vibration and tap tap tap sound from center of car on take off acceleration
 

I have an e320 wagon that I'm noticing a tap tap tap and vibration when I hit the gas from a stop. It doesn't seem to be there when cruising or even accelerating later. I've only noticed it on take off.

Any ideas what this could be?

Background on the car, bought it used fixed an exhaust leak changed the MAF sensor, put new tires on it. Seems to run good.

It was rear ended at some point. It doesn't look bad but I know the frame is bent a little bit. I can see a small crease in the roof metal between the two doors (front and rear) also the doors close a little tight. So I'm sure there's a little bend in the frame from the rear end collision. It drives fine and straight. But maybe this could be related maybe not.

What should I be checking?

thanks!
Nick

Ill bet its your flex disc.

What year car? 4-matic?

Flex disc or center support issue, don't forget the trans mount.

This is a 94 E320 2WD (EDIT: Great time to update my sig line - car added). I looked at the flex discs and don't see much in the way of cracks. I wonder if the P.O.'s rear end collision could have messed up the drive shaft angles? I would think that it's flexible enough being two pieces that it's probably ok. But maybe the driveline is pressed forward a little from the compression of the rear toward the front. I would think it's a pretty small amount but it's enough that the doors don't shut easily (tight slightly mis-aligned fit).


Would a bad center bearing cause this only at take off?

Could be the rear of driveshaft if it has U Joint , or center support , only way to check is to remove drive shaft and inspect

Is it possible to check the center bearing by pushing and pulling up and down on the drive shaft to feel for play? I'd guess it's a small enough bearing that any play that'd cause noise issues wouldn't be noticeable by hand but figured I'd ask since I don't know the answer to this.

any idea how to check the center bearing? Is it possible to check without pulling the drive shaft? It'll probably be a 2-3 hour plus job if I have to pull the drive shaft.

Plus it's almost pointless to do all that without putting money into new flex discs and a center bearing. I'm trying to keep this cheap.

Nick, as you're probably know there is a slip joint in the driveshaft. You need 41mm and 46mm open end wrenches to loosen the nut in order to "telescope" the driveshaft when replacing the flex discs. Before you go to the trouble of replacing the flex discs and center support you may want to simply loosen the nut to relieve any accident-related stress that is tending to bow the driveshaft. From my experience the rear flex disc is more problematic so inspect it carefully for cracks.

So when you say loosen the nut to relieve any accident related stress, I don't leave it loose I'm assuming right? I'm guessing I tighten it back up. Will breaking it loose and re-tightening help relieve stress or realign?

flexdisc or halfshaft CV joint.

Had the rear flex go on y C36- got to the point where sounded like someone banging on the car underneath with a sledgehammer under load.

Inspect it and it before the driveshaft rips through the floorpan and totals your car.

it looked like this
 

1500 miles from home when this happened. :mad:

Nick, sorry for not being more clear. Yes, you want to briefly loosen the nut to allow any accident-related stress to release, then retighten the nut.

It would be ideal if you could get your car on a dynamometer and observe the driveshaft motion when it starts to turn and makes the tapping sound.