rear diff fluid - have q's
Thread Starter
Racer
Joined: Apr 2004
Posts: 472
Likes: 0
From: Hartland WI
rear diff fluid - have q's
Couple of q's about changing my rear diff fluid. I have a 72 with positraction. So...
1) What weight should I buy?
2) How much do I need?
3) I went to the local Napa and was looking at a product called Royal Purple. It's fully synthetic and says it has the posi additive right in it. Has anybody used this? If so how has it performed? I read on their website that no additional additives are needed. Is this true, even with our cars?
Thanks for any advice.
1) What weight should I buy?
2) How much do I need?
3) I went to the local Napa and was looking at a product called Royal Purple. It's fully synthetic and says it has the posi additive right in it. Has anybody used this? If so how has it performed? I read on their website that no additional additives are needed. Is this true, even with our cars?
Thanks for any advice.
Racer
Joined: Dec 2004
Posts: 379
Likes: 0
From: Fairfield Texas
I changed out My 79 rear end fluid to Royal Purple and everything
is working fine.Probably have about 5 or 6 hundred miles on it since
the change. I did not add any xtra posi. additive to mine but most
folks on the forum seem to add it to the synthetic oils.
is working fine.Probably have about 5 or 6 hundred miles on it since
the change. I did not add any xtra posi. additive to mine but most
folks on the forum seem to add it to the synthetic oils.
Melting Slicks
Joined: May 1999
Posts: 2,897
Likes: 0
From: Moon Township PA
Asking which brand of differential lube you like is similar to asking what brand of engine oil or beer 
we like.
With that said, I use Mobil 1 synthetic and I add one container of GM brand Positraction additive. A lot of manufacturers claim that their lube offers the Posi additive but there is enough evidence on this, and other Corvette, boards that adding the GM additive will eliminate any chance that your positraction clutches will chatter or bind. If I recall correctly, there are two common weights of diff lube, 80W-90 and 75W-90. Either one is acceptable for your car, with neither one being better or worse than the other, imo.
My 72 uses 1 3/4 containers of lube plus the GM Posi additive. Each container is 1 quart. The way to do this is to drive your car for a few miles to warm it up then get your suction gun and draw out the old lube. The FIRST thing I add is the Posi additive to ensure that I always have room for it first. I then fill the differential carrier until the lube starts to run out the hole. Insert the plug and drive.
Gary
72 LT1
we like. With that said, I use Mobil 1 synthetic and I add one container of GM brand Positraction additive. A lot of manufacturers claim that their lube offers the Posi additive but there is enough evidence on this, and other Corvette, boards that adding the GM additive will eliminate any chance that your positraction clutches will chatter or bind. If I recall correctly, there are two common weights of diff lube, 80W-90 and 75W-90. Either one is acceptable for your car, with neither one being better or worse than the other, imo.
My 72 uses 1 3/4 containers of lube plus the GM Posi additive. Each container is 1 quart. The way to do this is to drive your car for a few miles to warm it up then get your suction gun and draw out the old lube. The FIRST thing I add is the Posi additive to ensure that I always have room for it first. I then fill the differential carrier until the lube starts to run out the hole. Insert the plug and drive.
Gary
72 LT1
Safety Car
Joined: Jun 2004
Posts: 4,652
Likes: 80
From: Lakeland Florida
hello,
I did the same thing to my 72 about 6 months ago.
Here is a photo of where the diff. plug is. One thing that really helped me was to take the extra time and take the spare tire carrier and clamshell out. With this out of the way you will have a lot of room to get inside and use your suction gun to get all the old oil out.
As GaryS said, put in the additive first. If you dont, then there may not be enough room once you top this off to put any other lube in.
Then go do your figure 8s to get it mixed up real good.
kdf
I did the same thing to my 72 about 6 months ago.
Here is a photo of where the diff. plug is. One thing that really helped me was to take the extra time and take the spare tire carrier and clamshell out. With this out of the way you will have a lot of room to get inside and use your suction gun to get all the old oil out.
As GaryS said, put in the additive first. If you dont, then there may not be enough room once you top this off to put any other lube in.
Then go do your figure 8s to get it mixed up real good.
kdf
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
If you're running an Eaton posi as most are, Eaton "strongly" recommends to NOT use synthetics with their posi's. Apparently they've logged a higher failure rate with the use of syns. Here's their page:
http://www.traction.eaton.com/prod3.htm
Then click on FAQ,..you'll see this:
What type of lubricant and limited slip additive should I use with my newly purchased Eaton Limited Slip Differential?
Eaton strongly recommends utilizing an API-GL5 approved Mineral-Based 80W-90 Axle Lubricant and one 4-oz bottle of Limited Slip Additive (GM or Ford).
Fyi,
Wes
http://www.traction.eaton.com/prod3.htm
Then click on FAQ,..you'll see this:
What type of lubricant and limited slip additive should I use with my newly purchased Eaton Limited Slip Differential?
Eaton strongly recommends utilizing an API-GL5 approved Mineral-Based 80W-90 Axle Lubricant and one 4-oz bottle of Limited Slip Additive (GM or Ford).
Fyi,
Wes
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
Originally Posted by Vette Rx
Couple of q's about changing my rear diff fluid. I have a 72 with positraction. So...
1) What weight should I buy?
2) How much do I need?
3) I went to the local Napa and was looking at a product called Royal Purple. It's fully synthetic and says it has the posi additive right in it. Has anybody used this? If so how has it performed? I read on their website that no additional additives are needed. Is this true, even with our cars?
Thanks for any advice.
1) What weight should I buy?
2) How much do I need?
3) I went to the local Napa and was looking at a product called Royal Purple. It's fully synthetic and says it has the posi additive right in it. Has anybody used this? If so how has it performed? I read on their website that no additional additives are needed. Is this true, even with our cars?
Thanks for any advice.
