Differential/axle Lube

[mints33]

Seems like there's no end to the work load on the 97 K1500 ... lol About to change the rear differential lube, owner manual calls for 80W 90 for front and rear. But can I use 75W 140? What is the advantage or disadvantage of using the 75w 140? The manual calls for 75W 140 in the 3500 w/ heavy towing. Heavy towing is rare here, but still happens. Please advise, thanks much!!!

[MS3DALE]

Your going to get some different opinions on this but....I'd stick with 75W-90 or 80W-90.

The 75-140 was only used in the C3500HD trucks which had a GVWR of 15,000lbs.

Also....DO NOT use any friction modifier,It is not needed nor recommended by GM.

[gvbhunt]

75W140 is a heavier oil. If the manual calls for 80W90, I would use it. According to the Amsoil guide, I would either use their synthetic 80W90 or their Severe Gear 75W90. The second is really good stuff.

[mints33]

Thanks for the replies guys, I really appreciate it! I was looking at the Amsoil lube, are there any issues w/ using synthetic oils with the RTV sealant? Thanks again!!

[merlin5577]

Your going to get some different opinions on this but....I'd stick with 75W-90 or 80W-90.

The 75-140 was only used in the C3500HD trucks which had a GVWR of 15,000lbs.

Also....DO NOT use any friction modifier,It is not needed nor recommended by GM.

 

+1. I use 75W-90 Royal Purple synthetic.

[pm26]

80W140 can be used in very hot climates or under hard towing conditions. It will maintain its viscosity higher under severe heat to provide proper film lubrication for the gears.