Before anyone flames me about searching, I've done so. Found multiple answers but nothing concrete. The basic consensus is for BW 9 bolts is to use Redline oils such as the one described in my link. Would this be ideal for my setup or would having an oil WITHOUT the additive be better?

Redline 75W90

 

This is a debate back and forth on this board that I came away with just as many questions as you. I just rebuilt mine and when i put new gear oil in i didnt use any additive. The only reason to use additive is if its doesnt go around corners smoothly (read it chirps and grabs and lets go). mine goes around corners just fine and hooks up strong. I doubt im hurting anything running no additive if its not making any wierd noises or shaking the car going around corners.

 

What oil did you end up using?

 

Oh yea sorry that would have helped lol. I ended up using valvoline 80w90. Anything around that viscosity will work though. I didnt bother going synthetic since i will probably just be in there again in 30k to change the oil again.

 

When I do mine, I'll probably use an additive.

Better safe than sorry & it can't hurt, huh?

 

I rebuilt my posi and it worked great with redline 75w90, but now about 2k miles later it is slipping again so I am assuming i did something wrong.. Next time I will be using regular stuff with posi additive.

Ill sell 2 quarts or redline fluid for cheap. I no longer have the receipt.

 

The only reason i didnt use the additive is i didnt want it to slip. Additive helps it slip and i had just gone through the hassle of shimming it tight so i wanted it TIGHT. lol. If you want, use the additive. I doubt it will make a difference one way or the other.

 

When i had my 9 bolt i would use the additive. Mine also slipped after awhile, so when i changed the oil next i didnt use the additive, and about 3 months later it was slipping. I always use mobil one in my rear ends though, im pretty sure it does not have the additive. Now ive got a 4th gen rear still using mobil one with the additive though. Its been argued about countless times. I researched it on my first oil change. It reall comes down to personal opinion, although from my experience it makes the rear more prone to slip because thats the purpose of it lol. But if your 9 bolt is slipping anyways its days are numbered before a rebuild is necissary.

 

I just rebuilt the entire rear. New seals, bearings, gears, posi etc. It's all new. I might end up using Valvoline 85W90 because I can find it locally for a decent price compared to say Royal Purple or Redline. Not 100% yet though. Thanks guys! If anyone else has anything to share on the oil they used in their BW 9 bolts, feel free to post up!

 

I just installed a brand new rear end last night in my T/A, 9 bolt 3.42 with a TrueTrac and all new bearings and seals and damn it was fun. But I just filled er up with the syn lube 75w90 we use at the shop for truck diffs. Mind you I haven't driven it lots yet but I see no problem with synthetic 75w90. According to the owners manual for 1990 Pontiac Firebird, the Standard rear diff and Limited slip diff require 80W90 GL-5 (GM # 1052271) but with the limited slip you require 4 ounces (118 ml) of rear axle limited slip lubricant additive (GM # 1052358). Sorry i couldn't be of more help

 

There's a truetrac available for the 9 bolt?

My 9 bolt lsd is slipping too. I doubt it's ever been rebuilt and it's got close to 180,000 miles on it. Does anyone think using the Redline 75-90 no slip will have any adverse effects on this thing?