The Brake Pedal "two-step"

F

Floridian Flathead

Member
Dear fellow Fordbarners:
I recently had to change the Master Cylinder on my '37 tudor, which has the 39 Brake system. I also changed all the Fittings, Hoses and Lines. With a friend's help the entire system was bled.
What happens now is that when I initially step on the Brake Pedal it travels about half way down. When I immediately step on it a second time it is pumped up and only travels about 1/2 inch down with good brake pressure. Holding my foot pressure on the Pedal does not cause any fading. At the next brake application, the same thing happens. There is no leaking in the wheels or ground. Could there be something wrong with the Master Cylinder? Is this normal? I am no Mechanic so any advice would help.
Thanks,
Richard :rolleyes:
 
Did the system work before you changed the master cylinder? When you say a '39 system are you using the '39 pedal assembly?

Charlie Stephens
 
check to see if you replaced the master cylinder with the same bore diameter as you removed. A smaller diameter cylinder pumps less fluid and maybe it takes the second stroke to fill your wheel cylinders.
 
Floridian Flathead said:
Dear fellow Fordbarners:
I recently had to change the Master Cylinder on my '37 tudor, which has the 39 Brake system. I also changed all the Fittings, Hoses and Lines. With a friend's help the entire system was bled.
What happens now is that when I initially step on the Brake Pedal it travels about half way down. When I immediately step on it a second time it is pumped up and only travels about 1/2 inch down with good brake pressure. Holding my foot pressure on the Pedal does not cause any fading. At the next brake application, the same thing happens. There is no leaking in the wheels or ground. Could there be something wrong with the Master Cylinder? Is this normal? I am no Mechanic so any advice would help.
Thanks,
Richard :rolleyes:
Click to expand...

Adjust the brakes and bleed them again and your problem will disappear.
Nothing wrong with the master cylinder.
Bill
 
After reading your post you have not adjusted the brakes shoes correctly and they are returning to far, thus the two pump chump issue. If you have correctly adjusted the lower shoes the upper stops must be adjusted, The upper 3/4" hexs at the 10 and 2 position are rotated outward to a point that the shoe just starts to rub on the drum. This adjustment is a return stop adjustment and prevents the shoe from fully returning and retains them in close proximity to the drum face. If these are not adjusted correctly or rotated inward it allows the brake shoe return spring pressure to collapse the shoes to a rest point that requires an additional pedal pump of fluid to move them to within clamping distance to stop.

To adjust you brakes correctly Rotate the upper stops outward so the shoes contact the drum, and place a small amount of pressure on the brake pedal, now move to the lower adjustment bolts, loosen the lock nuts and rotate the adjuster tangs outward to feel the lower portion of the shoes just drag on the drum face. Upon a slight drag lock down the adjusted nuts and the hub should barely spin. Go back to the top anchor and rotate them one flat to center and the brakes should release and the drum spin free. Check the pedal stroke by pumping twice and relaxing, them push down with one even stroke, you should have a soilid pedal witin 1" of travel.
 
Dick, I have a question for you; We've adjusted the brakes on our '39 CS (just as you describe) however, after driving a short distance, and applying the brakes several times, they go "out of adjustment" and once again require the "peddle pump". In your opinion (without actually looking at the brakes) what can we try to remedy the situation? Thanks for your help. Vic
 
All good advice above. I found the brake adjusters to be 11/16" though. A 17mm wrench will go on there and be a good tight fit.

Mart.
 
Vic, I am asumming you have a stock style master cylinder, my guess is that you nave NO play in the master cylinder push rod or NO return spring on the brake pedal. This keeps the piston from fully retracting and exposing the return port hole. While you think you have good brakes initially its because the pedal has not sufficiently returned and is actually holding pressure on the system, driving down the road vibrates everything to neutral and releases the built up pressure. Check the free play in you master cylinder and make sure there is a return spring in place and do a quick rebleed of the system.

Mart, Sorry got them reversed lowers are 3/4" uppers 11/16"
 
Just to back up Dick, when the piston is right back in the master cylinder (at rest) there should be a 1/16" clearance to the push rod.
A spongy pedal means there is air in the system. A firm pedal after pedal travel means the brakes need adjusting.
 
Did you use DOT 5 or DOT 3 fluid? Dot 5 is harder to bleed as pumping the pedal to bleed it will cause tiny bubbles in the fluid. Dot 5 synthetic is good fluid , but much harder to rid the system of air.
 
DICK SPADARO said:
Vic, I am asumming you have a stock style master cylinder, my guess is that you nave NO play in the master cylinder push rod or NO return spring on the brake pedal. This keeps the piston from fully retracting and exposing the return port hole. While you think you have good brakes initially its because the pedal has not sufficiently returned and is actually holding pressure on the system, driving down the road vibrates everything to neutral and releases the built up pressure. Check the free play in you master cylinder and make sure there is a return spring in place and do a quick rebleed of the system.

Mart, Sorry got them reversed lowers are 3/4" uppers 11/16"
Click to expand...

Dick, thanks for your reply. It is a stock system in the '39, and I do have a return spring on the brake pedal, but I will check the push rod and see if I can adjust it. Vic
 
What is the range for the clearance for the master cylinder push rod? What happens if the push rod has to much clearance? Are the procedures the same for a '47?
Thanks
Don
 
Pretty much the same with all cars that I can think of. The piston needs to come to full rest, back against the washer or circlip, with enough clearance at the push rod to allow for any movement, expansion, flexing etc. If you have too much, the pedal just has that little bit extra travel, which could be argued, adds to the reaction time of stopping.
 
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