8 3/4 center problem?

[whitey]

Had a problem with my 8-3/4” rear in my 73 Dart. Went to pull out from my driveway, light throttle, and I heard a mild snap then a grinding sound. I leaned out the door and gave a little gas and the drive shaft would turn but the car would not move. Pushed the car in the garage
and removed the axles and center section. The right side axles had ¼” of the splines shaved down (see attached pic); the ring gear turns when rotating the yoke. The axles were installed completely, all retaining nuts were tight and the axle retaining plate was flat against the backing plate.
I installed the axles (only) into the axle housing and measured from flange to flange and got 57-7/8”. With the center section on the floor I installed the axles till they bottomed out and took a measurement from axle flange to axle flange and got 57-5/8”, so there’s a ¼” difference. Using pry bars could not turn one axle less than the other like they are locked together. My axles measure 27-7/8” from end of splines to axle flange.
I removed the sure grip unit (Dana Power-lok, NOT a cone) and disassembled, there were some metal shavings and some ‘sludgeish’ film on the parts. I cleaned with 2+2 and used compressed air to clean and dry the parts. The clutches and disks do have some wear markings on them.
This center came out of a 67 Sattelite (741 case) and never had it rebuilt.

Can anyone tell me what the problem is? Also what is meant by a 2 piece side gear?

 

[Oklacarcollecto]

For sure the axle wasn't in the deep enough. What is the rear end housing out of? Aftermarket axles?

Maybe Crackedback will weigh in on this one.

 

[whitey]

Like I wrote with just the axles in the housing its 57-7/8" from flange to flange. when putting the asxles in the center section, outside the housing, its 57-5/8". only a 1/4" difference.
The axles are Yukon, I bought from Randy's a few years ago. I got the houseing off ebay a few years ago and measures 52-13/16" wide.

The splines are not eaten away but down.

 

[Oklacarcollecto]

I believe you axles are too short. The standard A-body axle is 27 11/16". It has to be longer with the backing plate/drum change if you went to big bolt pattern.

27 11/16 is stock SBP axle for an A body 8.75.

The length is LONGER when you go to a LBP axle because the standoff distance from bearing to axle flange is greater. The standoff is about .400 or roughly 3/8" greater.

so if you do some rough math 27 11/16 + 6/16 = 28 1/16 so the new LBP axles would be ~28" long.

None of this " math is hard" stuff applies if you are using SBP drums and redrilling them to BBP.

Want to buy axles, call Dr. Diff. He's got good axles that will be the proper length and service is second top none! His BBP axles with long studs and green bearings are around $340 delivered.

 

[whitey]

My axles actually measure 27-7/8", those axles actually go in all the waywith only 1/8" clearance.

 

[Bad Sport]

I'm certainly no expert, but when you installed the axles did you set your axle end play? It sure looks like you did not have enough engagement.

 

[whitey]

I have green bearings. That was what I origonally thought when I saw that axle. That why I started measuring. axle flange to axle flange, in the housing and out. With 27-7/8" axles which is longer than normal and the axles bottomed out to housing when bolted down.

I looked at distance between axles when they were in the housing by themselves, just looking at it, it was about 1-1/2". that when I measured from axle flange to axle flange and got 57-7/8". So I stuck the axles in the center section (out of housing just sitting on the floor) and got 57-5/8". So with 1/8" space from bottoming each axle out, I couldn't see how they were not engaging all the way. So I put the center section back in the housing and painted the splines with white teflon compound (all I had to use), and put the axles in and the compound pushed almost all the way out.

While the center was on the floor with the axles bottomed out in the sure grip unit (factory power lok sure grip unit), my father in law used a prybar to try and turn the one axle while I tried to hold on to the other to similate going around a turn. It seems like the axles are locked together from side to side.

So with the measurements indicating the axles are engaging splines and axles moving as if the limited slip has issues I disassembled the unit. Cleaned the inside and spyder gears with 2+2 and dried with compressed air. Nothing seems out of ordinary, inspected clutches and disks and shows some wear...But again for a 40 some year old unit, nothing seems out of ordinary.

Seeing I have 1/4" play and my axles are 27-7/8" (longer than factory) they do offer axles 28"axles.

Thanks for everyones help, it is appreciated and I'm trying to get all the imformation out.

Eric

 

[whitey]

I checked Randy's axle listing, it states the axles I have should not be used with factory posi with 2 pieces side gear, could this be the problem? The Power-lok (clutch style I believe is the 2 pc side gear).

 

[fishy68]

I checked Randy's axle listing, it states the axles I have should not be used with factory posi with 2 pieces side gear, could this be the problem? The Power-lok (clutch style I believe is the 2 pc side gear).

I saw the exact problem when a guy in our club used Yukon axles with a power lock. I didn't do any measurements on his but I did clean out the sure grip and checked things out for him and it looked like the axle just didn't engage into the inner set of splines like it should have. He bought a longer set of axles (28" long I believe but I'm not positive) and put them in and hasn't had a issue since. Another thing to make sure of is that the factory thrust pins are removed from the sure grip. If not they'll keep the axles from going all the way in. Another route you could take is to buy a 1 piece side gear kit from Dr. Diff. That'd be cheaper than buying new/longer axles and should work just fine since there's not much of your axle damaged.

 

[whitey]

Thanks for the info, much appreciated!

 

[crackedback]

I believe you axles are too short. The standard A-body axle is 27 11/16". It has to be longer with the backing plate/drum change if you went to big bolt pattern.

Winner!

The housing is wider than a std a body by a little bit and the axles are shorter than need be.

My guess at what's happening. The powerlock likely has a split side gear set up. When the axles are installed, you get full engagement on the outer set and minimal, where the axle is torn up, on your inner set. I'll go one further that the two gearsets are not lined up now, so the axle can't drop all the way in.

With a 52 13/16 housing, the outer drum to drum with LBP will be over 58". The axles need to be ~28 3/16".

The center gap on a 8.75 rear is ~1.5" So if you add the two axle length and 1.75, that comes up short on your required overall width. The 27.875 axle are right for an overall width of ~57.5"

Like Tracy mentions, easiest fix is one piece side gears and some file time cleaning up the splines.