Converting to Two MC's

[saltshaker]

--------------------------------------------------------------------------------

I need to change my MC after the accident last year.the car currently has GM metrics and Explorer rear disc with a 1 1/8" MC and a peddle ratio of 5:1 and the car doesn't stop well. Joe sent me a 7" booster and a 1" MC but the motor has 13" of vac so I'm not sure how effective this will be. So now I'm thinking it might be easier to use two separate MC's and a balance bar. I've read that a lot of you with Explorer rear disc use a 3/4"MC....what is used for the GM Metric's 2.5" piston?? I plan to change the peddle ratio to 6:1....unless
Someone has had success with a tandem MC...what size was it??

[bobcowan]

13" should be enough to run a brake booster. Especially if you have a resevoir.

The current pedal ratio is good for power brakes. 6-7:1 is just about right for manual brakes.

Your MC bore is probably too big. A bigger bore will move more fluid, but it takes a lot more effort to create pressure. You might do better with a smaller bore, more like 7/8".

The downside of a smaller bore is that it takes more movement of the pedal pad to make that pressure. And increasing the pedal ratio will do the same thing. But you gain the ability to modulate the brakes easier; the pedal is less sensative. It's a trade off.

You also need to take a look at where the brake rod attaches to the pedal. That pivot point moves in an arc. If at rest the pivot point is at, say, 6 o'clock, as you press the pedal, it moves in an upward arc, towards 9 o'clock. The further you depress the pedal, to less actual MC plunger movement you get.

To be the most efficient, the pivot point should be at about 3-4 o'clock at rest. If you change the pedal ratio, consider adjusting that pivot point - if needed.

[saltshaker]

Are you saying that I should use a 7/8 MC with a booster or with out?
Jon

[bobcowan]

If you're going to use a booster, then use 7/8" or 15/16". That should give you near factory brake pressures.

I have manual brakes and use 3/4" dual MC's. That works really well, especially with big wilwoods. But I started out with stock Ford brakes, and the same MC. For anything off the track, it was an excellent combo.

[saltshaker]

Thanks, I'm thinking either 1" or 15/16" with 7:1 ratio and no booster. Wilwood. Suggested a 7/8 for the front and a 1" for the back.

[mickmate]

I have an excel spreadsheet I put together to figure out the sizes and proportioning. If you would like a copy shoot me an e-mail address.

[Barnsnake]

Saltshaker,
With the GM Metric/Explorer brake combo your required pedal pressure will be too high with the .875/1.00 master cylinders, even with high CF pads. Some use .750/.750. I'm using .700 front/.750 rear. Many use a .625/.750 combo that provides great stopping power and easy modulation, but I found the pedal travel to be a bit long for heel-toe.

[Roscoe]

I upgraded my GM's to Outlaw 4 piston. I'm using a 7/8" in the front and a 1" for the Explorer's in the rear. Installed a Tilton Racing floor mounted pedal set with balance bar.