ·
Okay, I realize trying to diagnose a sound on the internet is pretty pointless, but I?m going to give it a try anyway. . . .

I have a low-pitched whine or growl when driving that seems to be coming from the right front of the car. The sound is not loud but definitely noticeable (although I don?t have any carpet to muffle the sound) - the best way I can describe it that is sounds exactly like a dry speedo cable ? in fact, I was absolutely convinced that?s what it was until I realized I have an electronic speedometer! The sound changes pitch based solely on road speed so I know its something in the running gear. The front right rotor was slightly warped and dragging during part of its rotation so I replaced it and carefully checked the backing plate around the rotor to make sure it wasn?t scrapping or making contact with the rotor, and since I was already in there I replaced the wheel bearings too. Even though the sound seems to be coming from the front end, I also changed the diff fluid- but the noise is still there!

I understand this isn?t much to go on - I guess I?m mainly looking for suggestions as to what it might be so that I can check!
 
#3 ·
It's definitely speed related, but sounds are funny so I wouldn't go much farther than saying that I THINK it's coming from the front. I did check the tires and didn't find anything stuck in the treads or rubbing against them- but I want to re-check now you have me thinking!

When you put the bearing caps back on did you put that brass do-dad in properly?
That's the "axle hub contact spring" and the ONLY reason I know that is because it was missing and I had order a new one! I have no idea what it does other than stir the grease up in the cap, but the car was sounding off before I installed one.
 
#4 ·
The axle hub contact spring is to give ground to the brake wear indicator.

Regarding your sound, if it's speed and not RPM related, you should be able to rule out engine drive belts, alternator, water pump etc. What about your axle? I agree it's difficult to isolate noise, so maybe it's not from the front, but underneath you?!
 
#5 ·
I agree it's difficult to isolate noise, so maybe it's not from the front, but underneath you?!
Possibly - I was planning to check/lube the u-joints until I found out MB didn't use u-joints!

What about your axle?
Can you elaborate? When I had the hub off I checked the steering knuckle/spindle and everything was tight and appeared to be in order... but I didn't know what else to look for.
 
#8 · (Edited)
How worn are you disc brake pads? Some brake pads are riveted and dust can collect in the rivets and cause some noise. The front bearings for my 83 were rather inexpensive so I replaced them all as a preventive measure. My SL has over 200K miles when I bought her. Thats the only things I can think of that would make a noise like that.


UPDATE: Sorry I apparently did catch that you had replaced the bearings. My bad.
 
#9 ·
How worn are you disc brake pads? Some brake pads are riveted and dust can collect in the rivets and cause some noise. The front bearings for my 83 were rather inexpensive so I replaced them all as a preventive measure. My SL has over 200K miles when I bought her. Thats the only things I can think of that would make a noise like that.
Replaced the pads along with the rotors (and bearings and the brass do-dad)... but just on the right side, which is where the sound seems to be coming from. I'm doing the left side this weekend - like you I can't think what else might be making this noise and hopefully this all turns out to be a function of bad hearing.
 
#10 ·
Probably not the do-dad then.

So does the noise happen when its under load, when coasting or all the time. could it be the fuel pump? noisy little buggers but if you have the sound insulation /carpets out the noise could travel... But not the do-dads... That's good, to rule something out.
 
#11 ·
I experienced a strange hard to locate speed-related sound from a cracked and de-laminating parking brake shoe. You can test for that by slowly applying the parking brake when it is making the noise (while pulling the brake release simultaneously... in appropriate traffic conditions).
 
#12 ·
I still haven't found the source and I'm getting frustrated. . . I've gone far enough through the process of elimination that I'm having this nagging thought that what I'm hearing may be a failing bearing on the transmission output shaft. There's a well respected Indie here and I think I need to concede defeat and have him find the problem.
 
#13 ·
Have you jacked up the car and tried rotating the frontwheel?

I spent several months tracking down an occational front grinding sound, especially when accelerating. Turned out that the starter solenoid fork was wrongly installed (by me). The pinion disk shall be securely held by the fork, easy to mount the fork on the inside, it can the slide towards the ringgear. This fault would be engine RPM dependent, but difficult to judge an occational grinding sound.
 
#14 ·
I was thinking of the drive axle. Could it be a worn flex disk or bearing where the noise "travels" so you hear it from the front? Seems like you've exhausted most possibilities from the front running gear, so maybe time to move back under the car to inspect.
 
#15 ·
Okay, after a little creative contortionism which involved my daughter driving and me riding bent over with my knees in the passenger seat I think the source of the sound is a little further back than I originally thought - it seems to be coming from under the center console, right where the flex disc/centering sleeve is located. Since getting to the front end of the drive shaft for in inspection means dropping the exhaust system this job is now officially beyond my something I can handle!
 
#16 · (Edited)
Maybe not. I did this by soaking the bolts holding my exhaust on with Liquid Wrench penetrating oil, as well as the pipes themselves at the junctures for several days before the job was to be done. Persistent pounding with a large hammer on the back of the muffler using a 2X4 to protect it and the thing started to come off.

In my case, I was just being overly cautious as the plan was to replace the muffler anyhow, which I did and the result was quite appreciable (Nice Ansa sound now). After removing the exhaust was when I decided to look over the whole drive system and good thing I did! Even though there were no signs of failure when driving, i.e. no vibrations, both flex discs were very much in need of replacement as well as the rear transmission mount. I'd have to echo something Nobby said a while back that flex discs should be a priority to check and replace if they are old. Mine were original and from a visual inspection, did not seem to be in bad shape. It wasn't until I got them out that I could see the real disintegration that had occurred.

So, if you take your time and are persistent, I would think you can handle this job....in any case, good luck finding the issue!

PS - Before I did the repairs mentioned above, I noticed when shifting from park to reverse there was a pretty noticeable clunk that I thought should not be there. After the repairs, the clunk is gone and now it just has the slight lift of the rear end that many of us notice. Does yours clunk by chance when you shift from park to reverse? If so, I would bet your flex discs need to be replaced.....just something I thought I would bring to your attention as a failure in that regard can be very, very unfortunate.
 
#17 ·
It's interesting you should mention Nobby, because I just finished reading his flex disc thread in the Encylopedia - which is ominously marked "Required reading for everyone or double dumbass on you." Even the front flex disc isn't the source of the sound I'm trying to run down I absolutely want to get in there and take a look! The good news is that based on Nobby's write up it looks like I don't have to remove the prop shaft, which hopefully means that I don't have to drop the exhaust system.
 
#18 ·
I probably could have gotten at it as well, but removing the muffler and the pipe "upstream" of it made access a whole lot easier. Not sure how one would get at both front and rear flex discs without removing the drive shaft, which is in 2 pieces on my car and needs to be marked so it is put back together the same way as it was taken apart. As I recall, there was not enough back and forth travel to get the things out without removing the shafts. While you're in there, don't forget the rear transmission mount as that is likely going to be something you'll want to replace. There are several types and yours will have some identifying numbers on it to use when ordering a new one. You will need to support the rear of the transmission before you go unbolting stuff with a sturdy jack though.
 
#19 ·
Finding a shop that would work on an older MB was a bigger ordeal that I thought it would be- the "big" Indie here only works on "modern" cars, but they finally recommended one of their former mechanics who went out on his own.

Anyway, it turns out that the center support bearing is shot, which allowed the drive shaft to drop just enough to scrape the cover plate and cause the noise that I though was coming from the front end. In addition, both flex discs were cracked and I also had them replace the shift bushings for a grand total of $903.95... does that sound about right?

Brian
 
#21 ·
Did you get a breakdown of parts vs labor......... I would expect about 6 hours of labor, raising the car, supporting the trans, removing the exhaust system and driveshaft without damaging the centering bushings.... i believe the drive shaft needs to be split, and the the center bearing is press fit so removal and replacement, then reinstall everything.... sounds ok to me....

Did he make any comments on the condition of the sub-frame mount and engine mount conditions????

RC
 
#20 ·
Thanks for coming back and letting us know what the issue was. I'm a little surprised that they didn't recommend replacing the rear transmission mount as that is in the same area and with all you had done would have been pretty simple job. Can't comment on the price since I did all the work on mine but maybe others can shed some light on that. In any case, you accomplished a lot and won't be sorry as those flex discs would have become a much bigger issue had either failed! Enjoy your "noiseless" ride, Brian!
 
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