Mopar B Body Manual Disc Brake Conversion

1. Mopar B Body Manual Disc Brake Conversion Kit
2. Mopar Disc Brake Conversion Kits

It definitely needs more pressure than manual 9' drums, since I did that swap last year (of course, they stop much better, too). Discs always require more pressure than drums, because drum shoes are designed to be 'self tightening' - as they grab the drum, the rotation pulls them in tighter, increasing braking force without requiring as much additional pressure. Discs are strictly linear - more pressure equals more braking. BTW, this is why disc/drum systems need a proportioning valve (it's not to 'balance' front/rear braking). You can adjust the amount or pressure required by choosing a different disc brake master cylinder bore - a smaller bore requires less pressure, by slightly increasing the pedal travel distance (like using a longer wrench to get more torque). Sizes available include 15/16, 7/8, 1, 1-1/32, 1-1/8 (not all will be listed for A-bodies).

Most people like 15/16 for manual brakes - this is 'stock' for early 70s A-body.power. disc brakes.

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Manual brakes came with the 1-1/8 bore, which is pretty macho. Stock A-body master cylinders were 15/16' for 9' drums, 1-1/32' for manual floating disks, 15/16' for power floating disks, and 1' for the KH disks. The 1-1/8' master cylinders were for the 70-72 B/E body single piston KH disks and weren't used on A-bodies. I like the 15/16' bore for manual disks. It's not really any more leg than was required for the manual 10' drums, which used the 1-1/32' master cylinder.

I actually think the 15/16' master cylinder improves your brake modulation capabilities quite a bit with the slightly longer travel, but it still provides the max line pressure. From the '73 service manual, 'L' is the Dart model. The 2.75' calipers were B/E body fare, pin style in '73 hence the 'floating' designation, the 2.6's were A-body slider calipers. From the '70 service manual, first the fixed caliper KH's used on A's And the single piston floating caliper KH's used on the 70-72 B/E.

You can see the wheel options on the bottom for Barracuda, Satellite and Fury models (Plymouth service manual). It definitely needs more pressure than manual 9' drums, since I did that swap last year (of course, they stop much better, too). Discs always require more pressure than drums, because drum shoes are designed to be 'self tightening' - as they grab the drum, the rotation pulls them in tighter, increasing braking force without requiring as much additional pressure.

Discs are strictly linear - more pressure equals more braking. BTW, this is why disc/drum systems need a proportioning valve (it's not to 'balance' front/rear braking). You can adjust the amount or pressure required by choosing a different disc brake master cylinder bore - a smaller bore requires less pressure, by slightly increasing the pedal travel distance (like using a longer wrench to get more torque). Sizes available include 15/16, 7/8, 1, 1-1/32, 1-1/8 (not all will be listed for A-bodies). Most people like 15/16 for manual brakes - this is 'stock' for early 70s A-body.power. disc brakes. Manual brakes came with the 1-1/8 bore, which is pretty macho.

Stock A-body master cylinders were 15/16' for 9' drums, 1-1/32' for manual floating disks, 15/16' for power floating disks, and 1' for the KH disks. The 1-1/8' master cylinders were for the 70-72 B/E body single piston KH disks and weren't used on A-bodies. I like the 15/16' bore for manual disks.

It's not really any more leg than was required for the manual 10' drums, which used the 1-1/32' master cylinder. I actually think the 15/16' master cylinder improves your brake modulation capabilities quite a bit with the slightly longer travel, but it still provides the max line pressure.

From the '73 service manual, 'L' is the Dart model. The 2.75' calipers were B/E body fare, pin style in '73 hence the 'floating' designation, the 2.6's were A-body slider calipers. From the '70 service manual, first the fixed caliper KH's used on A's And the single piston floating caliper KH's used on the 70-72 B/E.

You can see the wheel options on the bottom for Barracuda, Satellite and Fury models (Plymouth service manual). Stock A-body master cylinders were 15/16' for 9' drums, 1-1/32' for manual floating disks, 15/16' for power floating disks, and 1' for the KH disks.

The 1-1/8' master cylinders were for the 70-72 B/E body single piston KH disks and weren't used on A-bodies. I like the 15/16' bore for manual disks. It's not really any more leg than was required for the manual 10' drums, which used the 1-1/32' master cylinder. I actually think the 15/16' master cylinder improves your brake modulation capabilities quite a bit with the slightly longer travel, but it still provides the max line pressure. From the '73 service manual, 'L' is the Dart model. The 2.75' calipers were B/E body fare, pin style in '73 hence the 'floating' designation, the 2.6's were A-body slider calipers.

From the '70 service manual, first the fixed caliper KH's used on A's And the single piston floating caliper KH's used on the 70-72 B/E. You can see the wheel options on the bottom for Barracuda, Satellite and Fury models (Plymouth service manual). Click to expand.This statement is only true of the 'leading shoe'. On a typical drum brake, the shoe in the direction of travel becomes the 'leading shoe' if the wheel cylinder is at the top of the backing plate. I did a brake job on a '55 New Yorker that had a twin leading shoe front brake; it had two single ended wheel cylinders connected by a metal tube. FWIW, the rears were single leading shoe design.

When the parking brake is engaged, the rear shoe pivot point is at the top. As far as more pressure goes, I can't say. The '73 Dart mordor I converted to disk brakes already had a DB master cylinder on it.

I do not recall any increase in effort needed after I installed the single piston floating caliper units. Actually, IMO in typical stop-and-go traffic, effort with disk brakes stayed fairly constant, whereas with drums, more effort was needed to get the same stopping effect towards the end of a trip. This statement is only true of the 'leading shoe'. On a typical drum brake, the shoe in the direction of travel becomes the 'leading shoe' if the wheel cylinder is at the top of the backing plate.

I did a brake job on a '55 New Yorker that had a twin leading shoe front brake; it had two single ended wheel cylinders connected by a metal tube. FWIW, the rears were single leading shoe design. When the parking brake is engaged, the rear shoe pivot point is at the top. As far as more pressure goes, I can't say. The '73 Dart mordor I converted to disk brakes already had a DB master cylinder on it.

I do not recall any increase in effort needed after I installed the single piston floating caliper units. Actually, IMO in typical stop-and-go traffic, effort with disk brakes stayed fairly constant, whereas with drums, more effort was needed to get the same stopping effect towards the end of a trip. It definitely needs more pressure than manual 9' drums, since I did that swap last year (of course, they stop much better, too). Discs always require more pressure than drums, because drum shoes are designed to be 'self tightening' - as they grab the drum, the rotation pulls them in tighter, increasing braking force without requiring as much additional pressure. Discs are strictly linear - more pressure equals more braking.

BTW, this is why disc/drum systems need a proportioning valve (it's not to 'balance' front/rear braking). You can adjust the amount or pressure required by choosing a different disc brake master cylinder bore - a smaller bore requires less pressure, by slightly increasing the pedal travel distance (like using a longer wrench to get more torque). Sizes available include 15/16, 7/8, 1, 1-1/32, 1-1/8 (not all will be listed for A-bodies). Most people like 15/16 for manual brakes - this is 'stock' for early 70s A-body.power. disc brakes. Manual brakes came with the 1-1/8 bore, which is pretty macho.

Mopar B Body Manual Disc Brake Conversion Kit

The proportioning valve reduces pressure to the rear brakes and the hold off valve incorporated in the combination valve delays pressure build to the rear so the front not only apply braking first but also supply about 70% of the total braking.That's why going to rear discs is not usually a big improvement.since the rear only supplies about 30% of your stopping power.yes discs require much more pressure (3500 - 4000 psi) that's why the pistons are 2 5/8' or 2 3/4' in the calliper but only 1' or 15/16' in the wheel cylinder. Get the proper master cylinder and a manual disc front / drum rear system will stop effortlessly with very little leg pressure for a manual front disc / rear drum system most like no bigger than 1' or 15/16'master.a 15/16' master cylinder was stock for early A body manual disc front drum rear. Put a 1 1/8' master on a manual front disc car and a lot of guys won't be able to lock them up. Click to expand.Good comments.

Mopar Disc Brake Conversion Kits

One possible correction - research 'front metering valve' in the combo valve, which I think is the same as 'hold-off valve'. I recall reading that it holds off pressure to the front disks until the rear drum shoes move to contact the drums. I think it is simply a spring-loaded 'pressure relief' valve that pops open 10 psig or so. Lets not even get into comments in another post that rear disks are better since rear drums 'are not strong enough'. Nobody explained how that meshes with needing a proportioning valve to reduce pressure to rear drums so they don't lockup the rear wheels.