Master Cylinder for Disk Brake Conversion

[sasaeger]

I have a 74 with NO brake booster. I did the chevy disk brake conversion. The pedal goes to the floor and I have been told that its because my master cylinder isnt big enough to get the amount of fluid to the calipers. I have had the lines checked for air. So here is my question

I was told to get a MC from a 1976 Ford F250 Pickup 6.4L 390CI V8 4 Bbl dule piston.

It doesnt come with the push rod and I dont have the skills to make one.

I want one that is a bolt on. What is one that I can get that doesnt require a brake booster.

 

[Oatmeal]

You're going to get all kinds of different reccomendations so, I'll just tell you what has worked well for me (for about 22 yrs) I just used a m/c from a '76-'77 Bronco (had factory discs) and made some tight bends where the lines exit the m/c to clear the throttle linkage. I also removed the drum/drum distribution block and plumbed the front brakes right off of the m/c and the rears through an adjustable proportioning valve. Always stopped straight, even after going through deep water (my drums never did) Be aware that it'll take more pedal effort to stop because unlike drums, discs aren't self energizing. Anyway, that's how I made mine work ---------Hans

 

[StnePny]

On my '74, when I did the Chevy Disc Brake Conversion all I did was ake the check ball out of the M/C and had no problems.

Just my personal experience.

 

[sasaeger]

can you explain how you took the check ball out of the MC?

 

[Pa PITT]

like Oatmeal said your going to get a thousand answers & about 1/2 will say search because this has been beat to death here .. But the search button doesn't work for me either .. So I'll answer by saying I didn't have to do anything I'm using a 1972 M/C and I didn't even pull the valve .. M/c to ''H'' block down to calipers.. I do think I'm an exception to the rule.. But I have good brakes..

 

[broncnaz]

If your pedal is going to the floor then the MC probably has a bad seal. So its not building pressure. Theres many people using the stock MC with no issues. You should at least get a pedal with the stock MC worst case would be if pedal travel is a lot farther than it was or the brakes just feel soft then you may need a MC with a bigger bore.
In almost all cases your going to have to build a pushrod. A lot of the time you can reuse your old pushrod.

 

[cody72sport]

can you explain how you took the check ball out of the MC?

x2 on this. how do you do this?

 

[needabronco]

Most master cylinders don't have the check valve in it anymore. My 71' had the original stock master in it when I bought it, and it didn't have one either. But you take the brake line out and then pull the fitting out of the master, if there's a ball in there, you take it out. I don't remember which hole it was in, but it should only take 3 minutes to check both sides.

My experience was that the stock master worked just fine, maybe a little too good for the rear. I added an adjustable proportioning valve to the rear of mine and it worked great. It seems that those with success with the stock (drum) master and disk brakes is around 50%, I'm not sure why...

 

[VT_Don]

re: "the brakes just feel soft then you may need a MC with a bigger bore."

I'm a bit confused on the principle here. Could you please explain how a larger, master cylinder bore yields greater line pressure.

 

[hdmc]

I just did the same swap with all new parts from WH had the same problem took it down and had it power bled whala I got brakes . It took 7 quarts of fluid total to get all the air out

 

[broncnaz]

re: "the brakes just feel soft then you may need a MC with a bigger bore."

I'm a bit confused on the principle here. Could you please explain how a larger, master cylinder bore yields greater line pressure.

Usually if the MC bore is to small you have 2 issues a lot of pedal travel and brakes that dont work well or feel soft. Its not always albout line pressure its about volume of fluid as well. You could get a MC that develops 2000 psi of line pressure but if the volume is not there it most of the pressure will go to fill up the volume.
The smaller the bore size the higher the line pressure the bigger the bore size the less pressure you have. Vise versa for volume.
Actually this link might make it clearer. http://www.hotrodheaven.com/tech/brakes/brakes4.htm
A lot of people put on MC's with bigger bores usually to big and the pedal becomes harder now they have the volume but not the PSI due to bore size. This is were many people endup installing H boost as it reduces the pedal pressure. But that really doesnt mean the brake system was correctly matched. That is always one of the points I make when people start talking H boost because there brakes dont work well. To many people just cover up a existing brake issue with it. Does it work sure but they could have easily picked a different MC and gotten brakes that worked properly from the start instead of covering a issue.
I will concede that there may be some setups where you may have to cover up a issue but I think for the most part you dont have to cover up issues.

 

[ransil]

I used the stock manual M/C in mine, no issues.
Did you install the calipers with the bleeders up??
did you grind the knuckles??

 

[fordguy]

buddy just got through with a conversion, pedal is pretty stiff. unfortunately, i dont know what the bore size is ( i had the mc on the shelf got if from horsepower sales, supposed to be the right one). Seems like with as many conversions be done, we could have some consistency in the mc. just my two cents.

 

[Apogee]

I used the stock manual M/C in mine, no issues.
Did you install the calipers with the bleeders up??
did you grind the knuckles??

I agree with Ransil. When someone says the pedal goes to the floor, I wouldn't assume master cylinder first thing, I tend to think that there is air in the system. Are the calipers properly installed with the bleeders up. If a new MC, was it bench bleed, etc?

Tobin