fixit

Most shops seem to recommend the factory fill oil and friction modifier for the rear end. Longer life and good performance. One shop that does nothing but rear end repairs said to avoid sythetics if you want longevity. I tried RedLine 75W-90 on two vehicles (Ford PU and Toyota 4Runner) in the past and the pinion bearings wore out prematurely on both. Factory fill the best?

runner140*

Don't know what the best is but I use Mobil1 synthetic 75W90 plus two 4 oz. tubes of posi/diff additive. Works well for me (131000 miles on the clock).

steve40th

Very Good stuff , Mobil 1. But I personally had leaks due to the oil not being compatible with The Right STuff. DOnt know if this is true or not, its just someting I noticed twice with a D36 and D44. I use AMSOIL now, and no leaks.

GM's oil and additive are just fine I am sure, unless racing in road racing etc, where temps can be a problem.

MarkBychowski

Mobil 1 here with 1 can of posi additive. Has held up to several years of street and roadracing. I had never heard of a problem using it with Right Stuff but you never know.

fixit

Mobil1 gear oil is a consumer product and not quite as good as Mobil's Delvac 75W-90 synthetic which is more performance oriented. I'm still gun shy of any synthetic for my '94 though.

C66 Racing

Been running AMSOIL Synthetic Manual Transmission and Gear Lube 75w90 in my 02 Z06 on the track for years without issue.

steve40th

Hey Sub Driver, where are you stationed, ie what boat?

Klondike

I used the Mobil 1 and 4oz of posi juice after I rebuilt my D44. I wore out two rear ends in my Mustang with the Redline stuff they say is so good. I'll not be using any of that again. I'm not saying thair stuff is bad, but I didn't have any luck with it ! I've never heard anybody say ANYTHING bad about any Amsoil product, so I'd say go for it. I would have used it, but I was in a bit of a hurry when I put mine in and didn't have quick access to the Amsoil...so Mobil 1 went in and seems OK.

C66 Racing

Stationed in Bangor, WA. Dropped you a PM with more info.

Mekanic

astroglide.

Danspeed1

The only thing synthetic I run is the engine oil and depending on the car the power steering and brake fluid.

For my 89 Vette I used the factory fill in the ZF and in the Differential. The differential works perfectly, and once the ZF warms up it shifts like butter. I will probably change the trans fluid every 20K and the Diff every 30K so I am not too worried about it breaking down.

DG

ZBRA

That's what you prefer in your rear end?

Mekanic

best rear end lube I've found..

Mr. Peabody

I use Amsoil + the GM additive woiks like a charm

rocco16

I've had no problems using the factory recommended lube and additive.

Something else may be cheaper, and/or just as good, but I don't see how it could possibly be any better.


Larry
code5coupe

_________
not easily impressed....

Matt383

I'm a Mobil 1 guy but I do use Valvoline Syn rear diff with 1 btl Gm posi.

Danspeed1

When I was in school my professor used to always say the same thing every time I had a bolt or two left over after a project.

"GM put that there for a reason."

I feel similarly about servicing the vehicle. Synthetics have a few qualities that make them suitable for engine use and a few other uses, but overall you can't go wrong with the factory fill on factory parts. I have yet to hear someone identify the cause of failure in a factory differential as bad factory fluid. Yet, posi's burn out all the time on synthetics such as mobil one. Most of us will never experience these problems. I notice alot of guys who have posted good results using mobile 1 swear that 100K+ miles and no problems. You could run the diff on water and it would probably live, but why risk it. Dollar for dollar Mobil 1 is about the same price as a qt of factory fill. No performance benefits... really no longevity benefits, why bother??

Just my $0.02, I like to play it safe, what can I say,

DG