Later Master Cylinder with Kelsey Hayes Brakes?

[1972DusterPaul]

I am switching to factory front disc brakes on my 1972 Duster from the original drum brakes.

I already have a disc brake master cylinder from a 1973 Duster.

So I wondered if I could use that with my Kelsey Hayes brake set-up...or do I need to get the correct one?

Anyone know the difference between the two styles of disc brake master cylinders?

Are the bore size and stroke the same or different?

Anyone have part numbers for the proper disc brake master cylinder?

Thanks in advance for any help.

Paul

 

[shainphelps]

im doing the same swap on my duster i have a artical thats say 3461187 is the casting number for 71 to 74 disc

 

[wjajr]

Paul,
I redid the factory KH manual disk brakes on my 1967 Dart this last spring. I replaced the master cylinder with a later new “manual” disk brake unit. It is larger than the ’67 master cylinder that was on the car. It bolts right up, but you may have to install a reducing bushing or two to use existing brake lines if I recall.

Power brake master cylinder will be a different model number, and bore size.

I posted about this upgrade here: http://slantsix.org/forum/viewtopic.php?p=304772&highlight=master+cylinder#304772

The new master cylinder works great. By the way, I replaced all the front brake lines as well. If you have a question about this upgrade ask Slant Six Dan, he can probably help you.

 

[1972DusterPaul]

Cool..thanks for the information, link and the photograph.

I have manual brakes and my master cylinder (from a manual brake car) looks just like the one you have on your car.

Thanks,
Paul

Paul,
I redid the factory KH manual disk brakes on my 1967 Dart this last spring. I replaced the master cylinder with a later new “manual” disk brake unit. It is larger than the ’67 master cylinder that was on the car. It bolts right up, but you may have to install a reducing bushing or two to use existing brake lines if I recall.

Power brake master cylinder will be a different model number, and bore size.

I posted about this upgrade here: http://slantsix.org/forum/viewtopic.php?p=304772&highlight=master+cylinder#304772

The new master cylinder works great. By the way, I replaced all the front brake lines as well. If you have a question about this upgrade ask Slant Six Dan, he can probably help you.

 

[PocketAces]

I'm planning on using the power disc master cylinder from a 73 duster with 15/16" bore. It was recommended by others on this site and should give less pedal effort due to the decreased bore. The trade off is more pedal travel to move the same amount of fluid. I guess I will need to keep them bled. Wish I could give you my opinion on how it feels, but I haven't done the install yet.

 

[wjajr]

I'm planning on using the power disc master cylinder from a 73 duster with 15/16" bore.

I think you have it backwards, 15/16ths bore is manual brake master cylinder. Larger bore, 1 1/8” or whatever, is used with power assisted brakes. Theory is the longer piston travel, and smaller cross sectional bore provides lower foot pressure to move a given volume of fluid, in relation to larger cross sectional bore requiring more force with less piston travel to do the same work.

This is the same type master cylinder installed on my car, it works fine. You have to exert more foot pressure on the brake peddle in relation to power brakes, but you can still lock’em up. There is better peddle feel, more linear if you will, with manual brakes, than the mushy numb feeling vacuum boosted set-ups from the 60’s & 70’s.

 

[PocketAces]

I think you have it backwards, 15/16ths bore is manual brake master cylinder. Larger bore, 1 1/8” or whatever, is used with power assisted brakes. Theory is the longer piston travel, and smaller cross sectional bore provides lower foot pressure to move a given volume of fluid, in relation to larger cross sectional bore requiring more force with less piston travel to do the same work.

This is from rockauto.com for a 1973 Plymouth Duster:

DORMAN Part # M80266

{#3580112, 3879255}
w/Power Disc Brakes; Bore = 15/16"

This was confusing to me until I realized that the power brake booster includes linkage that multiplies the pedal travel and decreases the mechanical advantage. The vacuum assist compensates for the decrease in mechanical advantage.

Using this master cylinder on a manual brakes car should give less pedal effort, but also more pedal travel and possibly a "mushier" feel.

 

[wjajr]

I may have told a little fib caused by reading my notes incorrectly the other day when posting, that Raybestos MC 36412 I have mounted on firewall has a 1 1/32” bore. I still stand on smaller bore = less peddle pressure explanation.

 

[Oldmanmopar]

I used rebuilt for a 73 up and also aluminum for 87 dodge truck. I never saw a difference in braking. piston dia was never a thought but I would believe there has to be a reason for it. I just never thought of it and used what was available cheap. I probably was just lucky on my choice.