Gear Oil After Regear

[nicholas.craft]

I hate to do this, but there is so much info spread all over the web and nothing conclusive. I recently had my 2019 ORP regeared to 4.56 and added an Eaton front E-locker. So both diffs are open with E-lockers and 4.56 gears. I don't really care about brands, but am looking for synthetic vs conventional and 75w90 vs heavier weight gear oils. I really just want to run a synthetic 75w90, but am worried as some folks such as ECGS recommend the 85w140 dino. I have also heard that synthetic ruins regear gears. I live in Colorado (cold winters) and explore trails/forest service roads maybe a dozen+ times a year and take it pretty easy on my 4Runner with 33s, 3/2 lift, slimline/winch, skids/sliders, dual batteries, fridge, and rack/awning. The gears are Nitro and the break in fill was 80w90. At 500mi, after a very careful break-in, I swapped to Lucas 85w140.

Calling Around for recommendations:
Nitro - synth any weight or their branded synth gear oil 80w140
local installer that did the work - dino 80w90
another local shop - Synth 75w90
ECGS - dino 85w140 even for CO winters
Revolution Gear - dino 80w90
Marlin Crawler - Synth 75w90 (said to follow factory specs even with re-gearing)

As you can imagine it's been quite the journey and tons of scouring the forum as well as calling local shops and gear companies. Any help would be appreciated. Especially if you have experience running Synth 75w90 or whatever after new gears. Thanks, Nick.

 

[comtn4x4]

I hate to do this, but there is so much info spread all over the web and nothing conclusive. I recently had my 2019 ORP regeared to 4.56 and added an Eaton front E-locker. So both diffs are open with E-lockers and 4.56 gears. I don't really care about brands, but am looking for synthetic vs conventional and 75w90 vs heavier weight gear oils. I really just want to run a synthetic 75w90, but am worried as some folks such as ECGS recommend the 85w140 dino. I have also heard that synthetic ruins regear gears. I live in Colorado (cold winters) and explore trails/forest service roads maybe a dozen+ times a year and take it pretty easy on my 4Runner with 33s, 3/2 lift, slimline/winch, skids/sliders, dual batteries, fridge, and rack/awning. The gears are Nitro and the break in fill was 80w90. At 500mi, after a very careful break-in, I swapped to Lucas 85w140.

Calling Around for recommendations:
Nitro - synth any weight or their branded synth gear oil 80w140
local installer that did the work - dino 80w90
another local shop - Synth 75w90
ECGS - dino 85w140 even for CO winters
Revolution Gear - dino 80w90
Marlin Crawler - Synth 75w90 (said to follow factory specs even with re-gearing)

As you can imagine it's been quite the journey and tons of scouring the forum as well as calling local shops and gear companies. Any help would be appreciated. Especially if you have experience running Synth 75w90 or whatever after new gears. Thanks, Nick.

I've been following the ECGS recommendation on my ECGS gears for about 5 years/80,000 miles. I also live in Colorado and hit the high country regularly in the winter. No issues with regular oil changes

 

[Jetboy]

I've put at least 100+ k miles on aftermarket gears with synthetic oil in other toyotas. The main reason to run heavy gear oil is to quiet noisy gears that are either poorly cut/polished, have some inherent harmonic frequency you're needing to dampen, or setup in the diff in some problematic way that requires a heavier oil to retain the necessary fluid film thickness. I suspect the ECGS recommendation is based on the lack of precision in setup and lack of OEM quality gear cuts so that they need to run heavier oil to quiet the noisy gears. I don't think synthetic vs dino would make much difference in that respect. The weight would make more difference.

If I were going to run a front ARB - I would then for sure run heavy weight oil because the newer forged spider gears are not polished and, while very strong, are also very noisy. So in that case I'd run heavy oil weight to try to quiet them down for highway cruising in the front diff. For an OEM rear locker with aftermarket gears - I ran synthetic 75-90 without any issues. But it was for a relatively short time before I swapped around diffs again and ultimately sold my 4R, so it's not a very good long term sample.

In general Synthetics have a naturally higher viscosity index so the viscosity changes less (more stable) as temperatures change in the diff. That means that the film thickness or clearance between metal surfaces that slide or rotate against each other will remain more uniform across the temperature ranges. That's the general reason why you can use a thinner weight synthetic oil vs dino. The thinner synthetic oil can maintain the necessary film thickness at higher heat than a comparable weight dyno oil. So you end up with oils that can be thinner at cold temps and still lubricate properly at operating temps. My guess is that a heavier weight dyno oil ends up having about the same film properties as a the 75-90 synthetic at operating temps. So it's probably about a wash in terms of diff wear. But the synthetic should slightly reduce friction at colder temps.

TLDR; it probably doesn't matter as long as there's some oil in there and it's something heavier than engine oil and lighter than bearing grease.

 

[Jeremy556]

I've been running the Lucas 140w with my Nitro 4.56s for 220k miles, no complaints. I'm with Jetboy that it doesn't really matter much as long as you have some oil in there.

 

[rochmpr]

You should run regular gear oil during break in period. After, I have always ran, and still do, Red Line Heavy Shock Proof. It was nice when I would get gallon jugs for free, but never had an issue in 20+ years. I put 45k or so on my 4Runner after a regear before I sold it the Shock Proof.

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[Planetcat]

I’ve regeared 3 jeeps and my Ram 2500. Jeeps use Amsoil 75w-90 and truck has 80w-140. I’ve used a few major brands, mobile1, Red Line, Lucas, RP, but Amsoil seems quietest and smoothest with Detroit Tru-Tracs or factory lsd the diffs. Same with my SxS. Never had a need or desire for heavier gear oil in the 6-cylinder jeeps.

 

[jdm-v35]

You should run regular gear oil during break in period. After, I have always ran, and still do, Red Line Heavy Shock Proof. It was nice when I would get gallon jugs for free, but never had an issue in 20+ years. I put 45k or so on my 4Runner after a regear before I sold it the Shock Proof.

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Just curious if you also ran shockproof in the tcase as well?

 

[Engineer]

Any of your choices will have no impact on the life of the rear end under your use case and lifetime

I ran 75w90 when I got it for dirt cheap in an old job - now that I have re-geared with 4.88 I will run 85W140 per ECGS recommendation as that's who I got the 3rds through

I slept well with both

 

[JPOVS]

Nitro told me run what the factory recommended. Been running LT 75W-85 GL-5 for a couple years now.

 

[rochmpr]

Just curious if you also ran shockproof in the tcase as well?

Too thick. Ran MT90 in the dual case gear drive T-cases.

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