AbramHart

I have a 1990 4runner with the ADD system. The front tires seem to have some resistance on them compared to a manual hub. If I put the unit in 4 low it works fine but if you press in the clutch it seems to stop rather quick almost like the brake is engaged.

If I put it in 4 high the front tires lock completly. In other words they will not turn!

I have checked my vacum lines and they seem to be OK. When shifting I have no problems shifting and the 4WD indicator comes on with no problem.

I am almost to the point that I am thinking of replacing my Add system with one from a manual truck.

Has anyone had this problem? Does anyone have any suggestions?

mt_goat

This is just a wild guess, but are you sure your front and rear diff are geared the same? I'm no expert but it doesn't really sound like an ADD problem, more like a drive line or transfer case problem. The ADD is either engaged or disengaged. You sound like you have binding from something in the front driveline and maybe you just have enough torque in 4wd low to over come it, are your wheels turning freely in 2wd?

AbramHart

Yes they turn freely. Not like a manual hub would turn freely but they turn. I can get around 1.5 rotation with a firm spin if the front is jacked up. I am not sure that the truck is geared properly. I would assume it is because there are no signs of it ever beeing tampered with. Although the transfer case has been tampered with. Instead of seals/gaskets on it they have teh universal liquid seal on it. So I know the transfer case has been removed at one time. If I have to break the transfer case down and rebuild it do you know of anyone that offers a 4:1 gear at a resonable cost. It seems that this gear is quite expensive from offroad dealers. But all in all it would proably be cheaper to find a good used transfer case and replace the one I have.

mt_goat

So both the front wheels turn freely in 2wd? If the drivers side turns freely but the passenger side doesn't that will be another good clue. Keep in mind that with manual hubs in the unlocked position the cv's don't turn, however with the live hubs that come from the factory with the ADD system the cv's are always turning even in 2wd. So it is normal for there to be a little more turning resistance for wheels with ADD.

The reason I brought up the diff gearing is if your ratio in the front is different than the back, the drive line will bind up in 4wd and basicly put the brakes on one set of wheels. If you were in 4wd low you could have enough torque to break traction (especially on dirt or wet condtions) and relieve the binding, making you think 4wd low is ok.

I think the universal liquid sealer is factory stuff, is it red?

I have no experence with replacing a transfer case, sorry.

AbramHart

How do you determine what the gear ratio is on your front?

Robinhood150

And this is happening when you're driving in a straight line?

A quick and easy way to check the ratio is to jack up the truck and manually rotate the tire and count the revolution of the tire and the driveshaft.

mt_goat

Well for you right now the question should be is the front and rear gearing the same? One way to check that out would be to drive out to a dirt or gravel road in 2wd. Stop and put the truck in 4wd, get out and mark all 4 tires at the same spot (like the very top of the tire, 12-oclock). Get back in and slowly drive in 4wd(do not to spin your wheels) 20 or 30 feet in a straight line, no turning. Stop and get out and look at your tire marks, they should be all the same location (like for example all 4 at 3-oclock) If one of the front or one of the back is different then you MAY have a 2 different gear ratios in the front and back diff. Make sense? You might have to drive farther than 30 feet, I don't know. Of course this test depends on you having the same size tires front and back, if that is not the case that is most likely your problem right there.

Another way would be to rotate the wheels and count the rotations of the drive shaft for each wheel rotation. The front and rear drive shaft must turn the same # of times. Like for example 4.5 times per one wheel rotation.

Another way is to take the diff apart and count the teeth of the ring and pinion gears. But that would be very time consuming and costly.

I take it you haven't had the truck long and this is the first time you tried it in 4wd?

AbramHart

Actually I have had the truck for a year now. I have used 4 low but never 4 high. I tried to use 4high the other day because of snow. This is when I noticed the problem. My code on my truck states that the gears are 4.556. The rear end has had body work so i am wondering if they changed the rearend and put the wrong rear end on it. I will try the marking the tires tonight and see if this tells me anything. Now when I had my 4runner in 4 low in the snow it felt like the rear end was pushing the front.

mt_goat

I had that happen to me once, the rear 3rd member got changed and the ratio was different from the front. I ended up with 5.71 in the front and 5.29 in the rear. Going to 4wd with that combo was like someone hitting the front brakes.

Remember when you do the test that if you have open diffs, ie no locker, there may be only one wheel that is clocked different that the others.

AbramHart

OK i have more information. I am sure the gear ratio should be 4.56 but I think my front gear ratio is that. I think my rear is 4.10. I parked my 4runner and marked the tires in the up position. I put the 4runner in 4 low and 1st. I slowly let off the clutch and let it role around 40 feet. I stop the 4runner and get out and WOW :wtf: My front tire markings were straight up. The rear tire markings had turned a quarter or so more of a turn than the fronts. So I am now pretty sure that when the 4runner was damaged it damaged the rear end on it. Who ever repaired the ride proably put a 4.10 or maybee even a 3.90 rear end in it by mistake. But I have my eye on a 4.56 third member I may be able to get at a reasonable rate. Let me know if I am on the right track on fixing this.

mt_goat

Just make sure of what you have in front before you buy the rear gears. Short of tearing it apart and counting the teeth, the best way maybe to spin the wheels and carefully measure the rotations of the front drive shaft. I have done this with a string taped to the drive shaft and rolled the truck excactly one wheel revolution and counted the wraps of string around the shaft plus the partial turn. Just make sure you turn both front wheels the full revolution. If you do have 4.56 gearing your drive shaft will turn just slightly over 4.5 turns for every one wheel revolution of both wheels. Does anyone else know a better way?

AbramHart

OK!
I have had time to get some more info. I jacked up one side of the vehicle front and rear. Marked the tire and drive line. Turned both one complete revolution.

The rear driveline turned 2.05 times. So I assumed I could x2 this and it would be 4.10 gears.

The Front Drive line turned 2.25 or so times. So I assumed I could x2 this and it would be the 4.56 gear.

The tag on the door states that the gears are 4.56.

The rear has been damaged so I am thinking that they replaced it with a 4.10 chunk thinking that it was the correct chunk.

Now my question?
The 4runner is ABS equiped. Should I try to find a chunk with ABS and install this?

Or can I do what I want to do and purchase 4.56 gears and a Detroit truetrac for the rear?
If I do this will I have problems making this work with my ABS?

Also do I need to purchase factory toyota 4.56 gear or can I use any respectable manufacturer gear since only the rear and not the front will be changed?

Thanks for your help.

AbramHart

Also My dad has an 89 with a v-6 and 4.10 gears. This is where I came up with the x2 method. My fathers truck turned 2.05 times per wheel revolution front and rear.

Birdman

I'm not sure about a 2nd gen but with the 3rd gens, this should not matter. ABS has nothing to do with your gear ratio or gearing.

Doesn't matter ont the 3rd gen. Shouldn't be an issue.



Yukon makes some good gears, or so I hear. You don't have to buy Yota gears. Wish I had some 4.56s in mine.

AbramHart

Thanks for your informaiton on this.