Rear Differential Fluid Servicing
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Joined: Feb 2005
Posts: 61
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Rear Differential Fluid Servicing
I have a 1969 coupe (427 with a 3:36 posi-rear) that occasionally produces a "thump" from the rear end area when going around a corner. I do stress that its only on occasion and only on severe turns. My corvette shark buddies tell me its not untypical with the posi-traction rear and it needs just some fresh fluid servicing.
So what is both the process for changing that fluid (square bolt) and What kind of fluid & additives do I specifically buy?
I thank you all in advance for any feedback!
So what is both the process for changing that fluid (square bolt) and What kind of fluid & additives do I specifically buy?
I thank you all in advance for any feedback!
Burning Brakes
Joined: May 2008
Posts: 860
Likes: 0
From: Stratford Ontario
The best method is to remove rear cover but that means total rear suspension removal PITA. I would try to syphone (not sure thats how its spelled?) LOL. the oil out through filler hole (square plug). Then you need a little less than 2 liters (2 full quarts?) sorry about the metric Im starting to become converted after 30 years of using metric and fighting it. Any how put one small bottle of posi additve from any speed shop or Napa etc...use it between the two oil bottles. I like using 90 weight gear oil Synth. But if your just draining and adding I would use conventional 90 weight oil. Hope this helps. PS make lots of turns after adding oil to work additive through clutches. And just fill till oil starts to come out fill hole.
Pro
Joined: Sep 2002
Posts: 541
Likes: 5
From: Epping NH
the easiset thing to do
is to bring the car to your mechanic and have them siphon out the old gear oil with a pump, then replace it. Be sure to bring along a 4 oz bottle of "genuine GM limited slip" gear oil additive and have them put that in before they top off with gear oil.
I may be making this part up, but I seem to recall that you are supposed to work the new oil in by driving the car backwards in either direction a bit.
While you are at it and the car is in the air, have them siphon out your transmission oil and replace that at the same time!
I like to turn a wrench myself, but some things are easier done when the car is up on a lift!
I may be making this part up, but I seem to recall that you are supposed to work the new oil in by driving the car backwards in either direction a bit.
While you are at it and the car is in the air, have them siphon out your transmission oil and replace that at the same time!
I like to turn a wrench myself, but some things are easier done when the car is up on a lift!
Drifting
Joined: May 2006
Posts: 1,480
Likes: 2
From: Circleville Ohio
Vader Vette
1St rule get a big jar with a plastic lid get your shop vac get you a hose small enough to go in the drain hole make a vaccume pump take out the old fluid, replace with G.M. rear end lube and start with two bottles of posi lube also G.M. gonna cost around $80.00.
2Nd rule dont change rule #1 unless your say working on a chevette
2Nd rule dont change rule #1 unless your say working on a chevette
Melting Slicks
Joined: Apr 2001
Posts: 2,030
Likes: 363
From: Lubbock Texas
I drilled a hole in the bottom of the differential and then tapped it for a brass plug. Makes for easy servicing. There are some threads on the forum about how to do this and where to drill the hole.
Also, search for some posts by GTR1999. He rebuilds these units and has recommended the proper fluid in plenty of other threads.
DC
Also, search for some posts by GTR1999. He rebuilds these units and has recommended the proper fluid in plenty of other threads.
DC
Melting Slicks
Joined: Dec 2009
Posts: 3,229
Likes: 656
From: Thunder Bay
The clunk you are hearing is the posi clutches sticking. A bottle of GM posi additive will probably solve the problem if you are confident that the lube is OK. If you feel the need to change the fluid I recommend dropping the differential to do it so you can remove the cover. There will be a lot of sludge in the bottom of the diff that should really be cleaned out, and which won't be if you siphon the fluid out. Yes its a PITA but you have to decide if the car is worth doing it right.
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Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
1St rule get a big jar with a plastic lid get your shop vac get you a hose small enough to go in the drain hole make a vaccume pump take out the old fluid, replace with G.M. rear end lube and start with two bottles of posi lube also G.M. gonna cost around $80.00.
2Nd rule dont change rule #1 unless your say working on a chevette
2Nd rule dont change rule #1 unless your say working on a chevette
