old68olds

All parts are for a '72 A body. New master cylinder (bench bled), booster, calipers, correctly bled. What gives? The pedal is on the floor. Everything I have tried has failed to bring the pedal off the floor. Honestly I'm getting quite pissed. New fluid and wheel cylinders in the rear. It had the discs when I bought it 10 years ago. The pedal always sucked so I replace EVERYTHING....no change. What am I missing? It's not rocket surgery but I'm at a loss.

oldcutlass

Most times the reason for the pedal going to the floor is air in the lines or the master cylinder was not bled correctly.

66luvr

I had a car act like that. When I finally tracked it down the rod from the pedal inside to the power booster was out of adjustment. I took it loose from the pedal, pulled the stop light switch out, lengthened the rod by screwing the clevis out until it fit when the pedal was up against the "Stop". Then put the switch back in it's place. This solved my "Pedal on the floor" problem.
Also, there are 2 holes in the pedal, the rod should be in the lower hole for a power brake car.

Good luck,

gs72

If you had both front calipers off at the same time, make sure they are not switched. This will put the bleeder at the bottom of the caliper.

old68olds

Thanks for the input. 66luvr, I think you may be onto something. I'll give it a shot. I don't see what else it could be. I've spent hours making sure everything is correct and this is the only car that I have had the issue with.
Again, thanks for the input everyone. I'll let you know what happens.

old68olds

So I adjusted the pushrod and it did pull the pedal up to where it does not actually make contact with the floor. But the problem still exists.

With the engine running I can pump the brakes but they will not build pressure.
When I try to bleed the rear brakes there is very little pressure. The fluid will squirt a little bit when I loosen the bleed screw the first time. After that it barely trickles out even after pumping and holding the pedal. The front seem to flow normally during this procedure but the pedal will sink down and not hold pressure even after the bleed screws are closed. If I put the car in gear it wants to roll even with my foot all the way in the brake. What's strange is that when I'm driving it will stop without much effort but wants to roll when I'm stopped. I really have to jam the pedal to keep still.

I took the plugs that came with the master cylinder for bench bleeding and installed them while it was on the car. Started it up and pressed lightly on the brakes. The pedal felt great, nice and firm plenty of pressure.

I then removed the plug for the front brakes and reconnected the line. Very nice pedal. It could use some bleeding but was holding pressure.
It was when I connected the rear back up that the pedal sunk down once again.

I have tried gravity bleeding, vacuum bleeding and the pump and hold method.
I pulled the master cylinder again and checked it on the bench. All is good there.
Calipers are new and on the correct sides
New booster
New wheel cylinders
No leaks

Could the proportioning valve be the problem?
The car originally had drums up front. Would the original proportioning valve work correctly after the conversion?

I don't have a specific timetable for when this started happening because the brakes have been doing this since I bought the car. It seems that nothing I replace has any impact.

Sorry to be so long winded but I've hit a wall. Any help is appreciated.

joe_padavano

WHICH "proportioning valve" did you use when you did the conversion? A drum brake car does NOT have a prop valve, only a distribution block. The 1967-70 disk brake cars used the external metering valve under the M/C. The 1971-up cars used the combo valve on the frame rail.

In any case, the prop valve will not cause the brakes to go to the floor. You still have air in the system. Did you replace the rear cylinders? Rubber hose to the rear axle?

old68olds

I did not personally do the conversion. I bought the car after it was done. It would be 67-70 as the metering valve is attached below the master cylinder.
I did replace the wheel cylinders but not the rubber hose. I guess that's the next step.
Thank you for clearing up the whole "proportioning valve" thing.
I'll install the new hose after work today and keep you posted.

Rocketguy

Did you adjust the rear brakes properly? If the're a ways out that would cause your condition.

70cutty

I was chasing the same thing when I did my disc conversion. It turned out to be a loose fitting that had a barely noticeable leak, but it kept sucking in air every time the pedal was pushed.

old68olds

It was the rear hose. I can't believe I over looked it.
Thanks, Joe... and everyone else that chimed in. I could have snapped it in half it was so rotten.

White_Knuckles

Sweet, you'll probably get a Thank-You card from the brake fluid company. Well, it's a thoroughly inspected system now.