I want to install a posi unit into my 10 bolt. I know the gears are 3.42, but am unsure if the spline count is 26 or 28, because it's an '89. Right now it's an open differential. Let's assume it's a 26 spline, what all has to be changed to install a posi unit into this rear?

I tried searches but it didn't turn up as much information as I'd like. Thanks in advance.

 

All I know is that 87 and up is 28 spline...or 86 i dont remember but your year is a 28 spline.

 

and i know you're wrong

most likely the 89 is a 26 spline since the change over came late in the year, but you need to check to see for sure. to swap in a posi carrier you'd neeed a carrier of the correct series and spline count. that's it, change the ring gear over to the new carrier, check back lash and you'd be all set.

 

Is the carrier the actual posi unit? What if I'm using a posi for the same gear ratio, does the ring gear still nee to be changed, or can I just put the posi unit in, check back lash and be done? Also what is back lash and how to you check it?

 

Yes the carrier is the posi.

Yes you have to change the ring gear over to the new carrier; otherwise you won't have a ring gear in your rear, and your performance will be somewhat compromised. Especially your 60' times.

Backlash is the play between the gears. You use a dial indicator. Correct setting is when the ring gear has about .006" - .012" that it can move back and forth measured around its edge, when the pinion is held still. A little more is better than too little, because the gears "grow" when they gat hot, and if there's not enough backlash, then they will end up with negative backlash when hot; and as we all know, 2 objects can't occupy the same volume, without terrible and expensive things happening.

89 was the changeover year between 26 and 28 spline axles. If you have that year, YOU ABSOLUTELY MUST CHECK IT, or you will probably order the wrong part. The majority of 89s got the old 26-spline stuff, probably 80% or more. But as soon as you assume that you have whichever one you think it is, your parts will morph into the other, and whatever you buy, will become wrong. So pull an axle and check BEFORE ordering anything.

 

All I have to do is get the correct carrier (series and spline count), install the ring gear I currently have onto my carrier, check the backlash, and that's it? Should I do anything with the bearings on the carrier, or the seals on the axles? Can I buy a used posi unit, or will that mess things up with my gears? The rear end has about 113,000 miles on it and a v6 was pushing it, so I doubt that it has much abuse on it.

 

3.42 gears are probably a 3 series, but sometimes the factory used a spacer, and a 2 series.... Not sure what each series looks like, or how you'd know the difference...

You'll probably want to buy an install kit, it'll come with all your favorite shims and bearings etc, which are worthwhile to swap now. Budget $100 or so. Axle bearings and seals are also a good idea (probably not in the kit). Pinion bearings, pinion seal and nut should be in the kit.
If you get the kit from ratech, you can get the solid pinion spacer at the same time, rather then getting a kit locally, and the one part from ratech...

Used posi would be ok, but be wary of which one you obtain. Check the spline count on your axles, if 26, then you can get a posi from an earlier 3rd gen (before '89), or maybe S10 IIRC. If you have 28 splines, you can get one from a 90-'02 Fbody. Of course don't get a gov-lock, you can go for an auburn, eaton, or torsion, whatever floats your boat. (as long as the spline count is right).



very wise advice, no matter what you ***-U-ME, you'll be wrong.

Remember, you need to buy a dial indicator, and magnetic base to check your backlash. Maybe some gear marking compound too?

 

Is that backlash the same for the 26 and 28 spline carriers, or is there a difference?

 

Yes, the backlash is the same.

Also, when you change over the ring gear to the carrier, make sure u torque the new bolts you got in the install kit to the right amount, and in alternating order. I believe when i did mine we torqued them to 70lbs, installed it, then torqued them to 90lbs. works fine, but check ur user manual.

question for everyone else......the factory gm gov-loc is not the same as a factory eaton right? lemmie know.