I have the IROC back on the road after my Torsen install and I think I notice a little rear end whine when coasting between 30 mph and 50 mph. Maybe I'm just paranoid, but I never really listened for it before. Before I took the broken Eaton diff out, I had about .009 backlash. When I put the Torsen in, there was no preload, so I added .004 shim on each side and got more backlash than I think I started with, about .012, so I moved a shim over and got close to the minimum, about .006-.007. Now I'm wondering if I need more backlash. Does anyone know if too little backlash is what causes whine when coasting? The gears are quiet when accellerating.

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1985 Yellow IROC-Z 5.0 HO, T-5 3.73 Torsen, 4 wheel disks
PFCM pads, GTA wheels, Koni yellows, B&M Ripper, Dynomax

 

Did you check your pattern. If it's a little bit of whine from aftermarket gears it's normal. I got Richmond 4.10s and it was set up properly and a slight amount of whine. If your backlash is in range maybe the pinion depth is off a little. Usually I see a .035" shim under the factory pinion and this usually works for the replacements also. The pattern always tells the true story though (especially with used gears). A pattern centered is OK, but a pattern slightly favoring the inside of the ring and slightly deeper in the tooth is better as it compensates for wear/break in.

Sometimes the strongest setup isn't the quietest. Stay at the minimum backlash for the street. Excessive backlash causes the gears to "smash" together, shocking and possibly breaking them. Drag racers run all the way down to 0 backlash. Don't do this on the street, the friction and heat generated over highway drives would be outrageous, but for a 1/4 miler hey.....


If you plan on going to the track, or beat the wee out of it on the street (if neither why'd you get the gears...), before you launch preload the gears together to take up backlash. As this wouldn't be a problem with an automatic... unless running a ridiculously high stall converter, if you burned out and backed up to stage and just dropped the hammer, all that inertia from the flywheel, ect. takes up the backlash and blows the rear (possibly, maybe never, but it's good practice and most definatly will extend it's life)

I'm getting off the topic, sorry.... Just check the pattern if it worries you, but it's probably ok...

 

I agree w/ Joel 100%. To see everything he just said, check out this two part tech article: 10 bolt

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No, these are the same GM gears that were in it before the Eaton broke. I'm just not sure if there was any noise when coasting before. Like I said, maybe I'm a bit paranoid. I amost don't notice it that much anymore. What I want to know is what is this a symptom of? Will it do any harm if left alone?

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1985 Yellow IROC-Z 5.0 HO, T-5 3.73 Torsen, 4 wheel disks
PFCM pads, GTA wheels, Koni yellows, B&M Ripper, Dynomax

 

It may be either the settings are slightly off, or the gears are defective. I doubt the second. It depends how far out of the ballpark you are to whether you should worry. I heard some gears that whine terrible (wayyyyy out) but are still running many years later.

 

I will check the backlash in a few days before I put the gears to any hard use and open it up a couple of thou if it's low. Don't know which way it goes when they heat up, but it's better to be safe.

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1985 Yellow IROC-Z 5.0 HO, T-5 3.73 Torsen, 4 wheel disks
PFCM pads, GTA wheels, Koni yellows, B&M Ripper, Dynomax