Question about Gear Oil
Thread Starter
Safety Car
Joined: Dec 2005
Posts: 4,270
Likes: 20
From: Central Michigan
Question about Gear Oil
The thread about the posi additive got me thinking.....what would be the best weight differential oil for my application? There's a number of different weights out there, there's got to be a reason for that
Reason I am asking about "my application" is that I'm not into racing, just cruising, with longer distances in mind. The diff was rebuilt a year and a half ago by a local builder. I've got the diff pulled out and drained, need to replace a leaking seal, so now's a good time to ask
383 motor
200R4 BTO trans
3:73 Eaton posi rear end
Need more info, just ask
Reason I am asking about "my application" is that I'm not into racing, just cruising, with longer distances in mind. The diff was rebuilt a year and a half ago by a local builder. I've got the diff pulled out and drained, need to replace a leaking seal, so now's a good time to ask383 motor
200R4 BTO trans
3:73 Eaton posi rear end
Need more info, just ask
Advanced
Joined: Jan 2007
Posts: 62
Likes: 0
From: LaGrange Georgia
I use the Red Line synthetic shockproof, 75W90 in mine. Which I think is the weight recommended by the factory. While the Red Line may seem like overkill at ~$14 a quart, you don't need to buy a separate limited slip additive, so that kind of balances it out. And you only need a quart or so, not to mention you'll rarely need to change it.
Pro
Joined: May 2010
Posts: 737
Likes: 3
From: Pennington NJ
Randy,
I think the factory fill was SAE 90 with positraction additive. So the 75w-90 mentioned above or an 80w-90 would be good for it. No matter the grade of oil (GL4, GL5) I've always used an additional bottle or tube of posi additive. Like said on the stated gear oil thread a little more is better than too little.
Edit: Also this was not in my Corvette, that was done by the Corvette shop that did all of the mechanical stuff on it, I have changed the Differential fluid in a '72 Nova with a posi and a '78 Monza (Our school drag car). Just throwing this out there!
Will
I think the factory fill was SAE 90 with positraction additive. So the 75w-90 mentioned above or an 80w-90 would be good for it. No matter the grade of oil (GL4, GL5) I've always used an additional bottle or tube of posi additive. Like said on the stated gear oil thread a little more is better than too little.
Edit: Also this was not in my Corvette, that was done by the Corvette shop that did all of the mechanical stuff on it, I have changed the Differential fluid in a '72 Nova with a posi and a '78 Monza (Our school drag car). Just throwing this out there!
Will
Last edited by Will's'74VetteL-82; Feb 14, 2011 at 07:46 PM.
Thread Starter
Safety Car
Joined: Dec 2005
Posts: 4,270
Likes: 20
From: Central Michigan
Randy,
I think the factory fill was SAE 90 with positraction additive. So the 75w-90 mentioned above or an 80w-90 would be good for it. No matter the grade of oil (GL4, GL5) I've always used an additional bottle or tube of posi additive. Like said on the stated gear oil thread a little more is better than too little.
Edit: Also this was not in my Corvette, that was done by the Corvette shop that did all of the mechanical stuff on it, I have changed the Differential fluid in a '72 Nova with a posi and a '78 Monza (Our school drag car). Just throwing this out there!
Will
I think the factory fill was SAE 90 with positraction additive. So the 75w-90 mentioned above or an 80w-90 would be good for it. No matter the grade of oil (GL4, GL5) I've always used an additional bottle or tube of posi additive. Like said on the stated gear oil thread a little more is better than too little.
Edit: Also this was not in my Corvette, that was done by the Corvette shop that did all of the mechanical stuff on it, I have changed the Differential fluid in a '72 Nova with a posi and a '78 Monza (Our school drag car). Just throwing this out there!
Will
Yeah I was a little overwhelmed by the selection at the parts store, figured I better ask! Saw the 80w-90 and the L/S additives, that ought to work for the type of driving I do
Instructor
Joined: Jun 2003
Posts: 183
Likes: 0
From: Gordonville MO
Mobil 1 synthetic is a very good gear lube and is less expensive.
Synthetics flow better into tight spaces (i.e. bearings) when cold,
as well as withstanding heat better without breaking down.
I used to be parts manager in a heavy over-the-road truck dealership
and when several small fleets that we dealt with started using synthetics
(this was years ago) they nearly doubled their mileage in diff's & trans
between rebuilds and the temp gauges showed they ran cooler, too.
Synthetics flow better into tight spaces (i.e. bearings) when cold,
as well as withstanding heat better without breaking down.
I used to be parts manager in a heavy over-the-road truck dealership
and when several small fleets that we dealt with started using synthetics
(this was years ago) they nearly doubled their mileage in diff's & trans
between rebuilds and the temp gauges showed they ran cooler, too.
Burning Brakes
Joined: Sep 2008
Posts: 805
Likes: 5
From: Naperville Illinois
I chose Lucas 85-140 Heavy Duty. The way I see it, you have 85 weight viscosity when cold, which is virtually the same as the 80-90 many people use, but you have higher viscosity/better protection at high temps. I researched this when I rebuilt my diff, and several manufacturers (BMW comes to mind) spec 75W140 gear oil for their "performance" cars. Don't forget the posi additive
Le Mans Master
Joined: Oct 2007
Posts: 7,455
Likes: 977
From: RI, Now Franklin/Nashville TN
Mobil 1 synthetic is a very good gear lube and is less expensive.
Synthetics flow better into tight spaces (i.e. bearings) when cold,
as well as withstanding heat better without breaking down.
I used to be parts manager in a heavy over-the-road truck dealership
and when several small fleets that we dealt with started using synthetics
(this was years ago) they nearly doubled their mileage in diff's & trans
between rebuilds and the temp gauges showed they ran cooler, too.
Synthetics flow better into tight spaces (i.e. bearings) when cold,
as well as withstanding heat better without breaking down.
I used to be parts manager in a heavy over-the-road truck dealership
and when several small fleets that we dealt with started using synthetics
(this was years ago) they nearly doubled their mileage in diff's & trans
between rebuilds and the temp gauges showed they ran cooler, too.
Pro
Joined: May 2010
Posts: 737
Likes: 3
From: Pennington NJ
You're welcome! It looks like you got good answers, I'd definitely consider the synthetic fluid. The higher cost will be completely offset by the less wear in the differential and it also doesnt need to be changed often. Just something to think about
Will
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Melting Slicks
Joined: Mar 2005
Posts: 2,838
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From: Austin TX
By all means. Go with the recommendations from a few blokes on the internet instead of the engineers who design this stuff.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Eatons are a metal on metal cone idea. I ran one for a years with Valvoline syn power 85w-140 with one tube of GM posi lube.
While you have the pumkin cover off drill and tap it for a drain plug. Eatons add metal to the oil and ware out. My first indication that it was going bad was while jacking up the rear the passenger yoke had a bunch of in and out movement like the yoke was ground away. The posi cone had actually worn away. They are non rebuildable items.
They are better than stock against breakage and probably last twice as long, but they are not made for severe cornering loading.
While you have the pumkin cover off drill and tap it for a drain plug. Eatons add metal to the oil and ware out. My first indication that it was going bad was while jacking up the rear the passenger yoke had a bunch of in and out movement like the yoke was ground away. The posi cone had actually worn away. They are non rebuildable items.
They are better than stock against breakage and probably last twice as long, but they are not made for severe cornering loading.
Thread Starter
Safety Car
Joined: Dec 2005
Posts: 4,270
Likes: 20
From: Central Michigan
Eatons are a metal on metal cone idea. I ran one for a years with Valvoline syn power 85w-140 with one tube of GM posi lube.
While you have the pumkin cover off drill and tap it for a drain plug. Eatons add metal to the oil and ware out. My first indication that it was going bad was while jacking up the rear the passenger yoke had a bunch of in and out movement like the yoke was ground away. The posi cone had actually worn away. They are non rebuildable items.
They are better than stock against breakage and probably last twice as long, but they are not made for severe cornering loading.
While you have the pumkin cover off drill and tap it for a drain plug. Eatons add metal to the oil and ware out. My first indication that it was going bad was while jacking up the rear the passenger yoke had a bunch of in and out movement like the yoke was ground away. The posi cone had actually worn away. They are non rebuildable items.
They are better than stock against breakage and probably last twice as long, but they are not made for severe cornering loading.
I picked up a small bottle of limited slip lube from the GM dealer downtown, that stuff is expensive
Haven't bought oil yet, that will wait till this weekend
