Jackhammer sound when in Reverse Idle - PeachParts Mercedes-Benz Forum

imagesinthewind · #1 03-05-2008, 08:10 PM

So, the other day when it was snowy and icky out I had to drive my car.
It's normally a turn-the-key-start-right-up car at this time but on Monday
it kind of turned over a few times and then belched a bit smoke cloud out the back. Strange for this car that hasn't smoked a day in three years.
Then it was idleing REALLY loud and a bit rocky, for the first time I could FEEL the idle.
When I put it into reverse the jackhammer sound started and it rocked a bit more. Not a high pitched tinny sound, but a low grumbling jackhammer sound.
When it's in drive, Neutral or park, the idle is almost the same as normal. Just ever so slightly rougher. Just.

When I go to turn off the key the car hammers for about half a second or about 3-4 times before it dies.

I haven't checked under the hood, but when I do what should I be looking for?
Thanks!

mobetta · #2 03-05-2008, 09:51 PM

maybe tranny mount or engine mounts. also look over the exhaust system, see if it is missing hanger donuts or otherwise loose enough to hit the body somewhere.

TMAllison · #3 03-05-2008, 10:49 PM

I'd recommend checking the resistance of your glow plugs and testing the relay.

Go to dieselgiant.com and follow his tutorial.

pawoSD · #4 03-05-2008, 11:41 PM

Hammering sound can be collapsed motor mounts (drivers side has the most weight/torque on it when in reverse) tranny mount, or a part of the exhaust system banging on something.

Tymbrymi · #5 03-06-2008, 09:16 AM

Quote:

Originally Posted by imagesinthewind

When I put it into reverse the jackhammer sound started and it rocked a bit more. Not a high pitched tinny sound, but a low grumbling jackhammer sound.When it's in drive, Neutral or park, the idle is almost the same as normal. Just ever so slightly rougher. Just.

Can't explain why it started rough or anything (probably glow plugs), but the noise you described is almost certainly a bad engine mount.

imagesinthewind · #6 03-09-2008, 10:48 PM

Would a bad engine mount quiet after a while of driving? After a few miles, maybe 10 or so, if I stop and idle, the car is much quieter. It doesn't make the hammer sound.
When I am outside tha car there is little change in sound, just inside you can hear and feel the vibrations.
Outside the car makes only slightly more noise than before.
And why would the car shake more in reverse than in drive and less in neutral?

And the car has plenty of oil, excellent pressure and runs/drives exactly like it did before the noise started.

Skid Row Joe · #7 03-09-2008, 11:33 PM

Engine mount.....left. Change left and right.

rs899 · #8 03-10-2008, 06:45 AM

Quote:

Would a bad engine mount quiet after a while of driving?

Could be that your engine idles more roughly when cold (most do) and the bad mount is not resilient enough to dampen the vibrations. When it heats up, the idle improves and also the mount may heat up a little and become more resilient. I agree with everyone else, the mounts are the first place to look.