Rear Brakes stick because of my master cylinder

[2ManyZs]

Err, back up a minute.... you say you've got an early master cylinder on a 72?

That's could be problem right there unless the lines were swapped around when the early master was fitted. The 72 should have the later style master, unless it's one of the "transition" cars we've found to have early and late parts mixed.

You've got me confused when you say the rebuilt master wouldn't work... which style master was the rebuilt one?

[SledZ]

Hi 2Many,

the rebuilt was a newer one that have the cylinders reversed in respect of the front and rear brakes. It didnt work at all, the pedal went straight to the floor no matter what I tried. I did switch the lines around to match the cylinders/brakes.

I still have not purchased a new MC, taking a break on it for a bit until I figure out what I should do without wasting $150 and getting to frustrated!

I bought my Z in June and it had to be towed,, so while I redid the suspension etc. I also replaced all the brakes parts so they have never worked right from the git go.

Thanks!!

[frank13]

SledZ what was the end result to your rear brake saga? What end the end did you do to correct this problem? Also did you have the 5/8ths master or the 15/16ths master? :devious:

[panchovisa]

SledZ,

You said you changed one wheel cylinder 1st. Then Master, and finally 2nd wheel cylinder.

My quess is that you re-assembled the first rear brake with the "star" adjuster backwards.

The adjuster works to adjust the shoes when you apply the brakes moving in reverse. If it were installed backwards it would adjust the shoes tighter every time you use the brakes normally. Eventually the one rear brake would lock up before any of the other functioned at all.

Just a guess because the problem started with your origional repair.

Pancho

[SledZ]

I have not fixed my brakes yet, been working on my drag sled and have mothballed my Z for a spell.

I have a 72 but it has a 70-71 MC , can't remember which size it is though. The more I think about this problem makes me believe there is something wrong with that pressure valve in the rear. I would bleed the rears and the left cyl would suck fluid with ease and the right cyl would always be kinda clogged and not get a good flow. ( I use a mity vac and suck the fluid from the MC.)

Plus when the rears lock up all I have to do is open the rear valve on the MC and relieve the pressure and it's fine for another 10 pumps or so.

I have a new MC and need to try and find a proportioning valve sometime soon. Once I get it back in my shop I am going to disconnect all the lines from everything and blow them out and see whats up with that valve.

The way this dry winter has been going (no snow) I should be working on my Z shortly!

I'll definately let everyone know what the problem was cause it really screwed up my progress on it..

[waynekarnes]

the automatic brake adjustment is done when the parking brake is applied. if issue is the adjuster, then by pulling the wheel, removing the plug, one may back off the adjuster, thus the shoes move away from the drum.

if one, loosens the bleeder screw and it releases the shoes, it is not the self adjuster, as the hydraulic system, acts independent of the mechanical system used by the self adjuster.

the original hard brake lines only go in to the RWC one way. if you have the original hard tubes ( lines ) and it connects to the RWC with out butchering or twist it from its original shape, you can not have the RWC upside down or backwards.

the master cylinder operates the 2 rear wheel cylinders. another portion of the master operates the front calipers.

under the master on the frame rail is a distribution block. master to block, from there, lines to rear and front.

the same part of the master operates both rear wheel cylinders ( RWC ). if issue is in the master, both RWCs will be locked up. not, just one.

there is a residual pressure valve, located in front of the gas tank. remove the wheel, follow the brake line, you'll see it, under the car, on the floor pan, behind those little storage bins.

as stated earlier, it maintains pressure on the RWC, sort of a check valve, so that the shoes are held close to the drum and don't have to travel as far to engage. kinda balances em out to the discs on the front ( some people use em as proportioning valves, as they come in different ratings ).

if trouble only at one wheel, and cracking the bleeder sets the shoes free, then ... residual valve, or RWC. the residual valves are usually good for around a million miles.

that said, they are usually pretty resilient, ignoring rust and dirt. however, there may be a big chunk of crap in there. jamming that valve.

i'd bleed the brakes, run about a quart of brake fluid through the system, all 4 wheels, see if you clean any crud out. i'd do that before changing any parts.

then check out your springs, any of em backwards, weak, binding.

did you use the high temp grease, where the RWC meets the backing plate, the RWC needs to slide ? the contact points for the shoes at the backing plate also need to be greased. could be, that it's not pressure holding em out, rather weak springs, something jammed that's not allowing the shoes to push the fluid back to the master.

just my 38 cents.

i'm having issues with my mechanical adjuster, it keeps moving the shoes towards the drum, until they seize the drum. only having issues on pass side. haven't quite figure that out ... yet

wayne

[SledZ]

Finally they are Fixed !!!

It was the proportion valve. Took it off and it was full of crap, cleaned it out and blew air through the lines and then for the 50th time bled my brakes.

I must have braked 100 times and and they don't lock up.

Now on to the rest of the car!

[waynekarnes]

glad to hear that you got it squared away !!! bet it feels pretty good !!!

[frank13]

Good going sledz. Now you can come on down and get mine going.Like wayne said, bet it feels real cool. :devious: .