[Blue70SS]

Originally Posted by Apex Chase

When you go with harder differential bushings there is always the potential for increased gear noise. I say increased because it was always there but your mushy stock bushings were insulating it. Right of the assembly line some rear ends are set up more "loose" than others so it can vary from car to car.

As has been mentioned, a fluid change and adding an additive can help. I would make sure your buddy has plenty of experience messing with gears in a IRS car before he goes in there.

I had the LPE 3.70 gears with Jannetty posi fix, almost all Pfadt bushings (except used the BMR ones that came with trailing and toe arms and kept Pfadt ones for down the road changes). I have the Pfadt solid subframe bushings and at the time Pfadt's softer "street" diff bushings for the 2 front bushings and ran the harder "strip" rear diff bushing due to my increased power. Had some gear whine, but was told mine was nothing compared with Richmond 4.10s others had. Cracked the diff open once to inspect and everything checked out, including wear pattern.

Here's the interesting part... when removing the OEM diff to replace with LPE 9.5" I found the rear diff bushing extremely loose. Before removal I could rock the car back and forth using the tire while parking brake off and tranny locked in 1st gear. I could see the rear of the diff move up/down about 1/4" total. A little off topic here... but ended up replacing the 85mm long "torque to yield" mounting bolts that had shouldered ends and skinnier middle part, with 90mm 12.9 hardness black bolts that were the same thickness from end to end. It got rid of about 1/2 of the movement. HOWEVER, the harder diff bushing fell out of the diff when the unit was removed. IMO, Seemed like the impregnated lubricant was almost squished out of the bushing. It had grey grease on it, but I had used clear Sphon lubricant. The 2 front bushings were nice and tight.

I installed Pedders HD bushings on the LPE 9.5" diff mainly just to show it off with red bushings. The MAJOR difference I noticed (WHICH MIGHT LESSEN NOISE TRANSMISSION), is the center metal cylinder the bolt runs through is Shorter on the Pedders bushing. The Pfadt one makes contact with the subframe mount, while the Pedders one does not extend to the outside edge of the bushing. And if centered in the bushing, leaves the metal cylinder recessed about 1/8". On installation, the new bushings slipped into the subframe very tight (good). I had the 9.5" installed last week with 3.73 gears and have absolutely no rear end noise now. I'm sure most of it's the better rear end, but believe Pedders HD bushings should be quieter compared to Pfadt's "Strip" bushing - solely based on design differences I saw.

It would be interesting to compare the 2 harder version bushings in the same car, without changing anything else. I do know that Pfadt's street version was made solely because of increased noise found using the "strip" version, when combined with Pfadt's solid subframe bushings.