What rear

[steve from staten island]

I have a 8 1/4 open rear 273 ratio at present in my car. I also have a 8 3/4 sure grip 355 gears. The 8 3/4 is out of a 66 Charger or so was told and looking at the body specs it seems the rear in that car was about inch total shorter. I was thinking of using the 8 3/4 in my 69 Satellite. What do you think? Thanks of course.

 

[1967coronet]

I would measure them both backing plate to backing plate and the spring perchs.
If only 1" total diff I would sure use the 8.75

 

[Ironbuilt]

I agree with @1967coronet if the difference is only an inch, I would go with the 8 3/4. I know that you have the ability to relocate the spring perches if need be.

 

[PRND21]

Not being familiar with the 8 1/4, I would also measure from the axle centerline to the yoke and the width of the yoke to see if you can use your existing driveshaft.

 

[Kern Dog]

Sounds like a good plan. Your U bolts and spring plates interchange. The 66-70 B body leaf spring spacing is the same. No need to cut and relocate the spring pads on the axle. The brakes & backing plates interchange but some 8 1/4" axles only use 4 bolts to secure the backing plates while the 8 3/4 used 5. You may have to drill out the 5th hole in the backing plate or maybe it is already there....Check to see.
The drive shaft will need to be shortened because the 8 3/4 yoke is further forward. You may get lucky though. Install the axle and see if the shaft fits as is. Some drive shafts were shorter than ideal even from the factory. You want the front yoke to have at least 3/4 to 1 inch of forward movement into the transmission. (Before bottoming out) Check with the car resting on its tires to allow for fore and aft movement when the car is in motion and the suspension moves up and down. If the drive shaft is too long, the front yoke will bottom out in the trans and damage the guts including the front pump...REbuild time!
Good luck. The gear ratio change will be a noticeable improvement.

 

[snakeoil24]

Dump the 8 1/4 for the 8 3/4 big diffrence in durability.