45mph droning - PeachParts Mercedes-Benz Forum

SD Blue · #1 12-23-2010, 08:40 PM

I'm looking for ideas!

About a year ago, I started to notice a slight vibration drone at speeds above 40mph. Now it has become pretty persistent and I can't seem to find the source. As speed increases, the droning noise diminishes and pretty much is non-existent about 75-80mph and I notice it most with harder acceleration.

Currently,
Different driveshaft
new Carrier Bearing and mount
new flex disc
new front tires
rear tires balance checked

The only thing I haven't changed in a while is the transmission mount but it was replaced about 5 years ago. Has anyone else encountered a transmission mount causing this kind of problem?

I've raised the car and ran it up to higher rpm while checking the driveshaft but can't see any vibration of components. Of cours this is without a load on the drivetrain so I'm not sure of the validity of checking things this way.

I would like to send the driveshaft out for rebalancing, etc. but it's fairly expensive and would hate to go to that expense to only result in no change.

Could an alignment problem cause this? I believe it's been 2-3 years since last done.

Thanks for any insight on what I haven't tried.

vstech · #2 12-23-2010, 08:43 PM

have you looked at the exhaust mounting? my 82SD would drone at odd speeds and make a huge noise in reverse, the exhaust donut had the wrong angle and the pipe where the downpipe connects would contact the driveshaft tunnel bolt.

SD Blue · #3 12-23-2010, 08:50 PM

I checked the exhaust and hangers this past weekend and did not see a problem. The exhaust hangers are the "twin loop" type with a rubber buffer in the middle and not the "donut" style. At the same time, I loosened and retightened all the flex-disc bolts and carrier bearing mount bolts. Currently the tunnel cover is off the car to ease adjustment of the driveshaft.

I'll do some more checking of the exhaust, further forward, to see if something is making contact.

It's odd as the drone if pretty heavy at times, yet I don't seem to be able to feel it pronounced with a hand on the shifter.

Lampbum2 · #4 12-23-2010, 08:53 PM

I remember that sound, it was my center bearing on the drive shaft, I really don't believe you need your DS balanced unless you have bent it in some way.

The center bearing is the weak spot and make sure you check/replace your flex disks if they show any stress cracks at all.

How many miles in the drive shaft?

Lampbum2 · #5 12-23-2010, 09:00 PM

OK, sorry, I didn't see you put a new carrier bearing in, your description sounds like when my center bearing was starting to go out!!!

Did you use a new bearing or a used one? My bearing looked great when it was in the car, but when I took it out of the carrier it was dry and grinding!

Good luck!

SD Blue · #6 12-23-2010, 09:04 PM

Actually, it's a second new carrier bearing as a shop I took it to had installed the flex discs backwards. So I took everything back out and put new bearing, mount and flex discs front and rear.

Lampbum2 · #7 12-23-2010, 09:35 PM

I believe it is a bearing some where in the drive train, tail shaft on the trans.,3rd member, half shaft, it is hard to find and tell until it gets really bad and then you hope you are close to home when it goes.

I had a bearing on a printing press drive shaft that growled for about 4 years before I had to change it, we ran that press 24/7.

With that many miles on your car, there are a few bearings that are due to be changed....I'm in the same boat you are in.

vstech · #8 12-23-2010, 09:36 PM

Quote:

Originally Posted by SD Blue

I checked the exhaust and hangers this past weekend and did not see a problem. The exhaust hangers are the "twin loop" type with a rubber buffer in the middle and not the "donut" style. At the same time, I loosened and retightened all the flex-disc bolts and carrier bearing mount bolts. Currently the tunnel cover is off the car to ease adjustment of the driveshaft.

I'll do some more checking of the exhaust, further forward, to see if something is making contact.

It's odd as the drone if pretty heavy at times, yet I don't seem to be able to feel it pronounced with a hand on the shifter.

actually, I was not talking about the rubber mounts, I'm talking about the fitting that connects the down pipe to the horizontal exhaust. when my transmission shop reinstalled the pipe, it was slightly off center and allowed the horizontal pipe to touch the bolt head on certain drive conditions.

SD Blue · #9 12-24-2010, 01:32 AM

Quote:

Originally Posted by vstech

actually, I was not talking about the rubber mounts, I'm talking about the fitting that connects the down pipe to the horizontal exhaust. when my transmission shop reinstalled the pipe, it was slightly off center and allowed the horizontal pipe to touch the bolt head on certain drive conditions.

If I understand correctly, your talking about the main exhaust flange between the down pipe and the front pipe of the resonator. I'll check it but IIRC there weren't any clearance issues in that area.

strelnik · #10 12-24-2010, 07:28 AM

I don't mean to take away from the seriousness of this thread and I hope you find the answer to the problem.

BUT

When I saw the title " 45 mph droning" it immediately made me think of my ex-wife

Beastie · #11 12-24-2010, 08:21 AM

I think VSTECH has the right idea. An idie with no MB experience replaced 3 of the exhaust hangars ( before I got the car) When I installed the correct ones
I started to get a droneing sound. As I looked at the rear bumper I could tell that the exh was now not hung straight. Loosened connections, alignned, tightened..... no drone. Always check the simplest thing first.

mach0415 · #12 12-24-2010, 09:36 AM

Quote:

Originally Posted by Beastie

I think VSTECH has the right idea. An idie with no MB experience replaced 3 of the exhaust hangars ( before I got the car) When I installed the correct ones
I started to get a droneing sound. As I looked at the rear bumper I could tell that the exh was now not hung straight. Loosened connections, alignned, tightened..... no drone. Always check the simplest thing first.

X2 does the drone come in at rpm specific times/load? Perhaps if you pull it into drive and bounce rpm's up and down slowly while your foot is hard on the brake, you can duplicate the noise. By doing so you are torquing the engine, mounts, exhaust, and driveline, sans rotation, to load and stress any grounding out of parts. Be careful to put it in park or neutral and run above idle for a time to keep from cooking the torque converter. Good luck!

vstech · #13 12-24-2010, 12:12 PM

a customer of mine, brought me his 80 300D that someone shoehorned an 83 engine/transmission into, and complained his droning was unbearable. the muffler was about 3" short of exiting the vehicle, and the rubber donuts were pulling the tailpipe right up against the frame of the car. there is a little 1.5" x 2" bracket on the rear of the car, and I had to torch it out of the way to eliminate the droning. any metal contact of the exhaust, and all the engine vibrations get amplified into the vehicle.