No Brake Pedal

[seany-boy]

Well, not a good start to the day. My garage is on the top of a very sharp drive, started backing out off my parking hoist and brake pedal went to the floor! A fair bit of panic as i grabbed at the handbrake and tried to pump the pedal, must have grabbed the steering wheel at the same time and bounced off the hoist track and clipped my hoist. Not too much damage but enough after recently having the car repainted/rechromed etc.
Managed to get it back on the hoist and in the garage nearly needing a change of trousers too!

Drum brakes, power booster. I can pump the pedal and it comes up, leave it for a bit and no pedal. fluid is full, booster rebuilt a few years ago. No sign of any problem previously.
I have been reading a few of the threads about swollen hoses etc. Just looking for a few tips before I start looking. Blood pressure back down now!

Wondering if disc conversion should be on the table although obviously nothing to do with this issue.

[Jimntempe]

I would think swollen hoses would prevent fluid movement and so create a hard pedal, not one that goes to the floor. If it's not leaking fluid out, then it's leaking past internal seals such that it's letting the pedal go down without creating normal pressure cuz the seals leak. Only places I can think which would allow that are the master cylinder and the booster cylinder... that's if you are NOT losing brake fluid.. If a wheel cylinder is leaking you'd get the low pedal, but you should see a massive loss of fluid at the wheel. If you do seem to be losing some brake fluid but don't see where the leak is, the other places which could be leaking is the seal for the rod that is connected to the large diaphragm in the booster vacuum chamber or the control valve in the round thing that points off to the side with the mesh end on it. Those places could leak without there being any/much visual clue as the leaked fluid could be building up inside for a while. But those last two seem much less likely to be your immediate problem because leaks there are not nearly as likely to cause an immediate low pedal when you press on it. They are more likely to just be places where fluid leaks out relatively slowly. My guess is bad master cylinder or booster cylinder. You can move the flex hose from the end of the booster cylinder directly to the master cylinder and bypass the booster entirely to try and troubleshoot which is the problem.

[seany-boy]

Thanks for the thoughts. I will bypass the booster before trying to drive it on the road and probably before reversing doen my drive again!
After a few hours I decided to take a look it seems like it might be leaking from the old hydraulic brake switch. It seems to have been a recent thing as the brake fluid is not down much...yet.
I installed the mechanical switch a few years ago but left the hydraulic pressure switch in place.
I think I need to find the right bolt to replace it or the tee connector. Any idea of the thread or length to simply plug the switch hole?

[ward 57]

I'll go with jimntempe's diagnosis. Sounds like a classic M/C failure. Remember ,there is a back pressure valve at the front end of the M/C that prevents one from bench bleeding and must be blead in the car. Not likely the booster. Learned that by experience.

[RossL]

I had to replace the rear hose that feeds the two rear wheel cylinders. When I was trying to bleed them I would get a quick squirt of fluid, probably from the initial pressure of the pedal. When I cut the hose in half I could see the opening was about the size of a pin hole. I never lost my pedal and it seemed firm.

[seany-boy]

Thanks again for the advice. I will start with the pressure switch as I can see a leak there now. I will plug it and work towards m/c if I can find a bolt. I believe it us 1/8 NPT.
Then gotta do some paint repair and chrome on front corner as in my panic to grab the handbrake, I clipped my hoist

[Rusty57]

Jim’s analysis is very similar to the approach I would use to diagnose this.

The fact that you can get a pedal is a strong indicator that there a slow leak either internally or externally.

One remote consideration is that something has happened mechanically at either the linkage to the master cylinder or within one of the drums. For example, did the spacer between the end of the pushrod and master cylinder piston fall out or break apart? The one I have is plastic.

One other idea is that the piston in the master cylinder is stuck and will not return to the full home position. So only a portion of the pedal travel will move the master cylinder piston a small amount. Multiple pumps will possibly move enough fluid to make the brakes work.

My thinking is that this scenario is not dependent upon the type of brakes. They all use pistons with seals, hoses, and steel lines.

[ward 57]

The M/C rebuild kit from CASCO eliminates that plastic cap. The pushrod has been redesigned. I think the rubber cup on the piston is failing if he has to pump the pedal to get any resistance and then it fades away. I think a rebuild is in order.

[paul2748]

The switch is pipe thread if I remember correctly. Get a 1/8 pipe plug.- hardware store item or a parts store item.

Even a very slight leak can cause brake failure. I had it happen to me.

[seany-boy]

Thanks for all the advice. Will update with what I find

[ward 57]

A small leak will not cause your problem unless you are low on brake fluid which does not sound like the case. The M/C is the heart of the system. Just bite the bullet and rebuild your M/C. Sounds like it's due. They are cast Iron and rust where you can't see it and will contaminate the bore and chip/tear the rubber piston cup including just old age. Been there. They don't last forever and they weren't designed to. Standard maintenance procedure.

[seany-boy]

ok, that seems to make sense. I will plug the pressure switch hole and rebuild the master to cover all bases. It could so easily have been a major disaster instead of a minor one so it makes sense to be confident of the the system.

[ward 57]

Just rebuilt the booster & M/C and replaced the rubber brake lines in the last year. Boy, do they work well now. Hadn't changed the brake fluid in years and it took it's toll. Solid lines and wheel cylinders are good.

[seany-boy]

well thanks Ward57 and Jim, I replaced the switch with a plug and that brought the pedal back up - probably similar to before. However you had convinced me to continue on to the MC, as soon as I pulled the rubber boot off and fluid leaked out I knew you were right!
So off to get the MC rebuilt and possibly sleeved.
A question, is the plastic spacer on the end of the pushrod the same on other 50's Fords and will it impact the rebuilt piston- do I need to make the brake guy aware of the plastic spacer or will any rebuild kit still be ok with the plastic spacer?

[ward 57]

From my experience the rebuild kit from CASCO has a redesigned pushrod that eliminates the original pushrod with the plastic cap. Mine went back in with no adjustments and works great. Even though it was pretty rusty internally it didn't need to be sleeved.