View Full Version : Diff whine + tire pressure

08-08-08, 12:37 PM
My car has had a little whine ever since I installed the specter bushings.
A few weeks ago, I was on my way to PIR. It was a cool morning, and I heard nothing from the rear. On the way back home, it was much warmer. I had the usual whine.
Last week I put Amsoil in the diff, trying to get rid of the whine. At about the same time, I happened to up the tire pressure all around. I was pi$$ed that the whine got worse with the fluid change.
Last night, I took a ride out to Long Island. Before I came home I let out a few psi in the rear tires. The rear was niticeably quieter.

K,,,,either I'm gonna get bashed for this, or I stumbled on to something. :suspense:
What you guys think?


08-08-08, 12:46 PM
I have also noticed that my rear diff is much quieter when the fluid is cool. I just had my diff replaced, but my warranty will expire in a few months. I plan on trying a heavier weight oil if, and when the whine comes back. I suspect the lower air pressure allows less road noise to be transfered and added to the diff noise.

08-08-08, 12:51 PM
As far as te fluid type is concerned, I think the only way to affect pre-existing whine from the differential would be with a different viscosity - thicker fluid would transmit less noise. This change, however, should be short-lived because the difference would diminish as operating temperature increases.

The level of noise reaching the driver's ears should vary based how well it is being transmitted to the car's cabin. I would think that stiffer tires (more internal pressure) would absorb less vibration (noise) and transmit the rest to other components. Stiffer bushings would do the same.

08-08-08, 01:56 PM
You lowered the tire pressures...what would Obama say?! :)

You might have some other issues like dried out tire noise. I doubt the under inflated tires are absorbing diff noise.

If your running 75w140 Royal Purple the diff can be noticeable on a summer day cold start, then goes away when the fluid gets warm.


08-09-08, 01:50 PM
I always noticed the whine was more pronounced as fluid got warmed up. You couldn't even hear it until the car had run for a while. As far as tire pressure goes I wouldn't think that would matter much.

08-09-08, 09:48 PM
Doncha just hate it when there're several variables going on all at once?

I changed diff fluid and put on the KARS at about the same time. Then, drove to Summit Point, pushed the car hard including the diff, drove back, changed to Avon A/S tires, increased the air pressure to around 38 psi cold (Obama can eat my shorts!), and then really started to notice "the whine" getting more pronounced.

Part of my car's whine, it turns out, is the darn tires since it doesn't change much in amplitude when I let off on the throttle at 45-50 MPH. BUT, I do get a bit more whine when I (lightly) accelerate through 45-50 MPH getting onto the expressway. A bit heavier throttle opening, and the maggie enters into the whining contest and of course the exhaust starts to mask all that. So, it would seem, my car's whine is coming from multiple sources. :bonkers:

Don't know about tires absorbing or not absorbing diff noise, but, hell, dang near anything could be happening down under there!