ATRAC effectiveness - Take Two

[ShottsUZJ100]

Thanks for sharing that video. I'm excited to finally see another video of ATRAC where the system does not seem to be able to apply quite enough torque to the tire with more traction to get it to spin. This makes me feel a little more comfortable in that my ATRAC system may not be "broken" after all, but rather that I'm simply reaching the limits of the system.

I'm going to keep on diagnosing it.

I'm planning on going out to Rausch Creek again on Saturday April 24th, in case anyone with a 100 can make it at the same time. Would love to do some side-by-side comparisons to draw more definitive conclusions (I'm holding out hope that one of these days I'll end up wheeling with another 100 yet--so far it's 95% jeeps out there...)

That's not what I said in that post. It wouldn't surprise me if I wasn't clear.

My video shows the system is swapping power to the opposing wheels. Your video does not show such a thing. Your DS rear was in loose dirt. IF the system shifted power to it you'd see it move and throw dirt. That's why I bet your PS rear was spinning 24/7 (unlike my spinning wheels that would stop and go).

 

[sonk76]

That's not what I said in that post. It wouldn't surprise me if I wasn't clear.

My video shows the system is swapping power to the opposing wheels. Your video does not show such a thing. Your DS rear was in loose dirt. IF the system shifted power to it you'd see it move and throw dirt. That's why I bet your PS rear was spinning 24/7 (unlike my spinning wheels that would stop and go).

This is a good observation. You're right that it's not exactly an apples-to-apples situation because in my case the engine was held at a constant RPM (somewhere between 1,500 - 2,000). In your example (assuming that the center differential was locked), the engine RPM may not be constant; I'm inferring this from the fact that I see your drivers side rear tire vary in speed, while the passenger side tire remains relatively stationary--the only way this can happen is that the driveshaft driving the rear tires actually varies it's speed in lockstep with the drivers side rear tire, and since the driveshaft is locked to the engine rotation through the locked CDL, the engine RPM's too would have been varying (unless the torque converter is slipping.) Unless I'm missing something?

Given this, it is difficult to tell in your situation whether or not we're observing here an inability of the ATRAC system to apply enough brake to the spinning tire OR if the system was limited by the engine power provided. My guess is that it is the latter, since the system appeared to be able to stop the drivers side rear tire from spinning completely without spinning the passenger side rear tire. Thus, if more power would have been provided it is possible that ATRAC in your situation could have gotten you moving again (unless you were simultaneously facing the "limit" of the ATRAC ability to apply braking power, which is the situation I believe that I have encountered in my experience.)

 

[sonk76]

notice John's DS rear wheel. It is not "free spinning", rather "jerking" as the ATRAC grabs and releases, sending pulses of dirt back. Is that what your PS rear wheel was doing?

No. My PS rear was spinning at a constant rate (which is the only thing it can do if the engine/rear-driveshaft is spinning at a constant rate while the DS rear is stationary.

This does not mean that the system was not "trying" to do it's thing (i.e., apply brakes the the spinning tire), it only means that it was not applying them hard enough to either slow down the driveline/engine or get the DS rear to spin...

As I mentioned in my reponse to John's post. The "jerking" in one tire, when it occurs without any movement in the other tire, can only happen if the driveshaft itself is "jerking" it's speed--not something one would expect with engine at constant RPM and non-slipping torque converter. And it my case the engine speed was kept constant.

Normally, when we keep the engine RPM constant and watch the ATRAC do it's thing, we can see the "jerking" in one tire correspond to changes in rotational speed of the opposing tire.

 

[sonk76]

I think I finally joined the YouTube world... Like your pictues, its steeper than it looks in the video. Understand that traction, tire pressure, blah blah blah is all different...

That looks great. Exactly how I woud love to see the system always perform! Thanks for posting the video. It's great to increase the data points.

 

[ShottsUZJ100]

In your example (assuming that the center differential was locked), the engine RPM may not be constant; I'm inferring this from the fact that I see your drivers side rear tire vary in speed, while the passenger side tire remains relatively stationary--the only way this can happen is that the driveshaft driving the rear tires actually varies it's speed in lockstep with the drivers side rear tire, and since the driveshaft is locked to the engine rotation through the locked CDL, the engine RPM's too would have been varying (unless the torque converter is slipping.) Unless I'm missing something?

Gas was constant in my example (and at two different RPM's). And the same thing occured in both examples.

Try not to get too techy as far a driveshafts go. In my situation my drive shaft was turning properly though traction effects it's speed. What happens is:

When the spinning wheel is spinning the shaft is turning easily.

When my TRAC transfers the torque to the wheel with traction the truck HOPS. It instantly slows the drive shaft and it's that JERK that makes TRAC send the power back to the slipping wheel. This transfer is why you see the dirt fling cycling and the truck hopping.

No. My PS rear was spinning at a constant rate (which is the only thing it can do if the engine/rear-driveshaft is spinning at a constant rate while the DS rear is stationary.

Normally, when we keep the engine RPM constant and watch the ATRAC do it's thing, we can see the "jerking" in one tire correspond to changes in rotational speed of the opposing tire.

Not the case. Your DS can spin freely when your slipping tire is slipping. Then, TRAC should step in and instantly stop the spin, move torque over (which causes a shock to the DS speed and therefore the JERK) to the other wheel. HOWEVER...if forward progress is not made then TRAC ships the power right back to the slipping one. We do not see this happening on your videos. We do on mine. BOTH your rear tires are in super soft dirt while my PS tire had excellent traction. BOTH your rear tires should be cycling back and forth clawing for traction (and slipping cause it's so soft) and they do not. The one seen never turns. Not right.

The jerking is simply that transfer of power because yes, you do shock that drivetrain/driveshaft for a split second when TRAC cycles. That's why the locker works better in my video. I could have used more gas and got out of there with TRAC. The hopping would have been not good for the driveline.

 

[sonk76]

...It instantly slows the drive shaft and it's that JERK that makes TRAC send the power back to the slipping wheel...

I think we agree on this point (i.e., in your situation the jerking of the tire would have caused the driveshaft to slow down). What I'm struggling to understand is how can the driveshaft vary it's speed if the engine (which is connected to drive shaft through locked differential) is spinning at a constant rate? Only thing I can come up with is that the torque converter must then be slipping to allow for this... What do you think?

Not the case. Your DS can spin freely when your slipping tire is slipping. Then, TRAC should step in and instantly stop the spin, move torque over (which causes a shock to the DS speed and therefore the JERK) to the other wheel. HOWEVER...if forward progress is not made then TRAC ships the power right back to the slipping one. We do not see this happening on your videos. We do on mine.

Sorry, I didn't quite follow this. Probably just me. As far as I know, only thing TRAC does is apply brakes to the tire that is spinning loose when it determines that this is not the desired outcome (i.e., tire speed relative to engine speed is too high, which is same as speed difference between two tires across open differential being too great)

BOTH your rear tires are in super soft dirt while my PS tire had excellent traction. BOTH your rear tires should be cycling back and forth clawing for traction (and slipping cause it's so soft) and they do not. The one seen never turns. Not right.

I realize that this is what it may have looked like from the video, but the fact was that the DS rear tire had reasonably good traction, and bulk of the weight of the truck leaning on it (steep incline, compounded with a slight lean to drivers side.) It looked to me that it would have taken considerable force to get that tire spinnning. You are right about the PS rear tire though, it had much less of the truck's weight on it and was spinning relatively easily. This was not loose sand, but rather packed dirt.

The jerking is simply that transfer of power because yes, you do shock that drivetrain/driveshaft for a split second when TRAC cycles. That's why the locker works better in my video. I could have used more gas and got out of there with TRAC. The hopping would have been not good for the driveline.

Agreed on all of the above (as long as we're using the words "transfer", and "power" loosely, since technically torque applied to both DS/PS tires is always equal across the open differentials we have, and power [as a measure of work] is a function of speed and torque--meaning that the non-spinning wheel never technically did any "work" and thus did not absorb any "power").

I'm guessing that the ever greater "jerking" and hopping forces involved in forcing ATRAC do it's thing in extreme situations can not be helpful to the driveline


Btw, in all of this, I hope I'm not sounding defensive in any way. I'm merely trying to improve my own understanding of how the systems work and ought to work, and I really appreciate all the input and thoughts everyone is sharing on this. I'm learning more all the time. Thanks!

 

[ShottsUZJ100]

I think we agree on this point (i.e., in your situation the jerking of the tire would have caused the driveshaft to slow down). What I'm struggling to understand is how can the driveshaft vary it's speed if the engine (which is connected to drive shaft through locked differential) is spinning at a constant rate? Only thing I can come up with is that the torque converter must then be slipping to allow for this... What do you think?

No slip TC. It shocks the drivetrain and therefore the jerk. It's like when you turn real fast while hitting a big bump in the corner...you're on the gas and the front wheel lifts from the ground then drops and hits the asphalt and WHAM! JERK AND CHIRP for a split second though the truck/driveline doesn't "stop". Good way to pop an axle though.

 

[ShottsUZJ100]

Sorry, I didn't quite follow this. Probably just me. As far as I know, only thing TRAC does is apply brakes to the tire that is spinning loose when it determines that this is not the desired outcome (i.e., tire speed relative to engine speed is too high, which is same as speed difference between two tires across open differential being too great)

The jerk only occurs because the rig does not move forward. ReGuard's truck doesn't jerk because all the wheels getting power have traction...he keeps moving.

 

[ShottsUZJ100]

Btw, in all of this, I hope I'm not sounding defensive in any way. I'm merely trying to improve my own understanding of how the systems work and ought to work, and I really appreciate all the input and thoughts everyone is sharing on this. I'm learning more all the time. Thanks!

Oh, me neither! Videos vs real life vs web-writing...can get confusing!

 

[re_guderian]

No. My PS rear was spinning at a constant rate (which is the only thing it can do if the engine/rear-driveshaft is spinning at a constant rate while the DS rear is stationary.

This does not mean that the system was not "trying" to do it's thing (i.e., apply brakes the the spinning tire), it only means that it was not applying them hard enough to either slow down the driveline/engine or get the DS rear to spin...

could also be explained by a poorly functioning PS rear brake caliper... Get it checked.

 

[sonk76]

could also be explained by a poorly functioning PS rear brake caliper... Get it checked.

Good point. I think someone suggested that... It's on my to-do list!

 

[pman]

Good point. I think someone suggested that... It's on my to-do list!

I would just check the brakes and then find a similar 100 to wheel with. I would go with you to compare, but im kinda far......

 

[sonk76]

could also be explained by a poorly functioning PS rear brake caliper... Get it checked.

Ok, I finally got to it. Jacked up the car, pulled the PS rear tire (the one that should have been "braking" more in my video due to ATRAC):
- Pulled the caliber - saw nothing abnormal
- Checked the brake pads for glazing - looked fine to me (but I'm not 100% sure what I was looking for), and they look brand new (i.e., thick).
- Checked the piston and it was moving freely (out 1" + with brakes, and I had no problems pushing it back in again)
- Disks also looked fine, no unnatural/uneven wear - 17.7mm thick (normal range according to FSM is 16mm - 18mm so this seemed fine)

All in all, everything checked out well in my non-expert eyes.

So now looking forward to some side-by-side testing hopefully soon at Rausch Creek

 

[LandCruiserPhil]

Ok, I finally got to it. Jacked up the car, pulled the PS rear tire (the one that should have been "braking" more in my video due to ATRAC):
- Pulled the caliber - saw nothing abnormal
- Checked the brake pads for glazing - looked fine to me (but I'm not 100% sure what I was looking for), and they look brand new (i.e., thick).
- Checked the piston and it was moving freely (out 1" + with brakes, and I had no problems pushing it back in again)
- Disks also looked fine, no unnatural/uneven wear - 17.7mm thick (normal range according to FSM is 16mm - 18mm so this seemed fine)

All in all, everything checked out well in my non-expert eyes.

So now looking forward to some side-by-side testing hopefully soon at Rausch Creek

Get lockers and say goodby to TRAC - problem solved

 

[2000UZJ]

Here is a good one (Zane's rig)

YouTube - UZJ100 Toyota LandCruiser Wheel Lift Disney Oklahoma

 

[Topmounter]

pman's vid from another thread has some A-TRACtion in it too:

YouTube - Amicalola 2-27-10

 

[re_guderian]

Ok, I finally got to it. Jacked up the car, pulled the PS rear tire (the one that should have been "braking" more in my video due to ATRAC):
- Pulled the caliber - saw nothing abnormal
- Checked the brake pads for glazing - looked fine to me (but I'm not 100% sure what I was looking for), and they look brand new (i.e., thick).
- Checked the piston and it was moving freely (out 1" + with brakes, and I had no problems pushing it back in again)
- Disks also looked fine, no unnatural/uneven wear - 17.7mm thick (normal range according to FSM is 16mm - 18mm so this seemed fine)

All in all, everything checked out well in my non-expert eyes.

So now looking forward to some side-by-side testing hopefully soon at Rausch Creek

Good so far, did the caliper slide freely on the pins? How does pad/disc wear compare to the DS? Is each side wearing evenly?

Get lockers and say goodby to TRAC - problem solved

someday...

 

[Topoguide]

Good so far, did the caliper slide freely on the pins? How does pad/disc wear compare to the DS? Is each side wearing evenly?

Definitely check for the pin moving freely. Mine was bent (long before I got it) which in turn caused seizure of the piston... but prior to piston seizure I am sure the ATRAC was not functioning properly, I know it wasn't after it seized.

 

[2000UZJ]

When I go out Friday..

Sounds great, and thank you for doing this.

didn't make it out today, and realized i left my camera at my house which is 120 miles north

So next time I go home or find a camera I'll go out and mess with ATRAC and see what I can cough up. going out tomorrow to run some trails and hopefully the guys bring the camera to take a video.

 

[sonk76]

Definitely check for the pin moving freely. Mine was bent (long before I got it) which in turn caused seizure of the piston... but prior to piston seizure I am sure the ATRAC was not functioning properly, I know it wasn't after it seized.

Ok. Took the PS rear tire of again, and removed the caliber to check the pins. They both move "freely", however one moves noticeably more easily than the other.

While I can easily move either pin back and forth and they move smoothly, one of them slides VERY easily while the other just a little less so. One moves so easily, in fact, that the rubber sleeve around the pin is able to act almost like a rubber band whose force is enough to slide the pin back if I pull it out. The other pin moves around easily too when I push/pull on it, but not easily enough that the rubber sleeve could move it around by itself (as with the other one.) Now in my mind the forces that are applied here are so large that the difference in the observed movement of these two pins is probably negligible, but I'm not sure. Any thoughts?

How "easily" are these pins supposed to move?