Brake question

[CA Victoria]

This is a new system
1/4” lines
New 60s drum-drum MC
New wheel cyls
46-48 brakes
Bled with power bleeder
First 1/3 - 1/2 of pedal throw is soft then brakes come in.
Puzzled why I can’t get brake action from top of pedal as plunger starts to move
What am I missing?

[ford38v8]

Tim, the only two reasons I can think of are 1- maybe you didn't arc your shoes to the drums and adjust the slack out of them, or 2- if you used silicone fluid, you may not have bled them slowly enough to prevent inclusion of bubbles.

Pay me no attention though, I'm a mechanical brake guy and know nothing about juice brakes!

[Tinker]

Guess what you are missing. is it's a lot oh stuff to work out. Probably not a easy fix.

[cas3]

guessing you are using a duel master, you did not say, but either way, if you started with the farthest away wheel cyl and bled the rest in order I have to guess you do not have free play in the linkage at the master. If the piston does not return far enough to exhaust air/fluid out the port to the resivore you wont ever get it bled out. If a dual, did you bench bleed it ?

[CA Victoria]

Dual Mc
Bench bleed done
Light Flow observed thru compensator ports
Will verify Full return of Mc piston.
Thanks, T

[Bored&Stroked]

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In addition to what others said about bleeding, arcing, etc . . .

How well matched is the bore of the MC to the original Lockheed brakes? If your MC doesn't supply adequate volume for the initial pedal travel (too small of a bore), then I can see this happening. Many modern MCs have pretty small diameters in their bores.

One way to help it might be to install residual pressure valves - to keep some limited pressure on the wheel cylinders - which also means they are already extended out toward the drums.

[CA Victoria]

1960s ford 1” drum MC. Should be adequate.
Good tip on residual valves...

[Mart]

The master cylinder is smaller than stock so will need more pedal movement to move the brake shoes out.

Personally I would fit a new single circuit master and if all the other things are as intended it should work well.

Shoe arcing is important but can be achieved with sandpaper on the bench.
Make sure you have the pushrod length right. Too long and the brakes will bind up.
Too short and you will have lost travel at the start of the pedal.

Make sure the piston is in the right position when brakes are off. Just clear of the recuperation port is ideal so the minimum travel is needed to close off the port. If the piston moves more than the minimum then you have lost travel before the brakes are applied.

Look for a small blip of fluid from the port as the pedal is applied. If the blip is more of a healthy squire then you could probably shim the piston forward with a selected thickness washer to minimise lost movement.

But personally I'd go single circuit with the correct diameter cylinder, but still shim if necessary.

The single cylinder has the residual valve built in.

Mart.

[1948F-1Pickup]

Originally Posted by CA Victoria

This is a new system
1/4” lines
New 60s drum-drum MC
New wheel cyls
46-48 brakes
Bled with power bleeder
First 1/3 - 1/2 of pedal throw is soft then brakes come in.
Puzzled why I can’t get brake action from top of pedal as plunger starts to move
What am I missing?

If you’re now running a dual reservoir master, you’ve got two concerns….
1) generally a smaller piston diameter than was originally used, so you’ll get an easier to press pedal but more pedal travel
2) not all drum/drum master cylinders have residual pressure valves in their outlet ports. RPV’s keep some residual fluid pressure in the brake lines so that the fluid’s tendency to flow back to the MC is reduced….. you have less need to “recharge” the brake line, so the pedal stays higher in operation

[FRANK PKNY]

Arcing shoes is good but, on the brakes, you're using there's no way to adjust the bottom of the shoes the bottom anchors are fixed. what your experiencing is the shoes barely touching the drum. I use 66 Mustang dual master cylinders drum to drum. I have an arching machine, but it doesn't help with a fixed bottom anchor. I adjust the top of the shoes tight and run them in and readjust often till I get a good pedal. the prewar 39-41 style backing plates in my opinion are better because there are upper and lower adjustments, arching them is much better because you can get full contact on your shoes. Also the other comments regarding the throw and return are also in play here. I'm not sure what year Ford went floating shoes Bendix style are a big improvement over what you have.

[Mart]

^^ The lower pivots are allowed to float. The pivot is not fixed. The lower holes are slotted and have special washers to allow self alignment to the drum.

[Ken Henry]

Should there be any difference in pedal effort dual vs single MC, all else being equal (bore and wheel cylinder diameters, etc)? I’ve noticed a slight increase before when switching to a dual… ken