posi rear end question for you guys

[michael bustamante]

Ok I got my hands on a 68 posi rear end 12 bolt. my question is, can I take the posi unit out of this and install it in a 71-72 rear end or will it not work?
trying to decide if I need to buy the 5 lug shorter axles from ECE or not.

[nightmare]

it should work, as long as the series is the same (basically the gear ratio). IIRC, series 3 goes up to 3.42 (and a smaller 3.73), and series 4 goes from 3.73 up through 5.02 (or something to that effect).

[chevy_mike]

If you remove it from one housing and put it into another housing, you have to do all the setup work to get the pre load and backlash set correctly, otherwise your gears are not going to last long.

Typically the only time you don't have to resetup the rear end is if you remove and put back ALL the exact same parts. Change anything in the diff part (like bearing, gears) you have to set everything up again.

[michael bustamante]

so itd be best to have the posi set done by a pro huh? I was afraid so

[Hart_Rod]

Originally Posted by michael bustamante

so itd be best to have the posi set done by a pro huh? I was afraid so

If you don't feel like messing with it, I could take it off your hands.....

[michael bustamante]

Originally Posted by Hart_Rod

If you don't feel like messing with it, I could take it off your hands.....

ALways a joker in the group isint there?

[prostreetC-10]

What ever you do....don't try and use just the posi and ring gear with another pinion. These things all wear together. You can swap everything but man.....now would be a good time to get that perfect gear ratio and new gears all at the same time. Gears are not too bad $$$ wise the the mechanic is going to have to do the exact same thing whether it's new or used gears. Just a thought!

P.S. As said above just make sure, if you are getting new gears that you stay within the carrier series.

[michael bustamante]

another question, when I was removing the tires I had one tire on the ground and the lifted tire would spin. I thought that posi`s would spin if one tire was on the ground, I know it is aposi cuz I took the cover off, does this mean the posi unit is worn?

[LONGHAIR]

If the transmission is in neutral, or drive shaft disconnected, you could turn it...but if it turns easily, the clutches are worn.

[turp mcspray]

I have swapped LOTS of used gears around and only once did it make any noise. If you swap in the posi with your old ring gear and put the same carrier shims back in the same sides I think you will be fine. Kind of feel how much backlash there is before you take it apart and compare that to the backlash with the posi. I know it sounds kind of "back woods" but I've done this more times than I can remember, and I've driven these rear ends across the country and back.

[prostreetC-10]

Turp...are you talking using The same ring gear with a different pinion??

[special-K]

I think he`s talking about the set-up not being a big deal to keep the same.Like when swapping the 5-lug rear`s gear onto the`68 posi diff and putting it back in the 5-lug rear.

[turp mcspray]

NO! Always keep ring and pinion together. The pinion is set specificly for the housing. Ring gear back lash is really simple. After you've done enough of them you can pretty much set up backlash by feel alone. Ideally when swapping used gears you should swap the pinion shim so it stays with the housing it came with. I have a buddy who sets up gears and when he sets up a new set he always starts with the original pinion shim that was in the housing and very seldom does he ever need to change from that. When I swap used gears I don't worry about it. If I did this once or twice and got away with it I would probably figure I got lucky. But seriously I have done this more times than I can remember and for this guy to just swap the posi (with his old ring gear on it) I feel VERY comfortable saying DO IT!

[prostreetC-10]

Okay.....I feel better now!! lol

Yeah, I did the same thing but went the extra step just because I had the dial indicator. Started with .008 and when I was all done, finished with exactly .008. ZERO noise and she hooks like a tow truck!