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Posted

I just got a new race car. Giving the car a once over. Installed new hawk dtc-70 and 60 pads. The brakes are cobra front and rear calipers and rotors. With a wilwood combination remote master cylinder, balance bar. It is a recirculation system with a check valve. Wilwood front throw pedal set. The front master bore is 7/8 and the rear 3/4. The car weights 2770 lbs. Drove it down the alley to make sure everything was correct but the brakes feel like crap. This was not enough to heat the brakes up. The rotors had rust on them also. I did drag the brakes to knock off the rust, but still feels not so good. I know I need to heat them up to get them to grab. But is this a good design? Would upgrading the front calipers to 6 piston wilwoods work that much better? Or is it the bore of the master cylinder? Or just that the brakes need to heat up and they will be fine? New to the manual brake set up such as this.

Thanks

Posted

Manual brakes require a quite bit of pedal force to get them to work compared to power. The master bore sizes are in the normal for that type of car, if they feel excessively firm then you could go down a size on both masters. If memory serves me right the smaller dia master should be the one on the front, not the rear like you have listed.

 

The other thing is there might be a lot of rear brake bias in it which would make it harder to slow down. 6 pistons wouldnt be any better unless you are increasing overall caliper piston area an you have the extra money to throw at it.

 

http://www.stockcarproducts.com/wiltech.htm

Posted

Don't change anything until you've driven it in anger. If you start making changes now, you'll have no idea what it was like before you changed parts if it's doing something weird. The previous owner won't be able to help you if you really run into a problem.

 

MC size should be picked by piston surface area and then tuned by driver preference if he would like it firmer/softer, etc.

 

I'd go out an drive the car on the track first, that way you know if you even have a problem you need to spend money on.

 

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Posted

does any one know what the caliper piston area is on a cobra front caliper?

Posted
does any one know what the caliper piston area is on a cobra front caliper?

 

It's either 40mm or 38mm depending on the vintage of the caliper.

Posted

40mm is 1.57 inches. How would I get the area inches /squared to calculate bore size

Its a mustang cobra 2 piston PBR style caliper. 3/4 bore is on the front and 7/8 is on the rear. Rear is also mustang cobra.

Should have made the mustang cobra part more clear.

 

I will run the car as is and see what I have before making any changes. With a race only car in California its hard to check your work living in a city. i can not drive down the street to seat my new pads

 

I would like to avoid something breaking at the track. Its a lot of time and money just to get to the track and run.

Posted

Caliper piston surface area is calculated like so:

 

40mm x 1"/25.4mm = 1.57" piston diameter

 

Plug that in to the formula for area of a circle: pi * r^2 = 3.14159 * (1.57"/2)^2 = 1.936 in^2 per piston

 

Since it's a 2 piston caliper, multiply by 2 = 3.872 in^2 surface area

 

So, according to the equation, you can setup down your master cylinder size. Be sure to figure out what you're trying to accomplish (firmer/softer/etc.) when you make changes though, so you're not just throwing time and money at it.

Posted

thanks I thought you would add both together but was not sure. Which way will make my pedal softer up or down MC bore size?

Also is there a point where you are not moving enough fluid to the caliper?

Posted

Kindof but not really. When you go down a size on the master pedal effort gets easier but requires more pedal travel to make up the difference. 3/4 is about as small as you would want to go on any car for a front brake.

 

You could theoretically use a 1/2" master on your setup if you had enough piston stroke and pedal travel, and have brakes that would need a egg under your foot because they would be so touchy.

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