i have a 1997 f150 drum brakes and no abs. The issue i am experiencing is when i step on the brakes they go almost to the floor without the truck running. Pump them up a bit and there rock solid. Did bleed the entire system and did get air out with no change on the petal with the truck off. Also when its running with knowing the petal is rock hard it will drop to the floor. and when i go to stop does the same thing and makes it hard to stop. But if i pump it up it will stop good and hold without fading. But go to stop again in city driving i would have to pump em up again to get the good petal again. Been through this entire system and cant find where the issue is. Master cylinder is full and get good jet from the bleeders when bleeding, even at the mc. Just stummped on what it could be. And also no vac leaks and new check valve with rubber gromit, Im thinking internal leak on the mc but wouldnt that have little to no pressure when bleeding and low fluid level?

 

I would replace the mc just to rule it out. The pedal should get rock hard and remain that way with the truck not running. I had one go bad on my 00 and had similar symptoms. Pump it and built pressure but faded quickly.

 

i just dont want to replace it and still have the same symptoms. and i do not have any leaks anywhere.

 

MC will not leak if its bad. The internal seal is probably allowing blow by from one end of the pump to the other. Fluid levels won't change, but will not build good pressure.

 

thats what im suspecting but i am getting a good stream out of the bleeders when bleeding.

 

Yeah, the pump will create pressure. It just won't sustain it.

 

looking like a mc change in the near future for me

 

Being that its non ABS simplifies it. No worries of the brake motor not pumping, etc. You have a mc, booster, calipers, and wheel cylinders. If no fluid is getting out and you have vacuum to the booster, its likely the mc.

 

Its pretty cheap and easy to do. Get a lifetime unit and be sure to bench bleed before installing. Then bleed bleed bleed.

 

Yep. Sounds like the MC. If you aren't losing fluid, the fluid in the line is seeping back into the MC.