The title says it all! I snagged a used rear diff that has around 80,000 miles on it that is in really good shape, it was removed over 10 years ago and stored covered on a shelf. Anyway, it feels very smooth and very tight compared to what is left of my 180,000 mile unit that has been singing terribly for the last 50,000 miles! Is there anything that I should do to the "new" 3rd before swapping it in? I was thinking about shooting it with brake cleaner to clean the dust and old lube off then pre-lubing the bearings and slapping it in with fresh fluid. Any fluid recommendations? I run Redline fluids in my MX5 and have never had a problem, my truck has had Mobil 1 gear lube in the rear since the bearings started howling, they really never got much worse so I guess its OK to run .... I guess any good synthetic 80w90 or 75w90 would do the trick... Thanks again! ~Matt

 

FYI the "new" rear diff is also just a stock 3rd from an 88 V-6 automatic with 4:10's... I wanted to re-gear and go up a tire size but for what I paid for the used 3rd, the type of off roading my truck sees and the fact that re-gearing both ends isnt cheap I just decided to stick with 30" tires and keep it a dog with the stock 4:10's.......... for now

 

just get a new gasket and slap that puppy in!

lol, if your worried about it, just get some of the gear-mesh paint and put a little on the ring and spin it around to see where the pinion's sitting, but with only 80k on it, she should be in good shap; I'm having no problems (knock on wood) with the stock 4.10's in my 91 with 295k on it

if anything, I would at least replace the axel shaft seals with it, since you have to pull the shafts out to swap 3rd's anyhow

 

I would pretty much do what your suggesting, clean it up and then change the fluid.

 

Did the automatics come with 4.10's or were they 4.88's?

 

in 88 I thought they came with 4.30s?

 

This might help

 

I wish my 88 had 4:30's It came stock with 225/75-15" tires and according to the code on the fire wall its got the crap tastic 4:10's...

 

As long as it was misted with oil it should be fine. If its got rust on the gear teeth or the bearings, don't buy it cause it is useless to you.

 

I finally got my new to me Ebay 3rd bolted in last night, 2 hours and 2.5 quarts of Lucas gear lube later its all back together and sounds freaking great! I didnt realize just how loud the old rear had become!

 

its nice not to have to listen to that whining/grinding, huh?

i just swapped mine out... turns out the 4.56 pinion decided to blow its gear teeth all over the axletube but not before taking some of the ring gear teeth with it and marring the carrier...