Brakes won't bleed! Master Cylinder Gasket???

I'll try to cut to the chase...I've been trying to bleed the brakes on my '60 F100 all f'n day today and the rears just won't bleed. I know it's the rears because the brake lights work on a pressure switch and they don't light up as readily as they used to, and that switch is plumbed into the rear lines...

Anyway, the fronts work, but the pedal is soft, so I've driven it a little and when I got out to reconnect the brake light wires (dumbass) I noticed brake fluid on the firewall, and dripping down onto the header. I've tightened the lines as tight as I can, so I think the gasket is my problem.

1. Would a leaky gasket keep the pedal from being stiff?
2. Is it possible the bar that holds the cover onto the master cylinder isn't holding it tight enough?
3. The master cylinder was for a '75 Silverado with JB1 (manual disc/drum) brakes. The gasket I'm finding on all the online sites is rectangular, not rounded on one end like the one I have. I found one that looks identical, but I'm sure it won't work. This truck has fought me on everything I've done. I foresee more bullshit trying to find this...any tips on making it seal right with the existing gasket? Everyone always has some kind of a trick for shit like this...

 

Did you by chance use the valve mounted on the crossmember from the Chevy truck too?
If you did, there's a valve inside of it that needs to be centered.

 

no

yes, but how tight is something you know, if you have worked with those before. Someone who never really worked on them before, won't know a good fit, or poor fit. It really does not need to be wicked tight on the bail, but firm enough to seal the rubber to the bowl.


Like 31 Vicky says:
back to bleeding; is this master set up with the orig type GM proportioning valve with it's built in, brake warning light switch? That has a single wire on it. If that switch piston inside, is jambed to one side, you can run into bleeding problems, as it restricts the flow to one pair of brakes.

Some guys on here say it does not matter, but I have seen it cause problems. GM shows a tool that keeps that piston centered while bleeding

 

I have a proportioning valve also plumbed into the rear, and I've messed with that quite a bit, turning it all the way in, then out, then bleeding the lines, etc.

I really think my issue is the brake fluid spraying all over the firewall, though.

 

My proportioning valve is adjustable, made by Baer, I think, not an OE GM part.

 

But a leak at the top cover gasket won't cause bleeding problems.

And, if a line is leaking as you hold the brake pedal down, you should feel the pedal slowly go down a bit, untill the other circuit holds firm. A leak of fluid from a bad fitting up at the master should not cause a bleeding problem, as I doubt it can draw air in, unless it was almost falling out


If you dare to test drive around the block, feel all 4 brakes when you get back. A pair of cold brakes means they are not working at all.

 

I've driven the hell out of this thing already. The pedal holds enough pressure from the front, and I keep thinking I've gotten it solved so I've taken it around the block once, then down the highway at highway speed. It stops just as well as it used to with the 4 drums. When I got out to reconnect the brake light wires (my dumb ass forgot that part before I left) there was fluid dripping onto the header and sprayed onto the firewall.

I'll replace the gasket tomorrow, if I can find one, then do another test run. I know the fronts are working because it stops nice and straight, and sort of nose-dives.

The pedal feels like a power brake pedal, you know how it is soft at first but stiffens up? Not like any other manual brake system I've driven, where it's usually just stiff from the get-go.

 

Check the fittings at the master and the threads in the master. It almost sounds as if pressurized fluid is shooting out, which could also explain air getting into the system. Have had them crack. Have also ended up with screwed up lines that would not make a good seal.

Can you have someone work the pedal while you watch the master?

 

Your gasket may be screwed up, but even if there were no gasket at all you could still bleed the brakes.

The master may be screwed up or not bled fully and shooting entirely too much fluid out of the bowl and at the gasket, exceeding the gasket's designed ability. To me this sounds more likely and probable to cause both problems you are describing.

 

Ok, You switched from 4 drum brakes, to a non-power disc front??? If yes, the discs take a bit more foot pressure to work, but it should feel firm from the start of braking. Power disc would feel a little soft, then stop quickly

I'm not there to feel how it stops, but from this description, if non-power, I would think the back brakes are not working, or not enough, due to air? Feel the drums on the next trip. Drive normal, not mashing the brake, or overbraking. Then feel all 4 brakes.

 

has anyone mentioned if the brake pushrod is adjust OK? If you barely move the pedal by hand, you should feel some free play before the rod finally hits the master cyl piston. If that is too tight, and is holding the piston in, it won't bleed correctly.

 

Buy,borrow or rent a Phoenix brake bleeder tool and reverse bleed the rear brakes.Sometimes it's the only way to purge air out of the system.

 

HOW ABOUT A PIC OF YOUR MASTER CYLINDER AND THE "LEAK"
instead of guessing.....

 

I started with those Speed Bleeds, and they worked perfectly on the front, when wifey worked the brake pedal I saw a big geyser of fluid spraying out of them when they were open. The rears would spray a nice stream at first, but then just piddle out. After messing with those, working the proportioning valve, messing with those checking the pedal, etc., I reinstalled the stock bleeder valve and used one of those one man bleeders that builds vacuum. I put the hose onto the nipple, built up vacuum, then cracked the bleeder valve until fluid ran into the plastic reservoir. After that, the felt a lot better, but still not great...they felt good enough to trust on the highway, I'll put it that way.

I'm not guessing about where the fluid is coming out. I see brake fluid dripping off the master cylinder and onto the hot header, and there is spray on the firewall that looks, feels, and smells like brake fluid.

 

The pushrod is perfect. Just a CH of play before it makes contact.

 

If I remember correctly ...Proportioning valves from 70's GM, has a pin that has to be pulled out about a 1/16" while bleeding. Also the master cylinder leaking, sounds like the rear shaft (spool) seal...but without pics...

 

Since everyone wants photos...

 

You can start fresh by washing the area with brakekleen, sometimes the spool will leak inside the cab also

 

Are the rear drums adjusted good? You say the only gm part is the master correct? so the gm p-valve issues don't really pertain to his system. The master seems to me to be the issue if that's where the fluid is leaking between the master and the firewall. If you're getting air leaking in up there, you'd never get the rear bled out, until that's sealed.

 

One other thing I would check is to see how much travel the mc takes to bottom it out than measure how far the pedal is moving the rod. Not enough movement and you'll never get the air out.

Someone mentioned reverse bleeding which pressure is sent from the bleeder but if the lines are t new And residue or rust will end up in the mc.

 

Ok, here's how I'd start looking at this.
Be sure your rears are adjusted properly.
* this will give you a bad pedal.

Double check your free play, return springs, and pedal stroke ( without assuming they are perfect) and the pedal ratio.
* If any of those are off you'll have trouble getting a good pedal.

Be sure the master is properly bled. The standard procedure is called "bench bleeding" and google can give you lots of info. The master should have came with specific instructions on how to do this also. The theory is to isolate the master and have it bled independently of the rest of the system.
* if this is off, you'll never get a good pedal or be able to bleed the brakes.

Isolate the master and plug the ports. This should result in a rock hard pedal, no fluid gushers, no leaks, drips or anything else.
* if this is not the case, the master is bad or - one of the above bleed or pedal operation is wrong.

If and only if the above is 100% , then move on to the rest of the system.


With no fluid to the rears, you'll need to determine if its an obstruction in the lines or a problem sucking air. The lines can suck air and not leak fluid if full pressure hasn't been achieved. Obstructions can be crap and chunks in the lines of malfunction of valves. Bleed the rears at the joints and see where you loose the flow of fluid. Work your way back from the master.

It's not hard to outsmart the brake fluid- you'll find the problem with some methodical isolation.

 

I stopped by a friend's small engine shop today and he led me to believe that bleeding the system with new lines would take a long time, so I borrowed his Mityvac vacuum bleeder, which seemed to work better than the one I was using. I'm pretty sure the right rear is good, so I moved to the driver side rear and spent about 25 mins on that tonight. It's not just air coming out, but there's a bunch of bubbles still in it. I build up vacuum with the Mityvac, and crack the bleeder valve and it looks like fizz in the tube. The pedal keeps getting better, I think. I ran about a quart through the system today. I'm going to buy another quart tomorrow, mess with it tomorrow evening, and if it still isn't working I'll be asking about hot rod friendly shops in CT that will bleed them for me. I'm tired of this fucking truck's games.

 

Got a helper that will listen? Here is how I would bleed those rears;

Have your helper there, only to hold slight pressure on the brake. Then you crack a rear bleeder and let it out SLOW to look for air. When the helper says it's down, close the bleeder and have them SLOWLY let the pedal back up.

Slow movements are what is needed, not this pump-it-up crap. that just makes foam.

Do each rear bleeder with that one slow push at a time, until it runs clear, then do the other side.

 

I noticed how much better the system bleed when the pedal was pushed slow and easy.I ended up using speed bleeders so I could bleed the brakes by myself without worring about my helper getting impatient with the process.

 

do not use spent fluid but you knew that

 

I assure you that is an inanimate object, simply mechanical.
Of its giving you problems, its not the truck.

Giving up isn't the best option

 

How much fluid SHOULD it take to fully bleed the rears when the lines and hoses were replaced? I've got about 1.5 qts through it and that one driver side rear won't cooperate. It feels like it will keep doing what it's doing for days. One guy said it would take forever, my neighbor countered with "there's no way that there's a quart of volume from the master to the rear wheels inside those lines."

Who is right, because I know I'm not.

 

No way there's a quart in there.
Measure the line length and diameter of the line

Now just for shits and giggles,
a down and dirty "you are full of shit" comparison ignoring all math , pie, fluid conversions and wall thickness

Lets say you had 16" of 1/4" line, you would have only 1 square inch of line 1"x1"x1"

 

That's what I'm saying...How can it take more than a quart of fluid to bleed air out of a system that's less than a quart in volume? That doesn't seem possible, yet I'm over a quart into it, and messed with it for another 2.5 hours this morning.

I just reread your last recommendation. I think the next step is to plug that rear port (since the fronts seem fine) and see what the pedal feels like. I forgot that this master came with plugs to bleed the line (not ports and hoses, but rather plugs for some new-fangled way of bleeding the master) so I'll use the plug to see what the pedal feels like. If I conclude that the master is messed up, I'll try master cylinder #3, which will mean that 66% of all master cyls I've ever bought were shit out of the box.

Something on the master does keep leaking, though. I put a clean cardboard box under it (over the header) and there was fluid on it this morning from two nights ago, so I reefed on the lines again.

I adjusted the rear brakes again this morning, and they're good, the pedal ratio is 6:1, the spring is the same one it's always had, and there's probably 1/16" of freeplay- it moves just a hair before it starts to push on the plunger.

 

I dont think you are bleeding the system correctly first of all. Place the vehicle on jack stands so you can easily access all 4 wheels. Now adjust the brakes correctly if you have drum brakes. Start at the farthest wheel away from the MC. Start bleeding the air out of the system by appling pedal to the system (Do not pump the pedal up and down) just one push slowly and have your helper crack the bleader port at the wheel cylinder and close as quick as the air burps or the fluid sprays out. Release the pedal and go to the next wheel , again apply slow even pressure to the pedal and have your helper crack the bleeder and close as soon as the air burps or fluid comes out. repeat this process for all 4 wheels. Now to check the results, apply full presure to the pedal assembly and the brakes should lock down within 1" of stroke +-. If they dont slowly pump the pedal twice and notice if the pedal gains pressure and travels less distance. If it does, repeat the bleeding operation again as there is still air trapped in the line.

After repeating again apply pressure and the pedal should be solid with limited travel. If you still have a low pedal or double pump pedal you have another issue.