4WD/AWD newbie questions

I feel stupid asking these questions, but it's my first 4WD (or is it AWD?) vehicle, kindly don't laugh at me

1. Is there a thorough guide somewhere explaining how it all works? The manual is utterly useless.

2. Why does it take so long to switch to 4HI from 2WD? Sometimes it takes a few seconds, sometimes over a minute. Switching in park/neutral seems to not make any difference. Does it only work quickly when the transmission is warm? Does it help or hinder if I'm moving the wheels or the vehicle when doing this switch?

3. Is driving in 4LO sopposed to be so noisy? Is there a limit to how fast I can go in this mode? I don't feel the need to do it, but I'd like to know if I'll break something past a certain speed.

4. This set of settings gives me the biggest headache:
4.1 TRAC ON/OFF
4.2 VSC
4.3 AUTO LSD
4.4 Centre differencial lock
4.5 Tow mode

I'm guessing that TRAC disconnects power from a wheel that appears to have no traction.

Is VSC something similar, but it acts depending on how likely the truck seems to flip over? Is it controlled separately is its behaviour set depending on what else is turned on/off?

Is the AUTO LSD always on? Is that why it's one button to turn off TRAC and the same button to switch to AUTO LSD mode?

And on top of that there's the centre differential lock. Which seems to function independently of the other three.

When do I want to use which?

In my 2WD vehicles I made a habit of always turning off traction control in the winter, and that worked great for me. But there was only one ON/OFF setting. I feel I need to understand the components in this transmission better so I can make more appropriate decisions based on the type of driving I'm doing.

Does the tow mode have anything to do with the power distribution to the wheels or does it just change when the automatic transmission shifts between gears?

 

I suggest you pull out the manual and start reading. It’s a 4wd system. Not AWD, and should never be treated as such. There should also be a card on your driver visor explaining how to engage the 4wd system.

 

I've read it several times.

 

@AndrewSmith Unsure of if you're referring to your Sequoia or a Tundra. I'm going to assume Sequoia.

On the Sequoia, they have a center diff (and corresponding center diff lock) which gives you a little more leeway from the Tundra models that only have transfer cases that do not have center diffs.

Switching from 4HI -> 2WD is controlled by electronics, and mechanically done via an electric motor that is attached to the transfer case. The computer will determine when to perform the switch over, based on load conditions/other inputs. Normal for it to take some time if the computer deems conditions are not right.

4LO is noisy because of the gear reduction, this is expected. I don't know the specifics of the Sequoia transfer case, but if it's anything like the Borg-Warner cases in the 3rd gen Tundras, it will use a chain and a bunch planetary gear reduction.

TRAC/VSC are your traction control/vehicle stability control systems.

Auto LSD works by braking the spinning wheel to drive power to the other wheel. These trucks do not have any ability to "reduce" power sent to a wheel, they can only stop the spinning wheel from turning by independently actuating each brake circuit using the ABS system. Auto LSD functions in a similar manner to the A-TRAC system that is on the full-time 4WD trucks.

The center diff lock is used to lock the front/rear axle power, and thus, you can guarantee that "50%" of power goes to each axle. When you are in 4HI with the center diff locked, you are identical to a Tundra in 4HI. It negates the center differential. You would use this when off road in situations where you want at least 1 wheel on each axle to turn when power is provided.

Tow mode should not directly affect power distribution to the wheels. It only increases throttle pedal sensitivity and transmission shift points/behavior.

Your most ideal "I'm stuck" combination would be, center diff locked and AUTO LSD enabled. If you cannot get unstuck, you can "TRAC OFF" to disable traction control and spin your wheels if necessary.

If driving around on snowy roads, I would set the truck to 4HI and leave the center diff unlocked. If on a beach, I would run in 4LO with center diff locked. All entirely different situations off road and you'll have to just learn to make judgement calls based on your experience/conditions.

 

On my Sequoia, when going from 4hi to 2wd or 2wd to 4hi, it speeds things if just after I push the button, I give it a little gas, then back off the gas. One second and just a few hundred rpm’s is enough. My guess is that engage and release of power gives the transfer case motor a slack time to disengage or engage from 4wd. I could be all wet, but it has worked for me for 15 years on that rig. Otherwise it can take seemingly a long time and sometimes gives a noticeable thunk.

 

Thank you Chris and Pmac, that's very helpful!

Yes, it's a Sequoia I was asking about.

This auto-LSD system sounds confusing. I guess I'll figure it out over the years. I hope. It's hard when you can't see what each wheel is doing

 

You should be able to feel auto LSD functioning, like a pulsating power delivery as it is modulating the specific brake circuit.

fundamentally the auto LSD system is really not that complicated if you realize that the truck does not have a real limited slip differential I.E.it does not have clutches in its differential to prevent slippage. I found a good video that explains more of how the system operates and if you apply the concepts from this video in conjunction with the fundamentals of an open differential you can see that auto LSD is just braking the tire with less load to simulate a limited slip differential.

https://youtu.be/YUs8Vg-acKE

there are a lot of conflicting opinions out there on the effectiveness of the auto LSD system vs a real LSD or lockers, but IMHO it’s good enough for the majority of light duty off roaders. I used to have a 100 series land cruiser with A-TRAC and was always surprised by how effective the system was.

 

If you think about it this system moves maintenance burden to more conventionally consumable components, i.e. brake pads, rotors, and fluid as the open differentials do not wear like an LSD does. This fortifies the vehicle against negligent maintenance and abuse.

 

In 4 lo, it feels very slow or sluggish to me. Is that normal?

 

Do you mean slow to respond to a slipping wheel?

 

I haven't really tried it in off-road conditions. I only had it engaged when I first bought the car to make sure it was working. I was in a parking lot and had it engaged in 4lo then I went to add gas and it was probably slow to give me throttle response which was probably why I thought it was very slow. Then I watched an engineering explained video and the dude did like a 0-30 in 4lo and got a quick time so I don't know. Wouldn't want to try that on my car though.

 

4L has a 2.64:1 ratio from the transfer case. 4H is 1:1 in the transfer case. That’s why 4H has a normal throttle response where as 4L takes a bit more to get moving. 4L is a “granny gear”. It’s sole purpose is pure power and traction at speeds less than 15 mph.

 

I think Danny is probably spot on. Mine is a 05, so not sure if you have the same controls, but if you do. Take it to a gravel road or field. Engage 4lo, drop the tranny to 2nd and then push the L button. You are now in first. The throttle response should be fairly quick, but there is not really any apparent speed. Watch the tach, it should spin up fairly quick. I suspect the low gearing made it seem like the throttle was lacking a response. Then place it in D, and get it up to some speed so the tranny shifts into higher gears. While going about 20-25 or so, in 4th or so, hammer the throttle, it should wake you up so to speak. If it’s not doing any of this there could be some other issue.

 

Trac is ground trac of vehicle. Designed to cut power to engine to prevent the rear end form “coming around” if you try to accelerate too hard during a wet/slippery turn.

It’s suppose to prevent needing to counter steer into a drifting rear end to prevent loosing control and spinning around 180 degrees.

Auto LSD off means you want to spin a wheel, trac comes off because it would want to cut power to engine if a spinning wheel is detected.

The throttle is fly by wire, the sensitivity changes with 4L, tow/haul. I wouldn’t go faster than 15MPH.

It’s made for driving up steep hills and engine braking down steep hills. Much steeper than any public road would be. If the throttle were too sensitive the tires would break free from the reduced off-road friction and you’d get stuck.

 

In addition to what Danman said, yes the throttle curve in low range seems to be extremely damped down. On my Tundra it seems like you need to move the throttle 50% to get ANY actual throttle, which is totally different than every other 4wd I've owned (which subsequently don't have electronically controlled throttles), where the throttle is just as sensitive in low range as high range, just you have a huge gear reduction now. The reason I assume the throttle mapping is so sluggish in low range is because the truck in low range makes so much torque they're trying to make it somewhat manageable and not so throttle twitchy.

 

Don’t engage 4lo in pavement. It’s only for snow or off-road

 

Also, OP- you should engage 4H for about 10 miles each month to encourage lubrication and 4WD engagement. Pick a fairly straight stretch (no tight turns) and run it. I normally keep at or below 55 when I do my monthly 10. Usually I do it in two 5mi chunks.

I have also observed that if I turn the knob from 4H to 2H and pull my foot off of the gas, it quickly disengages.

 

I’ve used 4lo when going up or down steep inclines/declines. On steep declines, it helps keep the vehicle from barreling down due to gravity and prevents excessive heat from the brakes. It also gives you more control. Too steep a decline, though, and you’ll still need your brakes, especially with how much our trucks weigh.

I never use 4hi or 4lo on dry pavement. Otherwise, the drivelines can bind up if there’s too much tire traction and not enough slip. One way to know if it’s binding is if it becomes difficult to turn while in 4wd. Disengage and then make your turn. On icy/snowy roads I’ll engage 4hi if needed.

I try to “exercise” the 4wd system by finding a dirt or gravel road and engaging it. That kind of road allows the tires to slip more and prevent binding.

 

Thanks everyone! It would take me much longer to figure all this out on my own