4wd not working right.

[Devin]

Well I finally got my transmission in, and it only took 6 months! The bad news is the 4wd drive mode is acting very funny. It goes into 4wd fine but it drives really jerky. I can hear the wheels spinning out in little surges. And then it won't go back into 2wd without fiddling with linkage under the car. Any thoughts? Thanks.
Devin

[Petros]

Yes, it sounds like you have mis-matched front and rear differential ratios. Either that or you have different size tires at one or more locations on the car. Check your tire and rim sizes and inflate them the same amount. IT can also help if they are all the same brand.

A 1985 should have 4.1:1 front and rear diff, sometimes people will unknowingly install the earlier trans-axles from '83-84 with the 3.73:1 gear ratio, and it will not match the rear. The trans axles are identical and interchangeable, you do not know what ratio is in unless you pull the front cover off and count the ring and pinion teeth. It will behave just like you describe if they are mismatched.

Easiest check is to put the car in neutral, trans in 4wd, jack up one side so both front and rear tires are off the ground. Than put a chalk mark on each tires and rotate one ten times and watch if the other ones rotates the same amount.

If they are not the same ratio you either have to swap the front or rear diff out so it matches the other. Where did you get the transmission? do you know what year it came from? do you know if anyone ever changed out the rear axle or diff? Sound like you might get to do the job over again, or at least part of it.

PS: do not feel so bad, I bought an '86 Tercel with a bad rear diff, I installed another 4.1:1 and discovered the same problem. The previous owner (or his idiot mechanic friend) had replaced the trans-axle with one with a 3.73 diff. I had to pull the rear diff, find a 3.73 rear end and install it instead. After that I could finally drive it, and promply found a number of other problems unrelated to the drive-train I had to fix (including 9 vacuum leaks in the engine).

Good luck.

[xirdneh]

I have dealt with that situation twice
on one the previous owner put the wrong tranny in
and the other was when i bought a tranny from someone who told me the wrong year

i changed the rear differential on both
its a pretty easy fix

Petros's jack up one side of the car and count the rotations suggestion works real well

i would not put it in 4wd until you get it fixed
those trannys are getting hard to find
you do not want to break it

shifting out of 4wd while moving in reverse in a straight line almost always gets it out of 4wd (when its jammed)

[tercel4wdrules]

I remember you got a trans from Soshin Trade Corporation, you probably got the second or third to last transaxle before they exhausted their inventory. It's possible they may have sold you a 3.73 final drive trans. Did you notice any difference with the reverse light switch connector and the absence of the EL indicator switch? The 3.73 trans has a different connector style for the reverse switch I found out.

[Highlander]

Devin- I've got a 3.73 rear gear sitting on the floor of my garage if you need one, as well as a trans with 3.73 gears both are from my first T4WD, an '83. The change isn't very hard to do, pull the asles out, disconnect the drive shaft, drop the third member out. Installation is reverse of disassembly as they say.

[Devin]

Yea, I did get it from Soshin. And yes I did notice some differences with connectors. Shucks. The warrenty is expired too. Oh well. Highlander, that would be a life saver! I need to do some work on the carb first, but I will defintely hit you up when I'm ready.

[Petros]

If you still have your old trans, and presuming the front diff is okay, you can swap the front diff into the transaxle to keep the 4.1:1 ratio. You will have to pull the trans and spit the case, it is a pretty large job but I think it is worth it to keep the lower gearing. Just make sure you carefully inspect the front diff gears by pulling off the front cover before you start.

though it is much easier to swap out the rear diff center carrier with one 3.73 ratio, it takes about 2 hours. Less if you are an experienced mechanic. the 3.73 makes for some slow accelerations from a stop, and not as good off road as the 4.1, but it will drive much quieter on the highway (the engine runs a lower rpm at fwy speeds), and you might get a mile or two more per gallon.

[Highlander]

Petros- Isnt' the pinion the same on the 4.1 as the 3.73? If it is, he might be able to just swap out the ring gear and carrier from the front instead of pulling the whole trans out.

[Petros]

I do not know enough about how these gear are cut, the pinion for each gear set has the same number of teeth, but I do not know if the helix, shape of the gear, etc. is the same. Typically when you change ratios you will change out both ring and pinion gears as a set because they are made in a matched set. They may indeed be the same, but the other question is the gear lash between them has to be properly set with side shims. Both the pinion and the ring gear has to be adjusted (pinion in and out, ring gear side to side) so the face of the teeth mate properly or you could damaged the gears after you drive it. I would not attempt it but rather just swap the whole assembly out, potential for problems are very large if swapping out the ring gear only is not set up properly. And likely the amount of wear on different ring and pinions sets would be different, one set would have been wearing in for more miles than the other so they have to stay together, I do not know how that would affect it but knowing how sensitive proper installation is it would only be by accident of matching clearances that it will not suffer severe damage later. Swapping out the whole assembly so you there no change in the lash and relationship between the ring and pinion is much easier and less potential for future problems.

The fastest way to fix it is to do the job only once. You can try just putting in the ring gear mated to the old pinion and see if it works. If they trash each other than you will have to find another complete differential, and if the metal shards make it into the main trans gear cluster, you will be replacing the trans again too.

I would not do it, these transmissions are getting too rare to take any chances with damaging them.

[xirdneh]

the 3.73 has 11 teeth on Pinion 41 on Ring
the 4.1 has 10 teeth on Pinion 41 on Ring

[Highlander]

Ah, there you go, I knew one or the other had the same count. But as Petros said, they are matched and setting the lash is not typically an easy thing to do. BTDT on something else. So Devin, if you need a 3.73, I have one. PM me and we can work something out, at least there's no shipping involved!

[tercel4wdrules]

Yea, I did get it from Soshin. And yes I did notice some differences with connectors. Shucks. The warrenty is expired too. Oh well. Highlander, that would be a life saver! I need to do some work on the carb first, but I will defintely hit you up when I'm ready.

The warranty wouldn't of helped you, I think they'll only do something if the unit is defective. I remember I walked in one day and they told me that their list showed that the 83-88 T4WD transaxles were the same, I told them that was incorrect, but they didn't know anything about it. I have a friend that bought one from Soshin and it was a Z54F 4.10 final drive, probably second or the last one they had in stock. The 3.73 final drive does suck driving up hills and for overall acceleration, but it might just be worth that extra MPG or two if you only swap out the rear differential.

[evan_dl2]

haha well i just got struck with this problem. i have an april 1985 wagon, i just swapped a tranny out of an '87, i was assuming they would both be the 4:10, turns out that isn't the case. it's binding up in a straight line in 4wd...so i'm wondering if there is a cross-over period, possibly my '85 still has the 3:73's?? oh well i guess i will swap the rear diff out of my parts car, i guess it's not all that bad as long as my parts car wasn't messed around with and has the 4:10's like it should. we will see what happens.

[Petros]

The '85 should have had the 4.1:1, more likely someone replaced the trans and discovered they needed to swap the diff too. Does your '85 have the center dash console with the inclinometer and 4wd indicator? if so it might have been a late 1984 model year for some reason.

You should be better off with the 4:1:1 final drive anyway, swapping the rear diff is not too difficult. You are also fortunate to have the parts car available. I would save your rear axles if the bearing are good, it is easier to swap out the axle assembly that to just replace the bearing itself (requires a press to remove the bearing from the axles). If your rear axles seals or bearings are questinable, now would be the time to replace those when you pull the rear diff.

[evan_dl2]

thanks for your thoughts petros, well looks like someone must have indeed swapped mine out at some point in time, because my car is supposed to have the el light, but it has never worked. and the trans i pulled out of my car only has 2 plugs, and the new one has 3 so i was able to plug the el light in now.

i am excited to get the rear diff swapped now, good to know i am upgrading all around now anyways.

question, for the diff, do you pull the whole "drum to drum" or do you just swap the center section? if so you pull the axles, driveshaft and the cover, is it fairly straight forward?