ok, here is what I have:

Master cilinder changed, BUT because was getting a leak on back. The seals change didn't get success so went to change the complete assembly

Dist block/prop valve, was changed about 3 years ago( probably damaged the double action piston to the brakes failure sensor ) because was getting brake fluid emptied and going to the other deposit. This was the replacement unit:

http://cgi.ebay.com/ebaymotors/65-72-MOP...p4506.m20.l1116

Rubber lines all new/replaced in last 4 years.

Rear cilinders replaced about 8 years ago.

Front pads new last week

Rear shoes, fairly new.

Drums and disc all new replaced about 4/6 years.

Caliper seals, replaced 4 years ago

so after all this, and fix the leak, and one side of front pads WEIRDLY worn ( diagonally ), probably cause the rotor was some loosen , now I'm getting front brakes stuck.

All system bleeded, so practically all fluid inside is new.

Thinking on caliper seals damaged, went to a brakes shop ( I have my back hurt to make by myself ) and replaced seals there.

BUT...

After some minutes riding NICE I think I began to feel brakes coming stuck again. thinking again came in to mind:

what about the content of prop valve section ?, could get clogged by contaminated fluid there and fluid never replaced inside ( due the valve itself ) and then that is what is getting the front brakes stuck ?


THEN another question.

On my leak fix, when pumping the system at bleed, found a pressure leak at failure switch. tighten and then was gone. SHOULD I GET PRESSURE THERE ? isn't supposelly that a switch what feels the pressure variation witha double action piston what keeps both circuits isolated ?

of course that is on an original system. The replacement part does look is kinda earlier models, where the switch is not a push button, and more simply a fixed stud


your thoughts please

need to add to all the info...
when got stuck brakes and parking at night, I get prefect brakes at the morning, then riding, they get stuck again!!! so, somehow allong the night pressure at caliper is released by itself

I'd replace the rubber hoses up front, its what fixed by dragging brake problem.

-Daty

Do you have power brakes? If so, the pushrod in the booster is adjusted too long, this prevents the rear piston in the MC from fully retracting and this prevents fluid in the front system from returning to the reservoir.

shorten the push rod behind the master cylinder. Mine did the same thing when I 1st got my old car together. It should only need to moved in a little bit.

Hope that helps.

EDIT: Ahh, ya beat me!!

Yes, booster recently rebuild too.

well I measured the deep of master cilinder piston and made it match the pushrod... beside that I could mount the new MC without push or any force against, easily... but yes is something that could it be checked.

but ANYWAY ( and just thinking ), if the pushrod is too deep and making pressure against cilinder, is like get a new ZERO set, so same fluid being pushed, should it be the fluid coming back... doesn't it ?

and when mounting, the fluid excess should get back to the deposit, without any pressure in lines

Do a simple test. When the brakes feel like thay are hanging up, crack a bleeder and see if there is any built up pressure. I suspect one of the components ( prop valve maybe ?) are for a drum brake system , causing about ten pounds of line pressure to be in the lines at all times.

I had this happen to me,it was the master cylinder,It was a remanufacture from the local parts store,as soon as i installed it and drove it 1 time it started to apply the front brakes,the further I drove it the worse it got,after it sat awile it was fine for a few minutes and would do all over,had to replace it as well.

well... this MC was on a sealed bag from factory

To diagnose a drag you must work from the source (the pedal) toward the wheel(s) with the drag. These are actually fairly simple to nail down - especially on a car without ABS.

Keep in mind if you open a bleeder you have eliminated the entire brake system as a possible root cause and accomplished nothing.

When the concern is present, loosen the master cylinder from the booster (or firewall). If the brakes release, inspect the pedal assembly and pushrod for concerns – if OK replace the booster.

If the brakes do not release when the master is loosened from the booster/firewall, working from the master cylinder toward the wheel(s) that are dragging, loosen each line one at a time and see when the drag is relieved. The faulty component will be upstream from the last line loosened that released the brake.

ok, adjusted back the booster rod with a better precision measurement, and does look it fixed THAT...

now I feel some loosen the brakes and getting light on at cluster.

of course will check the tipical, rear shoes adjustment and better bleed IN ORDER ( as stated at shop, were fronts bleed first than rears )

but getting floated back one of the questions:

DO I MUST HAVE PRESSURE AT PRESSURE SAFETY SWITCH ENCLOSURE ? SHOULDN'T BE BOTH, FRONT AND REAR SYSTEMS ISOLATED ONE FROM THE OTHER AND JUST LINKED BY THE DOUBLE ACTION PISTON ? ( what does not mean fluid going throuhght the piston cilinder... or yes ??? )

the system halves are isolated from each other in the prop valve just connected(sort of) w the electrical contact in the middle. With the linings up/air out slghtly crack a line on the side that was good as someone pushes the pedal to shift the valve back centered(have key on so the light will be on & you'll see when it goes out.

yes I got that, BUT now I noticed I'm having a leak at switch ( at stud ). Dunno if the problem is THE switch, or problem is inside somewhere, because PRESSURE at switch what is not enough to hold because is not designed to that.

SHOULD IT EXIST PRESSURE THERE ?

when installed the MC and began to bleed was able to see a squirt coming from below the hex head. Tighten the switch and that leak was over

Light is coming on and off frequently. QUITE OFTEN just with road vibrations.

NOTE again: THIS SWITCH is not like the original with a push in button, is really a fixed stud and does look works similar to earliers kind. Is like the original at exterior ( on top )though

Brakes are working ? apparently yes... but I dunno if PERFECT really as it should be.

Alright I understand what you are saying. I'd take it apart & see if there's any seals/o rings that can be R&R'd

is posible that switch o-ring is gone and that si replaceable, but still.

Is normal brake fluid circulating on normal conditions allong the piston inside the dist block assembly ? I though piston keeped both systems ( rear and front ) isolated and linked between them...

If is normal... then, Is normal to have PRESSURE there to get a leak like a squirt ?

right now since I tighten the switch, is just a small leak on switch stud base. ( does have a plastic bushing there )

Is posible get a Brake failure light on when leak is at SWITCH ? if so... why ? if no one of the rear or front system is failing ? where would move the diferential pressure piston ?

Is not posible ( as far I know ) replace the piston O rings. I can't find the way to dissasemble.

Piece just have about 3 years mounted.

I'm getting somehow desesperatelly about this because I can't be buying stuff from USA anytime, specially when I don't know where exactly is the fail OR if I have to buy once again some probably bad quality piece, IF REALLY IS A BAD QUALITY PIECE .

This is something I fixed 3 years ago thinking on get saved by the next 25-30 years more. These Dist blocks/prop valves are NOT available down here. In fact they weren't either up there in USA 4 or 5 years ago. ( unless NOS )

The fail I got INITIALLY with the original part when I had to replace the dist block/prop valve is one of the MC cilinders deposit getting emptied and the other one getting overflowed. After many pistons, seals and couple of MC changes, simply discovered the fluid was going from one deposit to the other through the dist block.

I hope is not that AGAIN. just a 3 years piece!!! I have drove enough to check difference on MC fluid levels ( one against the other )

I will try to find a new O ring for this switch what as I'm telling you IS NOT THE SAME THAN THE OEM... looks the same from outside but works totally diff. Works like the drums brakes dist block kind switch

That prop valve should be tight as a drum, no hint of a leak which do tend to get worse w time. I dont think that the minor leak you are reporting would cause a psi differential enough to shift the valve over but I'm not for sure but you did just have an issue w one side leaking(or opened up) correct?. If this piece cannot be dissassembled or resealed somehow you may have to bite the bullet & scare up another one. Good Luck.

then also...

Is posible the MINIMAL LEAK I'm getting at switch right now is able to make me feel "uncomfortable" when pressing brakes ?