I need a BRAKE edu-muh-cation

[BA.]

I've got a pedal that always goes to the floor! It doesn't pump up. :(

I bought this old Jeep Cherokee recently to use as a winter vehicle.
The brakes on it were horrible, and mostly original looking so I knew a full brake overhaul was in order.


So, I've replaced the Calipers/pads/rotors. There were never any leaks of any sort, the Master cylinder does not leak, hoses all look good, hard lines look good.

I bled the brakes yesterday, front only, but used a method I had only read about previously.

I loosened the bleed-screw and put a rubber hose on it with the other end deep into a container of brake fluid. Supposed to prevent air from getting sucked back up the hose.

So, I get in the jeep and proceed to pump away and sure enough, fluid is leaving the Mstr Cyl and going into the container. I top the MC off, tighten up the bleed-screw and think I'm done.
I repeat for the other side and STILL my pedal goes to the floor.
WTH?
Could a bad Mstr Cyl. cause this, even though it's not leaking anything?
My only other plan is to do a traditional bleeding once I get a helper to pump the brakes.

One other detail, the rear drum cylinders leak so at this point that part of the Mstr Cyl. is empty. I didn't think that would affect my front brake work/function.

Help! :confused:

[bingham72]

Yes, a master cylinder could cause this. I've replaced several before where the master went bad. You could pump up the presure and then as you hold your foot on the pedal, it slowly goes to the floor.

[6'9"Witha69]

Bad MCs will do that and bad rear brakes will surely compound the issue. Also, one man beleeding does not get all the air out as the fluid and air merely travel up and down in the line and never gets out. 2 man method or 1 man with proper self bleeding screws work much better. Then there is forced bleeding, which is the best IMO.

[HILROD]

I recently had a problem that sound the same. I installed a brake kit that was brand new never installed but purchased several years ago. At first the brakes worked great, a couple of hundred mile later, to the floor the pedal went. Turns out The master had a bunch of shavings inside, causing the rear section's piston to stick in the bore. No warranty either as the parts are "old".

[BA.]

thanks guys....

new MC is on order, I'll have it tomorrow!

[MrQuick]

yep I agree.

Its is common for a master cylinder to fail after a full bleed or other brake failure.
The usual reason (theory) is when there is a failure or full bleed, the master cylinder piston is pushed into a section on the bore not normaly entered and the internal seals are damaged by debris and dirt that resides in these areas.

A few good tips:
~open the bleeders when compressing pistons,
~when bleeding a system do not compress master cylinder piston past 3/4 travel.
~ when bleeding always suck out the old fluid from the resivoire and replace it with new before bleeding.
~bleed system till clear fluid comes out of bleeders.
~never pump the pedal quickly when bleeding. Pump twice slow then hold.

[MonzaRacer]

Well if I ever bought an unknown car I would double check the rears as the rear drums being out of adjustment OR the drums turned out of spec( that made me replace a master on my truck and still have a brake light come on) then you will ahve a low pedal.
Double check your rear drums before installing a master cyl (as you can return it) and make sure your drums have a medium two handed drag (as the brakes will reseattle after driving) tapping fairly heaviliy with a hammer as you adjust.
Also if you have rusty lines you could be getting air in the system but not leaking as you push as the out of adjustment brakes take no pressure but lots of volume.
Also as for bleeding that way I hate it as it is a great way to still get air back in if the hose doesnt seal to the bleeder.
Now as for installingthe master , if you do put in solid plugs not the hoses and slowly stroke till no more bubbles come out, and then I loosen the plugs but not remove them, and push in, let them bleed, hold it in and then tighten the plugs and then let up. But if you use the lines to bleed DO NOT stroke the piston much more than 1/4 in at least till you get most of the air out from behind the seals or you can and will fold the newer seals over.
The reason you will flod them over is that they are making the new ones softer so they will ride over small amounts of corrosion and contaminates.
Now after install the tighten the lines, then have a helper sit inside the car loosen the lines and then have them push the pedal down and hold it, tighten the lines,keep doing it till you get straight fluid.
My preference is to reverse bleed my brakes as air goes up.
I just had to replace rear brake lines on a van that had rusted out, and I reverse bleed the lines from back to front and it had been driven for al ong time with no rear brakes, all I had to do after this was one bleed at the master cyl with looseningthe lines and it had a hard pedal.
This is what I use for bleeding brakes and clutches: http://www.brakebleeder.com/product.php?pid=1.
But the V12 also works.
I love the test strips too as they read the copper content that the old fluid eats from the welds in the steel line.
Good luck
Lee Abel
AFTERMARKET PERFORMANCE

[Fuelie Nova]

~when bleeding a system do not compress master cylinder piston past 3/4 travel.


Just out of curosity... why not press past 3/4 travel?
Tg

[MrQuick]

Just out of curosity... why not press past 3/4 travel?
Tg The usual reason (theory) is when there is a failure or full bleed, the master cylinder piston is pushed into a section on the bore not normaly entered and the internal seals are damaged by debris and dirt that resides in these areas.

It may sound funny but I see failures due to this all the time.

[MonzaRacer]

Well basicly Mr.Quick is right BUT. The best answer is that short slow strokes will give you the least chance of folding over the softer next generation seals as easily.
See back in the late 80s as I was just getting out of school and into work force and worked at a 3 bay gas station and we installed 7, of the 1531 master cyl(for the GM guys its the tilted disc/drum car master)on one car, cleaning all of the local parts houses out of them.
One issue was with the hone finish required for master cyl, and the factthat you would push the piston harder and not get a steady speed and you also have to remember the seals were made to last longer(ie not get hard as quick) but what kept them in place and in proper order and all was the resistance of the shoes/pads and the fluid behind seals.
The last one we messed up we pulled apart (at parts store request) and sure enough the seals were folded over.
Wagner came over and showed us how it did this, and even put out a bulletin on this issue.
Short strokes (generally 1/4 in or less) are the best AND the plugs are the best way to drive fluid into all open spaces.
Now me I like using my Phoenix Injector and reverse bleed master cylinders and have a lot better results. I still use plugs too, but first I reverse bleed them.
Good luck to everyone who bleeds brakes too.

[BA.]

UPDATE!!!

I did replace the master cylinder and a friend and I bled the brakes the normal way. Also found/replaced a bad line from M/C to the proportioning valve thing. (brakes bled afterwards)

So, my symptoms have changed and I now need advice again. It is not too surprising that this brake system has more than one problem. :)

Symptom now:
1. With Engine OFF - the brakes feel normal, they pump up a little bit and give good resistance. Pedal has a good hard feel to it.

2. With Engine RUNNING - pedal goes straight to the floor every time. It will not pump up at all.

3. With Engine RUNNING - plug off both sides of the Brake Booster vacuum line and the brakes feel exactly like #1 above. Solid, firm. Feels right.


Why does my pedal go to the floor only with the engine running and that vacuum source connected?!!??

A. Bad brake booster
B. Leak between M/C and Booster (noticed small bubble with soapy water when pumping brakes)
C. Rear lines have a leak
D. I'm FUBAR'd.


.

[Rantheman]

I have heard of brake boosters leaking

second check the vaccum going to the booster

[paul67]

I have noticed on your first post you said you put a hose on and pumped, when the pedal was to the floor did someone close off the bleeder , then when you slowly released the pedal to the top did you then open the bleeder and pump pedal down and repeated first opperation, or have you a 1 man bleeding kit which has a nonreturn valve in it.?

[BA.]

My initial attempt was a one-man deal with me just using the ol' "hose submerged in bottle of brake fluid" method. The bleeder is just barely cracked open. It did actually work to force all the old fluid out.

After the M/C replacement, and finding a bad hard-line from M/C to the proportioning valve, I did the two-man method with a friend on only the front lines.

[paul67]

I would still do the rears and the fronts again you;d be surprised how long it take's to bleed a master and check all the brake connectors with a spanner.

[BA.]

My brakes are *FINALLY* fixed!!! You won't believe what it was!

I had finished up the rear drum brakes with all new cylinders, pads and springs. I even made two new hard-lines from the cylinders to the little distribution block at the axle housing. (takes feed from the Master Cyl)

I bled from the RR to the FL several times and noticed some air coming out. All looked good. There were no leaks either.

My freakin pedal STILL went straight to the floor. In a test drive, it felt like there were just NO front brakes and only a little at the rear.
I finally gave up and took it to Midas. :)

Midas thought it was the M/C and replaced it but it didn't help. Replaced it again, thinking the new one might be bad. (re-manu)
Still no good.


Then the older guy, Dan, got to looking at it and he noticed the problem. The BLEEDER SCREWS on the front calipers were BELOW the hard-lines. This meant that there was air in the calipers above the hard lines that never got bled out!!
I had the freakin' calipers on the WRONG SIDES! L was on R and vice-versa. They swapped them which put the bleeders ABOVE the hard-lines, bled things and now it all works as it should.


I'm such a TOOL! (but I did learn something and hopefully someone else reading this will too!!) :hammer:

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