7 1/4” Rearend Disc Brake Swap

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chinze57

Push Button tranny and a Slant 6 that'll never die
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I’m looking at going from the rear drums I currently have on my 7 1/4” rearend to disc brakes. All of the common kits I can find are made for 8 3/4” or Dana 60. I found this from ScareBird, will it work for the 7 1/4” or does anyone know of another kit?

I currently have the 14” Mopar Rallye Wheels. I believe that everything front and rear is small bolt pattern. Front already has disc brakes.
 
The kit is you referenced is for the front. I’m not aware of anything for the 7 & 1/4 rear
 
The '9-bolt' rear (with 9" drums?) is rather flimsy and most of us wouldn't waste time upgrading to discs. Why not 10 inch drums instead?
 
You know that it is very easy to accidentally over-engineer the rear brakes right? The rear brakes are designed to do close to nothing on your car for a reason.
You know that you can adjust the amount of rear brake power in other ways, right? Like with increased fluid pressure, increased W/C power, and shoes with a higher CF, right? Right up until the rear brakes work too good and spin you out. I hope it doesn't happen in traffic or downhill.
With 4 skinny 14" tires, it is very easy to accidentally over-design the rear brakes.
 
What AJ said. I got the poo poo scared out of me on a downhill hard stop. The rear drums locked on me and the rear started to come around. Drums work fine but I don't like the way the pad transfer can suddenly lock the drum. You can play with brake cylinder bore sizing but an adjustable proportioning valve works great. Of course you must make sure your braking system is functioning properly. I use one with my 4 wheel disc set-up and adjusted it in a big parking lot with wet pavement.
 
You know that it is very easy to accidentally over-engineer the rear brakes right? The rear brakes are designed to do close to nothing on your car for a reason.
You know that you can adjust the amount of rear brake power in other ways, right? Like with increased fluid pressure, increased W/C power, and shoes with a higher CF, right? Right up until the rear brakes work too good and spin you out. I hope it doesn't happen in traffic or downhill.
With 4 skinny 14" tires, it is very easy to accidentally over-design the rear brakes.

I’m aware they’re not designed to do much. The bulk of stopping power should happen with the front brakes.
My drum brakes function, but the parking brake aspect doesn’t, and figure if I’m going to replace anything, I’d at least look for a more modern system. Unfortunately doesn’t seem like it’s going to be easy to find and I have no need to swap my rear end, so I’ll be looking at a new drum brake assembly probably
 
All I need to do is switch to BBP from SBP on my 7 1/4, don't have to have rear discs, would love to, but no need. What is the procedure for this? Ordering the Dr Diff front disc kit already. Have a guy that will redrill my axles, do you folks just redrill the drums, or is there a drum that will fit I can get from the parts store that is a bit of an upgrade maybe?
 
All I need to do is switch to BBP from SBP on my 7 1/4, don't have to have rear discs, would love to, but no need. What is the procedure for this? Ordering the Dr Diff front disc kit already. Have a guy that will redrill my axles, do you folks just redrill the drums, or is there a drum that will fit I can get from the parts store that is a bit of an upgrade maybe?

If you re-drill the axles, you have to re-drill the drums.
 
Isn't there a stock replacement drum with big bolt pattern if I ask for the right year? Like a 72 duster or somethjing?
 
Here is the deal- what happens if a drum goes bad? There isn't a big bolt pattern drum from another a-body that would fit on these brakes? Or am I going to have to redrill a drum everytime one goes bad?
 
The spacing between the axle/backing plate mounting face and the wheel mounting face on the axle is different between small and large bolt pattern. In order to run any of the commercially available rear disk brake kits, you would need to have the correct offset (or make your own modifications). In the 7 1/4, you still have to swap the whole axle to do this since apparently the axle shafts themselves aren't the same length.

So this would mean also that the drums are different widths. The small bolt stuff is kind of it's own game and doesn't have a lot of support.
 
The spacing between the axle/backing plate mounting face and the wheel mounting face on the axle is different between small and large bolt pattern. In order to run any of the commercially available rear disk brake kits, you would need to have the correct offset (or make your own modifications). In the 7 1/4, you still have to swap the whole axle to do this since apparently the axle shafts themselves aren't the same length.

So this would mean also that the drums are different widths. The small bolt stuff is kind of it's own game and doesn't have a lot of support.

NOt even going to try to get rear discs on this thing- was only going to try if there was an easy kit.

Thanks- I was hoping this wasn't the problem. Sigh. Well, it's not like rear brakes wear out that fast either. When I have the axles and drum drilled, I may have two or three new sets of drums drilled at the same time, and store them well. Usually I just throw away the 7 1/4 and go 8 3/4, but it is cost prohibitive and unnecessary in this car unless I find one cheap that will be shipped to Hawaii.
 
Goldduster318 mentioned our axle shafts in the 7.25 are not of the same length, which was a surprise to me so I went out and measured a set that I have ready to go in my 7.25 and they both measure 26 3/8" in length (from the "collar" to the end of the shaft). When I pull my original shafts out of the housing, I'll again measure and report back as I bought these as a replacement).

But yes, chinze57, us 7.25's do indeed have to go with an axle shaft redrill plus drum redrill (or like you mention lacks there in HI, a full on axle swap)...I just got a set of drums redrilled through Dutchman Axles as they are closer to us out West than Moser (in Indiana) and is actually less expensive on the actual job cost.

Unless of course yourself or someone you have access to, can redrill them for you ? I'm going your same route....I went with a Dr. Diff 11.75 disc set up front and will keep drums in the back.....
 
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