Differential Fluid Change
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Joined: Aug 2004
Posts: 94
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From: Houston Texas
Differential Fluid Change
Going to tackle the rear end fluid change tonight. Have a slight knocking noise coming from rear, checked spare tire, mufflers etc. All u-joints seem good by just visual and moving shafts. But going to replace them next. Heard changing rear end fluid helps this sometimes? If that's where the noise is coming from? Buying 80w-90 fluid and buying a fluid suction tool to remove fluid. How much do you add? Til it comes out of the top? Thanks!
Le Mans Master
Joined: Oct 2007
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From: Akron Ohio
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When do you hear this knocking noise? Is it constant when the wheels are spinning?
Yes to change the fluid, make sure the car is level and then add fluid until it starts to drip out from the fill hole. Should be just under 2 quarts.
Yes to change the fluid, make sure the car is level and then add fluid until it starts to drip out from the fill hole. Should be just under 2 quarts.
Racer
Joined: Jul 2013
Posts: 366
Likes: 19
Rear fluid
I bought a somewhat cheap fluid suction tool at the parts place. Did not work too well. Got a turkey baster, put a section of the tubing on that. Worked just fine. Took a little while, and be careful about the tubing popping off. That oil REALLY stinks! Gloves and eye protection. The two 4 oz bottles of GM additive really help. I went ahead and used GM rear fluid too. My 73 sat for a long time, and had a clicking noise. The additives, fluid, and doing "figure 8's" exercised the rear, and the noise went away. Can't say if that is your situation, but at least you'll have fresh fluid. Good Luck!
Burning Brakes
Joined: Sep 2005
Posts: 1,050
Likes: 205
From: Lewes Delaware
After getting all the old fluid out (I used a turkey baster and clear plastic tubing like Franks73 did), add the GM fluid first, then the differential oil until it starts to pour out. Tighten everything up, find an empty parking lots and do some figure 8's.Worked for my 73.
Fran
Fran
Last edited by Blue73Shark; Dec 8, 2016 at 07:01 AM.
Le Mans Master
Joined: Oct 2007
Posts: 9,682
Likes: 3,434
From: Akron Ohio
2025 Corvette of the Year Finalist - Modified
2024 C5 of the Year Winner - Modified
2023 C5 of the Year Finalist - Modified
2022 C5 of the Year Finalist - Modified
St. Jude Donor '09-'10-'11
I would also look into a good synthetic fluid that has the limited slip additive in it already.
I use AMSOIL rear gear oil and no need for any extra additive. I do not get any noises/chatter in my '71.
http://www.amsoil.com/storefront/svg.aspx?zo=1934716
I use AMSOIL rear gear oil and no need for any extra additive. I do not get any noises/chatter in my '71.
http://www.amsoil.com/storefront/svg.aspx?zo=1934716
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From: Crossville TN
Getting that plug out of the 'pumpkin' might be harder than you think. If it has been in there a long time, it tends to be very resistant to coming out. I couldn't get it out with a good sized air impact wrench. Eventually, I had to remove the spare tire and tub to get enough clearance for a 4 foot extension bar on a 3/4" breaker bar!!
Anyway, you might want to drive it for a few miles to get the fluid warmed up before you suck it out. Heat thins it down a lot and it's much easier to remove. You could also put some mineral spirits in after most has been removed, just to thin down the rest and get almost all of it out.
Put in one full bottle of lube; then put in the Posi-trac additive. Finally, put part of another bottle in until it begins to run out the plug opening. Reinstall the plug...but DON'T use a gun to put it in or use a LOT of torque to tighten it. GM specifies 20 ft-lbs; but that is when DRY. If there is lube in the threads, you should only tighten to 15 ft-lbs.
Now go out and do some slow Figure-8's to get the lube up into the diffy clutch plates. You should be good for another 5 years +.
Anyway, you might want to drive it for a few miles to get the fluid warmed up before you suck it out. Heat thins it down a lot and it's much easier to remove. You could also put some mineral spirits in after most has been removed, just to thin down the rest and get almost all of it out.
Put in one full bottle of lube; then put in the Posi-trac additive. Finally, put part of another bottle in until it begins to run out the plug opening. Reinstall the plug...but DON'T use a gun to put it in or use a LOT of torque to tighten it. GM specifies 20 ft-lbs; but that is when DRY. If there is lube in the threads, you should only tighten to 15 ft-lbs.
Now go out and do some slow Figure-8's to get the lube up into the diffy clutch plates. You should be good for another 5 years +.
Last edited by 7T1vette; Dec 9, 2016 at 11:06 PM.
Racer
Joined: Jan 2015
Posts: 314
Likes: 50
From: Woodbury NJ
+1 on driving it to get the fluid warm. i tried to use a syphon to get it out. it was like pulling maple syrup from a tree too early in the season. i used a plastic tube and put it in the diff as far as i could get it.