Chippycane

I hope someone here can answer a question for me. I have a 1990 4runner. My transmition oil temp light has come on a few times on the highway. My mechanic has noticed that the drive shaft to my front wheels always turns with the wheels whether the 4wd is engaged or not. I am sure the 4wd is not always engaged but apparently when he puts it on the lift and turns the wheels by hand the drive shaft turns. He thinks this could be causing drag. Is this supposed to happen?

Thanks, Louis

eric-the-red

If you have ADD then the passenger side wheel is always connected and will turn the diff. This might turn the driveshaft through friction in the gear oil, though it will turn slowly. You should be able to hold the driveshaft still and turn the wheels, if you can't then the ADD might not be unlocking. If you got lockable hubs on the front make sure they are unlocked.

Even if the front shaft is turning there shouldn't be enough drag to heat up the tranny that much. Did you check the trans fluid level, and also make sure the cooling system is working properly.

InternetRoadkill

Your hubs seem to be locked. But that shouldn't be a reason for overheating I would think.

Chippycane

The hubs are automatic locking. What controls them?

eric-the-red

Sorry, don't know anything about auto hubs, I've only dealt with manual hubs and ADD flanges.

smiljko

They are usually controled by front driveshaft(they are full of little springs and "clutches" that just love to break). But it is interesting if they are stuck in lock- if they break they usually stay unlocked.
It is neccesary that you drive in reverse few meters after disengaging 4WD-to unlock auto hubs-they suck bigtime . My reccomendation is to throw away autos(don't try to fix them-they will break again) and get manual hubs.
Cheers

Strap22

Your shaft turning is normal with ADD. As for the Temp light ....what size tires are you running?.....did you change the fluid lately?....they are very touchy about how much fluid.....too little they overheat....too much they foam and overheat. If you put larger tires on and are running the stock 4:10 gears you will overheat in overdrive. You can turn off the overdrive buttom and burn more gas and that will circulate the fluid faster and keep it cooler or re-gear. I had the same issue on my '91 and it turned out to be a combo of all these things. Solution for me was 1.) add a tranny cooler, 2.) re-geared to 4:88's. 3.) Set fluid level to the proper level. By the way I am running 33x12.50 tires and have no more problems

kyle_22r

if it's a '90 it doesn't have "auto hubs", but drive flanges and a vacuum actuator. often times, especially at high speeds, ANY rig will put a little drag on the front end with the axles unlocked, and you'll get a little driveshaft movement.

Strap22

Kyle you are right it is a vacuum actuated system. Toyota list it as a A.D.D. years 8808-9511. I guess I don't understand what you are saying. If you are comparing to a Tacoma style it is different but still A.D.D.. With my Manual Hubs unlocked my shaft does not move at all. His real problem is with the Transmission overheating. I simply stated what I expereinced and if you do a search you will see other write-ups on this very subject.

Chippycane

Thanks Guys, This is all very helpful info. I am not nearly the gear head you guys are so I’m forwarding all this to my mechanic for his thoughts. To answer a few of your questions, I just replaced the trany with a rebuilt unit but the old one did the same thing. It has only happened once on a road trip in the mountains but with a new unit I’m just sensitive about it. My catalytic converter was also fouled and had to be replaced witch my guy thought could have contributed. We talked about a second cooler and it sounds like a lot of folks have gone that route, but there isn’t a lot of room for it so we have to sort that out. She just hit 200K this week and has a new motor and trany in the last year so I’m not ready to give up just yet.

Thanks for the help, Louis