Tom Johnson

Can I use Mobil 1 Synthetic 75W90 gear lubricant in the rar end? Of coarse with the GM additive.

FeedVaal

You have my permission.

FeedVaal

Kidding.
I have nothing bad to say about synthetic oil except its way too expensive.
I

Jvette73

Not only could you...but you should you... :lol:

71coupe

I say no. Stick with GL-5 & the GM Posi additive.
I put some high dollar synthetic in the transaxle of my other car. It destroyed the syncros in less than 2 years.
Just because it's synthetic & expensive dosen't make it better for a car that came with regular gear lube.
Consider yourself warned :nono:

Tom Johnson

The rear end has about 2,000 miles on it after the rebuild. There was GL-5 in it. Any other thoughts on using a synthetic gear oil?

ScubaJKD

Check out http://www.redlineoil.com

69er

I'm running with Amsoil gear oil with the GM additive of which Amsoil says is not needed but can be added if desired.
Also use Amsoil 10w40 in the engine.

Chris Fowler

Along the same lines...how do you drain the gear so that you know you've got the right mixture in there?

bb69

The biggest problem with the Corvette rear-end is the clutch pack. The packs (this goes for any rear-end with a pack) are very sensitive to friction; thus the friction modifier. However, the modifier has a tendency to plate out of the oil, basically it breaks down and ends up as sludge on the internal parts. The axle manufactures are constantly searching for combinations of synthetic or mineral oil and friction modifier. The best alternative is to get rid of the modifier; it stinks, doesn't last, and has a tendency to eat seals and RTV. This is what several of the OEMs are doing, going with limited slip units that use gears instead of clutch packs.

Axle manufactures recommend using synthetic lubricant if you are going to use the vehicle heavily. They also recommend changing the oil more often. Synthetic will lower the operating temperature, and high temps cause a lot of damage. I would recommend using synthetic, and changing is every 15-20K miles. The price of two bottles of Mobil-1 is much less than a pinion bearing or ring and pinion set.

jsimpson

I tried synthetic with GM additive and ended up with chattering clutches after every above-90mph run. I changed to Amsoil racing gear oil WITHOUT posi additive and have a smooth running rear ever since!

Tom Johnson

Did you use the Series 2000 Synthetic Gear Lube, SAE 75W-90, GL-2 through GL-5, MT-1?

bb69

When you say you had chatter after every 90 MPH run, how long did it (chatter) last? Another common problem with the disks, is that they throw oil off at high speed. Customers complain that they get chatter when turning at the end of off-ramps; all the oil has been thrown off the plates. I have experienced this personally, and the chatter goes away quickly.

I've never used Amsoil products, but if it works for you, use it. It would be nice to see if they pre-mix any modifiers. The same goes for the friction modifier. It serves no purpose other than to lessen chatter, but it also tends to eat seals and RTV. If you like the performance without it, don't use it.

jerryp58

I'm afraid all I have is an additional question about using synthetic.

Does it promote leaking like (maybe it's a myth, but I believe it) engine oil does?

jsimpson

Chatter: it goes away after I do a few figure eights. It doesn't otherwise. Now that I use the series 2000 Amsoil, I never get the chatter anymore. If it has posi additives built in, so much the better. At least they don't sling out!
LEAKAGE: I've been using synthetics for 30 years in every conceivable combustion engine. Synthetics do NOT promote or cause leakage. If you already have a leak, it will leak more because synthetics are slipperier and you are probably running a lighter viscosity synthetic than you were dino oil (I often use 0-30). My 78 Vette has all synthetics. It does NOT leak.
Series 2000 75-90? YES, the bottle that says "Race Proven". The older gear oil did NOT eliminate chatter.

Tom Johnson

How much gear oil the the differential hold?

jsimpson

Been a while, but seems like it was slightly less or slightly more than 2 quarts!