1972 Front Disc Brake Conversion

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if your front disks don't stop you it could be a number of things as stated above
i'll sling in a couple more...

if the pedal travel is short and the brakes feel a bit like wooden blocks your master cylinder bore is too great. you end up with little brake feel and the fat cylinder is not creating enough pressure at the piston in the calipers to slow you well enough with the chosen pad material.
a narrower bore will help provided that you have enough peddle travel

the pressure needed in the line to the front to actuate a disk brake caliper properly is higher than that needed to do similar for drums, this means that for the same foot effort what caused the drum to be full on, is causing the disks to be half on, and increasing foot effort means any problems with bias ratio between back and front is accentuated.

SSBC brake kits for B bodies used to suffer this. the master cylinder sent out was a mismatch in bore terms and therefore for the lever lengths in the peddle set up and many got on much better with a standard one

i.e your rears are hard on and trying to lock before you have the fronts applied in a manner that slows you down effectively.
Given that the front is heavy, got a motor in it, and can stand more stopping power before lock up the front should be doing a bigger proportion of the braking effort and you can't do that with the front pad not being applied to the rotor well enough.

in an Australian A body with 9 inch rear drums and small claw slider caliper rotor combination and a master cylinder designed for disk brakes. (similar to post 73 US disks set up) I had to fit a standard brake bias part, that chrysler eventually started fitting in Australia from 1975 onwards (it had been fitted only to police and race cars previously) in order to get my disk brakes at the front to really work properly, Chrysler fitted it after some criticism in the press. this car weighs tiny bit less than a 1968 dart but is shorter and had the smallest rear drums offered on any mopar and still the back locked up first.

i'm not suggesting you find a hard to get australian part that automatically costs way more due to its association with the Aussie R/T models and the less than popular 1975/76 VK range.

Summit for an adjustable one or a late model US part from rockauto would do if you don't already have one
things can also be made better with very narrow bore rear cylinders

its the thumb tack demonstration . pressure = force divided by area

push a thumb tack into the board easy with the fat end against your thumb.
turn it over and put the spike against your thumb and try and press the fat head into the wall and you quickly discover a problem.

Apply this idea to the various pistons in the system and you can't go far wrong.
brakes don't work well if the master cylinder is a thumb tack the wrong way round

Dave
 
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I used a Pirate jack kit but manual.... and honestly i wish i had kept the stock drums... the discs don't stop as well and it was money wasted.. i wish i had my drums back at this point (trash it all of course) But with power i'm sure it will be fine. The pirate jack parts worked fine.

there is something wrong with your install then.. 73 style disc stop great. there has to be something wrong or mismatched on your install.. probebly an easy fix.
 
Need to know if they are 13" or 14" then. If they are 13" you are stuck. Can't do disks with 13" wheels. You can do 14" if you can find the right wheel that will clear the Kelsey Hayes reproductions that SSBC makes. You need 10" drum spindles for that conversion (I have a set that I saved from the scrap heap to help someone out who wants to use the kit that SSBC makes, I have them on my Dart with a way to powerful aftermarket booster in a way they work too good ;) ).
That's what I did, I used my 10" spindles but had to drill out larger for the attaching bolt.
 
I think they went out of business and started again since then. And based on their current business practices they may be looking to go out of business again.

Regardless, several of the wearing parts in those kits are custom machined, which means if they do go out of business again you'll have to source and machine your own parts to keep the kit.
True they went out of business and were bought. But that’s no problem.
The only custom machining they did was to redrill the rotors for small bolt pattern. Their kit like the leed disc kits uses Ford KH parts. So far those parts still seem plentiful new.
 
True they went out of business and were bought. But that’s no problem.
The only custom machining they did was to redrill the rotors for small bolt pattern. Their kit like the leed disc kits uses Ford KH parts. So far those parts still seem plentiful new.

You would probably know better than me, but I thought there was something other than just the bolt pattern that had to be changed. It wasn’t a big deal but it would have required machining, like changing the hub for a different bearing or seal? Maybe something has changed since then, I only looked into the KH style kits briefly quite awhile ago.
 
You would probably know better than me, but I thought there was something other than just the bolt pattern that had to be changed. It wasn’t a big deal but it would have required machining, like changing the hub for a different bearing or seal? Maybe something has changed since then, I only looked into the KH style kits briefly quite awhile ago.
I actually got a sales guy on the phone who was rather bitter about leed brakes mimicking their kits. Brackets everything are the same. The kits use a spacer and adapter behind the inner bearing to move the rotor outboard to match to the caliper location. It also provides the larger diameter seat to use the Phord inner wheel seal.
 
As a side note. Dynamic Friction makes new KH calipers for Mopar A bodies. You can use the Mopar caliper on those kits to retain the Mopar style brake line hardware. I plan on doing that with the kit for B body drum spindle since it uses the 73-76 A body lower ball joint.

KH disc brakes with BBP and no problems with rotor replacement etc.
 
I actually got a sales guy on the phone who was rather bitter about leed brakes mimicking their kits. Brackets everything are the same. The kits use a spacer and adapter behind the inner bearing to move the rotor outboard to match to the caliper location. It also provides the larger diameter seat to use the Phord inner wheel seal.

Ah, ok. I thought there was something with the inner seal, that makes sense. I probably got that out of the Mustang KH rotor thread where people were doing the conversion themselves.

As a side note. Dynamic Friction makes new KH calipers for Mopar A bodies. You can use the Mopar caliper on those kits to retain the Mopar style brake line hardware. I plan on doing that with the kit for B body drum spindle since it uses the 73-76 A body lower ball joint.

KH disc brakes with BBP and no problems with rotor replacement etc.

So this I don't understand. If you're using the B-body spindle, you have to use the large upper ball joint UCA or an adapter. And you say you're switching to BBP as well. So, why mess with any of the conversion kit at all? Just use the stock '73+ A-body disks. Large ball joints, BBP, and larger wheel bearings too. Plus 100% off the shelf OE parts with no adapters needed for bearings or seals, and no hub issues at all because it's all integral with the rotor.
 
I’m actually a bit torn. I have full KH brake systems for my project but as mentioned all of them are SBP. I have original BBP rallies in both 6.5 width and 7 width. I’m going for an original look. So even the SBP rallies would work. I even found a pair of BBP rear drums that look like the “darth Vader” drum that fits the 1 3/4 rear brake.
I guess in the end as for brakes the 73-76 disc is the most cost effective and most likely the smarter choice for all the reasons you mentioned. And for the OP it is actually the best choice. Put the 73-76 discs on and parts are very easy to get. You can even get new upper control arms.
The engineer in me wants to build something a bit more unique.
 
A couple factors will change the braking characteristics. First is like you mentioned is the size of the cylinder. Second If you change the weight distribution, you can increase the “work” the rears have to do. (Move the battery to the trunk and lighten the front)You can also leave the adjustment on the drums a little looser. As old as these cars are there are only a couple of brake compounds available so we can’t change the compound.
I advise not to use the 2 1/2 rear brake on 72 and earlier cars. Every article I’ve found from when the cars were new (68 and up)was that they already had too much rear brake. The 2 1/2 brakes were used on later cars as the weight of the Abody increased.
Unfortunately there are only two wheel cylinder sizes 7/8 and 15/16. This doesn’t give much to work with. The Dorman 7/8 bore wheel cyl pn is W 37236.
But I don’t want to completely hijack the thread. OP was asking about a brake conversion. I’ll be glad to discuss more in a new thread
 
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