1987 rear differential
Thread Starter
7th Gear
Joined: Jul 2013
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1987 rear differential
Hey guys, I have an 87 C-4 manual transmission with the 4/3 with 26k original miles. I changed out the rear diff lube with GL-5 80w 90w. after that I noticed a dragging noise coming from the rear end. I have looked at all of the owners manual and chiltins specs and recommendations and they say you never have to change the lube. Is that right? Any advice? Thanks for the help.
Team Owner
Joined: Sep 2003
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There's no truth in the "NEVER" that you mention. An early car '87 or earlier has a shoe style parking brake and it's of course possible there could be issues with them but I'd guess you just need to either have it checked or do some checking yourself.
How much fluid did you drain and how much did you replace? It might be wise to check the level again with the car "level" and maybe add a 4 OZ bottle of GM positive traction additive.
Check it or get it checked - don't just ignore it!
How much fluid did you drain and how much did you replace? It might be wise to check the level again with the car "level" and maybe add a 4 OZ bottle of GM positive traction additive.
Check it or get it checked - don't just ignore it!
Thread Starter
7th Gear
Joined: Jul 2013
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I replaced all of it and did not add any addative. I was under the impression that a true positive traction rear end would not need an addative. I am using all synthetic. In my manual it does say you only need to add to it and not replace it. Although it contradicts itself saying change it at 30,000 miles. I figured its 26 years old and has probably never been done. Confusing. I have service many other cars I have owned and have not ran into this issue before. I appreciate the advice. Todd
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From: Lacey WA RVN 68-69
NCM Sinkhole Donor
You definitely need to add the GM Posi additive!!
While it's true that the '87 Owner's Manual doesn't say anything about changing the diff fluid, it certainly doesn't hurt anything to change it at some interval like 50K miles or even longer. You did use the correct oil (although synthetic is not necessary), but the lack of the additive could explain the noise. It could be some chatter from the posi clutches. Add a bottle, then drive the car slowly doing some figure-8's and see if the noise goes away.
And toss the Chilton book. If you are going to do your own work, get a Factory Service Manual (FSM) for thw 1987 car. It's a two-book set and make sure you get the version with the red covers.
While it's true that the '87 Owner's Manual doesn't say anything about changing the diff fluid, it certainly doesn't hurt anything to change it at some interval like 50K miles or even longer. You did use the correct oil (although synthetic is not necessary), but the lack of the additive could explain the noise. It could be some chatter from the posi clutches. Add a bottle, then drive the car slowly doing some figure-8's and see if the noise goes away.
And toss the Chilton book. If you are going to do your own work, get a Factory Service Manual (FSM) for thw 1987 car. It's a two-book set and make sure you get the version with the red covers.
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Joined: Sep 2003
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From: Database Error Indiana
I have used GM axle lube in GM positraction axles for many decades. It just "works". Back in 1995, I put Vavoline GL5 85W/90 from a FLAPS in my 88 convertible because I didn't care that much about that car, I didn't have any GM on hand, and I figured "what could it hurt"? Within a day or two it began to squeal like a stuck pig around every corner. In either direction up to about 15 MPH it squealed. I changed the lube to GM, with the additive, and the squeal stopped immediately.
There ARE differences in axle oils. The GM lube is GL-3/4. It is NOT GL-5 which I believe is a spec that can only be met by a "synthetic". And the additive IS required for all C4 years' rear axles.
There ARE differences in axle oils. The GM lube is GL-3/4. It is NOT GL-5 which I believe is a spec that can only be met by a "synthetic". And the additive IS required for all C4 years' rear axles.
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From: King George VA
AMSOIL Slip-Lock Differential Additive (Product Code ADATB)
This can be squirted in the fill tube to a full diff. The few ounces won't matter for overfill. Then go do some figure 8's and see if the noise persists. If so, something other than the diff.
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Thread Starter
7th Gear
Joined: Jul 2013
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I appreciate the info all you guys have given. I wonder what the heck is in that 4oz. bottle that can make that big of a difference? whatever it is i`m going to use it. I am running a full synthetic in it now and will add it in. Weird... lol
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From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
Drain off about ten ounces of fluid and add at least 8 ounces of LS lube.
Finish off with your oil.
Yes that is double the amount called for.
That's what works and has been the call for many years around here.