FM characteristics for roller clutch type lockers?

[tdi-rick]

This is something I've pondered for a while, Weismann's famous (in the late sixties/seventies/eighties) road racing locker and latterly the Kaiser Locker from Brazil use a sprag clutch type arrangement to fully lock under load, ie. they have a series of rollers running in a case that cam out and fully lock under power.
These aren't to be confused with a cam and pawl (ZF) type diff.

The big advantage of these diffs is that they unlock on a trailing throttle (unlike a Detroit Locker/No Spin) yet fully lock under power and so reduce corner entry understeer compared to a fully locked rear end, ie a spool or Detroit.

The downside with these (or at least the Weismann) was that you needed a specific additive chemistry for the lube otherwise the rollers would suffer what was known as 'popping', where the rollers would slip under load.

LSD fluids are a no-no, and apparently most syn fluids don't work.
Weismann now market their own syn fluid, naturally enough called 'Snake Oil'

(someone there has a sense of humour)

Nekarth, the manufacturer of the Kaiser Locker in Brazil claim you can use any gear/diff fluid with their Kaiser Locker, but I know that behind an auto tranny this thing is pretty seamless, put a manual in front of it and it clunks and bangs and can bite badly with on/off throttle applications.
I'm guessing it's suffering the same as the Weismann did back in the day, so what sort of characteristics does the brains trust reckon the fluid needs for proper operation ?

I'm guessing something like an aggressive MTF additive package, an increasing coefficient of friction as the relative speed between the rollers and case decreases ?

Just throwing it out there for an interesting discussion.

 

[Shannow]

Detroits and lunchbox type lockers have the characteristic by design that when the power is on, the inside wheel drives, and the outside "over-runs" the speed of the inside, causing a pushing effect with power on, until the inside wheel breaks traction, and matches the speed of the outside and they "lock"

Reverse that for power off, and the outside wheel retards, with the inside "under-running".

Weight transfer makes all that transition to power off/on do strange things.

The sprag types can only do the same, with less ratchetting, to almost infinitely small ratches for roller sprags, but unless there's no capability of reverse, they all have the same characteristics, just less pronounced.

 

[Jim Allen]

The Weisman is very similar to the Warn locker of the '70s, or the Warn is similar to the Weismann, which Warn tried to market then. There were some engineering problems in the '70s that stalled it. They resurrected it in the '90s and tried to market it again with no luck. Not sure what happened that time. The Kaiser I had never seen but it's similar in concept. Both would seem to be exceptionally sensitive to lubricants. Imagine what would happen if the lube gets used up. What happens then the roller and ramps get even slightly worn?

The material I have from Warn is an engineering report from Jeep. Warn had proposed the selling the unit to Jeep. The machining for it was practically zero tolerance or the unit didn't wok right and they were rejecting more than 50% of the parts. By the '90s, the tooling was better. What little info I got then was grudgingly given. I had aquired the Warn folder form a collection of materials I bought from a deceased Jeep engineer's estate. It was really the "good, bad and ugly" stuff that companies don't like getting out. I got curious about it and called one of my contacts at Warn to learn more. That happened to be right when they had dusted off the old material and were trying to market it again. They were not happy with my having that folder. They actually asked for it. I told them no... it was a historical document to me, no more. I wasn't going to burn them with it. I got semi regular reports after that and the project was dead by the late '90s again.

Those types of lockers are great for racecars but not so much for an offroader. We don't like it when they unlock on decel (like on a downhill).

 

[Shannow]

Jim, so they were completely over-run with no retardation ?

If so, take back my post.

 

[tdi-rick]

Shannow, a Detroit is locked in a straight line, as you said the faster wheel overides during cornering and 'cams' out, but the locked axle on initial turn in induces corner entry understeer by design.

The newer soft lockers are supposedly much nicer to drive than the old style Detroits, the blokes I know that have them reckon they're pretty much transparent in use these days, particularly in full time 4WD's where the torque through the rear axle is reduced.
I've driven the old style in race cars and don't care for them one little bit, and they were just plain nasty in the wet.

The Weismann (and Kaiser) unlock on a trailing throttle, as Jim said it's not liked for offroad use but we all survived with open diffs for years on too steep downhills too

Jim, interesting re the Warn.
I've heard about it but never seen one or even a drawing.

The late Carroll Smith in his '....To Win' series of race car prep books constantly referred to the Weisamnn and it's lubrication peculiarities, which is why I was surprised by Nekarth's claim that their version wasn't lubricant sensitive.

 

[Jim Allen]

Originally Posted By: Shannow
Jim, so they were completely over-run with no retardation ?

If so, take back my post.


I don't know that they are. That was speculation based on what Rick said about the racing decel scenario. I've never seen either the Wesimann or the Kaiser in person nor know anyone that's ever used one.

I just dug out the Warn file to refresh my memory. The Warn was mainly going to going to be used as a center diff in a transfer case to be called "Autotrac." They used an IH TC-143 single speed t-case to fit a test center diff. Later, they designed one to replace the clutch based center diff in the old BW1339 Quadratrac. Some of the first dates in the folder are 1973 but one of the last is a letter from Warn to Jeep that says in part, "The demonstration of the Warn four-wheel drive systems with a manual transmission was disappointing to say the least, and leads us to the inevitable conclusion that such a marriage cannot be." On paper says the designs of the ramps and rollers were derived from Warns Lock-O-Matic automatic locking hubs. There is one hand drawn concept of an Autotrac in an axle.

 

[MolaKule]

Quote:
so what sort of characteristics does the brains trust reckon the fluid needs for proper operation ?


Just as a wag, I would think you would need a fluid with a specific "traction" coefficient.

The only way to determine the coefficient would be to test various lube formulations in an FZG and or a SAE 3 rig.

 

[tdi-rick]

Originally Posted By: MolaKule
Quote:
so what sort of characteristics does the brains trust reckon the fluid needs for proper operation ?


Just as a wag, I would think you would need a fluid with a specific "traction" coefficient.

The only way to determine the coefficient would be to test various lube formulations in an FZG and or a SAE 3 rig.


Cheers, so not exactly straight forward for the 'backyarder'

Just been doing a little reading on the FZG and SAE#2 tests...

 

[tdi-rick]

Just found a reference from the mid nineties that suggests an xW-90 non FM'd oil with 10% Lubrizol Anglamol 99 is the trick combination.
Swepco's old #101 gear oil was also cited (the closest I can find is Swepco 201)

Mola, any idea of the characteristics and why it would work ?
Anglamol 99 looks like a standard and complete hypoid gear oil additive package, I wonder what made it so special ?