I have inherited a 1990 240SX and am new to this forum. The car runs fine but there is an annoying whine or low hum from somewhere in the rear of the vehicle. I replaced the differential oil but this was not the problem. I am thinking rear wheel bearings or drive shaft center support bearing. What do you guys think is the problem? Any common problems in the drive axle system? I am trying to isolate the problem but need some advise.
Thanks for you time. Great forum!

 

You sure it's not coming from the brakes?

If not...could be the wheel bearings, never heard of DS center bearing going out.

 

I took off the rear wheels and put the car on jack stands and the noise seems to be coming from the differential area. The noise is the loudest from that area where the cv joints connect at the differential . The boots are not torn so It just might be the differential. What other year 240sx share the same differential? I have a 1990 2.4 liter 2 dr.coupe. I might have to check with the local wrecker for a used one.

 

89

Not 100% sure a differential from a 91-94 would just pop right in, but I think it will

 

How hard is it to replace the bearings on a differential? Has anyone done this?

 

Not very hard(might be a little time consuming)...but its a messy job!

 

I am probably gonna be replacing the driveshaft on my car. It's also a 1990 240sx and has either a worn bearing or u-joint. I hear its a very simple job. I have a noise coming from the rear also and I am being told it is close to the differentail also. My Differentail is leaking a lil and the bolt is not on properly I believe I may need a new bolt to plug the differentail. Well anyways I am getting a noise also from the back but it's not the same as yours. I get a clunk/knock sound everytime I accelerate. Can you tell me when the noise happens for you exactly. I may be able to help but I am also looking for answers.

Anyhow get back to me and give me some more info if your still intrested.

 

The noise starts off around 20 - 25 mph and increases as I speed up. It is not a clunking noise like yours is but a low hum that gets louder as the speed increases. I was going to detach the drive axles from the diff and run it to see if there is a difference in noise.
How can I tell if the noise is from the diff or the drive shaft?