Am changing oil, trans fluid and filters this coming weekend. 91 coupe, mostly stock, original rearend (quessing a 36), 113900 miles. I have put 28000+ miles on it in 4 years. Have never changed diff. fluid. Have read posts on how to change (suck it out, pump it in) but I am unclear on what combo to put in. I buy most of my parts at AutoZone (the manager owns 2 Vettes) and I trust him, but I trust the forum first.
Thanks
Subman

 

I just changed the diff. fluid on my 95 with 18,000 miles this weekend. Surprised how black and metallic the diff. fluid was with this low mileage. I always have used Mobil 1 gear oil AND one bottle (4oz) of GM posi additive as recommended by both Mobil and GM. As soon as i take the fill plug out i put anti-seize on it so i do not forget.
I suggest you buy an oil suction gun at Auto Zone ($7). It comes with a short lenght of thick tubing, about a foot long and maybe 5/8 or a little larger in diameter, This is too thick to fit past the gears and get to the bottom of the case so I insert about 3 to 5 foot lenght of rigid, thin walled polyproperlen ( sorry about the spelling) tubing ( looks milky white in color not clear and very thin walls) that Home Depo sells in their plastic tubing section. This thin tubing will fit right inside the thicker tubing. I push it in about 10 to 12 inches so it does not come out when/if oil gets to it. This thiner tubing goes right to the bottom on the diff. case. I filled the suction gun up about 6 times. Then when it is empty I take a small plastic bottle that my wife uses for her hair dye and put a tube to it's point cap and put the posi additive into the diff with that. THEN I pull the thiner tubing out and use the thick tubing to suck the clean new oil up and into the diff. The diff. takes a 3/8" allen to open it (at least my 85, 88 and 95 do). Be sure to clean the girt off around the fill plug before you unplug it and right after unplugging it so you will not get sand, etc into the diff. Do not get any gear oil on the spring as it can start the delaminating process especially if there are any nicks there. I just back the car up on Rhino Ramps. My driveway is slanted so if i put the ramps on the low end and back into them the car sits level. You do not want it in a position where more drains out than you can put in and it doesn't get filled. Good luck.
Also important for 2 reason is to get the car driven to FULL operating temperature (some high speed driving here) so you get all the sediment, metal flakes in suspension and not lying on the bottom. You want that crap floating around so it comes out. Also it will flow much better through that small tubing when hot as the oil IS thick when cold. Think that covers it

 

Just read Tech Tips-Bloomington Gold: Says that Gorden Killebrew suggests Mobil 1 synthetic gear oil and (2) TWO bottles of GM positraction fluid...

 

Anybody got a part number for the GM posi-juice?

 

Anybody got a part number for the GM posi-juice?

(You ALL know how it is asking a GM parts guy for smoething by name)
They look at you like you're speaking an alien language. :cuss :nono: :nonod:

 

Corvette Central: #582425 @ $7.95ea.... GM Posi Rear End Lube Additive (4oz)

 

Anyone try RedLine 75W-90? They claim it is already is posi compatible.

 

When changing the rear end oil or fluid should we refill all the way to the top?

 

Haven't done mine yet, have synth and 2 posi trac fluid, but I was told that it should be to the very top, just starting to drip out...

 

correct me if I'm wrong... but is the fill up screw or **** on the back side of the rear end and not the top?


[Modified by TheStef, 6:08 PM 10/1/2003]

 

The fill plug is located on the right SIDE of the diff. You fill it until it starts to drip out. I never had any noises or problems using only one bottle of posi additive so I will keep using 1 bottle. If I ever hear any noises i will use 2 bottles.

 

I had my gears changed last year in my rear end, I'm starting to wonder if it would be a good idea to change the oil since the gears were new ???