Rear end oil?
Drifting
Joined: May 2012
Posts: 1,353
Likes: 44
From: Calgary Alberta
I like the 80-90 GM axle lube. Can't remember the part number right now, but it is labeled GL-4 on the bottle...in fact the same stuff used to be labeled GL-5 previously, and was prescribed for your car. In short, it is the right stuff. Also add a bottle of the GM posi additive.
If you go outside GM products, get GL-5. Synthetic is also nice.
If you go outside GM products, get GL-5. Synthetic is also nice.
Last edited by Brcmpbl; Oct 9, 2013 at 10:02 PM.
Le Mans Master
Joined: Oct 2007
Posts: 7,453
Likes: 976
From: RI, Now Franklin/Nashville TN
75W-90 GL-4 is I believe specified by GM with a bottle of GM posi fluid. With that said, I have used Mobil 1 75W-90 for 25 years with no posi additive and the differential works perfectly-quiet, zero chatter and the posi operates as it should. Some will say that Eaton says to use only conventional gear oil with the posi lube so that is what they do. Just my opinion and 25 years of experience using a synthetic is that Eaton will not recommend much newer and better synthetic lubricants that were not available or tested by them when the diffs were designed and built-period-not because the synthetic will hurt the diff which is total insanity if you know anything about the chemistry of synthetic lubricants. I did not know about Gary Ramadei's recommendation (should have called before the most recent diff lubricant change) since I believe his word and experience above just about anyone concerning rebuilt diffs and he did a masterful job custom blueprinting/rebuilding my steering box. Next change-Mobil 1 75W-140!!
Drifting
Joined: Jul 2002
Posts: 1,995
Likes: 110
From: Garland Texas
Both the GM GL-4 and GL-5 recomendations by GM have been updated. The new GM lube is #89021671. (89021672 in Canada) The bottle states "exceeds GL-4 specifications". GL-5 should not be used in stock 63-69 differentials because the bonding effect is hard on the copper thrust washers. In 70 they changed to steel thrust washers and recommended GL-5. The recommended GL-5 lube has been upgraded to the new number stated above. It now can be used in 63-82 differentials and manual tarnsmissions.
Mike
Mike
Drifting
Joined: Jul 2002
Posts: 1,995
Likes: 110
From: Garland Texas
Jeff,
I don't want to voice an opinion about synthetic gear lube. There are some applications where synthetic is mandatory. Having met you in person and seeing your quality of work I know you are a person who doesn't go cheap on quality. But I will voice on Lucas gear lube. I build many more custom differentials than Gary ever will and maintain them during racing seasons. Lucas lube starts out all well and good but after it is run for awhile it's viscosity breaks down. Pull the drain plug and it comes out like water. Stick with the Mobil 1 you've been using.
Mike
I don't want to voice an opinion about synthetic gear lube. There are some applications where synthetic is mandatory. Having met you in person and seeing your quality of work I know you are a person who doesn't go cheap on quality. But I will voice on Lucas gear lube. I build many more custom differentials than Gary ever will and maintain them during racing seasons. Lucas lube starts out all well and good but after it is run for awhile it's viscosity breaks down. Pull the drain plug and it comes out like water. Stick with the Mobil 1 you've been using.
Mike
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Drifting
Joined: May 2012
Posts: 1,353
Likes: 44
From: Calgary Alberta
Agree with tracdogg about the GM lube, that's what I was trying to get across in my first post without much clarity. I think it is the way to go, but just my opinion. It is in both of my cars, a 70 and a 76.
Instructor
Joined: May 2013
Posts: 158
Likes: 1
From: Ct
Jeff,
I don't want to voice an opinion about synthetic gear lube. There are some applications where synthetic is mandatory. Having met you in person and seeing your quality of work I know you are a person who doesn't go cheap on quality. But I will voice on Lucas gear lube. I build many more custom differentials than Gary ever will and maintain them during racing seasons. Lucas lube starts out all well and good but after it is run for awhile it's viscosity breaks down. Pull the drain plug and it comes out like water. Stick with the Mobil 1 you've been using.
Mike
I don't want to voice an opinion about synthetic gear lube. There are some applications where synthetic is mandatory. Having met you in person and seeing your quality of work I know you are a person who doesn't go cheap on quality. But I will voice on Lucas gear lube. I build many more custom differentials than Gary ever will and maintain them during racing seasons. Lucas lube starts out all well and good but after it is run for awhile it's viscosity breaks down. Pull the drain plug and it comes out like water. Stick with the Mobil 1 you've been using.
Mike
Would you use the Gm or the Mobil in your 70?
Pete
Drifting
Joined: Jul 2002
Posts: 1,995
Likes: 110
From: Garland Texas
I run the GM lube in my own vettes and recommend it to anyone who's diff I rebuild. I run my 64 very hard on the street. If I was running a road course for an extended amount of time I might consider switching to synthetic if I wasn't running a cooler.
Mike
Mike
