Master cylinder

Mach1 Ian · Jul 18, 2009

I have SSBC front disc and rear drum power system. The problem is that the brake pedal is very hard and virtually no travel, not even enough to activate the brake lights but i have sorted the brake light problem, the brakes are so bad i have no confidence in the stopping power of them at all. Every thing has been plumbed in correctly and the proportioning valve is set correctly as far as i am aware.
The M/C has a 1" bore and i have been told that a smaller bore M/C Will solve the brake problem, before i buy another M/C i would a second opinion or two.

Thanks all the way from the UK!!

rbohm · Jul 18, 2009

do you have power brakes? if so is the brake booster working properly? yes going to a 7/8" mater cylinder will reduce pedal pressure.

Rusty67 · Jul 18, 2009

It doesn't sound like the bore size of the MC is the problem. Even if the pedal is rock hard, you should be able to get a reasonable amount of travel out of the pedal. I have an MC with a 1 1/8" bore and its hard to stop the car without a power booster but I do get pedal travel that in my mind equates to stoping the car. I will be adding a power booster to my Mustang. Its the next step on my list.

From your post it sounds like you have a power booster, but its ambiguous. Do you have power brakes or not ? If you do have a booster then I'd say you need to make sure its geting vaccume and that it is functioning properly.

Mach1 Ian · Jul 18, 2009

rbohm said:
do you have power brakes? if so is the brake booster working properly? yes going to a 7/8" mater cylinder will reduce pedal pressure.

Yes i have a power booster fitted and it is working correctly as it was only checked yesterday by a guy who drag races a Mopar and it suggested by him about the M/C bore.

wicked93gs · Jul 18, 2009

a 1" bore shpould give you no issues, especially with power brakes...is it possible you have a siezed caliper/wheel cylinder?

BarnStang · Jul 18, 2009

When you bleed the brakes, do you get a good solid stream of brake fluid out the bleeder? And does the pedel drop? Make sure you are getting good pressure at each wheel. A brake presure tester helps, but not absolutly necessary.
Do you have a stock distribution block? Is it possible the stupid safety pin has slipped to cut off the front or rear brake circuit? With everything hooked up right and the bulb good, the dash light would be on to tell you the pin moved. So many have the wire pulled off, the switched corroded up and non functional or the bulb burned out...so don't trust the light unless it's actually on...

2+2GT · Jul 18, 2009

Mach1 Ian said:
I have SSBC front disc and rear drum power system. The problem is that the brake pedal is very hard and virtually no travel, not even enough to activate the brake lights but i have sorted the brake light problem, the brakes are so bad i have no confidence in the stopping power of them at all. Every thing has been plumbed in correctly and the proportioning valve is set correctly as far as i am aware.
The M/C has a 1" bore and i have been told that a smaller bore M/C Will solve the brake problem, before i buy another M/C i would a second opinion or two.

Thanks all the way from the UK!!

Movement doesn't activate the switch, pedal pressure on the pushrod does. "Cupping" the plate on the switch, or replacing the switch does the job.

zookeeper · Jul 18, 2009

Movement absolutely does activate the switch. To test this, press your pedal with your hand, if it's adjusted correctly, the brake lights will come on before any brake pressure is felt.

Rusty67 · Jul 19, 2009

I agree with wicked. Either the MC itself is bad or you have a siezed piece of hydrolic equipment in the system somewhere.

Mach1 Ian · Jul 19, 2009

zookeeper said:
Movement absolutely does activate the switch. To test this, press your pedal with your hand, if it's adjusted correctly, the brake lights will come on before any brake pressure is felt.[/QUOTE

Hi again, if you can remember you gave me details how to adjust the brake light switch as there wasn't enough travel in the pedal to activate the switch.

One thing i forgot to mention in my post is that after a few miles and using the brakes, the fluid in the front bowl is forced into the rear bowl and then leaks through the seal onto the booster, SSBC have sent me 2 replacements and the problem still occurred that is until a small hole was drilled from the front bowl into the rear and it now acts as a overflow hole and refills the front bowl.

None of the calipers are seized, car stops in a straight line and a short while ago i fitted a set of EBC green stuff pads which has helped the brake performance and they were OK then and the brakes were tested a few weeks ago when it went in for it's yearly test.

The distribution block was leaking so it was replaced with a tee piece.

I have got a brake pressure tester, so i will give that a try.

2+2GT · Jul 19, 2009

zookeeper said:
Movement absolutely does activate the switch. To test this, press your pedal with your hand, if it's adjusted correctly, the brake lights will come on before any brake pressure is felt.

You say "press", then claim pressure doesn't activate the switch! Did you read what you wrote before clicking "Submit"?

I said "pressure", not "hydraulic pressure".

zookeeper · Jul 19, 2009

Hi Ian, How have you been? Fluid should not be transferring from one resevoir to the other. My wife's '69 Corvette once sprung a tiny leak in a rear caliper and drained the resevoir for the rear brakes bone dry, but the front brakes worked as usual. That's the whole idea behind a dual master cylinder. If your's is transferring fluid, find out where it's happening, I'd suspect it's the piston being too far one way or the other. I don't know how that could be corrected, but my thinking is the piston is too far forward. That would cause rock-hard brakes, since the front resevoir isn't working, but the piston travels far enough forward to allow fluid in at rest, then goes so far rearward that it's basically carrying fluid under pressure far enough back so it pressurizes the rear resvoir. Maybe I'm completely out of whack, but try this: remove the master cylinder lid so you can look into the resevoir and (if you've got good eyes!) see the piston move when someone (slowly!!) pumps the brakes. It could be that your pushrod is too long, and not uncovering one of the holes, but have a look and see what it's doing. Hope this helps, Jim

zookeeper · Jul 19, 2009

2+2GT said:
You say "press", then claim pressure doesn't activate the switch! Did you read what you wrote before clicking "Submit"?

I said "pressure", not "hydraulic pressure".

I'm sorry, I momentarily forgot you were such a stickler for semantics. Pressure of any kind is not a factor in the function of the brake light switch in any way, shape or form. The brake light switch will function even if there is no fluid at all in the system. No fluid means no pressure, are you with me so far? Good. The brake light switch contacts function by means of rotation, not pressure. As the pedal travels through it does so in an arc, since it's only attached at one end. The master cylinder pushrod, however travels in a linear fashion. The flat ends of the pushrod rest on the flat ends of the swtch, and as the pedal and switch travel through the arc, the lower part of the switch contacts the flat of the pushrod and completes the circuit, allowing the brake lights to come one. If ,as you claim, pressure were a factor, then the switch would need to fit loosely on the pedal so that the distance between the pedal and the pushrod would decrease, thus closing the switch. As I said the first time, you don't even need a master cylinder or return spring or any other means of pressure to make the brake lights work. Now before you hit the submit button, check your attitude...

Mach1 Ian · Jul 19, 2009

zookeeper said:
Hi Ian, How have you been? Fluid should not be transferring from one resevoir to the other. My wife's '69 Corvette once sprung a tiny leak in a rear caliper and drained the resevoir for the rear brakes bone dry, but the front brakes worked as usual. That's the whole idea behind a dual master cylinder. If your's is transferring fluid, find out where it's happening, I'd suspect it's the piston being too far one way or the other. I don't know how that could be corrected, but my thinking is the piston is too far forward. That would cause rock-hard brakes, since the front resevoir isn't working, but the piston travels far enough forward to allow fluid in at rest, then goes so far rearward that it's basically carrying fluid under pressure far enough back so it pressurizes the rear resvoir. Maybe I'm completely out of whack, but try this: remove the master cylinder lid so you can look into the resevoir and (if you've got good eyes!) see the piston move when someone (slowly!!) pumps the brakes. It could be that your pushrod is too long, and not uncovering one of the holes, but have a look and see what it's doing. Hope this helps, Jim

I am fine Jim!
I will look into your suggestion when my buddy has some spare time.
I bought the SSBC disc conversion as a complete kit including the booster so in theory it should all be compatiable, but stranger things have happened.

Take care
Ian

jcode68 · Jul 19, 2009

I know your friend told you the booster was working, but there is a simple test to be sure. With the car turned off, apply pressure to the brake pedal - this should feel very stiff and not give much if any movement. Start the car and you should feel the pedal travel some amount. I had the same problem with same setup (SSBC front disc, rear drums, power booster) and turned out to be a bad booster. Funny thing is the booster was brand new, never used, but it just simply did not work. It wasn't a bad check valve either, something internal was wrong. The supplier swapped it for me and the new one worked perfectly. What booster are you using and did it come with the MC already installed?

If it's not a problem with the booster, then my guess is the pushrod is not adjusted properly (too long).

Mach1 Ian · Jul 19, 2009

Mach1 Ian · Jul 19, 2009

jcode68 said:
I know your friend told you the booster was working, but there is a simple test to be sure. With the car turned off, apply pressure to the brake pedal - this should feel very stiff and not give much if any movement. Start the car and you should feel the pedal travel some amount. I had the same problem with same setup (SSBC front disc, rear drums, power booster) and turned out to be a bad booster. Funny thing is the booster was brand new, never used, but it just simply did not work. It wasn't a bad check valve either, something internal was wrong. The supplier swapped it for me and the new one worked perfectly. What booster are you using and did it come with the MC already installed?

If it's not a problem with the booster, then my guess is the pushrod is not adjusted properly (too long).

We have done the booster test numerous times and it has proved to be OK.
I haven't any idea what booster it is as i just delivered the parts to the mechanic who fitted it.
The M/C wasn't fitted to the booster
The mechanic told me that the pushrod was none adjustable as it stated in the fitting instructions that it may not be.
The problem is that the kit has been fitted about 3 yrs so it is now out of guarantee.

Thanks, Ian

2+2GT · Jul 19, 2009

zookeeper said:
I'm sorry, I momentarily forgot you were such a stickler for semantics. Pressure of any kind is not a factor in the function of the brake light switch in any way, shape or form. The brake light switch will function even if there is no fluid at all in the system. No fluid means no pressure, are you with me so far? Good. The brake light switch contacts function by means of rotation, not pressure. As the pedal travels through it does so in an arc, since it's only attached at one end. The master cylinder pushrod, however travels in a linear fashion. The flat ends of the pushrod rest on the flat ends of the swtch, and as the pedal and switch travel through the arc, the lower part of the switch contacts the flat of the pushrod and completes the circuit, allowing the brake lights to come one. If ,as you claim, pressure were a factor, then the switch would need to fit loosely on the pedal so that the distance between the pedal and the pushrod would decrease, thus closing the switch. As I said the first time, you don't even need a master cylinder or return spring or any other means of pressure to make the brake lights work. Now before you hit the submit button, check your attitude...

I like you, I really do. Excellent description, where we agree at least 80%. The pressure I refer to is pressure of the pedal against the switch. Only microscopic movement (that other 20%) is required to activate the the switch. All this assumes proper operation of the switch. The switch, of course, is mounted on both the pedal and pushrod, so that the slightest change in the fit results in activation. This can come from linear change (pressure) or rotational change (movement). A few thousandths of an inch either way operates it, a brilliantly simple system. It'll work even if there is no fluid in the master cylinder. The pre-65 hydraulic switch wouldn't do that.

Mach1 Ian · Jul 24, 2009

Spot the problem with my brakes

Well, as you can see the problem with the brakes wasn't any thing really technical, it just pays to look at the simple things first One of the previous owners for reasons known only to him self disconnected the crank case vent hose from the carb, plugged the carb off and reconnected the hose to the vacuum manifold where all the vacuum hoses are fitted and the the guy who fitted the disc conversion, teed into the same hose for the booster, so most of the vacuum pressure was going back into the crank case cover. I am a little embarrassed to say how long it has taken to find such a simple fault, so much for putting your faith in the so called experts.
Thank you to every one who has put forward ideas to solve this problem.

Thanks
Ian

2+2GT · Jul 24, 2009

Ah Ha! A plumber's nightmare. We live and learn.

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