7-1/2" Rear to 8-1/4" Rear -- Question

[RPMagoo]

Both are now large bolt pattern -- Are the backing plates, and brakes the same ? -- Is the driveshaft the same length ? -- Yokes the same ? -- It is a 65 Valiant.

 

[Professor Fate]

Both are now large bolt pattern -- Are the backing plates, and brakes the same ? -- Is the driveshaft the same length ? -- Yokes the same ? -- It is a 65 Valiant.

If by saying "both are now large bolt pattern" you mean you currently have a '73 and up 7.25 with LBP, then yes- brakes are the same. If you have a '72 and earlier axle with conversion axles such as the ones from Dr. Diff Mopar Axle Pkg 7 1/4" A-Body 5X4 1/2" Bolt Pattern (pair) , then no- the brakes will not fit an 8.25.
Driveshaft will need to be shortened to fit the 8.25.
U joints/yokes may be the same, but measure to confirm. It may be dependent on year and application.

 

[Dana67Dart]

Both are now large bolt pattern

That would mean that someone swapped in a 7 1/4 (I assume that's what you meant to type when you said 7 1/2) from another vehicle (B body?) or a very late model A body ro had axles modified or replaced.

Are the backing plates, and brakes the same ?

the A body backing plates (10x1.75) are unique to A Body, BUT not knowing anything about the rear you have it is not posable to make that determination

Is the driveshaft the same length ?

It is unlikely the drive shaft is the same length. Doing a 1967 7 1/4 to 1967 8 3/4 swap, the 8 3/4 is longer from the pinion U joint centerline to the centerline of the axle so the drive shaft needs to be shortened

Yokes the same ?

There is no way to tell. there are 3 basic u joints so the yoke needs to match. if you are asking if the yoke offa 7 1/4 will fit an 8 1/4 I doubt it.

1. 7260
2. 7290
3. 1310

There are conversion U joints



7260 to 7290

7260 to 1310

not sure about 7290 to 1310

It is a 65 Valiant.

Since you have a 65 Valiant and the 8 3/4 and 8 1/4 A body specific rears fit 66 to 76 its not likely to be a direct bolt in.


ALSO depending on the 7 1/4 you have (might be all?) the shock plates will need to be changes 2 3/4(IIRC) tube OD vs 3" OD for 8 1/4

 

[Professor Fate]

And don't forget about the parking brake cables, they may not be directly compatible.

 

[Dana67Dart]

And don't forget about the parking brake cables, they may not be directly compatible

 

[RustyRatRod]

Unless they went to a five bolt flange on the large bolt pattern 7 1/4, the backing plates are not interchangeable. I know the early 7 1/4 rears only had four bolt flanges. Just something to watch out for.