300SDL Clank in driveshaft - PeachParts Mercedes-Benz Forum

ggspeed · #1 07-20-2009, 05:59 PM

I replaced the flex discs as well as the center support, and the center support bearing. Yet when my 87 SDL downshifts and up shifts slowly there is still a clank in the drive shaft. Not as bad as before, but i want it gone.

Any ideas where this is coming from?

#2 07-20-2009, 08:17 PM

Are you SURE that it is the driveshaft? Have you checked your differential mounts?

The best way to find such a problem is with the 4 P's: Push, Pull, Pry and Prod.

pawoSD · #3 07-20-2009, 08:27 PM

The clank may be the trans itself downshifting. Mine does/did that. It actually stopped doing it once the trans began dying......

ggspeed · #4 07-20-2009, 08:51 PM

It makes the same exact sound as when i took the drive shaft out and flexed it to come out. We are thinking it might be the transmission mounts that are causing to to move a bit..

Any input on this idea?

Brian Carlton · #5 07-20-2009, 09:44 PM

All of them will make that sound if the shifts are too quick.

Put a vacuum gauge on the modulator line and take it for a drive. Report back with some data on vacuum at various operating modes.

My suspicion is that you've got a serious vacuum leak.

brandlj · #6 07-21-2009, 09:14 AM

Quote:

Originally Posted by Brian Carlton

All of them will make that sound if the shifts are too quick.

Put a vacuum gauge on the modulator line and take it for a drive. Report back with some data on vacuum at various operating modes.

My suspicion is that you've got a serious vacuum leak.

I agree with Brian, my 86 300sdl had a vacuum leak and it made the worst sound when it downshifted while coasting to a red light. It literally banged on the downshifts, and you could really feel the shifts, up and down. It turned out that i dislodged a vacuum line while changing my fuel pre-filter. Hooked it back up and all was well.

ggspeed · #7 07-23-2009, 09:58 PM

with a gauge on the vacuum line it sits around -15 psi at idle and will go to -13/14 when the rpms are about 2200 and up. Any suggestions as to where a leak may be? I have quickly inspected them and they all seem good. How can a leak be properly identified?

Brian Carlton · #8 07-23-2009, 10:31 PM

Quote:

Originally Posted by ggspeed

with a gauge on the vacuum line it sits around -15 psi at idle and will go to -13/14 when the rpms are about 2200 and up. Any suggestions as to where a leak may be? I have quickly inspected them and they all seem good. How can a leak be properly identified?

Which vacuum line did you put the gauge onto?

Did you route the gauge into the cabin so you and read it while your driving?
If so, what are the readings at 1/2 pedal, 3/4 pedal, and full pedal?

ggspeed · #9 07-24-2009, 11:25 AM

I put it into the line labeled TRA that comes out of the blue circle labeled vacuum. I had somebody sit in there and rev the engine for me so i could get readings at different rpms

ggspeed · #10 07-25-2009, 01:34 PM

could this be a transmission mount

djustin973 · #11 07-27-2009, 12:48 AM

Had the same problem with my 300sdl. Turned out to be the diff. Two large pins connect the carrier and ring gear. After 20 years and 400,000 miles the pins had opened their mounting holes into 2 inch slots! Every time power was applied the ring was clanking against the pin making a very ugly noise. Especially when downshifting! The easiest way to tell is put the parking brake on and put the car in neutral. Get underneath and try to turn the drive shaft. With a good diff you should get maybe 5 degrees either way. On my diff I was able to turn the drive shaft a full half turn before it stopped and made a familiar clank. Check your diff!

I found a picture. That slot should be a hole the size of that pin. Pretty huh?

fruitcakesa · #12 07-27-2009, 07:58 AM

Quote:

Originally Posted by djustin973

Had the same problem with my 300sdl. Turned out to be the diff. Two large pins connect the carrier and ring gear. After 20 years and 400,000 miles the pins had opened their mounting holes into 2 inch slots! Every time power was applied the ring was clanking against the pin making a very ugly noise. Especially when downshifting! The easiest way to tell is put the parking brake on and put the car in neutral. Get underneath and try to turn the drive shaft. With a good diff you should get maybe 5 degrees either way. On my diff I was able to turn the drive shaft a full half turn before it stopped and made a familiar clank. Check your diff!

I found a picture. That slot should be a hole the size of that pin. Pretty huh?

Ouch, Did you replace or rebuild that puppy?

djustin973 · #13 07-27-2009, 11:32 AM

I went and pulled the diff out of a 560sel so I could have the lower gear ratio. Now my car drives like it really should!

Oldwolf · #14 07-27-2009, 11:35 AM

What would cause that? Normal wear or lubrication problems? Doesn't look "normal" to me though.

Were there metal flakes in the fluid every time you changed it?

djustin973 · #15 07-27-2009, 09:54 PM

Well I think that was exactly the problem. I've had the car for 30,000 miles and changed it once (yes there were metal flakes) but who knows how often it was changed before i owned it. If it was changed at all. Even people who know almost nothing about cars know that the oil, antifreeze, and other fluids need to be changed but for some reason no one ever thinks about their poor differential.