68-72 rear end issue

[Jd63]

I took the posi diff out of a 68 and put in a 72 rear end housing but now I have axles that have in and out play at the Center diff pin, did I do something wrong or does that swap not work since 68 has a narrower housing

[PowerdbyChevy79]

Originally Posted by Jd63

I took the posi diff out of a 68 and put in a 72 rear end housing but now I have axles that have in and out play at the Center diff pin, did I do something wrong or does that swap not work since 68 has a narrower housing

What Axles did you use?

[Jd63]

Hi I used the 72 axles. So our other 72 doesn’t have any movement against the axle and Center pin, now the 68 posi carrier that I put in the 72 housing with 72 axles works but it has about .140 thousand movement between the end of the axle and the Center pin on both sides, which isn’t right.
I was wondering if the the 68 has thinner spider gears causing this issue amd how can I fix it
Thanks JD63

[LNP]

Originally Posted by Jd63

Hi I used the 72 axles. So our other 72 doesn’t have any movement against the axle and Center pin, now the 68 posi carrier that I put in the 72 housing with 72 axles works but it has about .140 thousand movement between the end of the axle and the Center pin on both sides, which isn’t right.
I was wondering if the the 68 has thinner spider gears causing this issue amd how can I fix it
Thanks JD63

They make shims that go behind the spider gear. I would check the carrier you took out and check to see if they are thicker than the ones behind the 68 spider gears. As a norm they generally look like the pic below. This of course assuming the two axles are the same diameter so they fit the spider gears equally the same.

[Wrenchbender Ret]

Have you checked the fit of the drums yet. There are differences in the length of those 2 axles. I don't remember all of it but someone will pop in & explain it. Have you tried using the axles from the 68?

George

[Jd63]

No I haven’t, but that diff is narrower than my 72, so they wouldn’t work unless I went back to the 68 diff. The spider gear isn’t the problem its the axle moving in and out on the side gear because it’s not tight against the Center pin which is leading me to believe that the axle gears are not as deep as the 72s

[Myself]

So it seems like you're saying that if the c-clip groove in the axle was a little further outward then the axles would sit a bit further INward, against the pin, right?

[Wrenchbender Ret]

I think when you put the drums on the will stick out. I think there are special axles for this swap. Of coarse the 68 has 6 lugs & the 72 has 5.
I'm surprised someone more familiar with this has not popped in.

George

[raggedjim]

JD, if I understand you correctly you are using the 72 axles in the 72 rearend with a 68 center carrier. This should work fine, I have done it before.

When you did the change did you rebuild the clutch pack? If not it probably needs to be rebuilt. If you can rotate one tire by hand with the other against the ground it needs to be rebuilt.

[Jd63]

I did rebearing it and inspected all the clutch plates and they looked fine, there certainly wasn’t enough wear to take up the difference I need to. I’m afraid it will wear on the axle c clips being able to move in and out and effect handling

[raggedjim]

I'm thinking that as long as you install the pin and the c-clip is still trapped in the cup of the gear so it won't drop out you should be okay. BUT i'm not a rearend guy (well kinda...) but I have had axles out of lots of these trucks and there is usually some play.

[LNP]

Originally Posted by Jd63

No I haven’t, but that diff is narrower than my 72, so they wouldn’t work unless I went back to the 68 diff. The spider gear isn’t the problem its the axle moving in and out on the side gear because it’s not tight against the Center pin which is leading me to believe that the axle gears are not as deep as the 72s

Sorry I said spider and I should have said side gear. The C clip sets inside a groove in the side gear so if the side gear is not shimmed properly or in this case maybe shimmed different from the OE carrier it will allow the axle to move to much in and out. Changing the shims can/ will increase and decrease this movement. Take a dial indicator and measure the in & out play to see if its in spec or not. If I remember right axle end play should be 0.10" - 0.25" Also check the axle in the c clip roove to insure theres not any excessive wear check the c clips as well. Hope this helps and you figure it out.

[Jd63]

I’ll do some checking and post what I find

[Jd63]

Hi
I took a reading and it’s 40 thou play. I have pictures but can’t seem to load them.
So 72 housing. 72 5 bolt axles. 68 posi unit rebrg 40 thou play on axle to Center pin on both axles
Everything looked normal when cleaning diff up. All plates that were there were installed but it’s like it’s missing one one each side which would push the axle gears closer to the pin to eliminate the play, but that won’t work as then the spiders wouldn’t fit.
🤨
Thanks for everyone’s ideas so far
Jd63

[LNP]

0.40 is a lot obviously theres something different between the two years in the differential. If you ever do figure out what it is let us know. Sorry I couldnt help ya more.

[Jd63]

Yeah and I’ve tried different 72 5 bolt axles and it’s the same thing. The end of the axle just needs to be a bit long after the c clip and it would butt up against the Center pin and all would be good.
I could go back to the 68 housing and buy new axles or stick with the 72 and buy a new posi unit I guess are my two options at this point unless there’s another way to resolve my problem .
Thanks Jd63

[LNP]

Just out of curiousity whats the difference between the 68 & 72 axles themselves?

[jerry moss]

Originally Posted by LNP

Just out of curiousity whats the difference between the 68 & 72 axles themselves?

68 axles are 6 lug and shorter.

[LNP]

Too bad not a hair longer. The six lug is not a big deal as I machine shop could redrill the for 5 lug. Oh well it was worth a thought.

[Jd63]

Yeah I figure by the time they redrill the holes at todays shop rate I will just buy new axles if we go that way

[LNP]

I'm not for sure what they charge would be worth lookin into both ways if you go that route

[Jd63]

Yeah I’ll post the answer if I ever stumble across the solution, I was hoping one of the many truck enthusiasts would have the answer.

[Accelo]

Originally Posted by LNP

Too bad not a hair longer. The six lug is not a big deal as I machine shop could redrill the for 5 lug. Oh well it was worth a thought.

So you know their is no way to re-drill a 6 lug for a 5 unless you weld up one hole on the axle flange.

[Jd63]

Yep I know that, but we’re out in the country and limited service’s

[raggedjim]

40 thou is .040 not .40

If it is .040 I would run it, if it is .40 I would not.