3/4" master cylinder?

[goldduster318]

I'm not actually clear that when you get 1000 psi or 650 psi, that everything including the caliper is "in the system". The pressure should be the same everywhere. The thing is there is an input/output force going on here so how much force is being applied to the pedal itself has a lot to do with the output.

650 psi is like 44 bar, this won't lock the wheels, that's clear.
1000 psi is 69 bar, probably enough to lock them on gravel, but barely.

Usually a car with really effective brakes could have a locking pressure of about 80 bar / 1160 psi and one that's not that great or has big tires could be about 120 bar / 1740 psi.

The changing of the pedal ratio just by moving the connection point to the pedal is a horrible idea, the piston rod on the master cylinder should never have an angle at any time in it's stroke more than 3 deg above or below the axis of the piston bore or it will wear out. You'd need to do it by keeping that constant but changing the pedal length or moving the pivot itself...or you'd have to move the MC on the firewall.

I would still think you have air in the system, put a block of wood in place of the rotor and make sure the bleeder is absolutely the highest point.

The other thing would be, are the rear brakes adjusted?

That block you have does nothing, I would just union the rear lines together and use a regular T on the front ones. To me its pretty bizarre that it's even made the way it is. Also remember that the MC port closest to the firewall is for the FRONT brakes and the port closest to the front of the car is for the REAR brakes.

 

[Bewy]

Duster,
You make some very good points that people rarely think about. Such as how the m/c connects to the pedal. I have made several brake pedals over the years for different applications. With brakes applied, a line drawn through the pedal pivot-m/c connection point should be at 90* with m/c shaft for max transfer of the pedal force. A small diam m/c will have more pedal travel, all else being equal, then a large diam m/c. So getting this angle correct is a bit more complex; may need a new pedal or a piece welded onto it that allows a new pivot hole to be drilled for the 90* angle.

 

[Kern Dog]

To change the pedal ratio, one could actually lower the mounting point of the pedal lever while raising the point where the pushrod attaches. This would allow them to maintain a straight angle for the pushrod.

 

[Icetech]

I'm not actually clear that when you get 1000 psi or 650 psi, that everything including the caliper is "in the system". The pressure should be the same everywhere. The thing is there is an input/output force going on here so how much force is being applied to the pedal itself has a lot to do with the output.

650 psi is like 44 bar, this won't lock the wheels, that's clear.
1000 psi is 69 bar, probably enough to lock them on gravel, but barely.

Usually a car with really effective brakes could have a locking pressure of about 80 bar / 1160 psi and one that's not that great or has big tires could be about 120 bar / 1740 psi.

The changing of the pedal ratio just by moving the connection point to the pedal is a horrible idea, the piston rod on the master cylinder should never have an angle at any time in it's stroke more than 3 deg above or below the axis of the piston bore or it will wear out. You'd need to do it by keeping that constant but changing the pedal length or moving the pivot itself...or you'd have to move the MC on the firewall.

I would still think you have air in the system, put a block of wood in place of the rotor and make sure the bleeder is absolutely the highest point.

The other thing would be, are the rear brakes adjusted?

That block you have does nothing, I would just union the rear lines together and use a regular T on the front ones. To me its pretty bizarre that it's even made the way it is. Also remember that the MC port closest to the firewall is for the FRONT brakes and the port closest to the front of the car is for the REAR brakes.

The distro block is made so you can just use stock lines and bolt it in, not other real purpose. The bleeds are at the very top, can't really get them higher.. but wouldn't hurt to try. I only move the MC connect point 1/4" there is almost no angle on the pushrod at all.. already planned to tilt the MC a tiny bit if i had to but it's not bad enough to need it.

Rear brakes are adjusted (i'm picky bout keeping drums adjusted properly)

I have been doing brakes for 40 years.. have never had any system act like this.. thanks for the advice.

 

[Icetech]

Duster,
You make some very good points that people rarely think about. Such as how the m/c connects to the pedal. I have made several brake pedals over the years for different applications. With brakes applied, a line drawn through the pedal pivot-m/c connection point should be at 90* with m/c shaft for max transfer of the pedal force. A small diam m/c will have more pedal travel, all else being equal, then a large diam m/c. So getting this angle correct is a bit more complex; may need a new pedal or a piece welded onto it that allows a new pivot hole to be drilled for the 90* angle.

Yup... when i had a FFR cobra we had to do whats called a "Dogleg mod" on the pedal to move the starting point back or it would go over center and the brakes would not work well.. Which is honestly how these feel, i will be checking that angle tonight.. if i have to i can pull the pedal box and move the pivot forward a bit to get a better angle, i had assumed since this is a factory setup and other people say they never have to modify the pedal angle.. This is why i shouldn't assume though

P.S. Didn't consider that this was also designed for drums which only need what... 400psi? i am curious what the pedal angle is on a manual disc brake box now...

Can't wait to see how much fun getting this pedal box will be.. the pedal was cake, i have seen guys post that doing the box is a nightmare though

 

[Icetech]

Duster,
You make some very good points that people rarely think about. Such as how the m/c connects to the pedal. I have made several brake pedals over the years for different applications. With brakes applied, a line drawn through the pedal pivot-m/c connection point should be at 90* with m/c shaft for max transfer of the pedal force. A small diam m/c will have more pedal travel, all else being equal, then a large diam m/c. So getting this angle correct is a bit more complex; may need a new pedal or a piece welded onto it that allows a new pivot hole to be drilled for the 90* angle.

I think you may have nailed it... just went out and looked (drove it to work today) and i am hitting 90* at only about 1" of pedal travel.. Looks like the box will come out pretty easily, will modify it this weekend (move the pivot forward and down a small bit) and it should fix it. It does feel just like my cobra before i did the fix, so... This would also explain why chasing parts didn't fix anything.

 

[Dave999]

I had a similar problem with new calipers new pads new soft lines new rear shoes and new rear cylinders.

my front calipers had to be hung on wire with the bleeder right at the top and bled with a block of wood in them. They were an absolute pain in the *** to get bubble free.
i also needed to reset my hub bearings as although there was little noticeable play there was enough to knock the pads back. reset to spec after new grease helped. just done as per the book.

and i had to bleed them with the rear brakes adjusted hard up against the drums, take them out of the equation to stop the brake safety/danger switch/idiot light triggering

once i had that sorted out there was still sponginess to the peddle I had to bleed the rears at the distribution block on the diff by snapping open each line a small amount while someone pressed the peddle and doing it up while fluid spurted out before they stopped pressing.

drove me mad for a week, mityvac pumping the fluid in from the bleeders with an adapter all kinds of mad stuff tried...

once done i had a hard peddle but my brakes didn't work very well
pulled the rears and found about 1 inch at each end of each shoe was doing the breaking
the rest of the effort was potentially just bending the shoe and material backing

the arc to the shoes was wrong..... and the drums were not worn out.
did not have a brake shoe cutting adapter.. (usually used on 1950s scooters and bikes)

so adjusted them up to rubbing the drum and went for a drive. pulled the parking brake one notch or so.... yes they got hot
after much messing about wearing away my new brake shoes, eventually got the full shoe to contact the drum....

finally had mediocre brakes....

standing on the peddle now caused the back to lock first and this is with 9 inch drums (early style ditch finder duo servo brakes)
the right hand side of the car would try to overtake the front in a skid in a really alarming way.

it was at this point i fitted my brake bias.... and what a revelation that was.
this meant for the first time in the life of the car i could put the brakes on hard in a manner that actually made the front calipers do their work effectively. i.e they got the pressure they had needed all along to work as the manufacturer intended... without the rears locking up...

i now have pretty good brakes

my problem was a combination of issues all conspiring to cause alarm at the same time,
and naturally you think its one issue and concentrate on one issue, until you get so annoyed that you start doing stuff that you didn't need to do.

the rear caused more problems than the front...
but it meant the front never got to operate at the appropriate line pressure to stop the car

Dave

 

[Icetech]

I had a similar problem with new calipers new pads new soft lines near rear shoes and new rear cylinders

my front calipers had to be hung on wire with the bleeder right at the top and bled with a block of wood in them. they were an absolute pain in the *** to get bubble free.
i also needed to reset my hub bearings as although there was little noticeable play there was enough to knock the pads back. reset to spec after new grease helped. just done as per the book.

and i had to bleed them with the rear brakes adjusted hard up against the drums, take them out of the equation to stop the brake safety/danger switch/idiot light triggering

once i had that sorted out there was still sponginess to the peddle I had to bleed the rears at the distribution block on the diff by snapping open each line a small amount while someone pressed the peddle and doing it up while fluid spurted out before they stopped pressing.

drove me mad for a week, mityvac pumping the fluid in from the bleeders with an adapter all kinds of mad stuff tried...

once done i had a hard peddle but my brakes didn't work very well
pulled the rears and found about 1 inch at each end of each shoe was doing the breaking
the rest of the effort was potentially just bending the shoe and material backing

the arc to the shoes was wrong..... and the drums were not worn out.
did not have a brake shoe cutting adapter.. (usually used on 1950s scooters and bikes)

so adjusted them up to rubbing the drum and went for a drive. pulled the parking brake one notch or so.... yes they got hot
after much messing about wearing away my new brake shoes, eventually got the full shoe to contact the drum....

finally had mediocre brakes....

standing on the peddle now caused the back to lock first and this is with 9 inch drums (early style ditch finder duo servo brakes)
the right hand side of the car would try to overtake the front in a skid in a really alarming way.

it was at this point i fitted my brake bias.... and what a revelation that was.
this meant for the first time in the life of the car i could put the brakes on hard in a manner that actually made the front calipers do their work effectively. i.e they got the pressure they had needed all along to work as the manufacturer intended... without the rears locking up...

i now have pretty good brakes

my problem was a combination of issues all conspiring to cause alarm at the same time,
and naturally you think its one issue and concentrate on one issue, until you get so annoyed that you start doing stuff that you didn't need to do.

the rear caused more problems than the front...
but it meant the front never got to operate at the appropriate line pressure to stop the car

Dave

Yeah,and i'm bad bout tunnel vision when i get an idea in my head.. Will see how it goes after i mod the pedal angle. My front and rears are totally separate.. My rears also won't get near locking. it's a pressure issue (shoulda bought the gauge much sooner)

When the pedal goes past the pivot point (at the top, not the MC rod) you lose a huge amount of pushing force on the MC (was looking for a diagram/chart showing it) and low pressure like i have. I built my cobra 28 years ago so just didn't think bout it, but i had to do the same mod and the brakes felt the same before the mod...

If i'm wrong it won't make things worse.. only a bit better. Will see how it goes.

 

[MV8]

Seems to be an issue with the braided hose construction, but what I was referring to by "offset pushrod". Just fyi.

 

[Icetech]

Seems to be an issue with the braided hose construction, but what I was referring to by "offset pushrod". Just fyi.

View attachment 1716447626

i'm on my second set of braided hoses.. 2 different brands. My next move is to change the angle of the pedal so i'm farther from 90* on the pushrod.. maybe this weekend.. i need to wash and ceramic coat my new truck before it gets too cold to do it which is coming real quick

 

[Bewy]

Post #59 puts into a drawing exactly what I was referring to in post #52. Anything less...or more.... than 90* with the brakes applied results in the LOSS of braking force being transmitted to the m/c p'rod.

 

[MV8]

Post #59 puts into a drawing exactly what I was referring to in post #52. Anything less...or more.... than 90* with the brakes applied results in the LOSS of braking force being transmitted to the m/c p'rod.

Not that simple. You must look at the net force. A few degrees do not eliminate the ratio increase, but seal life is reduced from what it would be. How much depends on how far we offset. Every brake pedal starts at less than 90 and may end travel past 90. It is a band aid and there are better ways.

 

[Icetech]

Not that simple. You must look at the net force. A few degrees do not eliminate the ratio increase, but seal life is reduced from what it would be. How much depends on how far we offset. Every brake pedal starts at less than 90 and may end travel past 90. It is a band aid and there are better ways.

I pulled my pedal box last night (wasn't bad except the stupid seat in the way..) going to modify it tonight if i feel up to it.. Right now barely pressing the pedal puts it over 90* going to move the top mounting hole forward a bit to give it a little more angle (and still keep the starting point/brake light switch in the same place)

 

[goldduster318]

Do you know the origin of the MC pushrod? Lengthening the pushrod should also adjust the angle. Guess some of that depends on where the pedal sits also.

 

[Bewy]

The ideal is to aim for 90*, brakes applied. Disc brakes self adjust, so that makes it easy. If using drum brakes, the self adjusters should be used & that will maintain a uniform pedal position.

A few degrees either side of 90* is ok, but aim for 90*. It will NOT wear out the seals because [a] the seals are fitted to the pistons which are a tight fit in the bore, & the pistons do the locating, not the seals the seals are made of soft COMPLIANT rubber to conform to shape changes.

 

[goldduster318]

The ideal is to aim for 90*, brakes applied. Disc brakes self adjust, so that makes it easy. If using drum brakes, the self adjusters should be used & that will maintain a uniform pedal position.

A few degrees either side of 90* is ok, but aim for 90*. It will NOT wear out the seals because [a] the seals are fitted to the pistons which are a tight fit in the bore, & the pistons do the locating, not the seals the seals are made of soft COMPLIANT rubber to conform to shape changes.

If you have too much angle to the pushrod it will push the piston against the bore and wear that out, hence why I mentioned not more than 3 deg deviation. Once the bore is rough or out of round, its basically over, its going to leak.

 

[John Borris]

So, I went through the same thing with my charger, what fixed it was a master cylinder with an 11/16” bore. The only place I could get that master was from the Ram man.

 

[Icetech]

So, I went through the same thing with my charger, what fixed it was a master cylinder with an 11/16” bore. The only place I could get that master was from the Ram man.

Ah nice.. if what i am doing today doesn't help i will contact him...

I modified my brake box last night to give me more pedal angle.. just so i know i'm not going much over 90*.. will rebleed and test it to see how it goes..

P.S. shoulda stayed drums.. coulda drove my car a lot this year

 

[Raskull]

Just curious if anyone knows if there is a 3/4" master cylinder that will bolt right in for manual brakes? I need more pressure and this is bout my last option..

My experience is that a 15/16 master cylinder will do the job for your disc & drums. I personally found that rear proportioning valves are a waste of money. Thoroughly check for blockages in your front brake lines. I highly recommend the #3 stainless steel flex lines. FYI - Wilwood recommends no more than 1200 psi at their front calipers. I discovered that you can't always rely on the rear reservoir on your master cylinder to operate your front brakes. One way of checking is to put a plug in one of the ports and leave the line connected to the other, hit the brakes and see what moves...brake shoes or calipers?

 

[Icetech]

My experience is that a 15/16 master cylinder will do the job for your disc & drums. I personally found that rear proportioning valves are a waste of money. Thoroughly check for blockages in your front brake lines. I highly recommend the #3 stainless steel flex lines. FYI - Wilwood recommends no more than 1200 psi at their front calipers. I discovered that you can't always rely on the rear reservoir on your master cylinder to operate your front brakes. One way of checking is to put a plug in one of the ports and leave the line connected to the other, hit the brakes and see what moves...brake shoes or calipers?

All the lines are new and bleed fine.. no blockage that i have been able to find.. And i did block the passenger port when playing with the drivers.. everything move ok, just low pressure. I'm gonna wait til i get the pedal back in and setup and go from there...

Which all depends on finding someone to hold the bolts in the engine bay.. grr.. last time i had the column out when i did it and reached through the hole

 

[Raskull]

Additional thoughts: block both ports on m/c, stand on the pedal & see if it stays firm or if it fades.
If it fades, try bench bleeding m/c on the car again. If that doesn't work, then the puck or faulty bore is the problem so replace it. If you insist on keeping the Wilwood adjustable proportioning valve, turn clockwise all the way in for full flow to the rear brakes. I've had good luck with NAPA MC36221 m/c 67-68 Barracuda or Dart. Maintain minimum .040 clearance on your brake pedal shaft to m/c.

 

[Icetech]

Soo... ended up moving the pivot point down and forward a bit, you can see the original spot in the pic... it's now at 90* right around max pedal force at normal levels. not standing on it.. also put a slice in the pedal to put the height back to near stock.. Did a quick test drive yesterday and this helped a ton... The brakes are bout 70% where i would like them, still cant panic stop but don't feel like i will randomly hit ****. Waiting for speed bleeders to show up for the rears (i bought the wrong size first time.. my rear cyls are 1/4-28)

Today i did a ceramic coat on my new truck and installed a bed cover... 1pm and i'm beat

 

[Icetech]

Additional thoughts: block both ports on m/c, stand on the pedal & see if it stays firm or if it fades.
If it fades, try bench bleeding m/c on the car again. If that doesn't work, then the puck or faulty bore is the problem so replace it. If you insist on keeping the Wilwood adjustable proportioning valve, turn clockwise all the way in for full flow to the rear brakes. I've had good luck with NAPA MC36221 m/c 67-68 Barracuda or Dart. Maintain minimum .040 clearance on your brake pedal shaft to m/c.

Thanks, pedal doesn't fade at all... third MC also with the same issue so i don't it's an issue (i changed them due to wanting smaller sizes, not bad or issues)

Can't leave .040 to the MC.. on the earlier cars the brake light switch is hit by the MC rod.. what i do is let the pedal sit at it's reseting spot then move the brake light switch into to meet it, so the mc isn't being held forward at all. but i can't really leave space.

I think there has to be air int he system somewhere still.. once the rear bleeders show up i will run a gallon through the system and see if it helps. I have one line i think i will remake also, just don't like how it's run..

BTW.. it's not a matter of insisting on keeping the wilwood valve.. i need some prop valve for the rear and people seem to use them fine?

 

[goldduster318]

I wouldn't worry to much about volume being pushed through, hopefully you have someone helping and use the pump three times, stand on the pedal, then open the bleeder pretty far, keep pushing until it hits the floor method. That usually works the best. The only other thing I'd usually recommend is a pressure bleeder that goes on the MC.

Sometimes with test equipment at work we have to apply as high a pressure as we can by applying the MC and then leaving it for several hours. That seems to get the air out of crevices after you bleed again. Practically doing that inside a car is a little tougher.

 

[Icetech]

I wouldn't worry to much about volume being pushed through, hopefully you have someone helping and use the pump three times, stand on the pedal, then open the bleeder pretty far, keep pushing until it hits the floor method. That usually works the best. The only other thing I'd usually recommend is a pressure bleeder that goes on the MC.

Sometimes with test equipment at work we have to apply as high a pressure as we can by applying the MC and then leaving it for several hours. That seems to get the air out of crevices after you bleed again. Practically doing that inside a car is a little tougher.

yeah tried a power bleeder and it wouldn't seal.. spewed fluid all over, glad i use dot 5 and last time i had to find help bleeding it took 3 weeks.. speed bleeders seem to wokr.. gonna give it a try. I just ran to the store to get some fruit and the brakes are actually ok now.. just need a couple of pumps so there is air somewhere.. will find it