ATRAC engagement with activated lockers

[Dobie]

I have been reading about others blowing their differentials while attempting to wheel over obstacles. From what I can recollect is that it happens when the vehicle has little traction and bouncing up and down making contact with the surface. I can understand why this would happen with ATRAC due to ATRAC time to detect slippage and then activating.

While out in Hollister yesterday I went up this stretch of trail which was steep with ledges and very loose quartz type rock. Had this been granite it would have been easy to go up; however the quartz made the truck work.

I locked both the front and rear lockers and started crawler up the hill. I reached this ledge and my front tires were losing traction. I noticed the green dash TRAC light illuminate and could hear it working. The truck started bouncing up and down all while the front locker was activated. I was wasn't really going anywhere at this point except side to side. I applied left foot brake and throttle and the ATRAC shut off and the truck again crawled effortlessly.

So my question now is: Why did ATRAC activate if the truck was locked front, center and rear? I don't fully understand ATRAC and was hoping some of you could help?

 

[sonk76]

any chance that one of the lockers did not engage even though the switch was set in the cabin? that could explain what you are seeing. Otherwise, I too am very puzzled.

 

[Dobie]

I will go out and test. That was my only explanation too, but every time I engage the front locker I get the steering bind indicating to me that it is locked. Is there any there way to verify the locker is engaging?

 

[Dobie]

They both seem to be working. There is definitely a bind when I lock the front. When I make slight steering movement (30 degree turns) the wheel violent wants to track straight if I let it go.

 

[hoser]

CDL not engaged?

 

[Dobie]

I thought it was engaged but now I'm questioning that. I know the front and rears were for a fact.

 

[RobRed]

CDL not engaged?

Good point. When Dobie asked me yesterday it didn't occur to me because I was angry about not being able to climb a hill in my ATRAC only rig!

I would think that the system would detect a torque difference in front to rear axles and possible engage if the CD wasn't locked.

 

[liveoak]

is there no way to disable atrac? if you have front and rear lockers and the atrac still comes on sometimes it seems like you could damage something. the atrac applies braking to one side so the wheel with traction will turn. if you have a locker the atrac will try and stop the entire axle(because it's locked) while you are pressing on the gas pedal. i would bet the truck would start bouncing if the brakes are being applied to the front axle while you are accelerating. i'm sure this has been discussed here before and i may not know what i'm even talking about, it just seems to me like you need to add a relay or something that disables the atrac when you engage the lockers.

 

[RobRed]

I thought it was engaged but now I'm questioning that. I know the front and rears were for a fact.

I got this figured out....

One of the ABS sensors was fouled with mud so it looked like one wheel was not turning at the same speed and fooled ATRAC into engaging.

Don't panic it's all good.

Sent from my iPad 2 using IH8MUD

 

[Dobie]

I hate mud

Very well could have been the case too. Thanks Rob.



But more on tech...is the stress I placed on the front end weaken it like break it down so to speak or should I be glad nothing happened and forget about it.

 

[RobRed]

I hate mud

Very well could have been the case too. Thanks Rob.

But more on tech...is the stress I placed on the front end weaken it like break it down so to speak or should I be glad nothing happened and forget about it.

The ARB setup is pretty stout. I'd say you are a-ok.

Sent from my iPad 2 using IH8MUD

 

[Mxndrnks]

What hill at Hollister? You guys need to organize some actual trail runs. I'd highly recommend you guys do the Barney Riley if you have never done it. And take the old jeep trail out. Nice and tight.....

 

[RobRed]

We use Hollister to practice skills. One of the advantages to that park is that the surface is constantly changing. We have a number of things on the drawing board for late summer including a death valley run in the fall - we'd love to have you along.

The hill Dobie refers to where he had ATRAC pop on is the upper Rock Quarry that parallels Fremontia Road to the north west.

Here is a screen grab from the mid-section, before it gets narrow and steeper. This section is about 25* incline.

 

[hoser]

I thought it was engaged but now I'm questioning that. I know the front and rears were for a fact.

I always notice when a light comes on the dash. But I won't always notice if the CDL light is NOT on. And I can't really foresee why one would want to lock the front and rear and not the center diff. It would be nice for a "check light" or maybe buzzer to come on if you engage the front diff without the center diff locked.

A friend in his '03 100 was attempting a sand dune climb with his F/R lockers engaged but CDL unlocked and it kept bogging down. After several attempts, he realized his CDL was not engaged. Tried it again and sure enough, made it.

 

[RobRed]

I always notice when a light comes on the dash. But I won't always notice if the CDL light is NOT on. And I can't really foresee why one would want to lock the front and rear and not the center diff. It would be nice for a "check light" or maybe buzzer to come on if you engage the front diff without the center diff locked.

A friend in his '03 100 was attempting a sand dune climb with his F/R lockers engaged but CDL unlocked and it kept bogging down. After several attempts, he realized his CDL was not engaged. Tried it again and sure enough, made it.

Without CDL your sending all the torque to the axle set that is spinning (open diff). With CDL you get 50% front and rear. Triple locked you get 25% to each wheel. Even with 3 wheels spinning 25% is usually enough to get you going.

Sent from my iPad 2 using IH8MUD

 

[AimCOtaco]

If the truck is not getting an ABS signal from one wheel does that not disable both ATRAC, ABS, and light up the warning lights? It should!

My bet is cdl was not locked and the truck was trying to stop the front from the perceived spin out.

 

[RobRed]

If the truck is not getting an ABS signal from one wheel does that not disable both ATRAC, ABS, and light up the warning lights? It should!

My bet is cdl was not locked and the truck was trying to stop the front from the perceived spin out.

Not exactly... have a glob of mud occluding the abs sensor would tell the ABS/VSC/TRAC ECU that one wheel was stuck while the opposite sensor would see a wheel spinning (moving)... The exact circumstance that ATRAC looks for.

Bottom line is we wont know for sure but based on conditions and what I know about ATRAC - my answer is the most plausible. But there is always room for other opinions.

 

[AimCOtaco]

So was ATRAC freaking out from the mud hole onward? If it saw 1 wheel stopped and 3 spinning should't it have started atracking then?
It should have been engaging the ABS every time he touched the brakes as well (to free the locked wheel).

Test your theory if you can. I have lockers but no atrac.

 

[RobRed]

As I said there is no proof - only a theory. There was so much residual mud on Dobies truck that the offending piece may have shaken loose, flung from a wheel or just been borderline until it happened. Remember when you are in low and locked the VSC and ABS are off.

 

[jOnathN]

Is it possible for mud to block the abs sensor? I am pretty sure they are Hall sensors (magnetic) so mud should be no trouble.