Brake pedal travel

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Stephen Toohey

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Hello everyone, i have a 65 dart gt. Have just fitted disc brakes to the front and replaced master cylinder with a dual system. The brakes work well but the pedal travels down to just off the floor. Master cylinder is 1 inch bore. I want to get the pedal up a bit as it just doesn't feel right. Do i need to get a mastercylinder with a slightly bigger bore. Thanks.
 
No, but something is still wrong
Does the pedal come up higher with multiple pumps?
Does the pedal get hard? It has to get hard.
Does it get hard then the pedal slowly drops? This is bad, get a different MC.
Have you adjusted the rear drum brakes?
What are the disc brakes off?

You could have a hydraulic issue, a mechanical issue, or a pedal-ratio issue, or a plumbing issue.
The factory pedal ratios are all the same AFAIK.
The rearmost reservoir on MOPAR systems gets plumbed to the FRONT calipers. The following diagnostic pertains to Mopar systems, plumbed as above.
Do determine the hydraulic versus mechanical , I recommend to remove the rear brakes and C-clamp the rear wheel cylinders into their bores, then check for a high hard pedal. If not found then remove the front calipers and C-clamp the pistons into their bores and retest. If the pedal is still not high and hard, and feels spongy, then either A)you have air in the lines :( and you know what to do; or B) the flex hoses are expanding/contracting in loc-step with the stroking; check them out first.
But if the pedal is now high and hard then the hydraulics are fine. So;
go to the back and reassemble everything and adjust the brakes up hard until the drums will not turn, then retest the pedal. Still not right? remove the drums, check them for round and if they have a ridge, get it cut off, then reassemble and retest the pedal.
Now high and hard? Ok ,Now you have isolated the issue to the recently installed front brake system.
You will have to install one side atta time and look for flex. Typically I find the problem is in the pads. They have to be dead flat. Take them out and place them face to face.The pad material needs to touch eachother from end to end, and the metal frames must be parallel from end to end. If they are wedge shaped as in worn at an angle then throw them away.If you assembled them with some type of silicon anti noise product, get rid of it. If the pads have an anti-rattle metal shim, set it aside for now.
But if they are flat and new, then prefit them to the disc. They must sit flat to the disc on both sides. If the disc has a perimeter ridge that prevents the pads from sitting flat, you will have to get rid of it. If the disc wobbles on the spindle, you will have to readjust the wheel-bearings.Finally check the pad anchor ways. They have to be smooth so the pads cannot hang up on them. With used parts, the ways often have to be repaired, having grooves pounded into them over thousands of miles.
Next if the calipers are retained with screw-in pins, then you will need to make sure that they are not bent, then screw them in, and make sure they seat parallel to eachother, and in the same plain..
Now remove the pads and set them aside. Remove the pins and assemble the caliper onto the bracket with the pins and test it's travel on the sliderpins. It should stroke fairly freely. You may have to lube the pins or the pin-bores or the O-rings, whatever system you have, with the special grease made for that.
Finally, blow it apart and final assembly it. Then back to the pedal. If now the pedal is high and hard, then repeat on the other side. If not, go watch the caliper as a helper works the pedal. You are looking for flex, excessive motion of the caliper. Do not proceed to the other side until you get the first side rectified. If you can't find it, then C-clamp the piston to the bottom and verify the pedal is still high and hard, indicating that the rears are still functioning correctly.
Then go look for flex, again. It may be that the caliper body itself is flexing. That would be highly unusual, and of course; BAD.
Keep hunting til you find and fix the flex. Then retest the pedal. When it finally gets high and hard...... then repeat on the other side.
The pedal must get hard and high.
When you finally get it, don't forget to back the rear adjusters off a few clicks, until the drums rotate with a bit of resistance.
Then roadtest it.
With a 1" bore MC,and NO booster, you should be able to have full stopping power with perhaps 1/3 pedal-travel.
If you have a booster; with the engine off, pump the pedal about 5 times to evacuate it, then hold the pedal down with just moderate pressure. Now start the engine and watch how far the pedal drops. About 1 inch would be normal. Add this amount to the 1/3 pedal travel. That should now be your total travel, namely 1/3 plus 1 inch. A bigger bore will finish higher and a smaller a little lower. But none should finish near the floor!!! I imagine 2/3s might be the max with a 15/16 MC AND a booster.
 
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^^Boil this down a bit^^

Pedal should be rock hard. If not you have air in the system, or a problem with shoe fit (arc) in the rear

Pedal height......adjust up the rears a bit and try again. if the rears are adjusted, the brakes bled, then you need a larger bore master

I realize this is "different" but my 67 used a Linc Versaille 9" rear with factory disc, and 73/ 74 Duster front disk, and the factory drum master. Used up not quite 1/2 the travel, and rock hard.
 
^^Boil this down a bit^^

Pedal should be rock hard. If not you have air in the system, or a problem with shoe fit (arc) in the rear

Pedal height......adjust up the rears a bit and try again. if the rears are adjusted, the brakes bled, then you need a larger bore master

I realize this is "different" but my 67 used a Linc Versaille 9" rear with factory disc, and 73/ 74 Duster front disk, and the factory drum master. Used up not quite 1/2 the travel, and rock hard.
 
Thanks for the comments. For your info i am in New Zealand, i found this car here in nz. It was imported by an american who moved here to live. He never got it running or legal for nz roads. As requirement to make it legal i had to replace the brakes, so had the drums machined and replaced the brake shoes and rubber hoses. Brakes were fine after that and passed the required tests. I came across some early mopar small bolt disc brakes so purchased these and had them machined and fitted them to the car. A dirrect fit which was great. But i lost a bit of pedal, not much but enough to be annoying, it went down a bit further than i wanted. So i came across a baracuda dual master cylinder with 2 output lines for the front brakes and one line for the rear. I wanted this for the safety factor. Put a kit in it and had it put on at a brake workshop due to having new metal piping to be done. Car came out of the shop with good brakes but way to much pedal travel. After reading your comments i think maybe find a master cylinder with slightly bigger bore. The current one has a 1 inch bore.
Any advice on which master cylinder i could try next.
I like this car a lot, it is rough and needs a bit of work. The body is sound and it drives very good. The interior is not great, needs carpet, some door armrests and general upholstry upgrade. The 225 is strong and uses no oil or water. Runs great starts everytime after reworking the carb, distributor, starter motor and almost everything else that had been played with by a novice.
Look forward to your suggestions on master cylinder choice.
Thanks
 
You can lose "some" pedal just in the drums. When you machine drums oversize, the shoes are "too small" diametrically. They can actually flex in the drum, or at least don't fit "soldidly" and act as to "soak up" pedal travel. You can sometimes eliminate this while diagnosing by adjusting them up TIGHT. If the pedal seems firmer you are on the right track. Obviously you don't move or drive the car while doing this.. Weak hoses can expand, as well
 
I doubt if a different size m/c will change anything. Is the pedal sitting at the correct height? I ask because some of these replacement m/c will require an adjustable pushrod.
 
If you are having excessive pedal travel related to the fronts after the rear drums are adjusted a 2 psi residual pressure valve can be fitted at each front brake line inline.
If it’s a piston retracting to far back for the given master cylinder size then this will help.
This will also help with any knock back that may be experienced while driving.
 
You can lose "some" pedal just in the drums. When you machine drums oversize, the shoes are "too small" diametrically. They can actually flex in the drum, or at least don't fit "soldidly" and act as to "soak up" pedal travel. You can sometimes eliminate this while diagnosing by adjusting them up TIGHT. If the pedal seems firmer you are on the right track. Obviously you don't move or drive the car while doing this.. Weak hoses can expand, as well

I test the drums being the problem by simply setting the E brake and see how it feels on the pedal.:D
This way you don't have to adjust and readjust the brake shoes in the drums.


If you are having excessive pedal travel related to the fronts after the rear drums are adjusted a 2 psi residual pressure valve can be fitted at each front brake line inline.
If it’s a piston retracting to far back for the given master cylinder size then this will help.
This will also help with any knock back that may be experienced while driving.

This is a good bit of info.
I recently swapped a 1959 Ranchero with manual drums over to power and the residual valves solved a first step low pedal. (pedal was much higher if you pushed it twice)
I put one between the master and distribution block for the fronts and rears both so I only needed one for both fronts. (of course I used 10lb for drums)
Now the brakes are right there on the first step of the pedal.
 
Hi all, going to try an adjustable pushrod. I think the problem could be due to the break pedal pivot point being slightly different to that of the car the master cylinder came off. I will let you know how it goes.
 
The adjustable pushrod fixed the low pedal problem. Adjusted the length to a little more than 1/4 inch longer than standard and got a very pedal. No brake drag, car roles freely and discs and drums do not heat up on driving. I am very happy with the result. Thanks everyone for the feedback.
 
The adjustable pushrod fixed the low pedal problem. Adjusted the length to a little more than 1/4 inch longer than standard and got a very pedal. No brake drag, car roles freely and discs and drums do not heat up on driving. I am very happy with the result. Thanks everyone for the feedback.

COOL!! I think the manual and boosted cylinders are different rod depths maybe you got into that trap.
 
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