84-85 transaxle ratio differences

[Red88]

I am buying an 85 tercel wagon sr5 that the seller tells me has a 84 transmission in it. (manual 4x4)
The differential/transaxle gear ratios are supposed to be different between 84 and 85. The seller says it drove fine.
How can I tell if the transaxle is not right for the car?
Did she do damage driving a mixed match?
Is there a way to inspect the transaxle (without taking it out) to know what year/gearing it has?
I also own an 84 that I put a junkyard tranny in when I bought it.
I have no idea what year the tranny was that I put in it.
Can anyone help me straighten this out?
Thanks
Rich S
Oregon

[irowiki]

Yeah, I think it's something like:

Jack up one side of the car
Put a mark at 12:00 on each tire
spin them and see if the marks line up the same each time

[Gottolovem]

Yeah, I think it's something like:

Jack up one side of the car
Put a mark at 12:00 on each tire
spin them and see if the marks line up the same each time

X2

Make sure 4wd is engaged so front and back turn.
At least 10 rotations the difference in ratios is minimal so the more turns the more accurate

[Petros]

welcome to the forum,

you can actually swap out the trans itself, and use the old front diff and bellhousing, and the ratios would not change. Best to do the manual test as outlined above (brake off, 4wd engaged, trans in neutral), when you have the tires marked, count ten rotations, and watch the number of rotations on the other wheel. if it is not the same, the front and rear diff do not match. so you either have to change the front or the rear diff assembly to correct it. It is easier to swap out the rear diff assembly once you locate a matching ring and pinion diff assembly for it.

You can drive it that way in 2wd, but DO NOT USE THE 4WD!!! or you will either destroy the trans or one of the diffs, it puts a lot of stress on the drive train. Okay to drive in 2wd however.

If the trans is damaged it will not be easy to find a good one, and the swap out is a major job.

[Red88]

Thanks for the help.
I understand the manual test however, if I jack up only one side, how can the tires turn?
Dont I have to jack up all four wheels for them to spin free?
I guess there is no way to tell the year/ratios by visual inspection.

[Petros]

with the open diff when you hold one side (the wheels on the ground) the rotation will be only on the wheels in the air. You can lift all four wheels off but you have to have all the bearings and brakes drag exactly the the same amount so they all turn the same (not likely, particularly brake drag) or you will get differential speed through the differential.

You can take the rear diff out, and the front cover off the front diff, and count the teeth (the 4.1:1 gear set has that number stamped in the side of the ring gear, for some reason the 3.73:1 has no marks on it. both of these require draining the gear oil and partially dismantling the diff assembly.

the rotation test is the easiest way, and it is reliable and accurate if you do it as described.

[Red88]

Okay. I believe you.
It just didnt make sense to me that the wheels would turn with the other side on ground.
But I thank you for the info.
Still a newbie
Rich Sommers
Eagle Point OR

[Petros]

It just didnt make sense to me that the wheels would turn with the other side on ground

understandable confusion, it has to do with the action of the differential, what you supposed would happen if it had solid or "locked" front and rear axles, but you can not drive a car or truck on a paved road with solid axles. Each wheel makes a different diameter circle when the car makes a turn, which means without a differential, the wheels would be skiing or slipping (and there would be a lot of stress on the drive train). The action of the differential allows smooth driving on paved roads, unfortunately a undesirable effect is that if one wheel has less traction than the other, the differential will direct power to that wheel and it spins. This btw, is why the Tercel4wd system is superior for off road than an AWD system, that has a center diff (which the T4wd does not, the front and rear drive train is locked together though a spline shaft). With AWD, one wheel out of four slipping means none of the other drive wheels get any traction, only the spinning wheel. In the T4wd you will have at least two out of 4 wheels being driven, but that also means it is not good for it to drive on paved roads when in 4wd, so you have to manually remember to engage it, or disengage it. or you risk damage to the drive train.

only with a limited slip differential would it not behave this way.

I did not mean to go so long, it is just that few understand the consequence, or even the reason, for a differential, how and why it works, and why a limited slip differential is beneficial for off road use.