Grinding noise when accelerating from a stop - PeachParts Mercedes-Benz Forum

jammer · #1 04-12-2004, 06:08 AM

This is about my W126 ‘89 300SEL with 105k miles. Lately I’ve been noticing a grinding noise which appears to be coming from the lower part of the engine. I can hear the noise and feel the grinding in my foot. It happens when I try to accelerate hard from a stop, especially when on an incline or accelerating hard on a left turn from a stop. Once the car picks up speed the noise goes away. I’m thinking torque converter or transmission mount. Is there any way to diagnose what’s causing this? TIA.

Paulwho · #2 04-12-2004, 09:48 PM

jammer,

Longshot here, check the clearance between the exhaust downpipe and crossmember bolted between the unibody. Durring hard accelleration the engine mounts\trans move enough to allow contact. Buzzing results.

Good Luck

fahrgewehr2 · #3 04-12-2004, 10:42 PM

I'm with Jammer. Replace all 3 mounts- two motor, one tranny.

BTDT.

jammer · #4 04-13-2004, 01:32 AM

Thanks Paulwho and fahrgewehr2. In my original post I failed to mention that the front engine mounts were replaced a few months ago because as Paulwho suggested the exhaust downpipe was touching the crossmember due to collapsed mounts. I didn’t replace the rear engine or the transmission mount. I'm not convinced the problem is with the transmission or the flywheel as there is no grinding noise in second regardless of how hard I rev the engine. I’ll replace the rear engine mount and let you all know if that fixes the problem. Thanks again for your input.

fahrgewehr2 · #5 04-13-2004, 02:29 AM

jammer-

I replaced the two motor mounts first and the grinding was still there.

Pulled the trans. mount out and it was petrified- hard as a rock. Problem solved.

Might want to check your flex disc for play while you are under there. And a tranny service too, if you want to make an afternoon out of it.

Good luck,
Mike

jammer · #6 04-13-2004, 03:42 PM

Good idea Mike. I was planning on servicing the transmission in the near future anyway. I have the required 10 liters of Febi ATF, gasket and filter. How can I tell if the flex disk needs to be replaced? Isn’t there a flex disk at the rear, in font of the differential, too? Should that be replaced at the same time or are they independent of each other as far as age and hardness is concerned? TIA.

fahrgewehr2 · #7 04-13-2004, 04:07 PM

Yes there are 2. I think they are different from what I remember,

Do you get any clunking when you put the car in drive or when you switch from drive to reverse? I knew mine was bad because I could rotate it by hand a few inches! and it made a nasty noise. Paid the shop to do this a while back (this forum didn't exist at the time). Mounts and tranny service I did myself.

Since my font disk is going bad again, I am going to replace both in the near future. Will probably do it myself so let me know how it goes.

Good luck.

jammer · #8 04-25-2004, 04:31 AM

I replaced the rear engine (transmission) mount today after replacing the transmission fluid and filter. The grinding noise is gone. Thanks all for the pointer. I didn't drain the torque converter. Gave up trying to get drain bolt to line up with hole after about 15 minutes of cranking. I poured 5 liters of ATF. I know I didn't follow the correct procedure which calls for pouring only 4 liters, starting the engine, shifting from P to R through N to D and back to P stopping for a few seconds in N and R, then slowley adding ATF. Now the ATF level is about 2 inches above max. How could that happen? Is it possible to trap air in the transmission? Do I need to drain 1 liter and follow the instructions or should I drain all the fluid and start over? TIA.

Paulwho · #9 04-26-2004, 09:45 PM

jammer,
You must reduce the trans fluid level. When only draining the trans pan a refill is 2-3 liters

Kestas · #10 04-26-2004, 09:53 PM

Quote:

Originally posted by jammer
...Gave up trying to get drain bolt to line up with hole after about 15 minutes of cranking....

That's why I have a mirror in my toolbox. I simply lean it against a block of wood so I can see the torque converter as I rotate the crank with my 27mm socket.

jammer · #11 04-27-2004, 04:46 AM

Paulwho,

I vacuumed a little over 1 liter after test driving the car for about 20 minutes. When I came back I noticed light smoke from ATF on the exhaust pipe. I think it was coming from a relief valve. After sucking out the excess fluid there are no more leaks. I’ll probably replace the fluid shortly as obviously I didn’t get all the old fluid out. I will just drain the fluid through the pan drain plug and the torque converter. I won’t replace the filter or the pan gasket . Do you see a problem with that?

Kestas,

I saw the torque converter plug several times but it was just about an inch short of the opening. I read a post here a few days ago where someone said they “inched” the converter with a screw driver. Does anyone know how that is done and how can a screw driver be used to rotate the torque converter? TIA.

Kestas · #12 04-27-2004, 09:55 AM

I also saw that post. It sounds like a good technique, especially if you don't have a 27mm socket. I believe you "inch" the torque converter by using the teeth on the flywheel. These teeth are for the starter engagement.

jammer · #13 04-27-2004, 05:40 PM

Kestas,

I saw the teeth and was very tempted to do exactly that but was afraid they might get damaged or at least scratched as a result. I figured that some other mechanical device is expecting to mate with those shapes and if their geometry gets altered as a result of my prying then that other device might overtime get damaged too.