Mustang II brakes

timkins · April 29, 2018, 10:37:19 AM

I am not happy with my current brake system. I cannot lock the brakes up and although they stop the car, I feel they do not work the way I want them to. I am one of those people that thinks braking is the next thing to VOODOO power.
I have a 32 Ford 2dr Sedan with a Mustang II front suspension on it. The brakes on the front are Chevy Metric with 2.75 oversize pistons in the calipers and 11" Grenada rotors with 14" wheels. It has a 7/8's Ford Master cylinder mounted under the floor with a 5.75 pedal ratio. I have just purchased a 1" Master Cylinder and was planning on installing that with any other upgrades. There is also a 2# and 10# residual valve on the brake lines to the front and rear. The rear brakes are Ford drum from a Mustang that I had custom fitted with Carbon Metalic shoes.
I have been talking to SSBC from Buffalo NY and they have a 2 Piston Caliper Model 148 E with a piston size 38X2. My question is will this give me more stopping power than what I am currently running.
I also have a call in to EIC brakes and I am looking at their Mustang II Big Brake Kit that uses full size GM calipers. The cost of both applications is about the same.
Which one of these applications would give me the greater stopping power?

kb426 · April 29, 2018, 11:56:06 AM

1st thought: The larger master cylinder will amplify the problem. I ran some numbers in a brake calculator spreadsheet that I found. The gm calipers as far as I know, are all 2.5" pistons. That makes 4.909" of area. The 2 piston caliper has 7.03" of area. The spreadsheet is setup with a pedal ration of 5.1. At 637 psi line pressure which is common for non power assisted, you would have 3127 lbs. of clamping force with the gm metrics and 2239 lbs. of clamping force with the dual piston caliper. From what I have seen lately, you can have one of 2 problems: incorrect proportioning valve or not enough power assist. I didn't design the brake spreadsheet. This came from a autocross website where they know way more than I do.

I have not driven anything with gm metric calipers that will lock up without a real power booster. I don't have a definitive answer, only more info.

timkins · April 29, 2018, 12:26:51 PM

Thank you for the quick reply. My metric calipers have been bored out to 2.75 so that would increase the pressure to the front. I was skeptical when speaking to SSBC when they told me the 2 piston calipers would increase the braking pressure. I will wait to talk to EIC and see what they have to say. Again thank you for the info.

chimp koose · April 29, 2018, 07:59:02 PM

How much pedal travel do you have ? can the pedal travel take the m/c piston all the way down ? Larger bore m/c will move the brake pads farther with the same pedal stroke but gives a harder pedal/lower pressure. just wondering if your pedal travel is allowing for full contact of the pads/shoes .

timkins · April 29, 2018, 08:39:06 PM

The pedal travels about halfway from the at rest position before it starts to stop the car. It does not go to the floor. I think the contact is full as the pads are wearing equally.

chimp koose · April 30, 2018, 01:15:52 AM

maybe it needs a good brake bleed . I have heard that the through frame brake line fittings are tough to get the air out of . Do you have any of those ? maybe some air in the master , did it get a good bench bleed? I would think you should feel pressure from the pedal almost as soon as you push it . rear shoes out of adjustment? I hope it is not something really wrong as my system is pretty similar to yours , 7/8 master , stock metric calipers on windstar 11" rotors , 8" ford diff with stock drums , 6:1 pedal . I think there is something about quick take up metric calipers that can cause a problem but I think they are from an s10 and your big piston ones wouldn't be those.

chimp koose · April 30, 2018, 01:21:31 AM

What stops the pedal from going to the floor ? is the pedal assembly travel limited by something or is it pushing the m/c piston to the end of travel ?

timkins · April 30, 2018, 08:33:55 AM

No thru the frame fittings on the car. I don't want anybody to think the brakes do not work because they do. Maybe the problem (?) is I expect them to stop like a modern day car and they don't. I have gravity bled the brakes by having the MC higher than the calipers with the bleed screws open and left them that way for 24-36 hours replenishing the fluid as needed. I have used an air powered bleeder. I truthfully think it is me as I go thru this every spring when I break the car out of the garage after hibernation but by July 4th I have accepted them as they are. Just the nature of the beast.

UGLY OLDS · April 30, 2018, 09:53:57 AM

This is just a thought ......Our Olds has GM metric calipers on 11" GM rotors ...( Heidts MII brake kit).....The rear brakes are stock Nova drum..( 10" X1 3/4" ??) The pedal "feel" & travel are VERY dependent on the rear brake adjustment..
If the rear brake adjustment gets a little "loose", the pedal travel increases dramatically ....
I also am using stock, OE equivalent, linings both front & rear....

Also ....Don't your rear shoes need to be "warmed up", like in a race car application, to work properly ??

Just a thought during AM coffee....

Bob..

timkins · April 30, 2018, 10:20:28 AM

The rear brakes may need adjusting, I never thought of that. Not sure about warming the rear brakes. Did not bother to ask when they were fitted. Thanks for the suggestions. Again, it's probably me getting older and more crotchety.

UGLY OLDS · April 30, 2018, 05:32:35 PM

Quote from: "timkins"The rear brakes may need adjusting, I never thought of that. Not sure about warming the rear brakes. Did not bother to ask when they were fitted. Thanks for the suggestions. Again, it's probably me getting older and more crotchety.

Gee...76 is not old .....Now that Enjenjo feller .....HE'S OLD ...

When God said "Let there be light"...Enjenjo said, "Hey...Neat Idea"... :?

Bob..

enjenjo · April 30, 2018, 07:05:10 PM

I was not around when dirt was invented, but I remember when it became popular.

Bruce Dorsi · May 01, 2018, 08:45:43 AM

Another thing to check is how much of the rear brake shoes are contacting the drum.

Ran into this on a friend's car. ....Chalk on the linings, then a few applications of the brakes, proved the shoes only made a small contact area.

Remember when brake linings used to be "radiused" on a machine to match the arc of the drum?

chimp koose · May 01, 2018, 12:09:01 PM

If you need to bleed your master cyl every spring you probably have a leak somewhere . Check all your lines and do a bench bleed . Gravity bleed would be hard to do if your master cyl is under the floor as your wheel cyl/calipers would possibly be higher than the master cyl .

timkins · May 01, 2018, 12:11:55 PM

I will check that using the chalk method. They were supposedly radiused to the drums when I had them fitted with the carbon metallic shoes but that was awhile ago so I will recheck them. Thanks for the suggestion.