Correct Rear Diff fluid for 1997?

[Paul H.]

I see lots of conflicting info for the correct rear diff fluid for a C5, 1997. Just bought a 97 last week and haven't owned one in a few years. Changing out all the fluids today. The owner's manual calls for 80/90 GL5 and one 4 oz bottle of GM posi lube, kind of like my 60's era Vettes. Many are using the newer synthetics that have the friction modifier already in it. I'm fine with those for the new Vettes (C6/C7), but am inclined to stick with the factory fill for the 97. Not into the boutique stuff like Royal Purple, Amsoil etc, although I'm sure they work fine.

So, do I stick with the 80/90 GL5 and the 4 oz bottle of GM posi lube and then do my figure 8's to work it into the clutches?

[Paul H.]

Re: Correct Rear Diff fluid for 1997?

Anyone? How about the newer GM #88862624 with the friction modifier in it. I see some are using it on the C6's. Is this OK for the C5. Car is in the air waiting.

Thanks.

[Duke W.]

Re: Correct Rear Diff fluid for 1997?

I don't know if the newer products actually have the friction modifier. They might work, but the generic SAE 80W-90 GL-5 is proven and you can buy it at any auto parts store. Brand makes no difference. Just make sure it's API certified to the above spec. The NAPA number for the friction modifier is NCB 4285B. Again, it's a generic product for all clutch-type LSDs. Any other auto parts store should be able to cross reference the NAPA number to whatever "brand" fiction modifier they carry.

[Paul H.]

Re: Correct Rear Diff fluid for 1997?

Thank you Duke. That is the way I am leaning, since I know that works well in the old cars. I have a bottle of the 88862624 Dexron LS 75W-90 Gear oil and it does say on the bottle, "Contains limited slip friction modifier." Not sure it's right for a 97 though.

[Edward J.]

Re: Correct Rear Diff fluid for 1997?

Paul, I would add as a safety measure a extra bottle of additive even when its already added to the fluid, your 97 takes 1.8 qts. subtract a few oz.s for the additive. and try and not to mix other fluids, use another QT. of GM 75w90.

[Paul H.]

Re: Correct Rear Diff fluid for 1997?

Thanks Eddie. Haven't played with a C5 for a while.

I do plan to do my figure 8's but read recently that GM recommends that you take it easy for 300 miles until the fluid is fully worked in? Any truth to that?

[Edward J.]

Re: Correct Rear Diff fluid for 1997?

Paul I think that you have the right idea figure 8's in a parking lot a few times.

[Joe L.]

Re: Correct Rear Diff fluid for 1997?

Anyone? How about the newer GM #88862624 with the friction modifier in it. I see some are using it on the C6's. Is this OK for the C5. Car is in the air waiting.

Thanks.

Paul-------


The GM #88862624 will work fine. As others have suggested, I'd add another 4 oz bottle of the posi additive.

You could also use GM #88900401.

By the way, what is the obsolete part number mentioned in the owner's manual?

[Paul H.]

Re: Correct Rear Diff fluid for 1997?

Paul-------


The GM #88862624 will work fine. As others have suggested, I'd add another 4 oz bottle of the posi additive.

You could also use GM #88900401.

By the way, what is the obsolete part number mentioned in the owner's manual?

Joe, The 97 Owner's Manual states to use GM Part Number 12345977 OR SAE 80W-90 GL-5 and to use 1 bottle of Limited Slip Diff Lubricant additive GM part # 1052358.

I ended up buying Lucas 80W-90 Heavy Duty High Performance Gear Oil. The label states: Exceeds Service Level API GL-4, GL-5, API MT-1, SAE J2360 (MIL-PRF-2105E), MACK GO-J, PG-2 Limited Slip. The label on the bottle also states: "Excellent for use in limited slip differentials. No special additive needed." So I bought one bottle of GM posi lube 88900330 (10-4003).

[Joe L.]

Re: Correct Rear Diff fluid for 1997?

Joe, The 97 Owner's Manual states to use GM Part Number 12345977 OR SAE 80W-90 GL-5 and to use 1 bottle of Limited Slip Diff Lubricant additive GM part # 1052358.

I ended up buying Lucas 80W-90 Heavy Duty High Performance Gear Oil. The label states: Exceeds Service Level API GL-4, GL-5, API MT-1, SAE J2360 (MIL-PRF-2105E), MACK GO-J, PG-2 Limited Slip. The label on the bottle also states: "Excellent for use in limited slip differentials. No special additive needed." So I bought one bottle of GM posi lube 88900330 (10-4003).

Paul-----

GM #12345977 is replaced by GM #89021669. The latter is currently available from GM. However, while this is a GL-5 lubricant, it's a non-synthetic, "standard-type" lubricant. Inexpensive, though.

[Paul H.]

Re: Correct Rear Diff fluid for 1997?

Changed it yesterday and did my figure 8's. Rear end is nice and quiet. Non synthetic was the original fill, so it just made sense to stay with that.