Differential fluid change
I would like to change the fluid in the differential of my 74. I plan on sucking it out with a vac pump. I have two quarts of GM differential gear fluid and one 4 oz. bottle of GM posi additive. Doe anyone know what the capacity of the housing is? Any tips from anyone who has already done this.
Happened to come across it in the 1975 assembly manual. 4.0 pints is what that says. let me know what kind of pump you used. I'm in the process of a full suspension rebuild and I might as well do the same since all the parts are out.
I drained mine with a hand pump. It worked. Just a tad slow but the pump was cheep and I was able to throw it away when I was done.
Getting the fluid back in was a different story. I couldn't get the oil bottle up high enough to gravity fill it so with a piece of clear plastic tubing a snug fit over the oil tip I was able to squeeze it in. I had a mess when I was done and lost a couple of ozs. But the job was done.
I put the fluid back in by using tubing with a funnel in the end and held it higher than the car,garden hose stuff would work if you can get the hose in the diff. Hope that help's.
Your quart bottle should have a tapered top that will insert into the opening of the gear case, then squeeze the bottle. Put the tapered top onto your bottle of additive and put that in first, followed by the gear lube. If this dosent work for you get a small piece of tubing from the local parts store and squeeze the fluids through it. It likely won't take all of the second quart of lube.
I did it with a hand pump, tedious but it worked. I would recommend putting bottle of lube in and then the additive. Then top off with the lube. That way you get al posi additive in there. Don't forget to do SLOW forward and backward figure "8's" in a parking lot to lube the clutches
Removing the fluid is much easier if you drive the car and get the gear oil warm. Sucks out much easier!! I always use the vacum pump to install the oil also.
You can buy a cheap "slurp" gun at PEP Boys, etc. Looks like a huge medical syringe with a 12 to 14 inch vinyl end. Put the end in the diff and suck it out. To replace the fluid, do the opposite. Load the "slurp gun" and push the fluid back in till it drips out of the hole. MUCH neater....minimal mess. That gear oil stinks to high heaven IMHO, it's tough if not impossible to use the gear oil bottle with it's little end to put fluid in. Not much room to get the bottle high enough, especially working around the exhaust system/ rear spring/ spare tire carrier. Chuck
1963 Corvette Conv., Red/Black, 327-360HP FI, 4 SPD, NCRS Top Flight
1969 Corvette Conv., Orange/Black, 427-400HP, Automatic, NCRS Top Flight
1956 Chevy 150 2 door sedan. HOT ROD. 355CI, 4 Speed, Vintage Air, NEAT cruiser
Gear Oil Capacity
Two 23-oz. bottles of GM Rear Axle Lubricant and one 4-oz. bottle of GM Positraction additive filled her up to the bottom of the hole.
GM dealer gave me a cap with a short piece of plastic hose that attachs to the Axle lub bottles. Went in with no problem. Just get the bottle up higher than the fill hole.
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