JoeMack

I am getting ready to have a set of GM 4.10 gears installed in my 02 Z28. What would be the best way to break them in? Also, should I use non-synthetic gear oil and GM posi additive for a specific amount of miles (for break in) and then switch back to a synthetic, w/additive?

GreenDemon

Well, what I would do is to be easy on them for a week or two of driving and use conventional oil (w/ lsd additive of course) and then maybe romp on them a few times. Then take the old oil out and inspect it for any large pieces of metal. If you don't see any problems dump your favorite hi-po gear oil in w/additive and away you go. Basically you're trying to get the gears to establish a set wear pattern before you add too much torque. The whole romping part is just a test to make sure there's nothing wrong- a good thing to do right before you inspect and change the oil. I'm going to have to do a gear swap soon, I can't stand these 3.23s anymore. How much is the whole setup (w/labor) costing you?

JoeMack

I bought the gears for $155, install kit $40 and the labor is going to cost $175. Thanks for the info.

revtime

I heat cycled mine a couple of times.
After the install drive for a short period and then let the differential cool completely, it will get really hot the first couple of drives and gradually start running cooler. Second drive go a little farther and let it cool completely, keep doing this a few times and it should be fine.
I did this with my 3.73 install and have had no problems for 60k.
I use mobil synthetic in the diff, I change it about every 20k.
I change out the tranny fluid about every 20k as well but I am **** like that.

Capn Pete

I went by Richmond's instructions, which is pretty much what "revtime" just said. Did a couple ~15 - 30 minute drives, then gave 'er the boots after that! My 4.10's have been working fine all summer, and no excessive gear whine.

Fast Caddie

Just drive easy for the first 500 miles or so and stay under 60mph as much as possible.

My case in point: When my 3.73s were installed i was in a rush to get somewhere (130 mile trip RIGHT after they were installed... right out of the shop) and drove 80% of that distance on the interstate at 75mph. Didn't want to do it but sometimes things just come up and you have to be there. Sure enough, by the time i got there i started smelling gear oil. The rear end got so hot it boiled the gear oil and the center section had heat waves flowing off it like a grill. In fact it was so hot the clutches wouldn't release and it would make a horrible grinding sound and the car bucked and jumped when i turned. Thought i F'd up the rear end. But the next morning it drove another 70 miles just fine. Changed the gear oil out the next week and it's worked great for the last 20K miles. Those gears are pretty tight when first installed and it takes a few heat cycles and easy miles for them to loosen up.

kgkern01

All 99-02 F-bodies, and some 98's came with the Torsen diff, unless otherwise opted for an Auburn (Don't know why one would opt for it but ). Torsens require NO limited slip additive due to being a gear driven limited slip unit as opposed to a clutch style limited slip, such as the Auburn or an aftermarket Eaton, which work better with conventional fluid and almost require limited slip additive. Torsens can always be used with fully synthetic fluid, conventional is not neccessary with them. Just thought I'd let you know so you don't waste your $ on some additive.

JoeMack

My owners manual calls for 75w-90 Synthetic Gear Lubricant and Limited-Slip Differential Lubricant Additive.

kgkern01

It may call for it, but you should have a Torsen diff, and they do NOT require the additive. The additive is used to facilitate the working of the clutches in a conventional clutch-type limted slip differential. Since the Torsen is a gear based differential, and completely void of clutches, the additive is not required. Another good feature of the Torsen diff is becuase it is a gear-type instead of a clutch type limited slip diff, it will never "wear out" and lose the ability to "posi-traction" like conventional clutch type limited slip diff's will.

Capn Pete

You don't need the additive. That's good 'ol GM trying to make an extra few $$$'s.

As for Torsen's not "wearing out", true, but I don't think they function as well as a clutch-type "posi", and those gears can break, can't they?

kgkern01

I hear they break no more easier than the spider gears in the Auburn. The Auburn will work a little while for drag launches, but if you do any autox or spirited driving around turns, the Auburn's cone-style clutch wont last long at all. Some regional and National level autox F-stock guys can wear out a new Auburn in a weekend of competing. I just put a rear end from a 2000 WS6 in my car and it is a big difference going from the Auburn to the Torsen. Torsen is much better than the Auburn, although I hear a New Auburn is better for launching at the strip.