I have a 1961 IH 3/4 ton crew cab with lockers in both front and rear. This truck is outstanding in the mud, virtually unstoppable, but the effect of having a locker in the front is very noticable when making sharp turns in 4wd, I have manual only steering (old military truck) and the steering wheel can and will jerk violently depending on how sharp the turn and how much power is applied- it still has the old BD six. This can be reduced a LOT with a steering damper and PS. Thumbs OUT of the steering wheel spokes please.
I would not trade this setup for anything else, but as mentioned before the driver has to understand the way lockers work and apply power accordingly. You wouldn't want to be in an all weight on one wheel situation and apply too much power without knowing you can twist or snap an axle- by the way-not the end of the world with a full floating axle since you can still drive on one, and the fix is easy...at least on the old trucks.

 

First - let me apoligize in advance for this long post. I hope it makes sense. Differentials are a confusing thing for sure.

I'd like to add a little bit to the theory behind the torsen type LSD in the 3rd gen's. It works on torque biasing. Its function is to apply more torque to the wheel that is going slower than to the wheel that is spinning faster. It does this by multiplying the torque from the faster spinning wheel. The bias ratio from what I have read is usually between 2 and 4 (depending on the specific differential unit).

So - how can you have one wheel spinning and go no where? Because the torque that is multiplied is the torque in the faster spinning tire. So - lets pick an extreme case - one tire on the ground, one free spinning in the air. The free spinning one has ZERO torque (at a steady speed). So the LSD can multiply that by lets say 4 times, and apply to the tire on the ground. But - 4 times zero is still zero so you don't move. Perhaps an even simpler way to view it is force to the road (which is proportional to torque). Lets say one tire is on ice, and the other on pavement. The tire on the ice spins easily, and lets say provides 100lbs of fwd force on the vehicle. The LSD multiplies that by 4 and puts 400lbs to the pavement tire. Now you've got 500lbs pushing the rig, but maybe it takes 800 to move it - and there you go - stuck spinning one tire.

Why does the ebrake help? Think of the ice situation. The ice provided 100lbs force, and now if you put the ebrake on you might add 500lbs resistance to both tires. So the net on the ice side is 600lbs force that the diff sees. So the tire on the pavement gets 600x4 = 2400 lbs to the axle - of which you have to subtract the brake drag which is 500 - so 1900 lbs pushing the vehicle! Wallah - you are now driving away (maybe).

Keep in mind - with an open differential - the brake technique does NOTHING - because the torque bias on an open diff is 1:1. Also - applying the foot brake would seem to be a bad idea as the monster front brakes being applied at the same time would surely keep you stopped. You end up with one tire trying to push 4 brakes.

So to summarize - a torque biasing diff can only only mulitply the amount of traction that the fast spinnig tire has. If it has zero (or very little) traction, the other tire can only get a multiple of very little.

Mathew

 

Mathew's explanation although it sounds accurate is a good example why simple is better. The good lockers like a Detroit will just work, no mumbo jumbo required and they will hold up to a tremenous amount of abuse.
I'm much more willing to put up with some poor manners in some situations to have a super reliable traction device that I don't have to drag my brakes etc. to get it to do it's intended job. To each their own. For me it's K.I.S.S.

 

tapping, pressing or flat smashing the brake doesn't help my 06' Dulley.

 

I was having a hard time when I first got my rig. The secret is don't apply the brake pedal but use the E-BRAKE. A couple of cliks is all it takes, try it to get the hang of it. With our tremendous torque the e-brake won't hold to truck when in gear. Give a try sometime you might be surprised!

 

I'll go try it in just a few minutes.......

 

To Matthew
I know a person who has a H1, which has the Torsen L/S differentials. He insisted that it would pull itself free if he jacked up 3 wheels in the air. I did not believe him because of the torque bias that you so well described. I called a tech rep for Bummers and he said the H1 will pull itself off. I have Dana Power Loks f&r, so for grins, I jacked up 3 wheels, and sure enough, the one remaining wheel, the front, pulled me free. I know that goes against what you described, and I know that you are correct, but I still pulled myself free.

 

Hmmm - very ineresting Baja ....

I believe the latest H1's apply selective brakes (i.e. LH front only) when a tire spins? Perhaps this is what your friends has and what the tech described? This is a high tech but very effective way to keep a wheel driving, especially with a torsen diff. Its getting to be more common on passenger cars with more advanced traction control.

The powerlocks have preloaded clutch packs so you will get at least the preload force when one wheel is off the ground, which might be enough. When you say pull free with 3 wheels off the ground, how much pull? Just enough to tip over jacks?

I certainly do not claim to be an expert - just an engineer that finds the various kinds of diffs and approaches interesting. On my dodge - just an open diff! If I go off road very far its on a motorcycle .

Mathew

 

This is a older H1, 2003 or so, I am not sure. He got it used. I do not remember if the rep talked about brakes or not. I stacked up 4x4's about 24" long lengthwise to hold up the truck during my test. The front wheel spun. I have a woodshop, wood is easy, and I did not want to ruin the jacks as they tipped over. I bought the power locs because they have a very high bias ratio, which can be increased by rearranging the clutch pack. If I am correct, the Bummer Torsens have a ratio of 5.2/1, 6 being their highest bias. I am like you, no engineer, I just find differentials interesting.

 

The AAM LS diff is a Torsen style but is apparantly not set up quite as agressively as some.
The best way to look at it is to think of the diff as trying to lock the two axles together. It won't really "lock" them but it will add friction between them. And it adds more friction when there is a greater load. The "friction" makes it harder and harder for the axles to spin at different speeds based on torque. It does not multiply the spinning wheels torque, it only tries to lock the two axles together based on how much torque is coming in through the driveshaft.
A fast spinning wheel that has little or no traction is transferring little or no torque. If you load that wheel up with the parking brake or by adding more weight or getting on a better surface, then more torque is transferred to the non spinning wheel. Remember spinning speed has nothing to do with torque. These diffs respond to torque.
Torsen diffs have no clutches. It's based on binding gears. Like trying to put power through a worm gear. In a worm gear system the worm can turn the bull but the bull can't turn the worm. A very cool design! They are agressive enough for normal use but not for extreme rock climbing.

Wetspirit

 

Man

all i know is that my rear diff, is really good, i can stomp on it and both tires spin equally, the front diff is really good as well and i know with my posi lock it locks and works awesome! Ive been in rim deep mud before and made it out, but man did the truck need persuasion... and being nose heavy helps none either..

Tx

 

Went to a buddies house last night. One side of his driveway is really steep....and that's where I parked, where I parked 50 times before in the GM. I go to leave and backing up the "big O'le Dulley" just couldn't make it! There I was peg-legged in the driveway, stuck on dry concrete in reverse. I tried a rolling start on this flat incline and that didn't work so I had to use 4x4 mode just to get out of a concrete driveway.



Is there anyway to make this rear "LOCK"..... electronic or otherwise, any way at all.

 

The only way you can make the rear wheels "lock" or otherwise, is to change the diff. I know the feeling, I was in 4wd in my old '62 chev suburban, with open diffs on a ice covered road. I could not get going at all, as this caddie with chains on was honking at me.

 

You're tell'n me that everyone here with an AAM axel is pretty much stuck and there is not solution other than an axel or guts swap? .......

 

I pulled the following from another board, not really a great explanation of the operation of the trac-rite, but does explain some of the problems we have with them. You've been told right Burner; for now, those of us with the AAM axles are pooched, though I hear Eaton is working on an air locker for us. I backed an empty 28' G/N cattle trailer through a pretty nasty mudhole the other day, and when the going got tough, I just gave the parking brake a couple of clicks, like N.Johnson said, and both rears started digging and away we went in 2wd. Play with it a little, I think you'll be surprised once you find the sweet spot.


Josh


The following is a S.T.A.R. Center Case Report:
Report created Jan 6 2004
Updated Jan 13 2004

Customer says his trac-rite rear diff is not working?
GCK1: 01/06/2004
Recommendation/Solution
Review AAM Trac-rite diff characteristics. Rear diff is working or truck wouldn't move. It will overrun like standard diff if operating on extreme differernces in surfaces. (Ice under one rear tire with other tire on dry pavement.) No further action.
:GCKI:01/06/2004
The 2003 heavey-duty Ram uses and American Axle helical differential or Trac-Rite. The Trac_Rite differential is different then Trac-Lok in that it uses helical gears (Trac-Lok uses clutches) to transfer power to the opposite wheel when slippage occurs. The transfer of power from wheel to wheel is torque sensitive and must have both wheels spinning (not stationary) to function. It is possible for the Trac-Rite differential to not send power to a wheel if is not spinning. Example: Accelerating from as stop and one wheel is on ice and the other on dry pavement. If accelerating to fast, the wheel on the ice may spin and never send power to the whell on the pavement side. A slower start may be necessary to start the vehicles momentum.
A written test procedure for Trac-Rite is not listed in the repair manual and the following points should be noted:
Testing the Trac-Rite differential while the vehicle is lifted and turning one wheel by hand, the opposite wheel will turn in the opposite direction. This is normal.
If the Trac-Rite assembly has and internal failure it will lock axles 100% side to side.
To test the Trac-Rite process, raise vehicle on appropriate lift, place into gear and accelerate quickly (hard launch). A second technician will witness both wheels turning at the same speed at the start of the acceleration.
Another test for Trac-Rite is to slowly drive vehicle in an open area and completely turn wheels to one direction and accelerate hard.. The vehicle will experience tire hop or shudder. This is normal. Trac-Rite differentials do not require friction modifier and should be used only with SAE75W-90 GL-5 synthetic fluid PN 05102232AA.
The Trac-Rite differential found in the American Axles may look like the helical gears have ground away the case. Six small half circles are noticable on the side of the differential opposite of the ring gear. These openings are desinged for oil flow and are not the result of the helical gears grinding through the differential. Please do not replace the differential case or any other part of the axle due to these openings.
Note: All American Axles require Mopar lube part# 05102232AA synthetic and does not use a friction modifier.
RAB40: 01/13/2004




Looks like both rear wheels must be rotating for it to operate properly , so not much help starting out on a slippery surface in 2WD.

Nothing like the old positraction with clutches the way I read it.