I have a '53 Ford F100. I have a PB conversion kit on it. The master cylinder & Booster are under the floor. I have used this setup for many years. Recently my master cylinder went bad. I replaced it with the same model. I bench bled it, and installed it. I also added a remote fill kit, since it's difficult to check & fill. Because of the booster, the master cylinder no longer sits under the hatch in the floor.

I got everything installed & connected, then bled all 4 wheels using a bleeder kit with an electric vacuum pump. The fluid runs clear & no bubbles, but I can't get a pedal by pumping. I have no leaks. I tried with the engine off, and running. I have felt soft pedals before, but I have no pedal at all, it just goes to the floor.

Any ideas?

 

Bad new master? Did you change anything else?

 

I installed the Remote Fill Kit, but that seems to be fine. As I bleed, the fluid goes down in the clear remote reservoir. That reservoir has two chambers, like the MC.

I have a buddy coming over today, maybe two heads are better.

 

No luck in figuring out what's wrong. When the pedal is pushed with the engine off, you can hear air hissing from the booster.

If the pedal is held to the floor, and the engine started, there is no effect on the pedal. The pedal should push back, when the engine vacuum is applied to the diaphragm.

When the pedal is pumped & held, and a fitting on the MC is loosened, a small amount of fluid comes out of the fitting, but not as much as it should.

It seems like the MC is not being activated much, when the pedal is pushed.

Could the booster cause this, or is it a problem in the MC?

 

You say in the first post that you replaced the MC because it went bad. What symptom?
Presumably you are using the same booster as before? Can you pull the MC out of the way to watch the booster actuating rod move forward when you push on the pedal? It should move at least an inch or so. Also, at rest, the tip of that booster actuating rod should be within about 20 though of the bottom of the pocket in the mc piston with the mc flush to the booster. Is the pocket in the rod the same depth as the old mc? I would also put vacuum to the booster to see if it will hold it.

 

The old MC was replaced, because the pedal went to the floor!!!!

about 20 though???? = 0.020???

I'll try to put vacuum to the booster. I can run the motor, then pull the check valve after shutting down & waiting a minute. I should detect air rushing in.

After that I can pull the MC away & check the actuator rod.

 

Yeah sorry- 0.020" but the closer the better on the actuating rod clearance, but you do need some. Best checked with the engine running because the vacuum can pull the rod in a smidge. It should be adjustable.

So all of a sudden one day you had no pedal? That's why you jumped to the mc as the culprit? I probably would have too. Does the system have a proportioning valve and/or residual pressure check valve? Look for leaks!

I'm leaning towards a bad booster, but usually you get a hard pedal when they fail. If nothing else has been changed, and you have no leaks then I guess focus on testing the booster and the check valve.

 

Yes, it has a proportioning valve.

 

The booster holds vacuum, but the booster actuator rod goes into a hole in the center of the MC. That hole was not there, when I bench bled it, or in the old MC. The new MC doesn't push any fluid, because the booster actuator doesn't push anything. I have no idea how that happened.
I guess that I'll have to get another MC.

 

Gotta be some kind of pocket for the rod to fit into. Pictures ?

 

This is a photo of a similar part on Ebay. The new MC that I purchased has that hole, while the unit that I'm replacing has a pocket that mates to the booster actuator.

Brake Master Cylinder fits 1967-1976 Chevrolet Corvette El Camino Chevell | eBay

 

I think that I need the 1977 version MC.

Brake Master Cylinder-New Master Cylinder Cardone fits 77-82 Chevrolet Corvette | eBay

 

I purchased a rebuilt unit from Auto Zone. Normally, I prefer a New part, but I would have to order the New part. The rebuilt unit was in stock. I bought a MC for a '77 - '82 Corvette. The old one was for a '67 - '76 Corvette Here are some photos.
'77 - '82 Corvette



'67 - '76 Corvette

 

It's installed and I have a good brake pedal. I took the truck out to get a wash, and all was good.

Thanks for the help. I know it was a bit off topic, but my truck is a Ford. A lot of this hot rod aftermarket stuff is GM.