Detroit TruTrack Torque Biasing Diffs
I've got trutrac (torsen) torque biasing diffs
front and rear on my 2 Door Range Rover.
The reasons for this are that I kept smashing
normal diff centers, and that I got good prices on the trutracs as opposed to
ARBs or anything else.
I fitted one to the front first, and then to the
rear. I avoided an auto locker at the rear as I was [it would seem
unjustifiably] worried about the self locking thing.
A few opinions from me;
On a permanent 4WD vehicle, a
trutrac on the front *does* very definitely and for the worse affect the
handling of the vehicle on tarmac. You get torque steer dependent on the
amount of gas you give it and the degree of turn on the wheel, and the direction
of torque steer reverses if you reverse the power flow through the
transmission. The front tyres must be close on identically worn in order
to prevent pulling. The suspension bushes must be in excellent
condition. The effect is very annoying but you get used to it.
The trutrac on the rear is
undetectable in on-road driving. When the thing engages or disengages is not an
issue as it is permanently engaged... it is the degree of engagement that
makes a difference, and it behaves very predictably. No nasty habits.
I used to occasionally spin a wheel
when pulling away around corners on wet tar, and be able to get wheel spin at the
lights if I was really going for it. I can't do that any more, and I have
really been trying (for testing purposes of course...).
Stability and drive on dirt roads is
much better than with open diffs. Less tendency to drift and almost as
stable with the centre diff unlocked as with the centre diff locked [dirt road
aficionados with Range Rovers should understand what I mean]. With centre
diff locked it is incredibly stable when compared to an open diff vehicle.
Tight corners taken at speed under
power are a joy, and the tendency for the front end to wander if the corner is
corrugated is reduced. I fully understand why rally drivers prefer these.
Off the road it is still fun to be
able to get stuck with one wheel of each axle in the air. If you don't get
a wheel off the ground, it is *very* difficult to get just one wheel of an axle
spinning. This is particularly noticeable when ascending loose slopes;
other vehicles get halfway up, sit and spin opposite wheels. Rangie climbs
the slope with all 4 wheels scrabbling. Descending slopes is also more
pleasurable - I've often experienced a few meters of mad slide when descending
under engine braking alone and losing traction on a front and rear wheel, easily
mopped up with the brakes, but it doesn't try to break away in the first place
with the trutracs installed.
The torque biasing on a trutrac
appears far greater in reverse than forward. This is why the fronts and
rears are not interchangeable, and why my car likes to reverse out of obstacles
even when it looks totally hopeless.
You can pull the vehicle through an obstacle with
only one wheel on the ground by using compensation braking. Maybe that should be
compensation breaking. I'm up to 4 half shafts and 2 cv joints, broken,
due to operator error. You can stand on the brakes and give it lots of
foot in 1st or reverse low range but something is going to break. Namely
half shafts and CV joints. The trutracs will put the torque where it is
needed but only until something self destructs. Those CV joints are very,
Trutracs are *not* diff locks. I haven't
managed to break any transmission bits when not using the brakes yet.
Following on from that, I can testify that
trutracs are very strong things. I've sat spinning wheels and generally
giving them abuse that would have finished off a normal diff in short
order. I've had them out a few times (replacing half shafts...) and there
is no sign of wear, metal pieces or anything else. I would reckon on
the pinion off before breaking one.
The best bit. Sand. This is where
they really perform. It's not a lock, so it doesn't affect your
directional abilities, but it gives all four wheels power most of the time
whilst allowing them to find their own speed. It doesn't mean you can go
up dunes any easier, but it makes the whole experience a lot more controlled and
there aren't usually any rooster-tails as you get stuck - all 4 wheels just dig
and go down like a diff locked vehicle. The effect is so good that you
don't really notice anything, but you get a sense of how much more easily
everything seems to be happening.
- Andy Grafton