Great data, though I have one quibble -- you don't want to confuse drum brake MC bores with disc brake MC bores -- they are different items.
Thanks for your input!!Hard to say. 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.
Thank you also!!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.
View attachment 1714959646
From the '70 service manual, first the fixed caliper KH's used on A's
View attachment 1714959645
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)
View attachment 1714959644
Thanks a bunch....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.
View attachment 1714959646
From the '70 service manual, first the fixed caliper KH's used on A's
View attachment 1714959645
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)
View attachment 1714959644
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.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.
4 wheel discs, stock 68 barracuda non-proportioning valve from original drum brake set up, w/ 87diplomat master cyl., works excellent.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.
Thanks.....Hard to say. 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.
Thanks..4 wheel discs, stock 68 barracuda non-proportioning valve from original drum brake set up, w/ 87diplomat master cyl., works excellent.
How much extra pedal pressure is normal for above over manual 10" drums? Thanks
Good comments. 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.... 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..