In the spring I will be changing the posi fluid in the rear end of my IROC. It's a 3.27 9 bolt B/W posi unit. I have to add some posi additive as well because last summer right before I stored my car I was periodically getting a rumbling sound when I took hard extended right turns. From other people I gathered that the fluid that is in there now must be old, wore out, or low, thus causing the gears to slip.

Anyway...how hard is it to do? And exactly what do you need to do... I have never changed rear end fluid before and I was wondering how you fill it back up? I know I have to jack the car up and remove the inspection cover.

What materials do I need? ( I know I have to get some of that posi fluid additive from my GM Dealer, its real cheap).

How much gear oil do I need?
What kind of gear oil? I have 1L of Synthetic 75W90 Gear Oil, will this be enough? Is it the right kind?

Do I need to wash the rear end out? Someone I belive told me clean it out completly with brake cleaner?? Is this right?

I know that this probably sounds dumb but its all a learning process right

Any and all advice is welcomed!! hehe

 

You will need something to drain the fluid in, a pan or large diameter bucket. Take the bolts out of the cover, leave one very loose in the top hole, pry it open and let it drain, remove the cover. You can clean it all out with brake cleaner if you want, but it's not necessary. I usually wipe it out with a rag. Clean the gasket material off the cover and it's mating surface. seal it with silicone or buy a new gasket, both ways work just as well.
You'll need two quarts gear oil and one four ounce bottle of friction modifier. There is a fill on the passenger side(7.5 and 7 5/8 not sure about the b/w), it's a plug that's removed with a 3/8 drive rachet with a short extension, sometimes it's hidden under dirt. Put in a quart, then the friction modifier then the other quart. Not sure how much the b/w takes, the others take just under two quarts. I have been told not to use synthetics in posi rears, I use 80w90. I know from experiance cheap posi additive doesn't work, use genuine GM or even ford (it's the same fluid).

 

I was wondering if anyone else has heard if sythetic fluid is a "No No" for posi rear ends?

Anybody change the fluid in a B/W rear end?

 

Anybody? Synthetic Gear Oil... Good or Bad??