Differential
2026 Loser of the Year
Joined: Sep 2013
Posts: 36,595
Likes: 7,043
From: New Or-leens Loo-z-anna
Use the above device to suction the old fluid out through the "fill plug" threaded hole.
Squirt the old fluid into an empty container.
Repeat the procedure until the differential is empty.
Refill diff. with correct fluid/oil.
Last edited by doorgunner; Jul 22, 2017 at 10:17 PM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
I hate to say this, because I perform almost all of the work on my cars...BUT, the best way to change diff fluid in your car is to take it to an oil change place and have them do it.
Why? Because they have the right tools to get that danged plug out of the diffy. And the right tools to suck the old fluid out.
I would go to a GM dealer/part dept. in your area and get a bottle of Posi-Trac fluid to take with you (they might have their own stuff, but it would be better to get the right stuff).
And, if the oil change place has trouble getting that plug out, then you know you are going to have to remove the spare tire tub to get at it with a big breaker bar and [probably] a torque extender bar. I had to do just that and put 4 feet of black iron pipe on the breaker bar to FINALLY get that plug out of the housing.
Why? Because they have the right tools to get that danged plug out of the diffy. And the right tools to suck the old fluid out.
I would go to a GM dealer/part dept. in your area and get a bottle of Posi-Trac fluid to take with you (they might have their own stuff, but it would be better to get the right stuff).
And, if the oil change place has trouble getting that plug out, then you know you are going to have to remove the spare tire tub to get at it with a big breaker bar and [probably] a torque extender bar. I had to do just that and put 4 feet of black iron pipe on the breaker bar to FINALLY get that plug out of the housing.
Last edited by 7T1vette; Jul 23, 2017 at 01:19 PM.
Melting Slicks
Joined: Apr 2001
Posts: 2,030
Likes: 363
From: Lubbock Texas
First thing to do is to make sure you can remove the fill plug. They can be stubborn.
One option is to suck out the fluid but there's another way.
You can drill a hole in the bottom of the diff and tap it for a drain plug. There are old threads on this site that show the proper location to drill. I went with this method. Fluid changes are now much easier.
Good luck.
DC
One option is to suck out the fluid but there's another way.
You can drill a hole in the bottom of the diff and tap it for a drain plug. There are old threads on this site that show the proper location to drill. I went with this method. Fluid changes are now much easier.
Good luck.
DC
Racer
Joined: May 2013
Posts: 296
Likes: 16
From: Edmonton Alberta
When I recently changed the diff lube on my '70, the old lube was right up to the bottom of the fill/drain hole. I used a suction gun to draw out as much fluid as I could. I measured the amount of old oil drawn out and compared it to the published capacity for the diff- I had drawn out all but 2 ounces of the old fluid. That's pretty good to me. In order to get that last couple of oz. out you'd have to, as someone else has mentioned here, install a drain on the bottom of the diff. Several vendors sell a kit to do just that if you're so inclined. There's some controversy over whether or not doing so will result in drill cuttings getting inside the differential housing though. From what I've read, many forum members have done so without any issues. As for me, I don't believe that the 2 oz. of diff lube remaining will really matter. Your opinion may vary of course. 
And as mentioned, don't forget the GM posi additive. It really does work.
And as mentioned, don't forget the GM posi additive. It really does work.
Last edited by Majoho; Jul 24, 2017 at 02:52 PM. Reason: typo correction
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Team Owner
Joined: Mar 2002
Posts: 44,674
Likes: 1,830
From: Huntsville AL
Pull the body and disassemble the rear suspension until you have the differential setting on your work bench. Now remove the rear cover and drain old fluid out.
Reverse the above steps and don't forget to add new fluid to the differential at some point along the way.
Somewhere in the middle of all that would be a good time to just do a frame off restoration because changing the differential fluid most always turns into a frame off restoration.
Reverse the above steps and don't forget to add new fluid to the differential at some point along the way.
Somewhere in the middle of all that would be a good time to just do a frame off restoration because changing the differential fluid most always turns into a frame off restoration.
Racer
Joined: May 2013
Posts: 296
Likes: 16
From: Edmonton Alberta
Pull the body and disassemble the rear suspension until you have the differential setting on your work bench. Now remove the rear cover and drain old fluid out.
Reverse the above steps and don't forget to add new fluid to the differential at some point along the way.
Somewhere in the middle of all that would be a good time to just do a frame off restoration because changing the differential fluid most always turns into a frame off restoration.
Reverse the above steps and don't forget to add new fluid to the differential at some point along the way.
Somewhere in the middle of all that would be a good time to just do a frame off restoration because changing the differential fluid most always turns into a frame off restoration.
