8-3/4 Rebuild Questions...

[493charger]

I have a '68 Charger that has a 742 posi. The pinion seal was leaking and I got a new one, but when I removed the yoke I found more damage. The outer pinion bearing is junk, and who knows what else. I have another complete 8-3/4 with a 489 posi out of a '69 Roadrunner that was rolled with only a couple thousand miles on it. My dad picked it up around 1970 and the rear end still had fluid in it until a few years ago when I was going to build it up for the Charger. But, it hasn't rotated in 40+ years and I'm unsure if the posi is still any good.

Here are my thoughts...
489
+ Stronger pinion
+ Posi has low miles
- Posi is most likely a cone type that isn't rebuildable, and has been sitting for years.

742
+ Clutch style posi unit that is rebuildable.
- Posi most likely needs new clutches.
- Slightly weaker pinion.
- I'm also not sure if there is gear damage or not

What if I use the 489 and swap in the 742's posi with a fresh clutch kit, bearings and a CSE?

 

[Meep-Meep]

The difference in the pinion strength between the 742 and the 489 is not worth mentioning, especially if this is a street car. You can even use the 741 without problems.

There is a carrier bearing difference between the two carriers but a swap is possible.

The 489 is a crush sleeve, so if you remove the yoke to change the seal you loose your bearing preload, or at the very least will have to re set it. The 742 just tightens to a shoulder so no big deal.

 

[5.7 hemi]

X2!!

 

[RustyRatRod]

IMHO, without a cruch sleeve eliminator, the 489 is the weaker of the two. However, when a crush sleeve eliminator is used in the 498, it is somewhat stronger, I believe. That said, I've been around cars turning wrenches since 1974 and have yet to see a broken pinion on any of the three cases. I know one guy from Florida that comes up every year for a Mopar race in Reynolds, Georgia that has 68 Charger. He runs a 741 case 8 3/4 with 2.94 gears and that car runs high 11s. No, I aint kiddin. He aint broke it yet.

 

[lewtot184]

in my opinion, the '489 could be stronger due to the tapered stem but mostly due to the larger pinion bearing. the bearing is the only thing that holds the pinion in position. due to the way the gears are cut. when a load is applied to the gears the pinion tries to push out the front of the housing. the only thing that controls that is the inner pinion bearing. eliminating the crush sleeve can help control the forward thrust. i think the '741 is vastly inferior to the '742 or '489 when being used in a high torque engine. the small inner pinion bearing can't control the forward thrust during extreme loading. keep in mind that even a 361 2bbl got the '742 case. the '741 has a spacer sleeve over the pinion stem to get proper inner and outer preload on the bearings. the '742 eliminates the spacer and allows for a larger inner pinion bearing, but this bearing isn't as large as the '489 bearing. carriers are basically the same on all three. the cone type and clutch type posies use different carrier bearings but both will fit either housing.

 

[Supershafts]

The crush sleeve is never a issue. All the non CC does it make anyone able to change the seal and have no knowledge needed for such a thing.

 

[493charger]

I'm planning on using a Ratech CSE (crush sleeve eliminator)... But the car isn't stock, it has a 500" stroker with 600+ lbs of torque. I cannot afford a Ford 9" or Dana 60 swap at this time, so I'm trying to build the strongest diff I can with the parts I have laying around.

 

[Cranky]

We've (couple of us that raced a lot in the 80's) shaved teeth off of all of them once the torque gets up high enough. In our case it was low 11's running around 3200 lbs and a 4 speed.

 

[493charger]

Here's my problem...
http://www.youtube.com/watch?v=KcNnY_j2T5k

 

[Cranky]

Here's my problem...
http://www.youtube.com/watch?v=KcNnY_j2T5k

Does it do that with the yoke bolted up on it? Without the yoke, the bearing isn't tied down....

 

[493charger]

Yes, but not to that extent, maybe about 1/3 - 1/2 of that... It was leaking excessively and the seal appears to be damaged pretty bad... I just assumed the pinion bearing was damaged.

 

[493charger]

I also had a question about fluids... The general consensus seems to be to use a non-synthetic 80w-90 and Ford friction modifier, but some frown upon this. I found this stuff at O'Reilly and thought it looked like it might work...