4H Pull

You are absolutely correct.

A problem with the 4WD actuators or engine electronics isn't going to produce a torque pull in 4WD.

The mere fact that he has a torque pull at all means the 4WD is fully engaged.

A slight pull when accelerating in 4WD is normal. It's caused by the difference in length between the two front CV shafts. Every front wheel drive car I've driven has done it to some extent. Both Toyota 4x4s I have had have a slight amount of pull with throttle in 4WD while on pavement (something I don't do often).

If it's bad enough that he's fighting to keep the truck from changing lanes, I think it's got something to do with the lift changing the geometry of the front end.

With an ADD front end, the transfer case shifts to 4WD first, causing the normally stationary front driveshaft to come up to speed. As this happens, the ring gear and carrier in the front diff comes up to speed as well, causing the axle shaft on the ADD side of the front diff assembly to change directions (it actually spins backwards with the ADD disengaged) and rotate at the same speed and direction of the outer shaft leading to the CV. Once all this has happened the ADD couples the two halves of the axle shaft on the ADD side together. Until that point, no 4WD, just like leaving one manual hub unlocked with an open diff on the old 4x4 trucks.

 

Great info! So, if I understand correctly: there's no possible way I could have only 1 front wheel "driving" (VSC/a-track aside). Correct?

 

Along those lines, the truck was aligned after adjusting the lift...in 2WD. I'm wondering what could possibly be done to make the Taco happy in both the 2WD and 4WD realms...

 

Correct. A long as both front wheels have traction. If one loses traction, at that point the wheel with no traction will get all the power sent to it. That's where the VSC and Atrac kick in to correct the problem. AFAIK those systems just modulate the brake and cause the spinning wheel to slow, which transfers power back to the wheel with traction.

 

Correct iff your add wasnt working you would have no 4wd. If you ever rip apart your front diff you'll understand immediately. The gears off the actuator lock the feomt diff in unison. I have the same pull right on pavement but mine is if i accel hard.

 

Clear. I've tested it with both of those on and off, with no change. That, and the pull is constant, or rather based on acceleration. If I didn't touch the wheel, I'd make a tight little circle of dust.

 

Yeah, mine's much more severe on pavement (tested it today at d'ship), but very prominent on dirt, too. If I accelerate slowly, it's pretty minimal. However, if I accelerate quickly or if I get to 20-25 mph, the wheels breaks sharp right.

 

Maybe and just maybe wheel alignment:/ ? When you fully engage your 4wd the front tire will instanly go to the way of least resistance? There an answer i pulled outta my butt to help for the cause! Best of luck man

 

If VSC / Traction Control engages it beeps as well

 

Yeah, I've had it go off on me. I also disengaged it today, but got the same result.

Just wondering what factor in the lift kit geometry would have an effect in 4wd...

 

Yep...it drove straight.

 

Dropped her off this morning...cruisin' in a Corolla now.

 

My old jeep YJ used a similar setup only it worked off vacuum instead of electronic. I'm in belief that a faulty ADD could very well be the culprit. I had a vacuum leak in the line running to the disconnect on my jeep and had the same symptoms. I knew immediately what to look for and found it. I eventually converted it to stay locked at all times when I put locking hubs on it.

Seems these days that if a "tech" can't plug a diagnostic tool into a vehicle and be told what the problem is, they don't know wtf to do.

 

Yeah...lol. They got a "driveline fault" yesterday...needless to say, they were perplexed since I have a lift...

 

What about a possible busted cv on one side?

the hubs aren't hubs anymore in the sense of old trucks. They are basicaly the same thing you get in a civic. The only disconnect that happens is in the ADD, so the only way i could see one side engaged is if there was a broken cv on the other, or a shaft popped out (seen it in fwd cars) but then im not sure on that either because it woud be an open diff and shouldnt get any power out the unbroken side.

Maybe bad control arm bushings or alignment of some sort?

 

Highly doubt anything's broken...we'll see soon, I hope.

 

So, maybe I'm missing something on how the ADD works on the Tacoma. What would keep one tire from getting power if the ADD failed? The whole point of the disconnect is better handling on the road and the ability to connect the axles when in 4 wheel drive. One tire HAS to have power from the driveline and the disconnect connects the unpowered wheel to it.

Which side of the diff is the disconnect on and which way is the truck pulling?

 

The axle on the passenger side is longer...the truck pulls in that direction.

 

Right, thats my understanding as well, but its still an open diff so if there was a disconnect/break like a cv then the diff, add locked or not would have a "free" side and spin.. losing most if not all of the power through it. There may be enough friction or something to still have some.. But without a locker it would, as far as i understand be the same as having the "broken" side off the ground.

Not in the tacoma, but im old yota's with ADD i have broken a cv shaft, add still engaged and had zero power that made it to either wheel after (broke each side seperate times too)

 

if it was a power to the ground issue (extra power from one wheel)

and somehow you were getting power to your driver side and not your passenger side it would pull that way.

Thinking about it some more here, if you have something on the ADD side that is not engaging, and ALSO not free spinning, im not sure how its possible, unless something is broken then you could get power out the other side