03' 2500 HD Gear lube???

Barrett66 · August 22, 2014

Rear diff gasket was leaking so I pulled the cover and did the gasket. I had a bunch of new Lucas 85W-140 kicking around the shop so that's what I put in the rear (14 bolt 10.5"). Is this to thick or will it be safe?? I don't want to junk a rear over $30 worth of gear lube.

gmtech4 · August 22, 2014

what does your owners manual say ?

it doesnt say 85 140 oil my friend

Barrett66 · August 22, 2014

It doesn't say 10W-30 Synthetic Mobil One for the engine either but that's what Its always gotten.......

txab · August 22, 2014

Better to have used 75w-90.

rfehler · August 23, 2014

Got posi / limited slip? Don't forget to add 4oz of friction modifier.

http://www.summitracing.com/parts/nal-88900330?seid=srese1&gclid=COGDns2LqcACFU4F7Aod3yoAcw

Has to be for GM vehicles but doesn't have to be AC Delco. Any parts store should have it.

8.1HD/ALLISON · August 23, 2014

Gm doesn't run friction modifier to my knowledge.

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sdeeter19555 · August 23, 2014

85w140 is not much different than a 75w90 at a colder temperature. The most I think you'll see is a drop in mileage because it thicker and the Lucas...well, I won't go there.

Barrett66 · August 23, 2014

Thank you to all for the input.

rfehler · August 23, 2014

Gm doesn't run friction modifier to my knowledge.

Really? I thought that was only if you have an Eaton G80 locker. And that it was still required for the limited slip posi units. Must be getting my 1500/2500 and year models mixed up.

8.1HD/ALLISON · August 23, 2014

I may be wrong. Its been a while since i did any. Not sure

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MORSNO · August 24, 2014

No friction modifier required on my 2012. My 2001 did require it.

rfehler · August 24, 2014

No friction modifier required on my 2012. My 2001 did require it.

So does my 2000.

Be nice to know what year/s and diferentials GM changed to that don't require it.

Back in my hot rod days runnin posi's & limied slips we never add anything. Chadder? What chadder? The motor shook the car so hard we wouldn't have felt it anyway. Lol.

Jonny5cam · January 30, 2015

Most GM 1/2 ton and up truck diffs use the Governor locker so no additive is necessary.

sdeeter19555 · February 8, 2015

I used Amsoil in mine, and was beginning to wonder if it was allowing the locker to work. Being we have had ample snow, it seems all right. I did not use additive.