94 W124 Knock when downshifting
 

Hi,
My w124 seems to knock once 'sometimes' each time it downshifts from4 -3-2-1 depending on which gear it is downshifting from. Upshifts are smooth as ever. Even when i down shift from D to 3 or 2 this happens but only sometimes. Does anyone know why this could occur? I'm new to MB's and cars in general but am willing to learn as much as i can.
Thanks for your help.

jm

Can anyone help... please?

Looks like you've got to get underneath the car and check out the drivetrain; flex disk, drive shaft center mount/bearing, transmission mount, differental mounts and/or anything else that my cause the problem. Could be a full can of beer in rolling around in the trunk. What areas of suspicion have you eliminated that will help narrow the scope of possible culprits?

If it only happens when your downshifting, maybe it is a broken rear motor mount.

I'm pretty sure its not anything in the trunk. But i'll check the underneath of the car. btw where is the rear motor mount and how do i check for damage?

Thanks guys

You can check to see if a motor mount is broken by having someone sit in the car, and with your foot on the brake, put the car in drive and give the engine a little gas. Have someone look at the engine move. Do the same thing with the car in reverse.

If the front or back of the engine sort of jumps up, you'll be able to see if the front or rear motor mount is broken.

Do you get a vibration at idle in the cabin?

You also shouldn't rule out some of the other advice given above.

It could also be a flex disc, center support bearing, or differential mount.

If you have a flex disc going out, and it fails while driving, it could cause some damage.

You really should take the car to an independent mechanic that specializes in Mercedes to give the car a once over.

It could be the cheapest $60 you'll ever spend.

I'll try that out today. The car does idle at normal speed and was vibrating noticibly but not too bad. After a short drive it was fine. The car has warranty on the engine and transmission. Am wondering if any of those reparis count in with the warranty
Thanks

best regards

JM

Maybe it is a bad motor mount.

You shouldn't feel any vibration at idle. An M104 engine is as smooth as glass.

Hi,
alright, i've determined that there is no vibration at idle. although it has occured about only twice this week. but the engine does move when in drive although it doesn't 'jump'. The knock noise seems to be coming from the right rear of the car near the wheel. Could this still be a rear transmission/motor mount?

ps you've been great so far suginami thx.

Unlikely, then. Check rear plastic sway bar links - known to break.

Steve

hi,
How do i check these? And how do they look like?

Thanks

JM