Rear End Gear Lube

[MikeyMan]

A few questions regarding the Gear Lube for the Rear End of a 72 C/10
It's a 12 bolt GM corporate, pretty sure it's NOT a posi. Haven't found the stamped code on the tube yet.
Planning on opening up the cover and confirming the ring gear numbers and ratio, & add new lube.

Can you use limited slip lube in a non-limited slip rear end?
What is the best weight?
I've used 80w-90 on other trucks, but a parts store has 85w-140 on clearance for $10 a gallon.

I'm in Chicago, so we see some very cold and very warm temperature variations. The truck will be a daily driver, nothing heavy duty or Hi-performance.
I see a lot of members singing the praises of synthetic, but not sure that would be necessary in this application.

[BADPURPLE70CHEVY]

Originally Posted by MikeyMan

A few questions regarding the Gear Lube for the Rear End of a 72 C/10
It's a 12 bolt GM corporate, pretty sure it's NOT a posi. Haven't found the stamped code on the tube yet.
Planning on opening up the cover and confirming the ring gear numbers and ratio, & add new lube.

Can you use limited slip lube in a non-limited slip rear end?
What is the best weight?
I've used 80w-90 on other trucks, but a parts store has 85w-140 on clearance for $10 a gallon.

I'm in Chicago, so we see some very cold and very warm temperature variations. The truck will be a daily driver, nothing heavy duty or Hi-performance.
I see a lot of members singing the praises of synthetic, but not sure that would be necessary in this application.

If you buy Ls gear oil it does cover both applications. Limited and non limited.

[Wrenchbender Ret]

I use 85-140 in all my gear boxes. It should be GL-5. If its a Posi you can add a can of posi additive.

[DnHolland]

80W-90 should fit your application. If you want to use synthetic you can go with the 75W-90. If your not sure if it's limited slip or not you can put the additive in, it won't hurt anything if it turns out you don't need it. You should only need 3-4 quarts to fill it up. Put your additive in first, and fill it up till it runs out.

[Stocker]

When you open it up you'll see right away whether it's a posi.... if not, then either oil (for LS or not) will work. I use synthetic 75W-90. You could use that 85W-140 but being thicker, it will hurt fuel economy a bit..... not that it matters much with these trucks anyway, but I wouldn't do it especially given your winter temps.

Even though synthetic may not be necessary, I never heard anyone complain about their oil being too good.... Besides, how often will you change it? It's not really a major expense to upgrade to synthetic.

[leddzepp]

You can't really go wrong with any of the above suggestions. As far as posi or not, just jack up the rear end, throw the tranny in neutral, and give the tires a spin. If they spin in the same direction, you have posi; if they spin in opposite directions, you have an open diff.
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[MikeyMan]

Thank you all for the advice!

I'm pretty posi-tive it's an open diff. I will jack it up and give the wheels a spin.
I want to have the lube and RTV on hand when I open it up. Then I'll clean, check, and paint the cover.
Also, try to find the stamped code on the tube.

[KEL]

before you take the cover off, make sure you can remove the fill plug !

[camrycurt]

Originally Posted by KEL

before you take the cover off, make sure you can remove the fill plug !

x2!!

Great reminder KEL.

[bugmasta]

Originally Posted by KEL

before you take the cover off, make sure you can remove the fill plug !

Been there, done that. Always a good reminder.
Posted via Mobile Device

[MikeyMan]

Thanks for the reminder!
The fill plug was easy to remove.
Also, the rear diff is an open one legger.

Now the bad news
While jacked up, I spun the rear tires in gear.
After cycling the rear end fluid, there is a pin hole leak in the center of the cover.
Now I need a new cover or JB Weld the leaky spot.