brake stopping problem

mrmustang · #1 (**permalink**) 08-03-2009, 03:35 AM

The following was sent to me this morning:

I have a Contemporary Cobra Replica brake stopping problem. It came w/Jaguar
suspension & Jag rear; the brake master cylinder is from a ‘86
Mitzubishi Starion w/built-in proportioning valve & no power assist.
It takes a tremendous pedal effort to stop this car & it's dangerous
to drive. Does somebody make a power brake master cylinder that I can
put on it that will do the job? The flange has 2 bolt holes that are
12-6 o'clock, not 3-6 o' clock. Appreciate any help or advice. Milton
Glodek, email: glom5062@verizon.net

Can anyone help out this guy?

Bill S.

mickmate · #2 (**permalink**) 08-03-2009, 04:54 AM

I'm making front caliper brackets to put the Wilwoods to both the solid and vented Jag rotors.

trularin · #3 (**permalink**) 08-03-2009, 06:16 AM

He needs to either share the configuration with the measurements so we can determine if it is lever or volume that is challenging him or take it somewhere where someone will do it for him.

Just my opinion.

Fastz06 · #4 (**permalink**) 08-03-2009, 08:14 AM

Can you e mail me the brake sizing/force formula? My contemporary has a 1 " MC and 1.375" Wilwood calipers. It takes alot of pedal force to stop. I suspect I need 1.75" calipers.

Thanks

Ray

trularin · #5 (**permalink**) 08-03-2009, 01:00 PM

Well, typically you need the fulcrum point and the distance to the actuator rod and the length of the pedal to the foot rest to calculate the pressure being exerted on the rod into the master cylinder. Then you need to know the size of the master versus the capacity of the calipers ( slaves ). Since it it hydraulic, it is a matter of pressure and volume.

So, you should be able to google this or get a high school physics book to give you examples.

Hope this helps.

trularin · #6 (**permalink**) 08-03-2009, 01:05 PM

Ray, if you make changes the volumes, you may have excessive travel. For example, if you have a cylinder 1 inch and a slave 1 inch ( diameters ). if you push in on the cylinder and it travels 1 inch, the slave will go 1 inch ( volume to volume ). Now, if you change the slave to 2X the volume, it will only go 1/2 inch for the same volume from the cylinder you pressed 1 inch.

I hope this helps!

mickmate · #7 (**permalink**) 08-03-2009, 04:49 PM

Hey Ray Tru makes sound suggestions on the measurements you need to be collecting. Shoot me a PM with an e-mail and I'll send you the excel spreadsheet I made up so you can just put your data in. There are some on line too that can do the same thing.

D-CEL · #8 (**permalink**) 08-04-2009, 11:14 AM

As I just recently went thru this while upgrading my SPF brakes.
Check the pedal ratio first!
For a manual system is should be a minimum of 6:1 but 7:1 is better.

A = Distance form pivot point to middle of push / pull point
B = Distance form pivot to point of push on master cylinder
P = Pivot point
F = Force or push

Once you get the ratio correct you can tailor the M/C bore size to provide the suitable line pressure.

Jason

racco · #9 (**permalink**) 08-04-2009, 07:09 PM

I have the same issue, plenty of power and poor brakes. I have wilwoods and vented rotors up front. They were installed in 1989, and the rotors are made by brembo. Would anyone have a part # for these rotors for future reference?
I will look into the poor braking in the next the next several weeks.

D-CEL · #10 (**permalink**) 08-05-2009, 11:00 AM

racco,

What chassis do you have?

Do you have the Brembo part#?

SF_SN888KE · #11 (**permalink**) 08-05-2009, 04:23 PM

There was good info on the SPF Braking thread a couple of weeks back. (do a search) Changing to softer brake pads, pedal ratio, master cylinder sizes, caliper size, adjusting balance bar, bleeding (interesting comments on bleeding), etc. similar to what Wilwood tech told me.

I had great solid pressure, 6:1 pedal ratio, front wilwood dynalite with 11" rotors with street pads (15" wheels) and 2003 Mustang Cobra rear calipers with street pads, but poor braking. It would take a gorilla to stop the car. After reading the thread, even understanding the math, it was easier and quicker to swap the MC from 7/8" to 3/4" on front, (test drive) and then rear. Car stops much better, but since it's smaller MC, the pedal goes down a little farther and just a tad softer.

racco · #12 (**permalink**) 08-05-2009, 07:19 PM

d-cel, I have 3155 but it was built in the mid eighties, the rotors are stamped 89'. I do not have a part number for them.

D-CEL · #13 (**permalink**) 08-06-2009, 10:18 AM

racco,

Is it an SPF? If so its a very early car and should have Mustang II spindles.

If not, what MFG is it?

Jason