Pop sound: W123 - PeachParts Mercedes-Benz Forum

mbzkid · #1 08-14-2006, 01:15 AM

My 300D has developed a popping noise that usually occurs when coming to a stop and when accelerating from a stop. It can be felt through the floor board and slightly though the brake pedal, not the steering. The popping is worse when the car has been run for a long time, especially highway driving. This is one of the reasons that I suspect the wheel bearings. I can also hear a high pitched click, but very rarely. Its a sharp click which I can hear from the front right and sometimes near the drivers seat, which iss probably coming from the front left.

The popping sound would be equivilant to someone smacking the coil spring with a mallet.

When coming to a stop, the sound will start at appox. 15 MPH and pop 1-6 times as the car comes to a stop. As the car accelarates from that stop, and the suspension unloads, it will pop another three or so times. Other times, the pop will occur almost constantly when coming off the highway. It will pop/rumble as the car travels down a fairly smooth road, but only after a highway run. Eventually (as the car cools down?) the sound will only occur when braking/ accelarating.

I checked the left front bearing and as I tightened the bearing, I was unable to detect a difference in effort when turning the hub. The hub made a sort of rumbling noise as I turned it, yet when I drive the car, I am unable to hear any of the typical bearing noise that would be associated with a worn bearing. I don't hear any bearing noise as the car turns, or when weight is shifted to the front.

A shop that is known for doing front-end work, inspected the suspension and claimed the suspension was "tight." We were told it was the shock, and the shop has never seen anything like this before. I installed two new Bilstein shocks and the noise was gone for 15 or so miles. Then it slowly came back.

Needless to say, I'm a bit concerned about driving the car, and would like to hear your input.

#2 08-14-2006, 01:59 AM

Check the engine mounts. I thought I had a bad ball joint, but I found the passenger side engine mount was missing the bolt.

mbzkid · #3 08-14-2006, 02:47 AM

Quote:

Originally Posted by ForcedInduction

Check the engine mounts. I thought I had a bad ball joint, but I found the passenger side engine mount was missing the bolt.

I'l check it out tomorrow.

Thanks

sixto · #4 08-14-2006, 03:10 AM

Check the guide rod mounts as well. Takes some heavy tugging to feel slop even when very worn.

Sixto
... stay tuned

mbzkid · #5 08-14-2006, 02:02 PM

Engine mounts and guide rod mounts appear to be in good shape.

sixto · #6 08-14-2006, 03:11 PM

Check the Fastlane link at the top of the page for a picture of a new engine mount and compare to yours. They can look intact but be an inch shorter from wear.

Tranny mount?

What's the rust situation?

Sixto
... stay tuned

mbzkid · #7 08-14-2006, 05:46 PM

Trans mount is good, same for engine mounts. Very little rust.

The front left wheel bearing is looser than the other side when the car is hot so it looks like I need bearings.

Wes Bender · #8 08-14-2006, 06:33 PM

Quote:

Originally Posted by Carson357

MBZKID with a bmw avitar???

The popping sound is from his avatar changing to MB on acceleration and back to BMW when he slows.

?? then Carson357 deleted his post??

mbzkid · #9 08-15-2006, 11:46 PM

Quote:

Originally Posted by Wes Bender

The popping sound is from his avatar changing to MB on acceleration and back to BMW when he slows.

Actually the benz brakes harder, and accelerates smoother, but the bimmer is quicker.

I ordered wheel bearings from Phil. I'll post back after I install the bearings.

carwithfarts · #10 08-16-2006, 11:31 AM

also check and make sure the caliper bolts and rotor bolts are tight because if these came lose it coould cause the same symptoms and be very dangerous especially braking on a ramp!~Luke

mbzkid · #11 08-24-2006, 12:37 AM

New wheels bearings and the sound persists. The calipers are tight and so is everything else I can see and touch.

doucy2 · #12 08-24-2006, 04:20 PM

i had a poping noise in my 300d t and all it was, was the air cleaner had come unmounted (i still havent fixed it, but you can set it back in place for a temp fix)

85chedeng300D · #13 08-24-2006, 09:54 PM

yeah! i agree! i might be the broken air filter housing mounting bracket or just a missing attatching hardwares.

... or if, as you described, that it only makes the popping noise when accelerating and braking, it can be the radiator fan touching the radiator shroud everytime you brake and accelerate. try checking your radiator fan blade's edges and all around the shroud for signs of chaffing and marrs. the blade and shroud gap is usually closer on the lower passenger side and the upper center part.

#14 08-24-2006, 10:06 PM

I don't know how familiar you are with the calipers and brakes, but check to make sure the pads are held in by the spring clip. The clip should be between the 2 holding pins and the pads. Sometimes they get put together wrong and the pads will knock around in the calipers rather noisily.

mbzkid · #15 08-24-2006, 11:22 PM

Pretty sure its the guide rod mount. I ordered a new one, and I'll post back with the results.

Its definetly suspension related.