Gear Fluid for Rear Diff (75w90/75w110)

Okay so I'm sitting at 23k miles on my truck and decided that I should change my fluids out soon.

After much research and recommendations I settle on

$29 75w-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75w-90 AmsOil Severe gear fluid for my front diff and transfer case.

The rear I am debating on, I'm sure the 75w90 would do just as well but however I intend to drive over 4000 miles from Alaska to Wisconsin to pick up my little race car and bring it home on a trailer. Car weights about 1700-1900lbs and the trailer I have weights about 900-1000lbs.

Would 75w90 be fine for the rear or would 75w110 be better? 80 percent of the time I do not tow anything, except when I tow my 4wheeler out camping.

This truck is my daily, would I take a mpg hit with the heavier fluid?

 

The heavy stuff is for heavy hauling, I've only seen heave gear oil be recommended for full size trucks that are rated for 10k lbs. I would go 75w90 since youre not towing a whole lot, and since it's a quality gear oil you should be fine.

 

Thank you, wow I learn something new everyday. Didn't realize that the heavier stuff is usually rated for towing much heavier loads.

 

The other thing is, where you are traveling the ambient temp wont be high.

 

I changed mine at 30K and it was nasty. Good idea to change it earlier.

 

The dudes who deal with diffs everyday recommend heavy, even for our trucks.

OFFICIAL 2nd gen 4x4 front differential bearing vibration thread

OFFICIAL 2nd gen 4x4 front differential bearing vibration thread

 

Now this got me all confused, he recommends 85w140 or 80w90 from what it shows.

I'm in an area that gets well below 0 degrees and sometimes even close to -30F in winter, lowest I've experienced is -45F (super cold), I'm not sure the 85w140 would be a good idea for me, that's why I even considered the amsoil 75w110 instead of the 75w140.

Hmm interesting read indeed, thank you for sharing.

 

85w140 seems over kill either way. They probably recommend it because they are catering to the offroad market where there is abuse, plus they sell numerically high gears that generate more heat than say stock 3.727 gears. So many 4x4 trucks and SUVs in the 2-3 ton weight range are using 75w90 without issues that switching to something heavier, although technically better just seems to be out of boredom. Even ECGS says changing the gear oil frequently has the most impact.

 

This was the rear diff fluid that came out, super black and contained lots of metallic particles, there was only 2 quarts in it! This was what Toyota filled it with, I expected 3 quarts but only 2 came out.

Filled it with 3 quarts of 75w90 Amsoil and good to go, I filled it with my hand pump and it sorta foamed up because my pump wasn't good. Hoping it'll settle down and be good later on. Got to do the transfer case too and that fluid was golden brown, a little dirty but not as bad as the rear diff.

I'll get to the front diff on another day, got too tired lol. This was at 23k miles.

 

Interestingly enough my diff fluid was very similar with only 5k on it. I guess when the ring and pinion break in it takes a beating on the gear oil. I know they say not to drive more than 15 miles at a time on new gears so the gear oil doesnt over heat but sometimes it's not an option.

 

Mine looked similar and the transfer case fluid looked brand new. Front looked bad too.

 

Yup, I drove 64 miles to and from work 5 days a week for almost a year with this truck, averaging 65-70mph on the highway. I was quite surprised how dark the rear diff fluid was and how much metal particles were in it. The fluid had a nice silvery film in it.

I'm going to do the front diff tomorrow and see how it looks like also. Probably just as dark. The transfer case however was pretty clean, a few metal particles but golden fluid.

To think Toyota wanted to wait until 30k miles. I advise others to check theirs at 15k at least. Probably even at 10k miles, that break in period seem to do a beating.

 

Definitely makes me want to get to the fronts asap.

 

I waited to change all three of mine until 50,000 miles....front and rear were filthy, transfer case looked brand new. For the record I do no off-roading and rarely use 4wd.

 

i did front diff, rear, and transfer case at 30,000 on my 2015. front and rear oils were dam near black with metal particles everywhere. transfer case oil looked brand new.

 

Who said that? Got a link? I've been working on cars since I was 15 and I'm now 61 and I have never heard that or seen it in practice.

My 20 year old Isuzu had the factory gear oil and transmission oil in it when I sold it. It ran fine and never had a hickup.

Another thought. The transfer case looked like new oil, because it is only ran when it is in gear. The differentials run all the time.

 

I change my gear oil every 15,000 miles.

On this truck, I am following ECGS's suggestion and running Lucas 85w-140. I have to agree - it clings really well.

I have only changed once with my new gears, and the old oil wasn't too terribly nasty.

We shall see...

 

Lucas seems to be very good oil.

I am using Lucas 75W-140 Synthetic. I have mechanical, factory installed Limited Slipp and I had trouble finding any oil that would work with correctly.
Lucas seems to be the right oil. With more than 80 000 miles in New England, my limited slip is still working. (used/tested this winter again)
Plus I live in a spot that puts a heavy workout on that limited slip, so the fact that still works is testament that good limited slip + correct oil make whole world of difference.

 

Did the fronts today and it was also dark too, glad I didn't wait until 30k miles. Everything came off easily. Had to remove the skid plate to get to the front diff.

Everything feels much smoother.

 

The factory fluid in rear/front diffs looked the same way at 18,000 miles. At 95,000 now and changed twice since then, comes out looking like it went in.