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I'm picking up my new 1973 this Saturday and trailering it home. When I crawled under the car during my inspection, I noticed the rear differential had been leaking fluid. Before I take it out for a shake down cruise on Sunday I want to check the rear differential fluid. I didn't see a separate plug to check the fluid. Is it the same plug to fill it? What is the factory recommended fluid and weight? I plan to change all fluids before I put any real miles on the car but since I don't know how long it has had a drip, I want to make sure its full before a put it on the road.
I beleive the weight is 75W-90 oil. To check the level the same fitting is used for the fill and checking it. The way I do it, get the car level with the wheel out. If you stick your finger straight in you should get some indication, if you have to bend your finger to see anything. Then you are low or very low.
My standard protocol is to change all the fluids when buying a use car.
The plug for filling is the same one you check it with... Remove the plug and stick your finder inside and feel for lube. If you feel lube you have enough.
We only run the GM lube and additive (if posi). 2.5 bottles of fluid, one additive per rear end. The lube is 75w90 and you can substitute other lubes of your choice but if you have a posi rear always run the GM additive.
-Willcox
Last edited by Willcox Corvette; Apr 12, 2016 at 01:45 PM.
Take the plug out and should be just at that level.
To change it, you will need to siphon it out.
I think it takes almost 2 qts? plus the additive. I used what the Chevy dealer had in stock....
If yours is like mine was, after you take it for that first drive? It will be leaking from every seal! Lol! Mine had only been getting a couple short distance drives for the 4 years before I bought it. PO would get all fluids completely serviced every spring.(had receipts, only drove it about 30-50 miles per year!) And really never drove it. I started driving it, 70 mile drive home. 130 mile drive the next weekend, 500 mile drive the following weekend. And there were drips and fluids everywhere!! Amazing how such small amounts of oil from valve covers, rear main, transmission, power steering and the diff pinion and side yokes make such a sticky, gooey, smelly mess under your car!!!
So, that was my first "while I have this out, I can/might as well....(.change/clean/replace)"
Big can of worms!!!! Started with addressing leaky seals and gaskets!! LOL
Best part is now I have a lift and lots more tools!
Thanks guys, I'll drive over to my local Chevy dealer and pick up what I need. I do plan to immediately replace all the fluids, belts, hoses, those leaking valve cover gaskets and any leaking seals. The previous owner had a mechanic who serviced the car for him on a regular basis, but he only drove the car a few miles per year, so there seems to be drips everywhere. That's have the fun of buying a classic.
I agree with CV62AIR when you change it. I have a 81 but I think I would pull the rear cover and replace diff gasket, add posi attitive and GM diff fluid.
When checking I would just push some rear diff fluid into the diff and let it drip out until dripping stops and replace fill screw. This way you know its full.
Last edited by spedaleden; Apr 12, 2016 at 09:06 PM.
Thanks for all the great points. I'll check it and fill it if needed for a quick drive on Sunday. Following that I plan to clean the rear unit, determine what is leaking then replace the cover gasket and the seals if needed.
Rear Differential Fluid
