master cylinder problem!!

1st64bigwindow · Post by **1st64bigwindow** » January 24, 2007, 12:17 am

I am ready to pull out my hair on this one!I put a 67 mustang dual chamber m/c on my 61 uni. ever since the front brakes drag after they heat up to the point the truck wont move untill the brakes cool down or I brake the line loose to the front brakes and the brake lights stay on due to the pressure in the line.I rebuilt the front brakes including wheel cylinders and brake hoses.My question is...is the master cylinder wrong or defective?I checked the length of the pushrod and that is good because even when the front brakes are locked up I still have free play at the pedal so the push rod isnt even touching the m/c piston.Do you need to install a combination valve?I did not think that one was needed for drum/drum brakes.I have one line going to the front brakes and one line going to the rear brakes.I am considering getting a m/c for a 72 4x4 with drum/drum.To me a truck m/c is better suited for a truck.I need some input on this one guys it is driving me nuts.Thanks
LATER
Chad

Johnny Canuck · Post by **Johnny Canuck** » January 24, 2007, 1:19 am

Chad I can't see how this would cause your problem, but do you have a disc/drum MC? or a drum/drum one?

I have also heard you don't need a proportion valve for your setup, but the stock setup is thru an equalizer block. Think that might make a difference?

~no help in canuckia

norville · Post by **norville** » January 24, 2007, 6:53 am

Do you have an adjustable push rod? is it tight on the button in the MC , meaning is it activating the brakes before you even push on the pedal?? Are your brakes bled good. Crank up the adjsusters on all 4 corners till the wheels won't move then bleed.

Stick with it.

bob

rbcyouthdude · Post by **rbcyouthdude** » January 24, 2007, 7:06 am

I have a mustang m/c in mine with no problems. I got one for drum/drum. I have no other valve installed. My breaks work great. Maybe the residual valve in the front chamber is holding to much pressure???
Hope you find the problem soon.

Michael

Paul Merrell · Post by **Paul Merrell** » January 24, 2007, 11:09 am

I think that you cannot use a master cylinder from a dics brake setup because it has a check valve inside the master cylinder. That is what is keeping the brakes applied

Uncle Skip · Post by **Uncle Skip** » January 24, 2007, 11:45 am

I have a dual Mustang cylinder/ disk brakes on my truck and I don't have that problem.
I ran the front brake lines to the back of the master cylinder and the rear brake lines to the front of the cylinder. The aftermarket proportioning valve is on the rear brake lines.
There is supposed to be "some" residual pressure on the disks to keep them from rattling but they shouldn't be heating up like you describe. I had a VW one time that did what you say is happening and it was because the rubber lines had swollen shut and wouldn't allow the pressure to release, but I'm betting you have all new stuff.
You should have 1/2" of free play on the pedal before you feel any pressure on the brakes so you might have the connecting rod to long.
OR maybe, just maybe, you have a bad master cylinder. It has been known to happen

Good luck and keep us informed when you solve the riddle.
U@ss

ICEMAN6166 · Post by **ICEMAN6166** » January 24, 2007, 1:15 pm

Uncle Skip wrote: You should have 1/2" of free play on the pedal before you feel any pressure on the brakes so you might have the connecting rod to long.
U@ss

had this problem long ago on a 67 that i put a new vac booster on ,old one was leaking, but after i put it on the front brakes dragged, got hot, and kept me in place.i had to let fluid out to retract the brakes.they still were too tight.luckily i was not too far from home.
the issue:
there is an eccentric bolt on the brake pedal that is used for connecting the rod to. not sure about the 1/2 inch of play but the mc rod must be short enough so there is some play. if you cannot adjust with the bolt, the rod is too long.
this is for both disc and drum setups.

Hawkrod · Post by **Hawkrod** » January 24, 2007, 2:45 pm

Since you mention that you have freeplay at the pedal and the brakes are still locked up then you need to check a couple of other things. First off, the rear half of the master should be connected to the front brakes. If this is correct then loosen the front brake line at the master cylinder. Is there pressure there when the brakes are locked up and the pedal is not applied? If so then it is the master cylinder. There is no check valve in a disc brake master cylinder, the residual valve is something you use with drum brakes not disc brakes so it is not something you need to check. If you have one good if you don't it will not cause anything other than possibly a little more pedal travel before the brakes apply. If you have no serious pressure at the MC then loosen the line at the frame where it connects to the front brake hose. No serious pressure there then go to the line at the wheel cylinder if you get pressure here but not at the line to hose connection then you have an internally colapsed hose which is actually quite common. If you do not have a major gusher at one of these points then you need to look at the brake backing plate wear point and make sure the shoes are riding in the proper location and that there is not an edge or line worn into teh plate or that the shoe is traveling past the wear point and hanging up upon return. Hope this helps, Hawkrod

Fanatic · Post by **Fanatic** » January 24, 2007, 7:05 pm

Chad,

You must have a disc/drum Master. On a drum/drum the resevoirs for the fluid will be equal size. On a disc/drim one -the rear-is about twice as big. Even tho you may have asked for a drum/drum M/C ........you know how those parts wizards at PEP Boys are.

Pull that cap off! And then get the correct master cylinder.

Tim

Hawkrod · Post by **Hawkrod** » January 24, 2007, 7:17 pm

That is not correct. Ford did originally make some master cylinders with the same size resevoirs, they did not really make many or for long. It does not matter if you have a large and a small as the volumes were not such that Ford needed to have them the same so in a cost cutting move they eventually used the same casting for either system. The only difference between a drum MC and a disc/drum MC is the drum one has a rubber valves in each outlet and the disc/drum one only has a valve in teh forward outlet. The rubber valve is a small part that is installed behind the brass seat so you can't see it but if you want to check it then screw a small screw into the center hole of the seat and use a claw hammer to pull the seat out and the valve will fall out. You can reuse the seat after you debur it as the contact area of the flare will be outside any damage you may have done and it is relatively soft brass so it will reconform. Hawkrod.

1st64bigwindow · Post by **1st64bigwindow** » January 24, 2007, 11:36 pm

Thanks for the input...I bought a m/c for a 72 f-250 4x4 drum/drum today and will install it this weekend sometime.I am thinking that I did get the wrong m/c some how. that is the only thing left try.I will keep you all posted

ICEMAN6166 · Post by **ICEMAN6166** » January 25, 2007, 1:21 pm

i have a brand new one in the box on the shelf for a 72 f250, if you need the part number i will post it.

Fanatic · Post by **Fanatic** » January 25, 2007, 7:21 pm

I'll take that as a lesson learned Hawkrod!!!

I NEVER heard of that. Dang...now I have MORE stuff to remember. LOL

Tim

FORDBOYpete · Post by **FORDBOYpete** » January 25, 2007, 8:25 pm

I believe hawkrod is dead on!

Those systems with valves are called residual valves. By keeping slight PSI in system they prevent/ keep calipers from "slamming" pads against rotors, by just keep slight drag until the pads seat. But on Drum brakes they will slow the wheel rotation down as the 1-2 or "primary by secondary" combo "self actuates" braking action so any drag slows rotation.

I always reccommend against mixing & mathcing brake parts to make up a braking SYSTEM because it's one system that needs BALANCE to work correctly. Most lay persons & novices don't understand enough about braking, let alone drum vs disc to know all these nuances. End result is usually problems of some sort, just like this. And here folks just thought I was anal, aHh . . . or stubborn, . . . .

Hmpfh

FBp

Lawrence Gilliam · Post by **Lawrence Gilliam** » January 26, 2007, 10:07 pm

? Did you put a disc /drum m/c on vs a drum/drum m/c. I mouted a PB mc from 79 that I used to put pb,ps and tilt wheel. I mounted the booster and mc on the firewall in place of the little mc from the 66 and still hadn't put the disc under the front end and was running te old drums all the way around. I TEED the front and rear brake lines into front line ie 2 into one line. Awesome stopping on the old drums. I had a mc rebuilt at a dealer when I had a front brake line replaced. On the way home the brakes kept building up pressure til I had to stop and loosen the return line on the mc. I took it back and the mechanic said there was no bleed back to the mc and it worked fine after he redid the job. You are getting no relief on the fluid going out and no return. Keep us posted.

Trapper

1st64bigwindow · Post by **1st64bigwindow** » January 29, 2007, 11:06 pm

yee haw!! I put on the new m/c and it works like a dream.I was suspecting the m/c all along but its hard to replace a new part You always want to look everywhere else before you blame the new part.I know this is not uncommon because I have been a mechanic for around 15 years or so and I cant tell you how many bad parts I installed over the years and it always makes you pull your hair out.By the way I pulled out the seats on the m/c and there were NO rubber check valves at all.Thanks for the ideas on this.Keep truckin' and hopefully see some of you at the super nats this may.

master cylinder problem!!

master cylinder problem!!

mc troubles