Differential oil grade??

[ClassicGuy]

I have a 71 C10 shortbed and I'm changing the gear oil on the differential. Does anyone know what grade of oil it takes 80or 90? And how much? It is a 2wd and 12 bolt rear end. I believe it has 3:83 gears but not sure.
Thank you
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[RexDodge]

Should be 90. I am sure some other guys will chime in.

[jhngardner367]

The manual I've got says SAE 80w-90gl5,or equiv. If it's a limited slip you'll need the additive,too.Add the lube through the check-plug,until you can put the tip of your finger in to the first joint,and just touch fluid(usally 2.25qts,if drained completely).

[cdowns]

i like the synthetic stuff either royal purple or mobil one are the two i usually use

last 3new gm vehicles i got came from the factory synthetic equipped

[POPO1984]

I use moroso climbing gear oil. Its 90w

[GASoline71]

3:83 gears?

Do you have an open diff? Or posi-traction?

Gary

[mud.man.rj]

I use synthetic in front/rear diff also trans and 205 T.case, gas mileage went up by 3 mpg, which I needed with a B.B.460. Shifts nicer too.

[raceman6135]

80w90 oil

Usually takes 2 quarts plus one (small) bottle of GM limited slip additive

[Jimsblazer]

Okay I have a 1972 blazer with 4 wheel drive.

We are going to change the diff covers front and rear and change the fluid as well.

How do I know If I have limited slip diff?

How much fluid do I put in. I did not understand the previous post about sticking fingers into the first joint? What is the first joint.

If it's not a limited slip and I put the limited slip additive in will it hurt the open diff?

Thanks
Jim

[mud.man.rj]

A limited slip basically will have clutch packs or spring type inside the diff, if it is wide open inside usually an open diff, as for gear oil most use 80/90 gear oil with a type of additive in it but not all, I use synthetic gear oil myself which is just a newer style diff (gear) oil. Think most of it is 75/90 weight and the additive if needed can be purchased separetly and won't hurt the diff if it is a posi type to drive without it but is a bit harder on the clutch packs and the clutches won't slip when turning a corner and try to lock up both wheels and not turn one faster than the other wheel. The additive just helps the clutches slip when cornering.

[Jimsblazer]

Originally Posted by mud.man.rj

A limited slip basically will have clutch packs or spring type inside the diff, if it is wide open inside usually an open diff, as for gear oil most use 80/90 gear oil with a type of additive in it but not all, I use synthetic gear oil myself which is just a newer style diff (gear) oil. Think most of it is 75/90 weight and the additive if needed can be purchased separetly and won't hurt the diff if it is a posi type to drive without it but is a bit harder on the clutch packs and the clutches won't slip when turning a corner and try to lock up both wheels and not turn one faster than the other wheel. The additive just helps the clutches slip when cornering.

thanks for the help.

Changed the diff covers front and back, new gaskets, switched to summit racing polished aluminum looks nice. limited slip in the back open diff in front, back gears looks worse than front gears but still acceptable.

thanks again.
Jim

[mud.man.rj]

Sounds like it worked out alright, good stuff and help is always here anytime, a lot of good guy's here and sure a few girls too that can help. Happy building.