The Torsen in the Hummer
Sent: Friday, March 16, 2001 1:47 PM
Edited / updated by Chuck Kopelson April 5, 2007
The White Paper above was brought to my attention in February of 2007 by a reader which contradicts the reason AM General gave for going from the T1 to the T2. AM General said that the T1 differential with the high bias ratio interfered with the new ABS which was mandated in the 1999 and newer trucks. The white paper says the following:
In braking situations where little or no torque is being conveyed by the differential, a four to one apportionment of torque between drive axles amounts to little or no torque difference between drive axles. Thus, the Torsen differential will not support any appreciable torque 'wind-up' between drive axles during braking and so does not interfere with the operation of anti-lock braking systems.
Could the reason have to do with the TT4 traction control system?
What's Missing ?
I own a 2000 AM General Hummer and am trying to figure out the difference between my differential and the ones in the 1992 to 1998 Hummers. I am unhappy with the TT4 traction control system and planning on removing it. From what others have told me, the T1 in the 1992 to 1998 trucks works better off road. I am debating about whether to install the T1 or install ARB air lockers. Could you tell me how you believe your T1 product to compare to a locking differential? I am leaning towards installing the T1 because it used to come standard. For a brief time AMG offered the T1 in the front axle with a Detroit locker in the rear as an option. What setup do you believe will provide me with the best traction solution?
To really answer your question, you have to consider how your vehicle will be used. A T1 differential is a limited slip with a high torque bias ratio (the diff's lock up rating). A locking diff is either open or locked. With a Torsen, you will never keep a wheel with absolutely no traction (i.e. in the air) from spinning up without using brake modulation techniques. A locker can do this for you. However, lockers compromise low-speed maneuverability. By being locked, they try to prevent turn-in, trying to force the vehicle straight ahead. Here, a Torsen will differentiate freely, and allow (in some cases enhance) maneuvering. The difference can be significant in an off-road environment.
Of course, the ARB can be turned off, but then you have just open differentials, which gives nothing. With the air lockers, you also have to install the compressor, air lines, etc. Running air lines to your axles adds something lower to the ground that could be vulnerable to damage. Really, with this type of vehicle, adding more complex systems also adds more risk of system failures, and the Torsen is simple and pretty bulletproof.
Obviously, I'm going to have a bias toward using the Torsen, and that would be my recommendation if the vehicle is to be used for primarily commercial purposes. However, the locker does have its advantages, and if you are an avid off-roader and you do a lot of serious rock climbing, then maybe that's worth serious consideration. Just the same, if it were me, I'd learn how and when to brake modulate and the Torsen, as it is a much more "well rounded" performer, whereas the locker is really only good for one thing. The Torsen can do 90-95% of what a locker can do off road, and with careful brake modulating, is just as effective.
We recently worked with a desert race team (running a Ford pickup), and for their purposes, they found that using Torsen's in the front and rear was actually better then using the locker set up they previously had. Ultimately, it's up to you to figure what best suits your needs, but generally, I'd say the Torsen T1 is very good off road and much more flexible then a locker.
What TBR (torque bias ratio) would you recommend for a T1? Does a higher ratio mean better traction? Can you tell me the TBR that is used in the T1 (for the 1992-1998 Hummers) and the T2 (1999-2001 Hummers)? I have looked at the online diagrams of the T1 and T2 and they appear to be quite different. Can I just change some of the parts, or do I have to switch the entire T2 to a T1? Could you please explain the differences between the T1 and T2? Thanx.
The TBR (torque bias ratio) of the Hummer T1 is about 4.5:1, which is actually quite high. The higher the number, the more locking effect the diff has. Basically, the TBR is a ratio that represents how much torque difference, or imbalance, the the diff will support while remaining locked. For example, with a 4.5:1 TBR, you can have 100 units of torque on one axle shaft, and up to 450 units on the other before the differential will unlock and begin to differentiate. This torque on the axles would be from the torque between your tires and the ground. As you can see, this torque is directly related to how slippery the ground is. What this all means is that the ground can be 4.5 times slipperier on one side vs. the other, and the Torsen will still stay locked, and not allow wheel spin to occur. To go to the extreme end of the TBR scale, a locker would effectively be infinity:1. Conversely, the TBR of the T2 in the current TT4 equipped trucks is about 1.7:1. This is real low, and was done so because that was AMG's requirement (for the ABS).
The key difference between T1 and T2 is the gearing arrangement. The gears which connect the side gears (axle shaft gears) together and to the housing - called element gears - in a T1 are perpendicular to the axis of the differential. These are almost like worm gears, and generate very high friction when operating. This is the primary reason why a T1 TBR is much higher then a T2's. The T2 element gears are parallel to the axis of the differential, and are more conventional helical gears, with lower friction generated during operation. Because of the differences between the 2 designs, there is no interchange of gearing or other internal parts.