ST 75w90, what do you use it in?

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Originally Posted by BlakeB
Originally Posted by wwillson
I'm running a 50/50 mix of SuperTech 75w-90 and 75w-140 in my 2018 Silverado 3500 HD and will post an oil analysis in about 20,000 miles.

I'm looking forward to your UOA.
I checked the rear diff fluid level in my 2017 3500 HD last night, it was 1.1 to 1.2 inches below the fill hole (spec is 0.6 to 0.8 below fill hole). It's slightly underfilled. I have 12.6k miles, I think I might wait until about 15k miles and change the front and rear diffs as well as the transfer case fluid.

I took my dremel and marked a 90° "dipstick" at 17 & 21mm to make checking my rear diff fluid easier in the future.

Now that's splitting hairs. I use a calibrated index finger.
 
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Originally Posted by Bullwinkle007
Nope, I only use Redline for gear lubes and ATF


Same here. Red Line Superlight Shockproof in the track car. Amsoil 75w-110 in the tow rig.
 
I used ST 75w-90 in my Chevy 2006 3500HD for a decade; never had any issues with it. Had to add some FM to adjust the chemistry so the clutches in the G80 didn't chatter, but other than that, no problems whatsoever.

I now have the same in my 2018 F250SD; dropped the factory fill after break-in and replaced with more ST.
 
I am going to use the FS 75W-90 in my Forrester front and rear diffs when I hit the 10k mile mark. I'll drain/fill again at 20k miles and then at 100k, 200k.
 
Originally Posted by dnewton3
I used ST 75w-90 in my Chevy 2006 3500HD for a decade; never had any issues with it. Had to add some FM to adjust the chemistry so the clutches in the G80 didn't chatter, but other than that, no problems whatsoever.

I now have the same in my 2018 F250SD; dropped the factory fill after break-in and replaced with more ST.


How long were your OCI's? Any heavy towing with your rig? I haul hay with mine, the gooseneck trailer loaded weighs around 24k lbs.
How much FM was needed? I have some on the shelf leftover from when I had a limited slip Tacoma. I think it's champion brand, 4 oz bottles.
 
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Originally Posted by BlakeB
Originally Posted by dnewton3
I used ST 75w-90 in my Chevy 2006 3500HD for a decade; never had any issues with it. Had to add some FM to adjust the chemistry so the clutches in the G80 didn't chatter, but other than that, no problems whatsoever.

I now have the same in my 2018 F250SD; dropped the factory fill after break-in and replaced with more ST.


How long were your OCI's? Any heavy towing with your rig? I haul hay with mine, the gooseneck trailer loaded weighs around 24k lbs.
How much FM was needed? I have some on the shelf leftover from when I had a limited slip Tacoma. I think it's champion brand, 4 oz bottles.

OCIs were 50k miles.
Yes- most of those were pulling my RV or Kubota; that's what I had the truck for. It was not my daily driver.
Way back, when I did the OCI, the ST full syn was only for "top off" of LSD diffs. I had to add about 3oz of FM. However the ST full syn diff fluids are now fully formulated with FM, so you should not have to add any, or only a tiny amount. Too much FM is as bad, or worse, than having not enough. If you have to add some, start small and add a bit at a time until the performance gets acceptable.
 
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Originally Posted by ka9mnx
Originally Posted by Miller88
I thought the 75w140 used to be rated for limited slips but turns out it isn't

The synthetic gear oil is. I emailed WD and they confirmed it.


Makes sense that it would be. I may have bought an older bottle set that didn't have it printed
 
Just a bump for this thread, WM now has 75w90 @ $6.97/quart in-store. If you get on Walmart.com you can buy a 9 pack for 58.95, making it $6.55/quart before tax.
 
I just bought a bunch to do diffs and TC on my 2012 4runner and the rear diff on my 2002 Suburban.
 
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