My Car Sounds Like A Jet! Why? - PeachParts Mercedes-Benz Forum

Subman · #1 08-22-2002, 11:24 PM

Well I have posted this same question before but now I have new news to report.
My car sounds like a jet when moving, applying the brakes does not matter nor does the gas. The noise is constant and gets louder with speed, the noise appears to come form the rear of the car. I can only describe the noise as a jet like sound from inside the car and a groan//humming noise from outside.
How may you ask can you hear is from the outside?
Well I put the car up on jack stands and ran the car.
Here is the weird part: The noise is not present until the speedo starts to move, once the speedo moves the noise appears.
I tested this by having my dad apply the gas while I would listen, he also heard the noise appear and pointed out that it corresponded with the movement of the speedo.

I have tired many things that did not solve my problem, I thought it was a wheel baring, but both rear were fine, so I had the rear sub frame apart I dropped the diff and had it checked out... it was fine. I also had the diff guy take a ride in my car and see if he knew what it was, but he could only tell me that it was not a ring and pinion problem.

Since the noise comes on with the movement of the speedo I think that the noise is some how related to the transmission.

Can anyone tell me what is wrong with my car?

BTW there has been no loss of performance.

Thanks
Subman

Edit: Yeah I know I can not spell, but I dont realy care, thanks though.

95E320cab · #2 08-22-2002, 11:43 PM

I think the car's spell checker is broken.

royaiii · #3 08-23-2002, 02:21 AM

Ive experienced similar results but there are so many factors that necisitate taking it to a trained professional. Almost anything relating to the Drive motion could be the culprit. Driveshaft could be out of balance. A machine shop would have to rebalance it for the tune of $500. Flex Discs arent it but if you havent relapced them by now, you should. Differential clicks, so it's not that. If not driveshaft check out rear axle. Are the tires inflated to spec pressures. (Hey, I had to ask). You say you checked the rear axle, so your transmission is a gonner.

omegabenz · #4 08-23-2002, 03:52 AM

why dont you trade me your car for my coupe straight across?

No, well one time I was driving home in the snow and it was really cold out like -10 or so, and the spedometer cable started to sound like a jet engine where it was like hitting the outside walls of the cable shielding....maybe its that. Take the spedo cable out and go for a drive. Sometimes noises sound from the rear but they are really from the front.

I know you have been having trouble with your differential. Well sometimes over time the pinion gear and the spur gear dont have the right "timing" and they make a clashing noise, usually a higher pitch ringing because the pinon strikes the spur at the wrong angle and it will create a humming noise. Maybe thats it. I wish I recorded it when my car did it. I just replaced the rear end.

I hope this helps tom,

Austin

-fad · #5 08-23-2002, 12:14 PM

suggest:

>reviewing the heat blanket (mounting points/ correct positon/ functioning) around the inner trans tunnel (underneath the car); only viewable from high lift inspection ; you can poke at it with a screw driver to further determine condition

I've seen this blanket come down and contact the drive shaft- result: noise/whine/roar/etc,.

Repair consists of dropping Tranny and replacing blanket with OEM new improved part, part is cheap. labor is $$$

hope this helps, good luck, and let us know what turns out

Subman · #6 08-23-2002, 09:50 PM

Quote:

Originally posted by omegabenz

I know you have been having trouble with your differential.

When did I say I was having problems with my diff? My diff is fine, I have been trying to figure out why my car makes this noise, one of my thoughts was that it was my diff. So no my diff is fine it is in perfect working order, it was never bad or broken.

The suggestions seem good, I have in depth knowledge of the underside of my car. I dont think it is the mat or something rubbing on it, because the noise suddenly appears when the speedo starts to move, if something were in contact with the driveling then the noise would be constant and always there, but it only appears when the speedo starts to move.

So I think it has something to do with the speedo cable or sending unit or sensor or something on that end.

Thanks for the suggestions and I will look into them all, and some new ones if I get any.

Thanks
Subman

JimSmith · #7 08-24-2002, 01:45 AM

Subman,

Does the pitch of the noise follow the speed of the rear wheels? Meaning, if you increase the indicated speed does the pitch get higher? Does the volume get louder with increased speed?

If the noise is a high pitch, it is not likely something heavy and large in diameter, especially if the pitch is high when the noise starts. Is the noise loud and obnoxious outside the car, where the pitch was noted to be a groan/humming sound instead of the jet noise? Have you disconnected the speedometer gear? This could be something that is capable of generating a high pitch. About the only other thing I can think of that might make a high pitch even at low rpm would be something externally rubbing on the drive train that is attached to the body, and you are exciting a resonance. Maybe if you go to a place with a lift and you get all 4 wheels off the ground, you can get under there when the noise is present and try to pinpoint it.

Good luck, hope this helps, Jim