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TRAC/ALSD Correlation to all tires?

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Old 11-10-2010, 09:31 PM   #1
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TRAC/ALSD Correlation to all tires?

First off, I am so sorry to be asking yet another question about the TRAC/ALSD/etc. It probably is a dumb question, but I figured it dumber to not ask.
I understand when the truck is in 2HI, the TRAC tries to keep the tires from spinning at different rates via braking, but also regulates power from the engine. ALSD does this same thing but with unregulated power when the VSC Off button is pressed. When the truck is in 4HI, the base mode is TRAC which is actually ALSD (unregulated power!). (Assuming this is correct, I'll keep moving along.)

My question is this; starting with the TRAC in 2HI, does the system try to keep all 4 wheels spinning at the same rate? Or is this only happen with the rear two wheels while in 2HI? Same thing with ALSD, all four or just the two "with power"? This would essentially act as though a LSD was in Diff C in my awesome drawing, but everything else is open diffs.
Then would 4HI act as though all four tires are at the same speed (a pretend LSD is at Diff A to keep the front two wheels together, LSD at Diff C to keep rear wheels spinning together, and LSD at Diff B to keep the front and back spinning at the same rate)? Or does the system act where a LSD is replacing Diff A and Diff C, but they are independent of each other? If the case is the latter, does the system suck when both the front wheels or both the back are on, let us say, ice?

The reason for this question is that the other day I spun my rear tires while in 2HI on an icy corner, but no light say "TRAC being used!!!" came on which, to my understanding, should have. So if both rear tires slip, but spin at the same speed, I could see my predicament the other day. But I want to know now if the same thing would have happened in 4HI. If Diff A and Diff C are uncoupled, it seems like the same thing could have because the rear tires were spinning evenly and the front tires were spinning evenly.

I would go out and try it but it was on a busy intersection and the roads are all pretty well cleared up now. I hope I am clear enough to get someone to explain it to me, but if not just shout! Thanks!
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Old 11-10-2010, 09:36 PM   #2
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The system works by reading the difference in wheel speed between the two tires on the same axle not the speed between the front and rear axle. SO lets say you are in 4wd high and you gun it causing all 4 wheel to spin at the same speed then there will be no traction aid. Also in your diagram it shows the T case as a diff when it isn't.
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Old 11-10-2010, 09:39 PM   #3
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Ok, so even in 4 wheel drive the front and rear axles are completely independent of each other? How does power get distributed when in 4HI (or LO)? If it is the path of least resistance than it would all go to the rear wheels when it's on ice, correct? And the TRAC(ALSD) only keeps symmetry between the left and right wheels in the rear?
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Old 11-10-2010, 09:41 PM   #4
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Quote:
Originally Posted by claw View Post
Ok, so even in 4 wheel drive the front and rear axles are completely independent of each other? How does power get distributed when in 4HI (or LO)? If it is the path of least resistance than it would all go to the rear wheels when it's on ice, correct? And the TRAC(ALSD) only keeps symmetry between the left and right wheels in the rear?
When you lock into 4wd power is split 50/50 at all times between the axles because there is no center diff. You can't spin one front tire and independently from one rear tire. The system keeps symmetry at the rear axle only when in 2wd and the front axle and rear axle separately front each other when in 4wd.

Edit: When you lock the rear diff then the system only works on the front wheels since the rear is locked together.
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Old 11-10-2010, 09:51 PM   #5
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Thanks Whippersnapper! That's what I wanted to know. Also, that link in your signature is quite useful! It breaks down a lot of the details pretty simply.
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Old 11-10-2010, 09:53 PM   #6
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Quote:
Originally Posted by claw View Post
Ok, so even in 4 wheel drive the front and rear axles are completely independent of each other? How does power get distributed when in 4HI (or LO)? If it is the path of least resistance than it would all go to the rear wheels when it's on ice, correct? And the TRAC(ALSD) only keeps symmetry between the left and right wheels in the rear?
The differentials are open (except if you lock the rear, naturally). Open differentails allow steering (important feature) as left and right tires rotate at different speed when turning.

TRAC 2WD/ALSD 2WD/TRAC 4WD are traction aids that limit the differentials action of allowing one tire to spin much faster than the other by braking the faster spinning tire and (in TRAC 2WD) regulating engine output. By slowing the loose, faster spinning tire, you increase torque to the slower or stopped tire that has more traction. This helps you to move forward.

There is NO TRAC LIGHT that comes on when it is doing this.
There is, however, a VSC blinking light and beeper that alerts you when you are driving crazy or the VSC is working to keep you on course and prevent you from spinning out-of-control. VSC and TRAC both use the ABS brake system.

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Old 11-11-2010, 10:04 AM   #7
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Thanks David, from what I had heard others say and read on other posts I thought that the light (car with squiggles behind it) would come on anytime the TRAC came into play, not when the VSC kicked in. In that case, it would make sense that I had one wheel slipping and the other finally got power and pulled me over the ice. Very cool.

Thanks for everyone's help.
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Old 11-11-2010, 02:36 PM   #8
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My pleasure Claw!

I came here almost a year ago to learn what these new traction controls were and how they worked (the dealer couldn't explain them, and the owner's manual was way weak)... The guys here helped me back then, and now I am paying back by helping others learn how they work... as I have field tested them a lot... and am continually amazed by A-TRAC (and TRAC, etc.)... When others put it down, I know they either don't have it or don't know how it works... If they did, the spending of thousands of dollars for front (or rear) locking differentials could go into other mods, IMO.

I no longer fear going alone into rediculous places with the A-TRAC. With just one tire having traction (even a front tire facing uphill), the A-TRAC can pull the truck out. TRAC in H4 is very good too.. way way improved over the pre-'09 Tacomas (I had two).
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