checking gear ratio on differential

[xirdneh]

About six years ago i bought an '83 tercel 4x4 wagon that suposedly had the wrong front differential. The guy had replaced the original blown diff/ tranny combo (i still have it) with what he said was an '87 tercel tranny (differential/tranny combo).
He also stated that it had locked up while test driving it and he had a hard time freeing it. I took him at his word and bought a used differential for the rear axle that supposedly had a matching gear ratio (from a toyota corrolla). According to the wrecking yard.
When driving on icy roads I've noticed a building up of tension in the drive train. On patchy roads i can feel the tires catching up when going from dry patch to icy patch. This does not happen on my other tercels so i'm pretty sure something is wrong.
How can i figure out what i really have in this car? Is there a good way to determine the gear ratio's?

[coltarms]

pull 'em and count and measure the ring gear and pinion teeth.

[keith]

I don't know how you feel tension in the drive train, but the steering does stiffen up on dry patches. If you steer the wheel on a dry patch, then you can't get the thing out of 4wd, there is tension on the drive train then.

[Typrus]

How? I can't explain it for me, but I certainly feel it. Even in straight-line.

The best way would be to drop the tranny enough to get into the from diff cover and count the ring/pinion teeth. Assuming you can see them both from there, which you should. Then do the same for the back. You'll need new fluid for the whole trans and for the rear diff if you do that, but new fluid never hurts.

[Mickey_D]

My car has all original parts, so they're supposed to be matched gear ratios.

When driving along on dry pavement if I slowly move the 4WD shifter towards the 4WD position, just past center I will feel the gears try to mesh. Now if I hold it at that point, right where the gears are "clashing", it will "bump" a little every 1/4 second or so at 40mph. This tells me that the gears aren't exactly equal.

Now, if I slowly let off the gas while I'm doing the above process, there's a point where the gears will exactly line up and there's no more "bumping". Until I let up on the gas enough that the bumping starts in the other direction.

So it would appear that there is a lot of "play" in our front ends that allows for what seems like a different gear ratio.


Now, saying that, it's not like there's a great bloody CRUNCH like when you don't get the clutch all the way in when changing gears, but you can definately feel that the front end is trying to do a slightly different speed than the rear.

[shogun]

i had that ssame issue, still looking for a 4.10 for my rear

[hornett22]

http://www.brian894x4.com/Gearratiosanddiffs.html

[Petros]

you do not have to pull the diff covers to determine the ring gear ratios.

Jack the car up on jack stands so all the wheels are off the ground, with the car in 4wd and trans in neurtal (parking brake off) do the following: mark a chalk line on each tire closest to the ground, and than crawl under the car and mark a chalk line on the drive shaft. Turn the drive shafe exacly four turns, and see where the wheel chaul lines end up. If they are all the same, you are good. If the wheels turned more than one complete rev. you have the higher ratio of 3-something. If they went little less than one rev, you have the 4.1 ratio. If they are different, you can see it.

I understand the collola has the 4.1 ratio, which should match the later tercel front diff. YOu should also check the tire size and pressure, and that your unjoints on the drive shaft are in working order. Other than that, the trans should lock-out front and rear, I can not imagine there would be any difference unless your frame or axle mounts are bent or misalingled.

The only time I feel any tension in my dirve train is when I am turning on dry pavement. I use my 4wd daily on my rual roads to get home, and I sometimes forget to shift it back into fwd going out the next morning, I do not notice unless I make a turn on dry pavment.

[Typrus]

One problem with that. I've yet to see my terc have both tires on either side turn at equal rates with each other. Sometimes one side will just stop.

[Mickey_D]

Sounds like Typrus has a dragging brake problem...

[Typrus]

Sounds like Typrus might have inequal wheel bearing wear along with other potential issues is more like it. My brakes are actually great. Hell, I even rotated them on a lift with the drums off and the calipers off just to see and it was the same story. Probably some axle stuff too.

[xirdneh]

[quote="Petros"]you do not have to pull the diff covers to determine the ring gear ratios.

Jack the car up on jack stands so all the wheels are off the ground, with the car in 4wd and trans in neurtal (parking brake off) do the following:



could i just jack up one side only. would that force the raised tire to turn?

[Petros]

Raising only one side would cause the tires to turn at twice the normal ratio, if the both wheels at each end of the differencial are not raised. Perhaps that could work, adjusting for the action of the differencial, though I have not ever done it that way. I suppose either way you would know if the front and rear ratio are the same or different.

[keith]

Actually you could jack up one side of the car so that both wheels on that side are off the ground. Now you make a line on each tire. With the transmission in gear and in 4wd, turn one tire several revolutions. If the gears in the front and back match, then the marks should stay in sync. If the ratios are different, then the marks will not stay in sync.

[Typrus]

That solves the problem I mentioned. Just remember, again, they will turn double-speed. So don't run the car. I don't think it has to be in gear for them to be meshed, and leaving it in gear would make it impossible to turn due to engine resistance. With it in 4wd and neutral they will still spin when you put the force on them. Neutral just takes the engine out of the equation, not the diffs.