I am running Torco in my Currie Trac Lok. They shipped it with the new center section. It is for use in Ford 8", 8.8" and 9" rear ends.

 

If you run too much of the friction modifier, it can cause the clutches in certain diffs to "slip" too much. I have used Valvoline brand in mine because it included the right ratio of modifier, some prefer to add their own, buy follow the directions either way for best results.

 

I’m probably not supposed to, but I run 75W-90 and I have for years. A lot less parasitic drag compared to 75W-140. Castrol conventional gear oil, it’s already got a friction modifier. And it’s cheap, $10/quart. I don’t run any ‘extra‘ additives, no chatter at all.

I run that lighter gear oil because I don’t drive my car for hours at a time at freeway speed. If I was, Id probably run the 140 weight molasses.

 

I ran non synthetic 80-90 in the Trac Loc with the bottle of magic and 80-90 non synthetic in the new Tru Trac without the bottle of magic. I don't know of anybody recommending synthetic anything for rear ends other than oem's

 

In friction clutch-type diffs like the Equa-Loc and Traction-Loc I use 75W-140 dino with Ford friction modifier. On lockers, helical-gear, etc., 75W-140 synthetic. On open diffs, 80W-90 of whatever-your-pleasure.

 

80w-90 conventional oil + Ford friction modifier in my 8" trac-lok.

 

Anything in print on a Tru Trac, a helical-gear locker, warns in LARGE PRINT against using any type of synthetic lubricant. I thought it was important to mention since my Tru Trac came with half a dozen orange labels stating as much!

 

What kind of oil should I use for my Detroit Truetrac? Can I use synthetic? Do I need friction additive/modifier?

• A quality, petroleum-mineral based, GL5 rated 80w-90 gear oil should be used.
• Synthetic oils are not recommended for Truetrac applications. While some customers have found that synthetic oils works well in this application, Eaton has not confirmed under test conditions that all synthetic oils are compatible with Detroit Truetrac applications.
• Friction modifiers should not be used because they will decrease performance (reduce differential bias).

 

This is what I got for my truetrac

Torco A248514CE Torco RGO Racing Gear Oil | Summit Racing

Free Shipping - Torco RGO Racing Gear Oil with qualifying orders of $99. Shop Gear Oil at Summit Racing.

www.summitracing.com

 

Whatever 90 weight is cheapest at oreillys.

 

I use Mobil 1 75w-140 . In traction loc 9” rears. Never an issue with wear or heat. Over 250,000 cumulative miles in several classic cars.

Also using the same in my daily driver ‘02 Jag XKR. 100,000 miles in it.

Z

 

Rotella gear oil with friction modifier already in it.

 

Pretty sure I have Mobil1 75w90 currently in the diff.

 

85-140.Better shock loading

 

Traction Lok diffs use clutches and thus need a friction modifier. I'd use Mobil-1 75w90LS. Great stuff and easy to get.

TrueTrac docs say to use a dino oil. But eff that. I broke it in with a dino oil then switched to DelVac 75w90. It's been great thus far. What I read was that the Eaton docs for the TrueTrac were developed at a time when they had not done any testing with synthetics. Lots of folks have used synthetics in them. They should update their docs.

-Kyle

 

late to the party ,as usual . when I put the 3.40TL in the sent me a bottle of (if I recall) Yukon modifier (stank juice) I think I used Valvoline 75/90 with it ?
Either way it was what ever these guys suggested

 

when I put the 3.40TL in the sent me a bottle of (if I recall) Yukon modifier (stank juice) I think I used Valvoline 75/90 with it ?

Same here. He builds them. So, I put in what he recommended.

 

Perfect timing, I have my new TL rear from 8 & 9 inches and was wondering what oil to put in it? They shipped it with a bottle of Friction Modifier, but no instructions for the oil.

 

Lube in my rear end?
Sorry pal, "exit only" here...

 

I'm going to type up what the pro gave me along with my new pumpkin. I'll put it here, verbatim.

• Only use high quality gear oils. I recommend Lucas non-synthetic 85w-140
• On initial run, drive lightly for 15-20 minutes then stop to allow differential to cool completely for 20 to 25 minutes.
• Avoid towing and heavy acceleration, as well as vary speed every 5 to 10 minutes while driving on highways.
• Drive conservatively and do not drive more than 50 miles at a time without allowing a cool cycle during the first 500 miles following installation.
• Allow 2000 miles for smooth quiet operation.

I have heard that some gears come with special treatment (cryogenics, vibratory polishing, etc.) that can reduce or eliminate some of the break-in process, because the faces don't have to wear as much to mate properly. I didn't pay for the fancy stuff, because I'm on more of a 'beer' type budget.

He also added (in all caps!)

PREMATURE OVERLOADING AND IMPROPER BREAK-IN WILL CAUSE GEAR OIL BREAKDOWN AND MAY RESULT IN RING AND PINION FAILURE VOIDING THE GEAR WARRANTY!

I figure on following this information carefully. Do you guys think I should change out the gear oil after about 500 miles to get rid of most of the break-in metal that's floating around in there?

 

“… Do you guys think I should change out the gear oil after about 500 miles to get rid of most of the break-in metal that's floating around in there?

yes.

Z

PS the anti-synthetic recommendations for rear ends borders on matching the anti-synthetic hysteria for engine oil. I’ve yet to see one verifiable issue with using the Mobil 1 75w-90 or 140 in any rear end with stock or aftermarket gears. You’d think I would’ve noticed a problem after 25-30 years & hundreds of thousands of miles , if there was one…..

Both of those lubes are labeled “LS” for limited slip units, but I always add the MotorCraft 4 oz bottle of additive anyway.

The quality synthetic oils and lubes have a well documented & established advantage over conventional petroleum products in reducing wear. Why there is still an unreasonable hesitancy to use the demonstrably superior products is baffling.

 

I checked with Alan at 8 and 9 inch rears and his response was:

”use the whole bottle of friction modifier along with standard 80/90 gear oil, No Synthetics, should take about 2-2.5 quarts”

 

For the 9 inch in the Mustang I use Valvoline Durablend 80w90 with Ford friction modifier. That is what the center section builder gave me with it when I had it built. Its been in the car since 2009 with over 30k miles on it and the LS is still operating smoothly and feels tight. I might consider switching to full synthetic next time it is serviced.

I use 75w140 Mobile full synthetic or Valvoline SynPower in the 5.0 Mountaineer and older F150 since that is what I've seen them call for. I think there is even a tag on the Mountaineer specifying it.