Center Diff Lock question

[Bushwacka]

4th Gen 2004 SR5 4WD model.

Went off road on a moderate trail. Easily shifted into 4L. Engaged the CDL. The light flashed momentarily then stayed illuminated. When the CDL dash light was steady-on the VSC light illuminated and was steady. I believed the CDL was engaged.

I was going slow in 4L 1st gear.

I tried the obstacles however my rear wheels performed like I had limited slip and no locker. One wheel spun and the other didn't assist. I tried to engage/disengage CDL several times with the same results. I was unable to clear some of the simplest rocks.

At home, I cleaned the rig. Engaged the CDL and heard the beeps as the dash light flashed. The beeps stopped after 10 seconds and the light was on steady. I also heard the actuator engage.

When I disengaged, there was a slight lurch forward like the CDL was releasing.

In my opinion, the CDL appears to engage.

Q1: Why would I experience limited slip on the trail?
Q2: Whats the best way on pavement to verify it's engaging?
Q3: Should I have been in 4L Drive or can I move into 3rd, 2nd, or 1st gears with it on.
Q4: Did 4L throw it for a loop?





Bush

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[Bumbo]

Your 4R appears to be functioning fine...

The center diff lock only locks the transfer case. This essentially locks the front and rear axles together, meaning there is a 50/50 power distribution from front to rear when locked, not side to side as you would expect with front and or rear diff lock.

Your 4Runner has open differentials (not limited slip) in both the front and rear, so what you experienced is normal.

If a wheel, left or right looses traction, or you get one in the air, there is no way for it to transfer power to the other wheel on the same axle with an open differential.

If your example, even if the fronts had traction, its only 1 wheel drive, and it obviously wasn't enough to clear that obstacle either.

If you wheel often, you could invest in some lockers for the rear and or front diffs, but this is where things start to get expensive...

Testing at home is easy... just jack up the truck and get all 4 corners on jack stands with the wheels off the ground. You can spin the tires by hand in whatever drive mode you want (2WD, 4H, 4L) locked or unlocked and you will have your answer(s).

 

[Inv4drZm]

A-trac should have kicked in automatically which brakes the spinning tire. Usually its pretty good at this and acts similar to a locker. You can tell its working when you climb over rocks when you hear grinding noises by your foot pedal area.

 

[techno]

I agree that the system sounds like it's working normally. Sometimes atrac reaches it's limit and cannot help anymore, particularly if the spinning wheel is not touching the ground or if the wheel with traction simply does not have the ability to get the weight of the truck moving over the obstacle. Same goes for mud, sometimes neither wheel will get sufficient traction so one will spin more than the other. Even really tight mechanical LSD's reach their limit under those circumstances. That's when you need a front or rear differential locker.

 

[Bushwacka]

Thanks for the description. It is fairly heavy so this makes sense. It didn't have enough strength and traction to get up the trail.



Bush

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[techno]

I don't know how much offroad experience you have so forgive me if i'm stating the obvious, but there are other techniques you can try in those situations. I find momentum is key most of the time. Sometimes people are a little scared to hit an obstacle at the required speed to get over/thru it. Tackling things from a standing start requires way more effort and is more likely to result in a spinning wheel. Also, some drivers lift off the throttle at the worst time and kill the momentum.
When I get stuck, the first thing I try is backing up and trying again a little bit faster, making sure to not lift off the gas until I know I'm clear. And yes, If more speed is going to be dangerous or have a big chance of damaging something, then I'll try other things next.

 

[RonJR]

Agree with everything said so far. One thing I'll add is that ATRAC works best with steady application of power. If you back off the throttle when you feel a wheel start to slip you kind of pull the rug out from under ATRAC and it won't be of much help. Remember, ATRAC is just a computer program, and the more consistent and sensible the inputs (including the throttle), the better results it will produce.

I got to try ATRAC yesterday on a moderately steep hill with deep diagonal washouts such that one or more wheels were periodically being lifted. I could feel the wheels slip, and then the ATRAC engage. The vehicle never really lost speed or momentum, and I easily cleared the obstacles. I've driven that kind of terrain often enough with open diffs to know that without ATRAC it would have been very difficult to climb that hill. I was pretty favorably impressed.

 

[Bumbo]

I don't know how much offroad experience you have so forgive me if i'm stating the obvious, but there are other techniques you can try in those situations. I find momentum is key most of the time. Sometimes people are a little scared to hit an obstacle at the required speed to get over/thru it. Tackling things from a standing start requires way more effort and is more likely to result in a spinning wheel. Also, some drivers lift off the throttle at the worst time and kill the momentum.
When I get stuck, the first thing I try is backing up and trying again a little bit faster, making sure to not lift off the gas until I know I'm clear. And yes, If more speed is going to be dangerous or have a big chance of damaging something, then I'll try other things next.

This is a very valid technique and one I have to use myself too since I dont have front or rear lockers...

That said, its pretty difficult to do with the stock suspension. I would have never considering using momentum or speed before I had my lift as I would have ended up bottoming out or smashing up the rig depending on the terrain.

After I got some decent suspension, you can actually have it work for you in a safe and controlled manner.

 

[Bumbo]

A-trac should have kicked in automatically which brakes the spinning tire. Usually its pretty good at this and acts similar to a locker. You can tell its working when you climb over rocks when you hear grinding noises by your foot pedal area.

Are we sure all 4Rs have ATRAC? v6 and v8 models?

I have a 2004 v6 SR5 4x4 like the OP and my dash lights look different than A-trac equipped 4runners... unless they just changed the dash lights and its the same thing... ive never actually noticed it trying to work.

That said, when I lock my center diff, it turns off VCS TRAC...

Either way, it doesn't work well for where I wheel... I need diff lock bad, but the ARB option is money.

You guessed it... I had to get pulled up by a friend who has F&R lockers who just walked up no problem. Sometimes momentum and speed would get you in trouble too, hard to tell by the photo but I would have rolled the rig it I hit this at speed.

 

[Inv4drZm]

Are we sure all 4Rs have ATRAC? v6 and v8 models?

I have a 2004 v6 SR5 4x4 like the OP and my dash lights look different than A-trac equipped 4runners... unless they just changed the dash lights and its the same thing... ive never actually noticed it trying to work.

That said, when I lock my center diff, it turns off VCS TRAC...

Either way, it doesn't work well for where I wheel... I need diff lock bad, but the ARB option is money.

You guessed it... I had to get pulled up by a friend who has F&R lockers who just walked up no problem. Sometimes momentum and speed would get you in trouble too, hard to tell by the photo but I would have rolled the rig it I hit this at speed.

Pretty sure all 4Runners have ATRAC. Keep it at a steady RPM around 2k.

The limited gauge clusters are different.

 

[techno]

...

You guessed it... I had to get pulled up by a friend who has F&R lockers who just walked up no problem. Sometimes momentum and speed would get you in trouble too, hard to tell by the photo but I would have rolled the rig it I hit this at speed.

Cool pic! I would probably go easy on the gas too in that case.[emoji2]

 

[Bumbo]

Cool pic! I would probably go easy on the gas too in that case.[emoji2]

Lockers vs speed, ill take lockers every time. Its amazing how casual and effortless my friends Tacoma drives over these obstacles with his front and rears locked.

I think picking the right line is more important than any tool you can bring to the trail too... I think its safe to say if I had lockers when I was really new at 4 wheeling, I would have probably got myself into a lot more trouble than I was able to handle.

Not having lockers really forces you to look at the line better, and use your brain a bit more before you just charge forward.

That said I really want ARB air lockers but its stupid expensive. Still looking for alternate options. Even if I only had a rear locker it would help out a lot because I dont like to get too crazy off-road.

 

[techno]

I had an ARB locker on a previous vehicle and absolutely loved it, but in the time before it I learned to pick the line, judge the conditions and really get technical on overcoming obstacles. But bang for the buck, the air locker was worth every penny! As soon as my kids start school and I don't have a daycare bill to pay anymore, I'll be locking my 4th gen with ARB's front and rear.