Limited Slip & Traction Control

[Bill Lalk]

I have an 04' with traction control. Is the TC 4 wheel? Because if it is - and I think it is seeing that I see 2 rear brake lines heading up front - how can that work with a posi or LS differential? My mechanic is telling me that my diff is an open end otherwise the 2 rears would lock together on forward spin which is impossible on 4 wheel TC. Any ideas??

[BODYMAN]

????? What are you saying

[SC Cheesehead]

I have an 04' with traction control. Is the TC 4 wheel? Because if it is - and I think it is seeing that I see 2 rear brake lines heading up front - how can that work with a posi or LS differential? My mechanic is telling me that my diff is an open end otherwise the 2 rears would lock together on forward spin which is impossible on 4 wheel TC. Any ideas??

Your mechanic is wrong.

IIRC, the T/C senses variance in wheel speeds, and will apply brake pressure to the slipping wheels accordingly.

That's why you've got to shut the T/C off on 300Bs and '04s when you run the same size tires on all four corners. Without the correct stagger, the T/C senses the front tires aren't rotating as fast as they should (i.e., thinks they're slipping) and applies brake pressure to the rear to compensate. Ask me how I know...

[ctrlraven]

Your mechanic is wrong.

IIRC, the T/C senses variance in wheel speeds, and will apply brake pressure to the slipping wheels accordingly.

That's why you've got to shut the T/C off on 300Bs and '04s when you run the same size tires on all four corners. Without the correct stagger, the T/C senses the front tires aren't rotating as fast as they should (i.e., thinks they're slipping) and applies brake pressure to the rear to compensate. Ask me how I know...
Yep, happened to me quite often until I finally got the pattern down of T/C is turned off before I even get out of Park. lol

[GetMeMyStogie]

You seem to be confusing ABS (anti-lock braking system) with traction control. These are two separate functions, though they are both performed by the vehicles braking system.

ABS acts on all 4 corners to keep the wheels from locking up whent the brakes are applied. Under heavy braking which would normally cause the wheels to lock up and slide across the ground (a skid), the braking system actually reduces pressure to the wheel(s) that are locking up.

Otoh, traction control acts only on the drive wheels to limit their spinning under acceleration. When accelerating beyond the threshold of the tires traction on the ground, the braking pressure is actually increased to slow the spinning wheel(s) down.

Without traction control, a rear-drive vehicle with an LSD would spin both tires when there isn't enough traction. If you add traction control, then both wheels would be prevented from spinning pretty much equally.

Traction control is an active system that uses the brakes to limit how much a wheel can spin, so it works well with an open-diff too, since the spinning wheel can be slowed and power applied to the one with more traction. An LSD is a passive system which accomplishes more-or-less the same thing, but with different side-effects.


Hopefully that helps.

[SC Cheesehead]

Stogie,

Excellent explaination.

I guess I would add that the sensors detect a "spinning" condition by a comparative check of rotating speeds between wheels, and the MM front/rear tire stagger fits into the algorithm. Thus, with a T/C car and the same size tires all the way around, the faster you go, the more the car thinks the rear tires are spinning, and the more brake pressure is applied.

First time it happened to me, it was like :eek:! Nailed the throttle going on a merge ramp on the interstate, and the more I pushed on the gas, the slower the car went. Not good. :cool: