| I’ve gone thought a rather lengthy process of creating then trying to eliminate rear end gear noise so I thought I’d share my observations. I started with a totally stock TT rear end with stock diff bushings and subframe bushings. The previous owner had managed to cut into the stock subframe bushings with the subframe collars and they dripped some pretty strange, sticky liquid forever. I decided they needed to go and since the car had pretty significant wheel hop in 2nd and also 3rd gear I went to the extreme and put in solid aluminum subframe bushings. This completely eliminated all wheel hop but it now sounded like I had a massive electric motor in the rear of the car. Shortly afterwards I got a set of Leader’s 4.10 gears and had a tranny shop install them in the diff. While reinstalling the differential I replaced the stock diff bushings with Energy Suspension urethane bushings. The gear noise did not really go up or down but it was so loud with the solid subframe bushings I’d have needed a sound meter to tell. Eventually the noise was driving me nuts so I replaced the aluminum bushings with Stillen’s Delrin bushings. The noise was less but still pretty significant. I experimented with placing different durometers of rubber between the delrin and the frame and this varied the noise a little but it was still pretty loud. Finally I replaced the Delrin with Energy Suspension urethane. This dropped the noise significantly but I still had gear whine. I had a pretty old set of Leader gears and Mark said that it could be a combination of older gears that had a defect (creating noise) and the shop may not have set up the gears correctly. Mark got me another set of gears and directly me to a shop he’s been using to install them. The shop said the old gears had been shimmed correctly but the yoke was not torque down correctly and it looked like this caused them to wander back and forth some. I reinstalled the diff and the rear end noise is almost completely gone. There is still a slight resonance in 5th around 2500 RPM, and sometimes when decelerating I can hear the gears whine a little but it is a magnitude better. In the final configuration (Leader 4.10 gears, ES diff bushings and ES subframe bushings) if you listen for it there is a very light gear whine. Around 2500 RPM there is a general noise increase. They make a gear chopping sound when decelerating for a couple of seconds and I kind of hear them when quickly accelerating though now it’s difficult to pick it out from the exhaust noise. So here is what I learned:
1.I would never recommend to anyone to install aluminum subframe bushings on an often driven street car. Unless you are totally deaf. Or you don’t like yourself. 2.I believe the subframe has a resonance frequency around an engine speed of2500 RPM. With the stock diff and stock diff bushings I had a significant noise increase around 2500 RPM with the aluminum bushings. I think the stock subframe bushings do a very effective job of dampening this out. The urethane bushings dampen some of it out but there is still a general sound level increase between 2200-2700 RPM. 3.Gear setup is critical. If you install a set of 4.10 gears, change nothing else and have a significant increase in gear noise then they are probably not set up correctly. I talked to Richmond (who makes them for Leader) and they said their gears do create a light whine, but they said it should be very subtle. After replacing all my bushings back to urethane I really didn’t want to pull the diff again but it was totally worth it to fix the gear setup and almost eliminate all gear noise. 4.In a car with stock subframe bushings, stock diff bushings and 4.10 gears there should be very little to no gear noise above a stock level. I’ve ridden in a car with this setup. If there is a large noise gain when changing gears they are probably not setup correctly. 5.Gear noise will reduce slightly after they break in. Leader and Richmond recommended driving the car easy for 30 minutes, letting it set for 30 minutes the repeat this two more times to ‘heat treat’ the gears. I’ve got about 400 miles since putting the new gears back in and the very light gear whine is even less than when I first installed it. 6. Wheel hop can be fixed with urethane subframe bushings and some decent tires (Nitto Drags). If only I'd known that before cutting the stock subframe bushings out. I’d like to thank Dr. Leader for all his help in directing me a good shop that knew what they were doing, getting me a new set of gear for nothing, and calling the shop to have them quickly get my diff set up.
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