auto-braking when in 4wd & turning?

so sorry if this has been asked before, or is a fundamental newbie
mistake with 4wd in general.

i have a 1999 4runner SR5 (manual), with just about 84K on it.
when i'm in 2wd, everything is just peachy.
when i'm in 4wdH, and trying to turn at very low speeds, i feel
a heckuva lot of resistance--as if the brakes were auto applying,
or as if there was an emergency brake problem. however, once
the wheels are aligned, and the truck is rolling, i feel no problems.
it only seems to occur at very low speeds (1st, or reverse), and only
when i'm turning. is this normal with 4wd?

TIA,
-steve

Sounds like a universal joint issue. Do you hear any clicking when turning?

Yes, this is normal. This is your drive train binding because you have the front and rear wheels locked together as a pair by the transfer case. Under these conditions, the front wheels must turn the same number of revolutions as the rear wheel. When you turn, the front wheels must travel a further distance than the rear wheels and thus must move faster (impossible with your transfer case).

Do not put your vehicle in 4WD on dry pavement unless you are driving in a straight line. Turning in 4WD requires that you have slippage on at least one wheel. If traction is good on all wheels, your drivetrain will bind as you have seen. There should be a card on the top of the driver's visor explaining how and when to use 4WD in your vehicle.

For general descriptions of how 4WD and differentials work see the following links:

http://auto.howstuffworks.com/four-wheel-drive.htm
http://auto.howstuffworks.com/differential.htm

Here is how your 4WD works. When you are in 2WD, the power from the transmission is given to the transfer case (by a chain drive) which drives the rear wheels through the rear propellor shaft (drive shaft). The front propellor shaft is free-wheeling and not locked to the rear propellor shaft. When you actuate 4WD, the transfer case locks the front and rear propellor shafts together and drives both of them with no slippage being allowed. Exactly 50% of the engine power is transferred to the front differential and 50% of the power is transferred to the rear differential.

In 2WD, your front wheels are splined to the front half shafts permanently (you don't have locking hubs that you have to manually engage to spline the wheels to the half-shafts). The front propeller shaft does not turn since it is not locked to the front wheels nor the transfer case drive mechanism. You can turn the front propellor shaft with your hand if you are in 2WD. When you turn on 4WD, your transfer case locks the front propellor shaft to the rear propellor shaft and the ADD actuator locks the front propellor shaft to the front half shafts through the front differential.

thank you both for your replies.

brian, you seem to have an awful lot of knowlege,
and also seem to have the tireless grace and patience to use it with newbies such as myself. i am VERY grateful. not to discount HaVoC's advice either, thank you as well.

brain, furthermore, thank you for taking the time to better explain the 4wd mechanism (as well as the links). i will explore more. as for the card on the visor, it is there, but it's description is vague at best. it said to engage it (4wdH) on wet, snow, or mud covered roadways. during some heavy rain last night, it engaged it (like to test it before the full-on winter weather hits). i noticed the resistance when backing out of a parking spot (i had engaged it in motion...est.10mph--driving forward about 5 minutes earlier). i guess i'll stay away from using it unless the situation dictates it's necessity. it's is EXTREMELY comforting to know that this is a natural occurance, and even more assuring to know why. that is something the visor could never have provided. once again, thank you for your efforts. this is the second time you have come to the rescue, and i am truly grateful.


regards,
-steve

You're welcome

just got thru reading all the info.
great stuff.
have loved "howstuffworks" for a long time now.
presently have another reason to love it.

thnx-
-steve

Thanks also for the info Brian. Is it ok to use 4wd in the rain?

You can use it in the rain, but it can be a problem. You shouldn't bind up often, but you have better control over the vehicle at medium to high speeds in 2WD than in 4WD. In 2WD, your steering wheels can follow the road and regain lost traction with no problem. In 4WD, they may not be able to regain lost traction and cause you to totally loose control. Much the same as a front-wheel drive car can. In a front wheel drive car, if you push too hard on the accelerator in the rain going around a curve, all of a sudden - bang - your front end is traveling toward the outside of the curve with no control. That can't happen anywhere near as easily if the steering wheels are just along for the ride.

IMO, only use the 4WD when you really need it to keep going and not at high speed.

Roger that, thanks again for the great info.

You're welcome

I know in the Toyota manual it says you have to drive in 4WD at least 10 miles a month, or something like that. But what if you would never use 4WD, do you still have to do this?

I use my 4WD on the same straight serious up- and down-hill on the way to work every day. It is a side street and I never get above 5 mph (1st gear), but it's about a 1/4 mile long. Just my way of making sure everything is working, as well as a small exercise.

I almost never use the 4WD either. Maybe a few times in the winter other than that. I bought the 4Runner a year ago and am still looking for local off-road challenges. :)

I bought it for it's reliability and strength more than it's off-road ability. Best vehicle I've ever owned.

hey brian,
do you have the limited slip (rear) on your '00?

-steve

No, I have the SR5 4WD with an open differential. I bought it a year ago with 30k miles on it. From the looks of it, it stayed in a garage and only drove the soccer mom to and from the school. I couldn't pass it up, even though I only wanted to pay at the most $18k (paid $21k)

4 wheel drive indicator in the rig won't stop flashing, any ideas on that?

differential fluid low maybe?
is there a code for the flash pattern?

-stev=o

Nope, it just flashes continuously, it won't engage nor dis engage, it seems stuck in the void. Changed Diff fluid not too long ago, and have tried all forward and reversing options. Local Toyota dealership said maybe vacuum hose, but couldn't see that either. Was wondering if anyone else experienced this too and what they resolved. Very odd, and very frustrating!