Rear axle gears

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JDNightFox
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Rear axle gears

Post by JDNightFox »

Still looking for the 3.83 gears for the rear so I can match them up. I have the 4.10 gears (and the entire front hub assembly) that I can trade. I’d rather just swap the rear gears because the rear input seal is leaking so it will need to be pulled apart anyway and there’s no need to put twice the effort into both axles
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tallsailor
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My tercel:: '83 4x4 w/blue plaid

Re: Rear axle gears

Post by tallsailor »

I have an '83 4x4. I just replaced the tranny and front diff with an '85 or later donor. I like my new 4.11 gear ratio, but I need to match the rear before it snows in the U.P. of Michigan for real.

If we can work something out, I could swap my rear third member for yours. What repairs are needed to yours before they are serviceable? Generally speaking, where are you located?

Best,
John

tl:dr want to trade my 3.83 rear 3rd member for your 4.11 rear 3rd member...
'83 Tercel 4x4 blue plaid interior
'95 Previa SC AWD rally machine dadvan
Sadly deceased: '95 Tacoma 2.7l 4x4
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Petros
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Re: Rear axle gears

Post by Petros »

replacing the rear input seal on the thrid member will distrupt the relationship between the ring and pinion gear. You many need a shim kit along with the new seal to make sure you get the clearance (the lash) correct between them.

It is not that complicated (the procedure is in the FSM, and you can find youtube tutorials on it), it is just one more step to be done before you put it back together. However, if done incorrectly or if you neglect to get it back into the same position after you get the seal replaced, the diff will not last very long. It is possible that not getting the lash correct can result in gear teeth soon breaking off and very quickly wrecking the diff assembly.

It is something important that the gear clearance be checked and adjusted if necessary, before you complete the reassembly.
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tallsailor
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Re: Rear axle gears

Post by tallsailor »

Thanks for the insight on that. I have always said I wouldn't re-gear anything because I didn't want to have to adjust the lash!

Since I haven't looked into it extensively, maybe you can clue me in on the process a bit more: To replace the input seal, will the entire carrier have to be removed? Or can the seal be replaced with the pinion in place?

(Secret reason for asking is that if I'm in there I might try to find a spool to lock up the rear end... bad thoughts... but if no need to pull the carrier then I would be reasonable)
'83 Tercel 4x4 blue plaid interior
'95 Previa SC AWD rally machine dadvan
Sadly deceased: '95 Tacoma 2.7l 4x4
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Petros
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Re: Rear axle gears

Post by Petros »

you have to remove the input flange, which requires removing the large nut that holds the whole input shaft and pinion in place. It might be possible (if you are lucky) to just replace the seal and than re-torque the nut, and hope the lash is not affected. But I doubt that would happen since you disturbed the whole assembly and are unlikely to get the big nut and pinion shaft threaded and torqued back into the exact same position.

The problem as I see it is that the factory did not use solid steel shims to adjust the lash, which would likely all go back into the same place if they did. They used a soft crushable washer, common with most production cars these days, and even without taking the diff apart, they tend to compress on their own over time just from normal driving loads (and occasionally you have to pull the diff to readjust the lash after a lot of miles). I have seen otherwise good diff assemblies that had uncomfortably large amount of lash from this soft washer compression, that has never been disassembled.

What I think would happen is when you remove the large nut, and unload the washer, to replaced the seal, it seems unlikely to retorqure back to the correct amount of lash since the washer would compress again, or some more, when you torque it down. interesting is that the FSM has you use shims to reset the lash, not the factory crushable washer. the crushable washer, as a means of getting correct lash, may just be an assembly line time saving process (likely done automatically), and not suitable for a shop repair process.

What is involved is not that difficult, you have to install shims of different thickness behind the pinion to change the gear lash. You torque it up with a 'best guess' shim thickness, than check the lash and gear wear pattern, than take it apart and adjust the shim thickness accordingly. The different shim thicknesses moves the pinion in and out in relationship to the ring gear. It is trial and error, so it can be time consuming, but it is not difficult. The more differentials you do, the faster you can zero in on the correct shim thickness. The factory service manual gives you a table of shim thickness vs. lash to guide you.

The wear pattern is checked at the same time by putting a waxy die on the gear faces, rotate the gears after it is torqued up, and than observe the contact pattern. The contact should be centered on both the ring gear tooth and the pinion tooth, if it is off center, than you have to change the shim thickness until it centers the wear mark on the face of the gear teeth. There should be shim kits for the diff that give you a variety of different thickness of shims, might even come with a seal kit. They do not cost much as I recall.

this process always frightens people, but I have seen it done lots of times by experienced mechanics I had worked with many years ago. It is not difficult, your assurance is that when the lash and wear pattern is correct, it will run trouble free for many many miles. If people ignore the process, and get the clearance wrong (and do not bother to check it before they install the diff assembly), the diff disintegrates and has to be completely replaced. So it gets a reputation for being "difficult". not so much difficult, it is just an important and time consuming process that must be done, and people are tempted to skip it and hope it will work okay once it is back in the car and you can not see (or hear) that anything is wrong until it bundles itself up miles down the road.

It would be like rebuilding an engine and never bothering to check you got the right size pistons in the bores of the cylinder block. bolt it all together and hope it will run after you get the engine installed. It is a bad idea, and I would advise against it.

Sorry for the long post, but I could not think of a way to explain it without going into detail so it is understandable. Now, go look at the FSM process, it will be more clear I think.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
teranfirbt
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Re: Rear axle gears

Post by teranfirbt »

Generally the shims on the pinion are there to set where the pinion teeth ride on the ring gear teeth, as in are the contact points centered. Lash is set with the large threaded wheels on either side of the carrier assembly, they are used to move the carrier left or right relative to the pinion to set the lash. When I'm back home I'll post a link to a dude who documents setting up Toyota diffs for trucks in extreme detail.
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tallsailor
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Re: Rear axle gears

Post by tallsailor »

I burned an evening the other night looking at pics of gear/locker builds by a guy in AZ. I think I've got a pretty good idea now. Definitely not something I'm stoked to tackle in my spare time at the moment!

Fortunately, it turns out that the guy who gave me the tranny also has a rear third hiding in a closet with 4.1 gears, so I should be able to go pick that up this evening! My wife will be happy to have 4x4 back!

Thanks all for the advice.
'83 Tercel 4x4 blue plaid interior
'95 Previa SC AWD rally machine dadvan
Sadly deceased: '95 Tacoma 2.7l 4x4
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