1986 Tercel Wagon 4WD (lurching)

[Cbileske]

Well, I just picked up my 86 Tercel 4wd yestarday. Given to me from a friend.
Im pretty new to these cars and would like input on the 4wd. When it is engaged in 4wd it lurches even while going straight. I had to find a couple tires for the front to drive it home yestarday so i put some 155/80/13s on the front, the rear has 160/80/13's. So all the tires are the same height, just the 2 fronts are a little wider. On the rear one tire has about 50% tread and the passenger side is a slick, This is what im thinking is what is causing the lurch, one tire wants to spin and the other is grabbing.
What do you guys think? The car should be able to shift in and out of 4WD on the fly, correct? Right now it will shift into but not out of 4WD on the fly, have to go into reverse to shift out.

Thanks for the help

[keith]

For the 4wd to work best, the tires should be within 2/32" tread depth and all the same size. The side to side is not real critical as there are conventional differentials at each end. The center coupling is not a differential, its a coupling so the output shafts at each end have to match or it puts pressure on the gears making it difficult to disengage.

I strongly urge you to not use the 4wd until both ends match, otherwise you can damage the coupling, and it won't be cheap to repair. In an emergency, if you are on a very slippery surface and you need to get the vehicle moving, you can use the 4wd as the slippery surface as the tire slippage will take tension off the gears. It should not lock the coupling under those circumstances. Actually, that is the only time you should use the 4wd anyway.

Even with matching tires, on a high traction surface, the front and rear tires only turn at the same speed when you are going straight ahead. Any turns will put tension on the gears as the front tires take a longer path in a corner than the rears.

[Cbileske]

Thanks Alot for the reply keith. I will hold off and find four matching tires. Or two to match the front two.

[danzo]

What Keith said - I wouldn't use the 4wd unless necessary and/or you find out what the problem is. If you have good front tires you might be surprised how well the car works in fwd.

But FYI - your rear tires are slightly taller (larger diameter and circumference) assuming they are 165/80/13s. The aspect ratio (80 in your case) is a percentage of the width - 80% of 155mm is less than 80% of 165mm. But this may not be causing your problem since it's such a slight difference.

Good luck and welcome to Terc ownertude, you'll enjoy yourself. I wish I had friends like yours!

[xirdneh]

were you driving on dirt or pavement when this happened?
on pavement (not a good idea) the lurching will be obvious on turns
on dirt not so obvious
has the transmission ever been replaced? (could have missmatched tranny to rear differential)

[Cbileske]

It was on a snowy Paved road. It has got to be the tire size difference, I had my tire dimensions messed up. So the front two are 155's and the rear two are 160's. It seemed to work fine up till they were put on. I wil just leave it in front wheel drive for now, untill some matching tires are put on.

[danzo]

I'm curious - what tires do you have on the rear? I've never seen a 160/80/13. If you don't get snow often, it may serve you well to stick with the tires you have.

[Cbileske]

I'm curious - what tires do you have on the rear? I've never seen a 160/80/13. If you don't get snow often, it may serve you well to stick with the tires you have.

Sorry they are 165's on the back and 155's on the front. I live in the BC interior.. so we get snow. I wont be driving the car this winter, gonna leave the insurance on the Toyota Pickup for now.