Hot Rods 1" master cylinder with disc/disc. Help needed urgently.

Front and rear systems are totally desperate, connected to seperate ports on the M/C. There is a #2 residual valve in both systems, though I have since removed the rear one whilst struggling to get this all working.

I may pull out the piston tomorrow and see if anything looks amiss internally, broken spring, torn seal etc. It did surprise me the way it worked.

 

Right, off to bed, 11pm here. I'll do battle with it tomorrow again.

 

I had a similar problem on a disc/drum car. Fought it and bled it, fought it and bled it. Assuming the M/C is the right one, make sure the rear rubber brake line is clear (NEW). I had a hard time taking this advice, but mine was collapsed and crudded up, just like everyone said it was. I know it isn't the sexiest problem or solutions, but if you haven't checked, you should.

 

Just a thought but do you have the front port to the front brakes (furthest from the mounting flange)

 

Morrisman I can't tell by your pictures but do you have 3/16" brake lines running back to the disc on the rear if not that may be your problem aiso if all else fails Ford put 4 wheel disc brakes on Bronco's in the 70's these master cylenders were not power assisted and stopped my roadster on a dime..good luck

 

It looks, in the photo you posted (post #15) of the sub-floor mounted master cylinder, like you have the brakes plumbed backwards at the master cylinder. According to the picture, your proportioning valve is on the rear circuit but plumbed into the smaller reservoir port. They should be on the larger res. port. The smaller res port is for front brakes and the larger is for rear. It's that way on every car I have ever seen. I used the Wilwood dual circuit master and even though it looks the same front to rear they state you must plumb the front brakes to the front res and the rear brakes to the rear res (in relation to the mounting flange).

Also which way is the proportioning valve set? All the way open or all the way shut? Prop valves reduce the amount of pressure to the rear so the rear doesn't lock up before the front and if you have it turned the wrong way that may cause issues. Put the 2# residual valve back in the rear circuit (make sure it points the right way), plumb the rear to the larger reservoir and check where the prop valve is set and try again. I used a hand held vacuum pump to pull fluid from the master to the wheels and started with the furthest wheel first. Once I had fluid at the wheels I had a friend pump the pedal and finish bled the wheels. Had solid pedal and no issues after that.

 

I bought a similar floor mounted M/C only w/booster for my 33 Chevy 5W.
It came with a 1" cylinder. After bleeding issues I called the company and they say I need a 1 1/8 bore M/C. They gladly exchanged it for me. The 1" just doesn't move enough fluid for calipers. I still have very poor brakes; just can't get a decent pedal. Everything is new, 2 lb. residuals mounted within 12" of the M/C. I have done everything but stand on my head with nearly every type of bleeder known to our world. Even a new Phoenix bleeder [it's a great tool] hasn't solved my issues.
I installed a similar system on my 55 F100 a few years ago. Bled it once and it's great.

 

In spite of what some have stated or suggested, your master cylinder is plumbed correctly. The visibly larger reservoir always goes to the front brakes, regardless of port size, and whether it's the primary or secondary (closer or farther from the mounting flange), on disc/drum, drum/drum and disc/disc.

Normally, you want residual(s) to be as close to the master as possible, before any prop/metering/combo valves, but I don't think that's an issue in this case.

Make sure the pedal can fully bottom out the master before it runs out of travel.

I hope your master has a deep push rod counter bore, because you don't want that long and heavy push rod to fall out. The counter bore should be near the total stroke length in inches.

I agree with some others that you would be better off with a disc/disc master vs. the disc/drum you have, as you will minimize/eliminate any possible displacement issues.

 

In my opinion there are a few things wrong in this pic




You have the front port plumbed to the rear brakes and the residual valve should be on the master cylinder side of the prop valve, also residual valves should be as close to the master as possible. HTH

 

did you take the check valve out?

 

you may have it reversed, some masters use the front reservoir for the front, others use the rear reservoir for the front. It isn't even the same in all GM cars. A corvette 1" (equal sized reservoirs) was opposite of what I though I knew. swapped lines, had brakes.

 

Ok, let's start over. Make plugs for both master cyl connections, bleed them and attain a solid, and I mean solid pedal.
Than connect the rear, (the fitting closest to the pushrod) and bleed that circuit....hows the pedal? ........to be continued.....

 

My 2 cents here.

I mounted a 1.25" piston diameter, shallow p/r hole, 2-reservor M/C on my '67SSRS Camaro car to activate my 1969 Camaro big single piston front calipers and 1980 Cad Seville e-brake jobbers in the rear.

13" 1988 Vette front and 11.75" 1989 Camaro rear rotors all on homemade caliper brackets. Used '67/'68 2-piece rotor front hubs on 1974 Buick Apollo disc spindles and the rear on my 12-bolt.

I made a copper pipe nipple cap pushrod in-place holder that fits the M/C great once cut shorter and peined to the rubber boot groove so that the p/r couldn't fall out!

pdq67

 

Front calipers on correct, those are not upside down?

Check rear calipers again and rachet out again.
I know you checked, but these rear calipers are famous for producing these situations
Good luck.

 

Good tech guide down load link:
http://www.piratejack.net/index.php?option=com_remository&Itemid=5&func=finishdown&id=2

 

I look at the post 25 and for some reason it looks wrong.
The whole thing looks 180 degs out,need bleeder up top.

 

Cool, lots more answers.

Several people have mentioned that maybe I have the pipes plumbed to the wrong ends, some say yes, some say no. I will connect them the other way as I have little left to try other than bleed some more.

Today I'll try the vigorous bleeding method, see if there is air trapped in any pipes.

And then I'll try to block off the master cylinder ports completely and see if I get a solid pedal.

All four calipers do have the bleed nipple at the top, or as close to as I can get them. I can unbolt them and shuffle their position slightly to optimise things.

All hoses, pipes, MC, residuals are brand new. Front calipers are the only used part in the system, so Ja***ese things I modified to fit.

Proportional was wound right in, as 'out' is less braking. I've tried it in several positions as well with no difference, and now it is off the car completely.

 

In the tech guide I posted it suggests raising the end of the rig your are bleeding - page 10 - and shows an exploded MC view labeling front and rear reservoirs - page 13.

 

From the MC rear should have residual then adjustable valve,try half open.
Its been said you have a bad master cylinder.
I had a bad one same as you from speedway.
Went to napa and 72 mustang with disk brake.
end of problem.

 

I've just been out and bled some more, no air from either end. I do notice however, that when I bleed the front end I get a solid 4-5" of fluid along my clear bleeding hose, with a full stroke of the pedal, but when I do the rears I'm lucky to get 1 1/2". It is like almost no fluid is coming out the rear port. Or at least it is not reaching the ass end of the car.

 

Is your push rod adjusted correctly?. Never mind the line being plumb in the reverse, this help's me to ask what I just did. It could be that the primary piston (that's one right now in your pic that is working the rear caliper) is not returning all the way back. And for what ever reason (could be you bled the front first) the secondary piston is compressing the spring between the two pistons and allowing the secondary to expose the port to fill the bore but the primary can't if push rod is out to long and keeping piston in slightly.

 

Can I get a picture of your rear caliper where I can see the position of the bleeder? The position can actually trap air in it and look right depending on where it is clocked.

 

^^^^^ Post # 25 has a shot of it. Can't see it well, but it's clocked like it should be.

 

Go to post #45 and go to the link listed. "Piratejack" Being you are working on a rod, it has straight forward descriptions. Still have a dought, call MBM.

 

Residual valves, prop valves, disc/drum master cylinder and which port goes to which end of the vehicle are not going to matter as far as getting fluid at the back brakes, you have to figure out why there is no hydraulic pressure.

 

Rear:



Front:

I have it open now in front of me. Just been to the store to buy a second quart of brake fluid.....

 

If all else fails change MC to a
67-76 Corvette - 1" bore manual four wheel disc brake master cylinders.
I think the mustang is to small for rear calipers.

 

I just reversed the M/C connections, and now the rear brakes work great, but the fronts don't, so size is the key I think. Or the MC has a bad seal inside.

Looks like a 67-76 Corvette M/C may be in my future.....

And just to make the day even better, the tranny is still stuck in drive. No reverse or neutral. I checked the 'S' linkage, then I fitted another valve body, put it all back together, and it is still in permanent Drive, or one of the forward gears anyway.

 

Are you dead sure you bench bled the m/c properly? Know what properly is? The far end of the m/c has to be inclinded downward else there'll be air trapped in the the end. And everything you're describing suggests that's the score. Could do it on the car - just need to jack one end up sufficiently.
Chris

 

You position of calipers is correct.
It sounds like maybe the disc drum master is working correctly.
It is supposed to push more fluid to the front disc calipers then to the rear wheel cylinders. It is designed that way.
Get a disc disc master and you will be good to go.