I found a really good deal on a 3.92 diff in my area, but the sc400 it was pulled from was badly maintained and beat to crap. Should I have any worry about problems with it, or are these things bulletproof?

 

Generally the rear differentials are near bulletproof. You'd have to open it up to visually inspect the internals for sure... but chances are it's fine inside there even if the gear oil is very old and long overdue for a change. These rear diffs can take at least 3-4 times the stock NA horsepower and are very strong.

Now if the owner welded that diff and drifted around on it a lot... then in *that* case you might want to look for another 3.92 SC400 diff. But if it's just a stock unmodified open diff that only ever saw the stock engine power... I think it should be fine so long as it makes no funny noises when turning the axles and input shaft by hand.



Cosmetically:

If it's got a coat of surface rust you can address that with POR-15 de-rusting spray (I forget what its official name is) in several passes to neutralize the oxidation. Just follow the directions on the spray bottle. Then when it's dry mask off *everything* that rotates, has a bolt head or metal seam that might need to separate in a future rebuild, and mask off all around and over the aluminum cover. Then apply POR-15 coating with a one time use foam sponge paintbrush and let it dry outside on a pallet or whatever safe to permanently stain surface works. You'll need to let one side of the diff dry before turning it to do the other side as POR-15 is drippy stuff.

It also dries very quickly so pour out what you need into a shallow work paint container, wipe the edges of the POR-15 can as best you're able to and apply a layer of saran wrap over it... then put the lid back on. This will make it possible to actually get the lid off the can again later. Not doing that is a good way for the paint to hard bond the paint can lid to the can so hard you won't be able to get them loose again.

Oh and very important: wear 7mil nitrile gloves to protect your hands and wear a dual filter respirator mask! The fumes from POR-15 are very toxic and are no joke! Protect your lungs and your body when working with that stuff. Don't risk your health breathing it directly just to paint an old car differential.

Also use the POR-15 UV protector finishing spray on coat when it's all dried and cured.

....however whatever diff rebuild work and LSD installation you want to do should be done before you do any cosmetic restoration of the differential.

Driftmotion sells complete seal and bearing rebuild kits for this 200mm type SC300/400/Soarer/MKIV/GS/Aristo/LS430/SC430 type differential. But.... they do not sell the OEM Toyota side carrier shims since you or your diff builder will have to measure for the exact thicknesses you'll need and then order those from a Toyota dealer. If you hand over the diff to a professional driveline shop (highly recommended unless you've got prioer experience building differentials) for the rebuild and LSD installation they will handle all of that for you.

 

Thanks as always for the quick reply and useful information! I think I'm going to go for it! I was definitely looking into getting an LSD and restoring it. Might not happen soon, but it'll be nice to have it on hand when I finally get around to it.