GoFastBroncos.com

140wt?

Read your owners manual and use the gear oil specified.
Definitely not 140
I discussed this very subject with an engineer for the factory before they sold the business to Eaton. He said the DL does not need special gear oil.

What rear end?

85w is what I have run in the my Currie 9in for many years.

Man I hate typos. Need edit, at least for a couple minutes after post.

I run transmission fluid. It's all the rage. Went from 11 to 20 mpg.

PaulW wrote:Read your owners manual and use the gear oil specified.

Don't have the owner's manual anymore. But I'll see if I can find a pdf.

hobbyturnedobsession wrote:What rear end?

9"
35 spline axles if it makes a difference

I ran 85/140 in my old 9"

yikes wrote:I run transmission fluid. It's all the rage. Went from 11 to 20 mpg.

Thanks for the tip Brian...this is so gonna help

The original question was about a Detroit locker.
The engineering comment was about the same question. What the engineer meant was the locker portion of the diff is not controlling with regard to lube requirements.
As you all know there are constant discussions on what diff lube to use and guys with different uses swear by their choice of lubes. These discussion vary by application.
Like synthetic vs non-synthetic
Like light weight vs heavy weight.
Like aftermarket stuff vs auto store stuff.
Like additives like Moly or ZDDP vs no additives.
From my quires it seems the racers are choosing by trial and error and when they find a lube that works good the others also use it. Some of the guys wont tell or do not know and just leave it up the the diff builder.
The things in a diff that need lube are bearings, lockers, and tooth to tooth interface.
The tooth to tooth friction and extreme pressure is definitely the controlling item and is why diff gear lube was developed. The high temperature that high power applications have throws in another factor for high temp resistance and is why some racers use active cooling systems.

The lube for my 9" spool desert Bronco uses a different lube than my other stuff and the reason is the application is different. The desert bronco has aftermarket stuff from a big can that Glen puts in all his builds. My F350 10.5 DL uses Amsoil 75-140 full synthetic and has over 130k on that stuff with no issues to report. My low mileage D44 Jeep with ARB has Mobil1 full syn 75-140.
BTW, the diff lubes for the F350 & Jeep use lube per the owners manual.

In all my reading using motor oil or ATF in a diff is still unknown or even tested for function.
However it is true that transfer cases and manual trannys do use ATF or motor oil, but ZDDP is usually added. Different application because these gears are not subject to the extreme sliding friction and high temps like are present in a diff.

PaulW wrote: In all my reading using motor oil or ATF in a diff is still unknown or even tested for function.
However it is true that transfer cases and manual trannys do use ATF or motor oil, but ZDDP is usually added. Different application because these gears are not subject to the extreme sliding friction and high temps like are present in a diff.

I'm 53.4% Brian may have been kidding

In the Trophy Truck and the Pro 2 we run 250wt....

I think 250 wt but I would recommend synthetic it you can afford it..

Manual says " use hypoid gear lubricant SAE 80 or 90"
However the use of heavier has been used for years. Also the ATF use does also work but may not prevent wear as efficiently . 250 is what I used per my uncles recommendation for longevity of my gears.

robertcrav wrote:

PaulW wrote: In all my reading using motor oil or ATF in a diff is still unknown or even tested for function.
However it is true that transfer cases and manual trannys do use ATF or motor oil, but ZDDP is usually added. Different application because these gears are not subject to the extreme sliding friction and high temps like are present in a diff.

I'm 53.4% Brian may have been kidding

Close Robert. 99.99999999% which = snowballs chance in hell I would run ATF.

I use a gear lube with moly as it seems to work and I was told that the moly helps with the shock loads the gears experience in off road racing. Who knows, works for me.
With heavy lubes like 250wt, you really need to jack the rear end up and run the truck in gear to preheat the lube before running. I like a 85-140wt as you can jump in a go cold.

For transfer cases, I use the same gear oil on gear driven transfer cases like the 205 in our racer, but I use ATF in chain drive boxes like the 1356 in the play bronco.

The Detroit Locker vs other diffs, should not affect the lube decision. Clutch style limited slips need a friction modifier to reduce chatter but gear driven limited slips like the Tru-Track do not need this.

Paul W hit the nail on the head!

I am the aftermarket engineer for Supercharger here at EATON and that gives me a lot of face time with one of the engineers in torque control that was hired when EATON purchased Detroit Locker, he is actually helping me with my bronco project. Put whatever you want in it, he even alluded to mud cut with gasoline. The locker doesn't care, run what you like and trust for your gears, don't worry about the Detroit.

A quick plug for the Destroit Locker. I bent two 8.8 housings and the same DL survived the carnage. I eventually sold the locker to a friend and it is still running strong years later. Now I have a 9" with a Detroit Locker. never had a problem with it. Ran 85w in both and at times I did not change the gear oil as often as I should have.

So really, just what is best for the gears?