need help from the drum brake gurus

I can't quite figure it out. I have a '49 stude 1/2 ton with stock master and front drum brakes, the rear is mid 70's firebird drum. I was told when purchased that when i started to run the truck I should replace the master cylinder due to soft pedal. I replaced the master last year,same problem. First pump 1/3 pedal, second pump 3/4 pedal, third pump full pedal. brakes work good but this is not right. I know there is a residual check valve in the '53 and newer master cylinders,but don't know if there was in'49. Thought of addind a valve,but don't know if I should put one on the front , or back or both. There is no proportioning valve,and is still the single cylinder master. After a year of being laid up I finally got back to it the other night thinking maybe needs to be bled again. Flushed system and vacuum bled,same thing. What have I missed? Thanks in advance for any help.
Funk 49

 

This has to be too simple....but it sounds like air in the sysstem when you explain that you can pump the pedal up!

LARRY

 

That is what I thought at first, it has been bled numerous times and flushed,and then vacuum bled and still the same.

 

I'm not a brake guru but my advice is;

Get rid of that fruit-jar MC and bolt on a dual reservoir MC, that way you'd won't be laid-up
again soon.

Bleed, Bleed & Re-Bleed!

Click here: BRAKES..Residual Check Valves -Tech Week - THE H.A.M.B.


Good luck with the Stude.

 

Thanks unkledaddy for the link. I didn't find that.

 

You should install residuals if the master lacks them, if all the air is out of the system what you are describing on the pedal is usually an indication of too small of a piston not moving enough fluid to fill or expand the wheel cylinders...I would install residuals in both lines first if the master lacks one (you said it was stock easy to verify) then re-bleed, if problem persist I would look at the master piston size and consult the experts so you don't buy it twice.......just my 2 cent's worth

 

Are the brakes adjusted and working properly? Is there enough linning on the shoes and are the drums thick enough? Also there should be no loops or U shapes in the lines that air might get trapped in.You can clamp off the flexable lines and see if it gets higher and harder, that would indicate a problem past the clamp. Good luck.

 

New shoes, no U shapes and brakes are adjusted. Thanks

 

Adjust the brakes again. Run them out till you cant get anymore out of them and back them off till they slightly drag.

 

Adjusted to slight drag all the way around. Thanks

 

and how old are those rubber lines - the two in the front and the one to the rear axle?.....old ones no goodie....

 

Did you compress the wheel cylinders all the way and then back them off or just out till there was slight drag?

 

Lines appeared to be in decent shape,and not ballooning when the pedal is good,but that may be the next thing to eliminate. Thanks.

 

Wheel cylinders were compressed when shoes were done, but not the last time brakes were bled. I'll try that.

 

Brake hoses can appear good on the outside and be complete junk inside. I would replace them all before bleeding again.