1974 Satellite, disc/drum car 318.
Today, new steel lines on rear, new rear hose, existing steel line front to rear, existing steel lines MC - prop valve, existing steel lines prop valve to caliper hoses, new hoses to calipers.
Did rear brakes, adjusted tight, not too tight.
Put in new master cylinder (MC). Bench bled MC, installed on car, bled entire car. no air. Have checked several times.
PROBLEM. We get a hard pedal bleeding. Start car, goes to floor, little to no pedal at all. Not spongy, not low, but damn near on floor and barely holds car. Turn car off, brakes will pump back up to hard pedal.
Reading FSM, a troubleshooting step is to pump up brakes, hold, start car. Says brakes should drop a little, then hold. If it does not do this they say replace booster. What they do not say is if the pedal does not fall replace booster, or if the pedal falls too far replace booster, or if either, replace booster. I really dont want to spend $150 on a booster for now reason.
Any other ideas? I have read through all search results on "brakes" and now I am going to search on booster and MC. But maybe one of you guys knows what this is. I could use the help.
Assuming the components are in new/good condition, eliminate the basic possible installation errors: (1) booster to master cylinder rod air gap/adjustment, improperly adjusted this can cause low/no pedal or hard pedal/dragging brakes, you need to adjust any time a replacement master is added to the system
(2) are the front calipers on the correct side of the car?, are the bleeders located at the highest point in their mounting to allow air to be properly bleed?
(3) when bench bleeding the master did you bottom out the piston?, if so you may have damaged the piston O ring(s) by over stroking it, if so, it'll never create/hold pressure once installed in the system
These are just some of the basic problems, but from your description I would tend to think your issue is in the booster to master air gap, I would start there...you need between .020 to .060 max air gap
