75w-85 in Rear Differential???

SavageSierra · October 14, 2016

I plan on changing my rear differential fluid soon and i took a glance at my manual and it calls for 75w-85 synthetic axle lubricant (GM part no. 19300457). I haven't been able to find a 75w-85 anywhere and in previous vehicles that had the G80 rear end i always used 75w-90. Would it be safe to use a 75w-90 in the rear end or will it cause issues?

***UPDATE***: called my local dealer and told them that my manual calls for a 75w-85 and they said just use a 75w-90. This came straight from a dealer tech.

LongrangeLauber · October 14, 2016

Use 75w-90, I changed mine at 5k miles and has been in there for 50k miles, not a single issue. Make sure to use full synthetic though, I believe that's mandatory for the G80

SavageSierra · October 14, 2016

Sweet, i figured it would be alright to use the 75w-90, i just wanted to hear from others before i went for it.

O_J_Simpson · October 14, 2016

I plan on changing my rear differential fluid soon and i took a glance at my manual and it calls for 75w-85 synthetic axle lubricant (GM part no. 19300457). I haven't been able to find a 75w-85 anywhere and in previous vehicles that had the G80 rear end i always used 75w-90. Would it be safe to use a 75w-90 in the rear end or will it cause issues?

Why is your dealer not carrying the proper lube? I would find a new dealer/

SavageSierra · October 14, 2016

Has anyone else changed the differential fluid in their 2014-2016 trucks? If so what viscosity did you use? Any Issues?

Colossus · October 14, 2016

75W-85 is very hard to come by, it is not very popular in many parts of the country. Even at dealerships. Don't worry about it, 75W90 is perfect. However- use caution with 75W90 or 75W85 and make sure it is ok to use with your G80 locking diff. (if you have em)

Colossus · October 14, 2016

If I remember right, my 2008 called for 75W85 and there was NONE to be found within a reasonable distance. None of the parts stores had them and the dealer did not have any. They were willing to order it in however at an extra cost. After talking with a few mechanics, they said 75W90 is the norm now.

gone_fishing · October 15, 2016

I used Amsoil Severe Gear 75W-90 when I replaced the fluid in my Sierra's rear axle. That was about 40,000 miles ago. The only reason I can see why GM used 75W-85 over the more common 75W-90 is trying to squeeze and extra 0.01 MPG's.

07Softail · October 15, 2016

I use 75w-90 and have changed the lube twice and my truck has less than 8000 miles. No synthetic here... the diff works a lot better with mineral base oil.

RT

newdude · October 15, 2016

I used Amsoil Severe Gear 75W-90 when I replaced the fluid in my Sierra's rear axle. That was about 40,000 miles ago. The only reason I can see why GM used 75W-85 over the more common 75W-90 is trying to squeeze and extra 0.01 MPG's.

Correcto. That's why the GM bottle says High Efficiency right on it LOL.

elcamino · October 15, 2016

I put 100% synthetic 75W-90 in my 2015 Sierra 25,000 miles ago. All 75W-85 is is a more fuel efficient lube in effort to improve the CAFE of the trucks.

I replace ALL the oem fluids asap. No lube in my truck is oem, all premium 100% synthetic.

Cowpie · October 18, 2016

I have been using 75w90 syn for most of this century in about every vehicle and different brands. 75w90 syn is a solid performer. As a side note regarding that, the commercial truck differential OEM's will automatically increase the warranty by using a 75w90 syn... by 50%. Yep, from the stock 500,000 mile diff warranty up to 750,000 miles just by using a 75w90 syn. Shouldn't that tell you a little about why it is good to use in a pickup also? Amsoil SG, Mobil 1, etc.... pick your favorite and have a good time.

Essayons24 · October 30, 2016

I use 75w-90 and have changed the lube twice and my truck has less than 8000 miles. No synthetic here... the diff works a lot better with mineral base oil.

I'm NOT challenging your claim, but I'm curious how it works better.

Cowpie · October 31, 2016

There must be something to it if on my commercial trucks, the diff OEM will extend the base warranty from 500,000 miles to 750,000 miles by using syn 75w90 vs a non syn lube. Pretty sure it has to do with syn ability to handle shearing forces better.

Essayons24 · October 31, 2016

Most commercial trucks run full synthetic in the transmission and rear axles. My KW actually calls for full synthetic 75W90 in the rear axles. I know synthetics handle heat better among many things, i was just curious how he determined his diff worked better. Maybe it indeed does work better, seems my diff works sketchy at best.....so im curious.