Nasty banging sound from W123 - PeachParts Mercedes-Benz Forum

cantabridgian · #1 02-20-2008, 03:19 PM

My 1985 300CD (about 188k miles) has developed a nasty sound while driving on the highway, but I can never re-create it for my mechanic! Help? It occurs after driving between 50-75 miles on the interstate (usually I drive about 75-80mph, traffic permitting), never sooner. The sound begins as a soft thudding noise, eventually escalating into a giant banging, clanging sound. Interestingly, the noise only occurs while pushing the accelerator. When I take my foot off the gas completely - complete silence! - just the Benz cruising beautifully down the highway with no banging noise whatsoever. When I push the gas pedal again - bang! - there it goes. The banging will last until I pull off the highway and bring the car to a complete stop for about 15-30 seconds or more (like at a traffic light), and then it will go away completely until I get back on the highway. Then the banging will start again after about 30-40 miles driven or so, as before. The mechanic has assured me that it is not the exhaust. The right (passenger) side half-shaft was replaced by a previous mechanic about 5,000 miles ago. My current mechanic insists that this wasn't even necessary. Needless to say he (a) has never driven it far enough to hear the noise, and (b) says everything else is in good shape. Rear bearings have been replaced about 8,000 miles ago. Front end it in excellent condition. Meanwhile, the banging-clanging persists. Friday it started at mile 55 on a drive from MA to CT for work. After leaving CT, it started again after about 60 miles. Tuesday, driving from VT to MA, it started after about 93 miles driven (the first 35 miles on Route 4 at lower speeds, then about 58 miles at interstate speeds on I-89). By the time I got near Boston it was violent and horrible! And then after I got off the highway and stopped at a light...quiet again. Help!

TheDon · #2 02-20-2008, 03:25 PM

check your flex discs on the drive shaft

Is the banging constant when it happens?

holthoff · #3 02-20-2008, 04:00 PM

Most likely a boot covering one the rear axles' CV joints has torn/broken and dumped the oil inside, causing the joint to go bad.

cantabridgian · #4 02-20-2008, 04:34 PM

Yes, the banging is constant. Occasionally it goes away, but when it comes, generally it is constant.

diesel don · #5 02-20-2008, 05:59 PM

My guess is a half shaft again, agreeing with the former poster. They can be erratic, but are generally the noisiest malfunction on the entire car.

If you get a chance to go in reverse for a hundred yards or so, see if that cancels it for a few miles.

Or, check the boot, like the poster encouraged, squirt a ton of grease in there, tape it up and see if that helps. At least it will help diagnose it

diesel don

toomany MBZ · #6 02-20-2008, 06:38 PM

Quote:

Originally Posted by TheDon

check your flex discs on the drive shaft

Center bearing too.

sublettm · #7 02-20-2008, 06:40 PM

Having had to replace the center bearing and the half shafts on mine, the sound you describe sounde like the half shaft. They make quite a racket when they go bad.

barry123400 · #8 02-20-2008, 07:43 PM

As mentioned the most likely suspect is a constant velocity joint. If it is pretty dry of oil it will take some time to warm up and act up. Your mechanic has examined both rear sides?
You could be in for quite a tow bill if it lets go out on the highway somewhere. If it is a cv joint it will fail at some point. If a boot is defective I would change the axel. If the boots are intact I would add some lubricant to each side.
This may be your cheapest overall solution. Beats being at the mercy or lack of it in a strange garage a long way from home. Your mechanic should already suspect a constant velocity joint as the problem. Also visually check your rubber disks at each end of the driveshaft. I really would not continue highway use without doing something at this point.
Adding lubricant might provide a fix with no additional action required at this time. If nothing else it should help to isolate the problem.

cantabridgian · #9 02-21-2008, 07:51 AM

Okay! Will check both half-shafts (again), cv joint, axle boots, and flex discs (both) and report back to this board. I saw from careful research that many have had similar issues. I will report back ASAP!

spugeddy · #10 02-21-2008, 09:06 AM

I had one of my CV go out last year, and it was intermitant, and never completely failed. It cost me about $90 for the remanufactured part at CarQuest. and about $150 labor????? Mine was at low speed when I was acclerating especially. If I coasted the sound would go away....

Cervan · #11 02-21-2008, 09:52 AM

Quote:

Originally Posted by spugeddy

I had one of my CV go out last year, and it was intermitant, and never completely failed. It cost me about $90 for the remanufactured part at CarQuest. and about $150 labor????? Mine was at low speed when I was acclerating especially. If I coasted the sound would go away....

Sounds like when mine went out.. my left side got so bad after awhile there was ALLWAYS this gigantic "clicking" sound coming from the left side of my car, when i pulled the joint. i could easily slip the cup from the shaft :O

mobetta · #12 02-21-2008, 10:21 AM

I had a CV clicking a bit when I would change from forward to reverse. I went to menards and bought a marinade injector for turkey frying.
I then jacked up the car and slid under w/ a tub of grease and the horse needle. pumped about 3 shots of grease into each CV, no noise since. it has been about 15K since then.

this may help diagnose the issue, but It seems you rely on this car for a lot of miles a week. therefore I would recommend a proper parts replacement, if the cv's are deemed failing.

charmalu · #13 02-21-2008, 01:51 PM

I had the r/r changed twice the 11 yrs we have owned the car. both times it started with a light thumping sound. It would come and go, sometimes getting louder. the first time I had them replace both sides, figured the other side is just as old, and a little preventative maint. can`t hurt. wow that bill$$$ hurt. I just had the R/R changed 2 yrs ago again, same thing a thunking clunk sound.

Yours sounds really bad and I would get it replaced soon before you are stranded or stuck in a snow bank in one of your long commutes. My mechanic said they usually don`t come apart, but that doesn`t mean they won`t. the longer you drive with it like that the greater chance it will.

Charlie

vstech · #14 02-21-2008, 02:00 PM

Get a set of ramps, set them up on a level spot, then go for a 30 minute drive, with some high speed. get home, pull up on the ramps immediately, then start feeling around for hot parts. nothing on the driveline should be HOT, warm yes, but not OUCH hot. don't touch the rotors, as they will seriously burn you. anything else should be warmish. find the hot part and you find the problem.

cantabridgian · #15 02-24-2008, 02:37 PM

I'm going to try and get straight to a lift after a long drive sometime this week...will post results ASAP. Mechanic insists that c/v joint and half-shafts are good. He wondered whether there was a vibration that accompanied the clanging/banging, and there is a mild one...apparently if it comes from somewhere "behind" the driver's seat, it could be the flex discs. Who knows? I'd better upgrade to AAA "Premium" (or whatever they're calling it these days) ASAP!!!