I need an 8 3/4 lesson. Better late than never!

-

89on35s

Inferno Red Duster
FABO Gold Member
Joined
May 11, 2006
Messages
2,534
Reaction score
3,557
Location
Martensville Sask. Can.
So for my spring upgrades I installed an 8 3/4 diff in my 74 Duster. It has a 360, an A-500 OD auto trans and my 8 3/4. I put it together with an original housing that I got sand blasted and powder coated, new Dr Diff large bolt pattern axles with non adjustable bearings, 10x2.5" drum brakes and a 4.10 geared cone sure grip equipped 742 center section. It was a supposedly good swap meet special.

When I put it together I first installed the center section, next the brakes, and finally the axles. When installing the axles, I had to tap them in with a rubber hammer to get them to where I could start the nuts and snug up the bearing retainer plates but everything seemed to go together as I expected it would. The only thing I was unsure of is whether I had to remove the spacer in the axle hole of the sure grip. What I read told me I didnt need to remove this, so I didn't.

As I was pulling out of the garage for the first test drive I heard a loud bang. I stopped, jacked it up and rotated the diff and all seemed smooth. I took it for a couple mile test drive and all seemed smooth till I turned into my driveway and I heard another loud bang. I pulled it apart tonight to find broken teeth on the spider gears. Not sure if it will be visible in the picture but there is a piece of spider gear tooth between the case and the spring. I could see 2 teeth that had been sheared off through the spring window in the case.

What would cause this? The spacer i didnt remove? I have a new clutch style sure grip to put in there but I don't want to wreck it too. Any ideas?
Cley
20190417_221037.jpg
 
The spiders were seized on the pin. The block is nowhere near the spiders. Only made noise when u turned. Happens a lot. That’s 1 reason I won’t buy a cone type Sure grip. Kim
 
If the block was a problem when you installed the axles you would have bent the retainer plate on one side or the other.
In which case you could have ground a 16th of an inch off the axles one at a time untill they fit correctly.
 
When you put the new power loc in make sure to use the motorcraft lsd additive in the sure grip fluid.
The new unit may pop untill the lube gets worked in but I have had to add a second bottle some times too.

Be sure to clean the inside of the housing real good.
 
Mopar still sells the diff additive but broken chunks does not come from no additive. That’s a failure. Could had been cracked before you purchased the unit.
That stinks.
 
The retainer plates are good. I guess I just got a bad deal on that center. Now I will learn about diff setup. Plan is to leave the pinion alone and just replace the sure grip using the same ring gear of course. If I put it in and set backlash I should be good right?
 
If I put it in and set backlash I should be good right?

Check the backlash before you disassemble it, and set it back to that setting assuming this is a used R&P. If you set it to factory you 'might' get some howl (gear pattern will be off from it's wear pattern).

If you are running the roller bearings leave the thrust buttons in there. If you are running the Green bearings you can remove it. Very easy to do on a clutch type suregrip.

Also, you stated you had to tap the axles, that's because (most likely) the two sets of splines weren't lined up. There are 2 sets of splines for the axle to go into on each side.

I usually mark the bearing caps and put them back on the way they were. Don't forget the ring gear bolts are left hand thread. When you put them back in I would use a drop of RED Locktite on them and torque to spec.
 
Flush out the front of the housing real real real good. Things collect in the passage under the pinion.

The autocraft additive works better than the Mopar. If you use the Mopar to be brand loyal be sure to get 2 or 3 bottles. lol
If you are using the tapered axle bearings leave the button in the carrier. You don't need it if using the roller bearings.
Do not tap the axles into a power loc clutch type unless you want to pull it back out to rebuild the clutch pack.
 
Could the need to use a rubber mallot be due to the o ring around the wheel bearing?
 
Why change out the case? Just replace the sidegears and spiders as a SET. You can clearance the cones right away while you got it apart, to ensure years of trouble free operation. I set that to about .080 (not critical) by machining off the bottom of the cones. Then I shim the side gears back toward the center of the case by doubling up the sidegear washers; the sidegears have to have a lil backlash to operate smoothly. So you may need select fit washers. I get mine at the Mustang dealer,lol.
Finally I set the turning torque to, in the range of 110 to 120ftlbs, using the oil and additive ratio that I plan to run,well mixed. A hundred# is not enough and too much more than 120 will make it want to act like a spool with skinny tires.... 120 works well with my baked-hard 295BFGs.
To do that, I do whatever it takes in terms of spring preload. If you do this right, it will be a once in a lifetime deal. Ok, I confess; once in 20 years or 125,000 miles for me and still going.
 
Why change out the case? Just replace the sidegears and spiders as a SET. You can clearance the cones right away while you got it apart, to ensure years of trouble free operation. I set that to about .080 (not critical) by machining off the bottom of the cones. Then I shim the side gears back toward the center of the case by doubling up the sidegear washers; the sidegears have to have a lil backlash to operate smoothly. So you may need select fit washers. I get mine at the Mustang dealer,lol.
Finally I set the turning torque to, in the range of 110 to 120ftlbs, using the oil and additive ratio that I plan to run,well mixed. A hundred# is not enough and too much more than 120 will make it want to act like a spool with skinny tires.... 120 works well with my baked-hard 295BFGs.
To do that, I do whatever it takes in terms of spring preload. If you do this right, it will be a once in a lifetime deal. Ok, I confess; once in 20 years or 125,000 miles for me and still going.

They don't make new side gears and spiders and the PIN for the cone type Sure Grip.
You see the guys rebuilding these by Machining the side cones down and shimmying up the springs. You cannot get new internal parts for these carriers.

I suggest before you put that carrier back up under that car that you stick an axle in each side of that Sure Grip unit and make sure that the clutches are lined up so that you don't have to fight that thing to get the axles in.
If for some reason the axles will not slide in and out of that carrier you will have to loosen the bolts, line the clutch disc backup using the end of your axle and tighten the bolts down with the two axles stuck in there to keep things lined up.
 
Thanks so much for all the tips. This site is great! Now that I have it out, I'm not sure what I had. Can anyone identify my old SG from this picture

Cley
20190418_203412.jpg
 
I believe it is called an Auburn unit. It is the cone type not rebuildable. Although we have found ways to get past that.

Look at the Cross Pin hole in the side of the housing and see if it has egg-shaped.
The bolts that hold it together are left hand thread I believe so don't try to loosen them and find yourself tighten them.
 
I already have another one. I got the ring gear on and back in the case last night. I'll play with setting backlash when I get back from the Easter weekend.

Cley
 
-
Back
Top