Brake pedal goes to the floor?

[Dano65]

I know this is B-Body forum and I work on them also but this question is for a 73 Challenger I'm working on. Brakes were fine on it till a line was accidentally pinched while installing a tubular front end and it lost the fluid, I replaced the line and bled the brakes but can't get a pedal? Tried multiple times to bleed manually, gravity, and used a vacuum pump and still no pedal. I can pump it up but the pressure slowly bleeds off and the pedal drops. No leaks anywhere either. I tried a new master cylinder, went through the same bleeding procedure and it's still the same? Took it back and tried a third one thinking my luck can't be this bad....and it is, still the same? Bled and bled different ways and the pedal still slowly drops! I'm at my wits end here! Anyone have any ideas I can try? Oh, and I did bleed the master cylinder before hooking the lines up. Thanks for any help with this.

 

[R/T Boy 67]

Did your tubular front end come with disc brakes, and are the calipers mounted with the bleeders on the top?

 

[Dano65]

No, we used the stock calipers in the front and the bleeders are on the top still. Back has strange calipers with bleeders on the top and bottom and I've bled both.

 

[70chall440]

As depressing as it is to go through all the work and not get any pedal, it is a simple hydraulic issue so long as everything is working and it isn't leaking, solving it might not be all that simple. Given what you have said your possible problems are;

A. massive amount of air in the system: only way to remove is keep bleeding, could try having someone pump up the pedal (as much as possible) and crack some lines as well as the bleeders. I usually start at the MC and work down/back; I know you are supposed to bleed from the furthest to the nearest but when you have no pedal at all, its easier to start at the source. Basically, pump up what you can, crack the lines, repeat (over and over again).

B. Your combination/proportioning valve is stuck: there is a sliding valve behind the brake light switch/sensor on the valve, if it gets stuck to one side it can be an pain to bleed: the solution requires removal of the valve, removal of the switch and then try to slide the valve to the center position.

C. Your MC took a crap for some reason (unlikely), have you bled it independently?

 

[Bad B-rad]

What line got pinched?
A rubber flex line or steel?
(Just curious)
Just spit balling if u have NO LEAKS, maybe in the valve/ distribution block?

 

[Dano65]

One of the new steel braided front lines that replaced the original rubber flex lines. I've pumped the hell out of them and looked underneath and see no dripping. Pressure's going somewhere but I can't find it. Would a bad distribution block cause this?

 

[Bad B-rad]

Not the distribution block, but maybe the prop valve COULD be internally leaking.
Like 70Challenger440 said that valve with the light on it, may be stuck(air locked)
Not knowing what (make)brake system you are running, I am not sure what valving is on your car.


I would try cracking the line loose at the valving, if you don't get air, or an improvement, you could plug the lines and try and isolate the master from the system, and check if it holds pressure of if it bleeds off, to find your issue.

I think 70Challenger440's advice is correct about the air.
Good Luck.

 

[70chall440]

Let me suggest this as well, you need to do this one of 2 ways;

1. Use a Power Bleeder so that you have positive pressure in the MC (don't need a lot). This can be a one man job this way; put some pressure in the system and then begin to crack lines working down through the system. when you get to a bleeder, crack that as well.

2. use an assistant with a strong leg and nothing to do; have them pump it up and do the same thing outlined in #1.

Pinching a SS braided line should not have done anything unless you really smashed it or cut it. They should be PTFE lined (plastic) or rubber which doesn't collapse like metal.

 

[Dano65]

Man this sucks. We've bled almost a quart of fluid out of the lines already but I do agree that it's a hydraulic issue. I'm gonna try all of your suggestions though. Will try the prop valve if bleeding all the lines/bleeders doesn't work. This is the third master cylinder so I'm assuming that wasn't the problem. Yeah, the line was smashed bad enough that the fluid leaked out

It's the stock brake system as far as the master cylinder/proportioning valve/brake booster. We are bleeding with the engine off but I don't see how that would affect it besides the pedal being a bear to push down, car's too loud to run and talk to my helper. Brakes have been fine till pinching the line caused this headache.

Thanks for all the suggestions!

 

[70chall440]

So we all understand, you are running drums in the rear and disc in the front? Was this an original disc/drum car? Maybe a better question is, were the brakes all good before this happened?

IMO you either have a lot of air in the system or you are sucking air in from some place which is why you cannot build pressure but are getting fluid out.

 

[Dano65]

So we all understand, you are running drums in the rear and disc in the front? Was this an original disc/drum car? Maybe a better question is, were the brakes all good before this happened?

IMO you either have a lot of air in the system or you are sucking air in from some place which is why you cannot build pressure but are getting fluid out.

Disc/Disc setup. It has a narrowed fab 9" in the back with strange calipers. Brakes were fine till the break in the line. Never had this problem with it before.

 

[Bad B-rad]

This might sounds crazy, but perhaps MAYBE, when the line got smashed, a small piece of rubber, or whatever came off the inside of the injured line and is now stuck in system somewhere?
I had this happen before on rubber flex lines, they were rotting from inside out, and caused the calipers to STICK closed.
So it is not the EXCACT issue you have, but it really sounds like you know what u doing, so it has to be something out of the "NORM"
You should have no issues bleeding with engine off, I gravity bled my Charger, and no issues.

 

[70chall440]

I am going to say that IMO your combination/proportioning valve is where some of your problem lies. Did you change that valve to one for a Disc/disc set up? Did you leave the stock metering valve in the system?

 

[Bad B-rad]

I am going to say that IMO your combination/proportioning valve is where some of your problem lies. Did you change that valve to one for a Disc/disc set up? Did you leave the stock metering valve in the system?

I was thinking same thing about the proportioning valve, (maybe being the disc/drum, not disc/disc)but he said it worked fine, before the line, got pinched.
And after the line replacement, the issue started.
So almost like air trapped in valve, or leak, internal or external.

 

[70chall440]

A lot of people do that conversion and say it works for them and I would guess that it must to one degree or another, however when I have done it I have change out the MC to a 7/8 bore and changed the P valve to one for a disc/disc set up to make it work correctly. I think in a system with a booster, it is not as noticeable, but if you try the same disc/drum set up with manual brakes it does not work very well.

 

[Dano65]

As far as I know it's the stock disc/drum valve but yeah, it's been fine for the last couple years...just a damn pinched line caused all of this. I've always hated bleeding brakes but in all my years of working on cars, never had a issue like this. Will try again in the morning to get this fixed. Thank you all for helping.

 

[Bad B-rad]

I feel for you!!!, good luck, may the MOPAR force be with you.

 

[Billccm]

Are you getting bubbles at each and every bleed? If so, then perhaps the line you replaced is sucking air. I had a similar nightmare and it ended up being a bad double flare. Did not drip or leak, but sucked air. This was a new In Line Tube line that caused my headaches.