Disc Brake Master Cylinder

[RangerRat]

What master cylinder are you guys using after doing a disc brake conversion? The lines came in on the opposite side of the m/c on the 1973 doner truck compared to my 1972. Can I use a 72 f250 disc brake m/c? Does the lines come in on the driver side of those? Thanks

[colnago]

I used an MC from a '68 F250 on my '67. The ports are on the driver side. The reservoir for the front discs is towards the firewall. You can probably use a different MC for your truck, but the port fittings might be a different size on the MC (I found that the caliper fitting was 7/16-20 for '68 - '71, and 3/8-24 for '72, so I wouldn't be surprised if the MC also used different fittings).

Joseph

[RangerRat]

Thanks for your response. So on the original mc the front reservoir is for the front brakes. But on the F250 mc the rear reservoir is for the front brakes? That's good to know. So you just moved your front line to the rear port on the F250 mc? I didn't think about the fitting size. I'll have to compare those as well.

[ultraranger]

The MC port closest to the firewall is for the primary side of the brake system --goes to the front brakes. The port on the MC closest to the radiator goes to the secondary side of the brake system --goes to the rear brakes.

This is true on all Bumpside F100-F350s.

[RangerRat]

I didn't know that. Good info. Thanks

[PetesPonies]

This is true on most every vehicle. When you press the pedal, you are mechanically moving the primary, or front brake piston. The secondary or rear brake piston, is actuated by hydraulic force from the primary piston. When you loose front brakes the pedal goes almost to the floor, because now you have to force the primary piston into contact with the secondary piston. This is setup this way for safety.

[ultraranger]

This is true on most every vehicle. When you press the pedal, you are mechanically moving the primary, or front brake piston. The secondary or rear brake piston, is actuated by hydraulic force from the primary piston. When you loose front brakes the pedal goes almost to the floor, because now you have to force the primary piston into contact with the secondary piston. This is setup this way for safety.

Except for those cast iron Corvette MCs that come in a lot of aftermarket power brake setups. Their ports are plumbed backwards from Ford.

...and as you explained, for the (visual) benefit of others, how a tandem brake MC works.

https://youtu.be/bGKJOICWmFQ

[PetesPonies]

why I said "most"

[colnago]

Good video! I didn’t realize that the primary and secondary plungers were physically separate. That explains why the primary (front disc) circuit is towards the firewall on "most" applications.

Joseph

[PetesPonies]

Pistons, not plungers. Right, you want to be able to physically push the primary piston, so you have less chance of problems. But if all else fails, you push the primary into the secondary piston and at least you have rear brakes. It seems/feels real bad when this happens because you have to push the primary piston much farther to physically make contact with the secondary piston.

[colnago]

Pistons, not plungers.

Oops! Sorry, wrong nomenclature. Words are important. Thanks for the correction.

Joseph

[RangerRat]

Called a couple auto parts stores today to get a 1972 f250 disc brake mc. They ask if it was a Bendix casting. I had no clue what to tell them.

[colnago]

I know the Bendix is more expensive, but I don't know what the performance difference (if any) there is. I think the Bendix cover is more oval, rather than being flat at one end. Can you take a photo and post, or show the guy behind the counter at the auto-parts store? Or maybe you can google it.

Joseph