Swapping in posi - which way to go

[BJM]

I just bought an entire posi axle complete for a good price. Its all there but its really rusty and has much higher mileage than my own car (not sure exactly how much). The open differential in my car is mint, clean, no rust, but no posi. I figure I have two ways to go.

1. Clean up the whole axle assembly and swap it in.

2. Swap the posi carrier from this axle for the open one in my car.

Which way would you go and why?

 

[Eddyman]

I swapped in a posi in place of a open rear on my 86 T Type a couple of years ago. Just keep track of which side each shim goes. Also the ring gear bolts are left hand thread for r and r. I don't remember the torque spec. but the lash should be .006-.008. Some new diff. lube and G.M. posi additive and your good to go. Maybe a two hr. job.

 

[TurboRegal84]

Why not pull the posi carrier, and rebuild it with new Gears, and Clutches...then install it into your current rear?

How do you do this?

There is a great write up on GNTTYPE:

http://www.gnttype.org/techarea/suspension/posi.html

 

[BJM]

I read the GNTTYPE instructions and I am not sure of something. If I switch carriers, don't I possibly have to change the shims used? The carriers are shimmed because the housing width equals the carrier plus shims total size. Doesn't this method ignore the chance that the new carrier might be a different width. Also it doesn't mention checking the gear pattern after the swap. Maybe its assumed you know to do that and how to adjust it.

 

[Crazi]

I think what Eddy is saying is use the shim out of the other rear so the tickness is the same as the one you took it out of. The only problem I can see is the space between the axle tubes being different or the pinion being in a slightly different place the in yours.

But here is how you find out if you want to do it. Switch it all over, and make sure you put the shims that you take out of the other rear on the same side they came from in your rear. If you do this and you have any play, you might have a problem. If you do this and it fits like the old one, you should be good. I just changed my axles and while out, I had to change the bearings on the center housing and changed the axle bearings and seals while I was at it. The way I see it, it was cheaper to do it all then have to back in it if something breaks.

 

[gnturbo]

why dont you take the whols posi housing and gently blast it replace the axle seals and bearings,check the brakes out, bushings,repaint and put it in the car without messing with changing gears out and hold on to your stock axle instead of having a bunch of unassembled parts laying around ,this way you have your "complete"original open rear end sitting there safely wrapped in plastic.That is what I was gonna do but just settled for getting and eaton installed

 

[BJM]

More details

I just opened up the cover and drained out the fluid. The ring gear has a chunk missing off of two teeth. Each chip looks the same and they are on nearly opposite sides of the ring gear making me think it happened at two different times. The affected teeth are missing the outer 1/3 of contact area. Does this mean the gear is scrap? The pinion looks fine.

Also how do I measure the 8.75" dimension. The gear ratio seems about right (by eye). With a measuring tape and bad lighting I see about 8.5". What distinguishes the GN axle from a lowly 10 bolt? The axle measures 57.5" flange face to flange face. Is there a stamping somewhere amongst the rust.

I am guessing I should keep only the carrier and rebuld it alone. Where can I get a rebuild kit for one of these axles?

One last thing, there is a large ring magnet inside the cover, is this a factory thing?

 

[UNGN]

Re: More details

Originally posted by BJM
I just opened up the cover and drained out the fluid. The ring gear has a chunk missing off of two teeth. Each chip looks the same and they are on nearly opposite sides of the ring gear making me think it happened at two different times. The affected teeth are missing the outer 1/3 of contact area. Does this mean the gear is scrap? The pinion looks fine.

Also how do I measure the 8.75" dimension. The gear ratio seems about right (by eye). With a measuring tape and bad lighting I see about 8.5". What distinguishes the GN axle from a lowly 10 bolt? The axle measures 57.5" flange face to flange face. Is there a stamping somewhere amongst the rust.

I am guessing I should keep only the carrier and rebuld it alone. Where can I get a rebuild kit for one of these axles?

One last thing, there is a large ring magnet inside the cover, is this a factory thing?

Here's a link that shows some photos of an 8.5" 10 bolt. Note the 2 "corners" at the bottom of the pumpkin that signify an 8.5" vs. a 7.5"

Photo guide

if any teeth are missing, junk the gears. If the missing area is not in a contact area, I'd keep them.

 

[Eddyman]

Re: More details

Originally posted by BJM
I just opened up the cover and drained out the fluid. The ring gear has a chunk missing off of two teeth. Each chip looks the same and they are on nearly opposite sides of the ring gear making me think it happened at two different times. The affected teeth are missing the outer 1/3 of contact area. Does this mean the gear is scrap? The pinion looks fine.

Also how do I measure the 8.75" dimension. The gear ratio seems about right (by eye). With a measuring tape and bad lighting I see about 8.5". What distinguishes the GN axle from a lowly 10 bolt? The axle measures 57.5" flange face to flange face. Is there a stamping somewhere amongst the rust.

I am guessing I should keep only the carrier and rebuld it alone. Where can I get a rebuild kit for one of these axles?

One last thing, there is a large ring magnet inside the cover, is this a factory thing?

Was this assembly out of a stick car? With the ring gear chipped, it could be. Any way if youve got the right carrier, you just want to put your ringgear on in place of the chipped one. You should get new bearings pressed on and new axle seals as well. Use the shims out of your "open diff" keeping track of which side they came out. Check lash should be .006 to.008.

Eddyman

 

[BABY BOEING]

I wouldn't intermix gear sets buy just changing the ring gear. I think this would give you a nasty howl. As far as which shims to use, I would try to use the correct one's for the rear. Gears and carriers are for the most part persison pieces with minimal variences from one to another. On the other hand rear end housing are not. In my past experiences if the gears you are removing have a good wear pattern the new one's will to with the same shims. Install the new gears and if the wear is to heavy on the heel increase pinion depth, too heavy on the toe decrese pinion depth. Set carrier shims for correct back-lash. Hope this helps. Thanks Jon

 

[BJM]

Just to clarify....

I would keep my whole rear axle assembly except I would be swapping in the posi carrier. I will put my original ring gear onto the new carrier.

I figure I could use a CMM to measure my old carrier size and compare it to the new one, that way I would know how much the shim pack total should be changed.

Also, since my pinion will never move, I assume that it should not need to be reset in any way. The new carrier has to rotate about the axle centerline which is fixed by the housing. The only thing I will need to adjust is the side to side position of the carrier by playing with the shims.

Where should I get bearings, clutches, shims, etc. Is one of the those Summit rebuild kits the way to go?

 

[GNFURY]

Like the man says, spend some money and do it right. I am rebuilding my whole damn car. It does not have posi, so I ordered

-moser 30 spline axles

-eaton posi unit

-new motive ring gear

-t/a girdle cover

-master seal and bearing kit

Needless to say, I wont have to crack my rear open again for quite some time ( I hope!)

 

[Eddyman]

Re: Just to clarify....

Originally posted by BJM
I would keep my whole rear axle assembly except I would be swapping in the posi carrier. I will put my original ring gear onto the new carrier.

I figure I could use a CMM to measure my old carrier size and compare it to the new one, that way I would know how much the shim pack total should be changed.

Also, since my pinion will never move, I assume that it should not need to be reset in any way. The new carrier has to rotate about the axle centerline which is fixed by the housing. The only thing I will need to adjust is the side to side position of the carrier by playing with the shims.

Where should I get bearings, clutches, shims, etc. Is one of the those Summit rebuild kits the way to go?

Sounds like your on the right track BJM.

Eddyman.