Differentials

[smitty1259]

Hi Guys:

Thanks for your advice on differing differential ratios, as I brought up in an earlier post. It sounds like having different ratios between front and back is not a good thing if one plans on using the 4WD.

Question: How difficult would it be to find an 83-84 rear differential? I live in a very rural area of Southern Illinois. Largest nearby city is 13,000 people and it's 30 miles away!

Thanks,
Smitty

[MootsMan]

I've been running an '83 transmission in my '86 wagon for a couple of years now, and have never had a problem, other than the speedometer being off, but that is partially due to 14" wheels and tires, too. That being said, I don't do any heavy 4-wheeling at all....only time I will use 4wd is in snow or ice. I would like to know all the in's and out's of mixing transmissions from one gear ratio to another.

[Petros]

With different final drive ratios you would have the front wheels traveling at a different speed than the rear. On a slippery surface like ice you may not noitice but you will make the car act more skittish since you will be forcing one set of wheels to always slip or spin. In the Terc4wd all the wheels are "locked out" like the true old style four wheel drives (one reason I like it better than the newer AWD). This means one of the pairs of wheels will have to be slipping since they are moving at different speeds. Not good I think on a slippery surface either.

DO NOT EVER put it in 4wd on a hard dry surface with different diff ratios! It will bind and put all kinds of very heavy stress on the drive train, perhaps even enough to damage the transmission. IT will make the tires scrub and heat up, put a lot of stress on the cv joints and u-joints, very bad. It likely would put so much load on the drive train you could not get it out of 4wd until you jacked up two tires to unload the drive train.

Once you find either a matching front or rear diff, it is not too hard to swap it out so it matches. IF I had a choice of the two, I would swap out the whole rear "third member", the center carrier you up bolt after removing the rear axle half shafts and the drive shaft. you can just swap the whole assembly without having to mess with the gear lash adustments. Is the rear axle that the car the transmission came out of available?

I have never done it on a Tercel, but I suspect swaping out the front driffernical ring and pinion gear set would be a lot more work, parcially dismatling the transmission to get the diff and imput shaft out. You likely will have to carefully check the gear lash and contact area of the gear teeth. Which means you might have to adjust it by replacing and installing fine shims on the output shaft and carrier barings. At least that is the way it is normaly done on other differncials, but as I said I have never had to do it on a Tercel.

So my suggestion would be to locate rear third member differncial assembly to match what ever the front is, and swap that out. If you have access to a whole rear axle assembly, you can even swap that out complete and not have to break open the axle assembly. But that likely does not save any work, it is just a differnt way to change out the rear ratio. I beleive the same year RWD Corrolas have the same 4.1:1 rear end as in the rear axle of the '85 and on Tercel4wd. So that would give you more options to locate a new rear diff.

Good luck

[SynthDesign]

Running a 4.34 and 3.73 mixed diffs leads to catastrophic transmission failure.

I replaced a rear end in my 2nd 4wd tercel w/0 checking what the front diff gearing was. It drove fine for the first six months. The 2nd time putting it 4wd in the snow and kaboom. Transmission became stuck in 2nd gear and 4wd. I snapped the bolts holding the carrier bearing and drive line to the frame too. I had to have it flat bedded home.

Expensive and embarrassing.

Always worth checking.