ok guys here is my problem. when i push down on the brake pedal it goes to the floor the first time. the second time i push on the pedal i get a little brake an the third time i push it i have good brakes. now let the truck sit for a minute an i have no brakes again. i have replaced 3 wheel cylinders and the master cylinder. i have bench bled the master cylinder before i put it on an i have bled the entire system after the new wheel cylinders. i have bled the system over an over an it keeps doing the same thing. i have looked for leaks in the line an have not found any im at a loss as to what to do next any idea's?

1965 4x4 f100

 

sounds like a bad master cyl.

 

its new from napa any other idea's

 

Did you bench bleed it first, before installing it on the truck?

 

BP...the OP said he did bench bleed it...

You say you replaced 3 of the 4 wheel cylinders...were these fine foreign replacements or MUCH better...and proper fitting US made cylinders...like Wagner brand ??? If all of the cylinders LOOK good with just the drum off...pull back the very outer lip of the wheel cylinder boots...DONT remove..If there is a bad cylinder the outer edge of the boot will be wet. If any of the backing plates inside or outside are wet/damp...most likely a leaker...It would leak from ABOVE the axle housing. It may also be damp/wet around the adjuster hole in bottom of the backing plate or the edge of the brake drum.
Another thing to look at...the flexible brake hoses front AND rear...Look for incorrectly installed replacements or tire rub areas on the front hoses...oversize wheels/tires will also cause this. If theres flat spots...replace it!!! On the rear(and fronts) look closely for cracked hoses...thats age...i would replace it. If any of the metal lines appear to have been replaced prior...look for leaks where this was joined into the system. Also, if the lines ANYWHERE have been serviced from the wheel cylinders, etc. it IS possible to overtighten the fittings and ruin the flare fitting and thus a leak.
Look on the axle housings front and rear where the brake lines are and look for heavily rusted or smashed lines too...on a 4WD anything is possible. Also look for damp/wet spots here too. On the frame rails...same thing...look for dampness...metal lines run along the inside of the LH frame rail.
If after all of that and all of the metal lines look good and the wheel cylinders are good...master cylinder could be bad...look for a poorly sealing lid(possible with a wire bail type retainer), a bad seal on the lid itself, or leaking past the piston and cups and thus leaking out the rear most likely...this would be able to be seen possibly on both inside or outside or seperately...it just depends. If you swipe your finger along the bottom of the m/cyl...cylinder is leaking out the rear or from the lid or possibly from brake light switch at the front. If thats all good, look inside on the firewall...look/feel for dampness and it will be wet or such if the cylinder is leaking.
I personally would ALWAYS buy brand name brake parts number one...you know they will fit first time and the quality is sure to be better then foreign stuff. A good brand is Wagner for hydraulic parts...and inexpensive relatively too...remember...brake parts quality is your neck...how much do you value it...The few extra bucks do make a difference.
If EVERYTHING above checks out ok...Bleed it out...should be clear and not all dark and icky in color...no air bubbles...start at RR wheel, then LR wheel the RF wheel and lastly LF wheel...furthest from master cylinder to closest...ALWAYS.


Let us know how it turns out.

- cs65

 

Sigh.
Thanks for the correction - and sorry about that!

 

hi camper ive looked all over the truck for leaks in the lines an havent found any. the rubber lines have been replaced a couple years back. i checked them again to be sure an there fine. i got the wheel cylinders from autozone an i didnt pay any attention to who made them but they are not leaking any more. the master cylinder is new an is not leaking any where around it but thats not to say that its not leaking internally how do i test it to see if its working properly to me it acts like is sucking air somewhere in the system

 

Did you look under the dash where the brake rod goes into the master?

 

i would have them warranty my master cylinder and then bleed the brakes well again and see what happens. i have had similar problems and found a bad master cylinder before

 

I am helping another FTE member doing brakes up front on his rig...ran into wheel cylinder fitment issues...from AutoZone too(their line is called Brakeware p/n 33462...total crap) The autozone part is a foreign piece that had bolt holes that were off by 1/2 of the hole width...
The Wagner p/n is WC41719...thats the RF one...fit like a charm...the cylinders interchange up front is 65 F100 4WD, 65-67 F100 2WD only. The rear is 64 and 65 F100 4WD and 68-72 F100 4WD only..the front wheel cylinder bore size is 1 1/16" and the rears are 7/8" bore.

the Wagner cylinder I ended up getting cost 3 dollars more then the AutoZone foreign one...


As for the master cylinder fluid is probably getting past the primary piston and the secondary is picking up the slack...thus the 2 pump to get a good pedal scenario...mine is doing the identical thing as yours is btw...just havent gotten around to replacing it yet.

Its interchange is 1964 F100 2WD, 1964-65 F100 4WD...its last part no. shown in the MPC is C3TZ2140H This has probably been superceded since the Jan. 1975 final version of the MPC There is 1 other variation for 65 F100...but thats for 2WD...


- cs65

 

I am going to suggest that your brake shoes are out of adjustment and/or the self adjusters are not working properly. If you had air in the lines, the pedal would always be mushy no matter how many times you pumped the pedal. If the shoes are too far from the drums, each time you pump the pedal, you are pushing the wheel cylinders out futher with each pump until the shoes make contact for a firm pedal. With the truck on jackstands I recommend you remove the rubber plugs from the backing plates to ratchet the adjusters until the shoes just begin to drag on the drums. Then pump the pedal a few times and be sure you still have slight contact. I think you will find you have very firm pedal. If the pedal eventually becomes low again, you should pull all of the drums and check the self adjusting mechanisms. Drum brakes are almost a lost art with a lot of misconceptions floating around. If you can pump the pedal and eventually get a firm feel, the hydraulics are working.

 

I'll second the brake adjustment theory. Especially since you had them apart to replace the wheel cylinders.