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Discussion Starter #1
I have never had a brake system stump me before, until now.

Ok so the entire system has been replaced or rebuilt by me.

New rear wheel cylinders
New booster and Master Cylinder
New adjustable prop valve
Rebuilt calipers
All lines flushed and cleaned
DOT5 fluid

I have no front brakes. I just put a new master cylinder on yesterday and just took it for a test drive and still got nothing, I thought it may have been the other new one. I did bench bleed it very well, then bled the lines WAY more than should have been needed. The prop valve wont do me any good because it only goes to the rears. Without vacuum in the booster the pedal feels fairly stiff, but start it up and it goes damn near to the floor. I can feel the back brakes grab during movement, but get nothing from the front, but that is at almost the floor.

So, what gives? Do I need to go back to that crappy paint eating DOT3? or am I fine with the DOT5?
 

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Check to see if you mounted the calipers on the correct sides. You can put the right one on the left side and the left one on the right side but they will not bleed all the air out and you will get the symptom you are describing.
 

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Discussion Starter #3
I should have mentioned that as well, they are mounted on the correct sides. Bleeders at the top pointing towards the rear. Thanks though.

I just can't understand why it would be doing that. The DOT5 fluid shouldn't have anything to do with it. I thought maybe the pushrod was adjusted too far out and that was causing it. When I put the new master on I turned it in a few turns and now the pedal has too much play in it, but not enough to cause this.
 

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I can't think of anything else that could be wrong.

I did have one time that I could not get a firm pedal after redoing the brakes on my cougar. After an excessive number of tries bleeding the brakes, I finally gave up and had the system pressure bled in a shop. This worked. I have redone the brakes a nember of times since and have never experienced the problem again.
 

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Fluid won't make a diff - but why aren't you getting pressure up front? hmmm I take it you got a good amount of fluid out when you bleed them, so that should mean you have enough travel in the pushrod. Unless you bleed them under no pressure.... Do you have good holding power in the rear when you have vac on the booster - or just so-so? Try bleeding them with it under pressure (running) on the fronts and see if you are actually putting and pressure at all. If it doesn't come outta there like crap through a goose, I'd question the MC or lines/path. Are you using a non factory prop valve?
 

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Sounds like the same trouble i encountered when i put disc brakes on my cat, first off, i would not recommend the DOT 5 fluid, it´s silicone based, and it may or may not ruin your brake hoses internally, i´ve seen those that suddenly got no brakes due to the DOT5 fluid, and also those that experienced the brake would not release after braking too, due to the silicone based fluids swells up the inside of the brakehoses, use a DOT 5.1 or DOT4 instead. Unless you have hoses that are designed to take the DOT5 fluid

My trouble was just the same you have, firm pedal when engine was off, but lack of braking power when running, and it was caused by air in the front calipers, tho i had bleed them again and again, i had someone pumping the pedal for me, and they did it too fast, resulting the air to just go back and forth in the system, so i took control of the pedal pumping myself.

Build some power to the system and hold a slight pressure on the pedal, have your helper open the bleed valve, then press the pedal very slowly towards the floor, and get them to close before the pedal hits the floor, then very slowly release the pedal, and also slowly press/release the pedal to build pressure again, and repeat the procedure.
I also had a couple of pauses within this procedure, when i just held good pressure on the pedal for a while, before starting the bleeding proses again, it took some time, but i got all the air out eventually, and now my brakes are just perfect :)

On my cat it was due to the 4 piston caliper, so it took some time to bleed the entire caliper, as the fluids had to go trough the first chamber, trough a line and into the chamber on the other side, lot´s of nooks and places that an air bubble can hide and play tricks on you in there
 

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Discussion Starter #7 (Edited)
The rears don't grab as good as they should, you really have to push on the pedal hard to stop it when backing down the drive. Then again, rears don't work to great going backwards anyway, they seem to work pretty good going forward, and could probably get them to lock up if I tried. Also, In all I have bled them 5 times now. This last time I bled 2 oz. of fluid at each line 5 different times, which is why I said way more than it needed earlier.

I have stainless braided soft lines that are rated for the DOT5 fluid, so that shouldn't be a problem.

Also, I have speed bleeders all the way around, and they do work correctly. I wrapped them several times with teflon tape before threading them in and they seal well.

I have thought about the pressure bleeding thing, but can't see how it can be much better than the speed bleeders. I have an old master cylinder cover that I can modify to use as a pressure cap, but am afraid of it pushing the fluid too fast. What pressure do you set the air at to do this?

I may just give that a shot set it at around 20 psi and work from there.
 

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Did you bleed the front brakes with someone pushing the brake pedal? or did you use a suction bleeder?
 

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Discussion Starter #9
I tried both. With the speed bleeders I can bleed them myself. They have a ballcheck in them to keep fluid from flowing back, and I verified that they do in fact work quite well.

I just tried to do a pressure bleed. Good thing I used DOT5, that crap is all over my pretty new engine now. I used my old cap and drilled a hole in it and welded up the existing vent hole. Used my blower nozzle with a pointed rubber tip on it to supply the pressure. Lets just say the wire hold down clamp doesn't hold down tight enough to contain the pressure, sprayed a fine mist of brake fluid from all around the cap and got all over everything. I ended up having to use a big C-clamp to tighten it down to get a seal, that worked, for a bit. With the multiple times of having to take it back off and on to put in fluid, the thin cap had warped to the point of not being able to hold pressure any longer, no matter how much I tightened. I got a few bubbles out of the drivers side, but by the time I was starting the passenger side I could no longer hold pressure.

Tomorrow I will cut a scrap piece of 5/16" steel plate and pop a couple of holes in it. Maybe that will work better for me. I may actually use a piece of scrap 1 1/4" bullet resistant lexgaurd that way I can see when my fluid needs topping off.
 

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Mike - IDK, but for some reason it sounds like you are getting the pressure inside the MC itself and not towards the brakes..? maybe that's where your troubles are? -- Wonder if the piston in there is either to far out or not far enough in once you have the power assist (booster) in play? I have heard that adjustment can be a bit tricky. I must have got lucky when I replaced my MC -- I only had to bleed it 3 times more than I thought I would have. Even if just your back ones are working I would think you could get way better stopping power under power than what it sounds like you are....kinda points to the MC don't you think?
 

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I'm thinking that the piston in the master cylinder isn't centered.
 

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Discussion Starter #12
What do you mean not centered? This is the second new master cylinder, I can't imagine 2 of them being bad. If it helps, when I push on the pedal with the cap off, you can see a little stream of fluid pushing up, same when you let off.

I am hoping it is just a spot of air that is a pain to get out.
 

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I agree w/ Scott - it's not the MC itself but the positioning of the piston at the time it should be going out both sets of lines, rather than out the cap (because it has no where else to go) and barely towards the rear.....could be you got a nasty air bubble still. It should have a very solid fell even without the booster. I'm thinkin what's happening is your piston isn't travelling far enough when you push the pedal to complete the fluid push to both the front and rear ones (although I'd swear it's designed to push front first....?). Then it should pull it back to the resevoir (MC) when it's fully retracted. That silicone fluid is nice because it doesn't compress as much as DOT3 (or overheat) or suck up water! It should seem "touchy" comparatively once it's right.
 

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Mike, One trick I've read about is tapping the calibers with a hammer while bleeding.
 

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It sounds like the proportioning valve. There is a procedure in the owners manual for re-centering it. Did you follow that? Mine did that to me as well. I could bleed all day but had no brakes.
 

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Discussion Starter #16
I have an aftermarket prop valve on it, brand new. It only controls the rear brakes, the fronts are on a tee fitting.

I am about at my wits end on this thing now. I tried the pressure bleeding with a piece of steel for a cover plate, vacuum, and standard pumping. I still got nothing. I even unhooked and re-bench bled the master (in the car of course), then bled all 4 corners 10 times each with 2 1/2 ounces of fluid each time. I don't know what the hell to try now. The only thing i can think of is to buy one of those reverse bleeders. The only problem with that is that I did that with a syringe and it didn't help then either.

Damn, I finally have a brake system get the better of me, and it was my own damn car.
 

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you can easily check to see if the booster push rod is too long---take 4 ea 3/8 flat washers and hacksaw out a slot , making "c" washers---loosten up the m/c and install the washers between the booster and the m/ try bleeding again--if its better , your pushrod s too long--btw , i sometimes have to bleed one front AND one rear at the same time to get the m/c to stroke all the way
doctordesoto
 

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Discussion Starter #18
I know that the rod was too long because the pedal traveled about 2 inches before it engaged the master, but that it a rather good tip, thanks Doc. Also good tip on multiple wheels at a time, I used that.

So I believe I have become triumphant over this bastage of a brake system. I took the master back off again and bench bled it, again. Adjusted the rod back out and now have 1/2" of pedal travel before it engages. I also loosened up the prop valve and turned it upside down, so that the adjuster knob is pointing sorta down. I may have been getting air trapped in there, not sure. So I got it all put back together and tightened up. I seek out some extra clear tubing and clean peanut butter containers to try doctordesoto's tip, but take it one step further. I opened up all 4 bleeders and proceed to pump away. I bled +-15 resevoirs worth of fluid through. After 10 rounds, I lost count and started countin' again. Then I closed them off one by one and did 2 rounds between each. Now the pedal its pretty firm, finally. Oh, and James, I tapped on the calipers and cylinders a few times as well.

Now I will go for a test drive if it isn't too wet in the morning and report back.
 

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I would also look at the plunge rod . I had a similar problem and had to make it longer to mate tighter with the booster.

GG
 

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If your diverter valve isn't centered you won't be able to bleed your brakes.
Is your brake light on?

In the factory service manual it describes the procedure to re-center the diverter valve. To summarize, you open the opposite side bleeder and depress the brake pedal until the light goes out.
 
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