3.42 Borg Warner. Time to change the rear end fluid. What's recommended. Still got a old bottle of the GM posi additive. Do I need it or can I go with some LUCAS or something like that. Thanks! TJ

I swear by Lucas and synthetic Lucas if it's a newer car or posi. I liked it but the synthetic was spendy at 10 bucks a quart.

plus you never have to flush it again!

I only use Mobil 1 synthetic..

My dragster, 3rd gen, my tow vehicle, daily driver, and 67 camaro all have it. I would not use anything else.

well i have full synthetics in eng. [lo3] , trans. [t5] , diff. [3.08] . daily driver with mild mods. and get 27-29 m.p.g. hwy. . lots of hype on each brand . check bobistheoilguy to compare and decide .

http://www.thirdgen.org/techboard/tr...-use-posi.html (what fluids to use in posi differential????????????)

Another vote for Mobil1 synthetic...

Dino oil I run 80/90...

royal purple/ no additive

royal purple

GM axle lubricant with GM posi additive works best for me. Made the difference between a very, very slight whine (using Valvoline axle lube) from the Richmond gear set I installed to a nice, quiet rear axle. I haven't had good results with synthetic lubricants...at least with engine oil. Bill

Believe it or not, my pinon seal started dripping pretty bad. After a few days, I knew the rear end must be low. I filled it back up with valucraft 75w90. Still leaked, but slower. When it got low again, I filled it up with walmart's SuperTech 90w140. Almost stopped leaking. Next time, i only jacked up the right side, and overfilled it a little. It stopped leaking completely and hasnt since then.

My best guess was that the factory fill had thinned out enough where it was like water. The new oil must have thickened it up enough to stop it.

i run fully synthetic of every single fluid in the vehicle. iv had best results with mobil 1 full synthetic, and GM "performance parts" has an additive for posi specifically for use with the mobil 1 (since most new GMs actually say "mobil 1" everywhere), but it can take some convincing to get them to admit they have it, since the cars and trucks didnt come originally with synthetic. my 85 'maro is driven hard and put away wet, one more vote for mobil 1

If you have a OEM diff. the oils suggested by everyone will be fine. Bear in mind that some posi units(Eaton) use only mineral based oils,no synthetics. I have tried to find out why but have gotten no e-mail response from Eaton. I recently installed a new Eaton posi unit and their instructions were to that effect. Anyone maybe know why they only specify mineral based oils?

i was curious to that as well badman. running an aftermarket eaton with lakewood gear oil.

Running Castrol Synthetic lube in my 9" with an OEM open rear axle. No complaints here.

Torco 85w-140 in the 12 bolt (non synthetic).

Mobil1 with GM additive in the 9 bolt.

Lubrication Engineers 703 Monolec

regular gear oil - Strange actually reccomends not running any of the sythetic/magic oils out there. They say they've seen too many rear-end failures due to these supposed "better" lubes.

I think I've got 85/140 in mine...could be 80/90, regular Castrol. No additives here, but tru-track posi unit. - we run castrol 50w gear lube in the 10.5 car.

i vote for lucas since you need no extra additive and i works great!

Royal purple ftw

valvoline with trans-x posi additive

I got lucky last year and a sponsor supplied me with 3 bottles of Lucas 75w90 for the diff.

Race tracks hate the synthetic diff oils. It's hard to clean up when a diff explodes. I saw a pickup truck blow the pinion out of a 9" last year right on the start line. Took a while before they got it all cleaned up.

3.42 BW with locking diff..

AC Delco 75W90 w/ POSI additive. It's like a $50 gear oil change, but it won't ever go bad.

i run motorcraft (yes ford) 75/140 synthetic only cause i work at a ford dealer and it was freee!

I was told by a 2 diff shops in New Zealand that I visited that rebuild 9 bolts = M78 Borg Warner all the time (they are in ton of cars in NZ and Australia) to use Redline Edit oil was Redline 75W140 #50304 with NO additive. The cones will bang and clunk a little bit, but this will be totally normal and doesn't hurt anything.
If your cones are worn, use the Redline heavy shock oil, otherwise the normal stuff will do. The additive is a friction modifier or reducer and reduces the effectiveness or grip of the posi unit (cone type).

That's what I run with just under 400HP to the wheels on drag radials with no issues. The cones don't even make much noise..

http://www.thirdgen.org/techboard/tr...-use-posi.html (what fluids to use in posi differential????????????)

http://www.thirdgen.org/techboard/tr...dline+gear+oil (Rear End Gear Additive, Part 2 (9-bolt owners please read!))

No additive in 9bolt. 9 bolt is 345 ratio 342 for ten bolt.