Brake conversation question

[RAT ROD AL]

I have this kit from Pirate Jack brakes.
Fits 8.75 rearend. My question is will this possibly fit a 7.25 .
I know the bearing retainers are 5 bolt on this kit, and the 7.25 has 4. But will the 4 fit ths pattern ?

 

[RAT ROD AL]

@acavdragoon

 

[Dana67Dart]

I'm thinking not...

The drum backing plates have been modified to work (IIRC) by enlarge the center and relocating the mounting holes so that suggests the axle flange to housing flange spacing is the same BUT DON'T QUOTE ME ON THAT!

 

[MoparLeo]

No directions ? online maybe ?
Negatives outweigh the positives on a rear disc brake conversion.
Just read the posts from everyone who has done it.
The vast majority of the time they either can't get a decent pedal or no pedal at all.
The rear disc brakes do only about 20% of the braking.
Stick with the drums and just use better quality shoes and drums for added braking efficiency.
Flush the rake system with a sealed bottle of brake fluid.
Never use a container that has been uncapped for any period of time.

 

[RAT ROD AL]

Thanks Leo,

I'm trying to sell this kit ! But all opinions and input is appreciated !

 

[junkyardhero]

okay, so full caveat that i don't have it sitting right here in front of me... but, i don't think it will work because the diameter of the hole on retainer plate.

the 7.25 axle bolts in and the "flange" retains the bearing and axle together. i *think* the hole on the brake kit retainer is too big and the bearing would just slip right thru.

beyond that, *if* it would work, you'd need to press the bearings off the axles and install new. as well as double check the thickness of the plate-- although there's probably enough take up in the brakes there to account for the 1/16~1/8 that it'd be different. i think. maybe.

 

[Inertia]

You may have to modify or fab the mounting plates, they often mount behind the axle (backing plate) mounts, but there's everything there to do the job.
Mount the rotors with a couple lugs to hold it in place, then figure out which caliper mount plate locates the caliper best.

As a note..... Those are the " Cobra " calipers folks struggle with.
Once mounted the emergency levers need to be "ratcheted" back and forth till the pads are in total contact with the rotors, before you will get any brake "pedal" resistance.
The caliper pistons are notched, and the inner pad has a "pin" to fit in the notch, to prevent piston turning when you ratchet the emergency lever.

Good luck

 

[junkyardhero]

are those the cobra calipers or those caddy ones?

i know i had a HELL of a time bleeding them down (same MBM/jack/classic kit). the upgraded 12pt levers help, but it's still a slog to get them set up right.

 

[Dana67Dart]

i don't think it will work because the diameter of the hole on retainer plate.

the 7.25 axle bolts in and the "flange" retains the bearing and axle together. i *think* the hole on the brake kit retainer is too big and the bearing would just slip right thru.

7 1/4 bearing OD is 2.74"
8 3/4 bearing OD is 2.92"

Don't know which calipers they are but they work the same a 76-80's Mercury Versailles. One thing I remember is having to remove the e brake lever to turn the piston in at pad change. then realign the lever to the shaft and then put the pad in.


I bought the calipers and the mount and the other hardware ( red arrows) and made from a drum backing plate and some strap steel, the bracket that mounts to the axle housing green arrow. the stock mount would not place the caliper in the right spot. they worked flawlessly

 

[Killer6]

I have this kit from Pirate Jack brakes.
Fits 8.75 rearend. My question is will this possibly fit a 7.25 .
I know the bearing retainers are 5 bolt on this kit, and the 7.25 has 4. But will the 4 fit ths pattern ?
View attachment 1716469150

It would depend on the year & model, & whether the kit is adjustable for both A & B-body 8.75" apps.

 

[Killer6]

LBP A-body, F-M-J-bodies, & 1st-Gen. Dakotas all use the same backing plates as the 8.25" & B-body 8.75"'s...

 

[AbodyBB]

So the OP mentioned a 7 1/4 vs 8 3/4. If the 7 1/4 is SBP then the short answer is no. Housing flange to axle flange on A body ALL up to 72 was 2.38 inch. Not sure if the number is exactly right so don’t hang me out to dry. BBP ALL were 2.5 inch housing flange to axle flange. Those kits are sold like that and available because with a couple hole relocations they will bolt on fords and AMC. Both used the same wheel bearing size as Mopar.

 

[72bluNblu]

No directions ? online maybe ?
Negatives outweigh the positives on a rear disc brake conversion.
Just read the posts from everyone who has done it.
The vast majority of the time they either can't get a decent pedal or no pedal at all.
The rear disc brakes do only about 20% of the braking.
Stick with the drums and just use better quality shoes and drums for added braking efficiency.
Flush the rake system with a sealed bottle of brake fluid.
Never use a container that has been uncapped for any period of time.

LOL!

The negatives outweigh the positives? Not even close. Rear disk conversions improve both stopping distance and brake feel.

The problem is that people use cheap kits, don't consider the changes they're making in the hydraulic ratio between the MC and the caliper piston size and how that changes F/R bias, and use calipers they're not familiar with. Every rear disk brake conversion I've seen go wrong was improper installation or adjustment (or a faulty part that needed to be replaced).

Learn how to do the installation properly, and become familiar with the calipers that you're installing and the procedures needed to adjust them properly and rear disks will outperform the factory drums all day long.

So the OP mentioned a 7 1/4 vs 8 3/4. If the 7 1/4 is SBP then the short answer is no. Housing flange to axle flange on A body ALL up to 72 was 2.38 inch. Not sure if the number is exactly right so don’t hang me out to dry. BBP ALL were 2.5 inch housing flange to axle flange. Those kits are sold like that and available because with a couple hole relocations they will bolt on fords and AMC. Both used the same wheel bearing size as Mopar.

This. If it's a BBP 7.25 the kit will work. If it's a SBP 7.25 it probably won't.