Brake Pedal Modification

One of the weak spots in the FFR Cobra seems to be the brakes. Matt Mengelkoch read an article and brought and issue to my attention. When pressing the brake pedal... if the angle between the lever arm (part of the pedal between the pivot and push rod) goes beyond perpendicular to the push rod, you loose a significant amount of leverage and brake pressure. This gets progressively worse as more pressure is applied. This would explain the fact that many people claim they can not lock up their brakes.

I have performed this modification on both our Street Car and the Spec Car, and am pleased with the results.

On the street car, I am running a 1994 Mustang Cobra master Cylinder. It has a bore diameter of 15/16". I had been running a standard shortrened mustang pedal with a ratio of 5.5:1. This produced a Very firm pedal. Actually too firm.

By changing the Pedal ratio to 6.5:1 and putting a "Dog Leg" in the pedal, my brakes went from very firm, too firm with more travel and modulation. I used a 5/16 female Heim joint and a long threaded Grade 8 bolt as the push rod. I cut the head off the bolt and rounded the end to finish off the rod. The threaded bolt allows for pedal height adjustability. I should note, I used a new pedal for this change and did not find it necessary to shorten it from the stock power brake length.

I can now easily lock the brakes up at will. I think the important factors hear is the pedal ratio and the Dog Leg that makes sure the leverage angle is correct at full compression.

 

On the Spec Car, I tried a different master cylinder.This required a different pedal ratio. I am using a 1984 Mustang 4 cyl Power Brake MC. This MC is right around 7/8"(21mm) and cost a wopping 13.00 with lifetime warranty from Kragens. Working from Mike M's idea, I created a new pivot hole in the Pedal Box beween the two existing holes.

I also moved the hole back a bit for more leg room. In addition, I changed the pedal ratio by lowering the push rod hole on the brake peda byl 1/2 inch. I also created the Dog Leg in this pedal. Again I think this is very important in getting the right leverage through the pedal range.

As Mike stated in his post on the CobraForum, this also gives a nice firm pedal. I have not tested this setup on the road yet, but the pedal feels great and believe it will work well.

This might be a good option if you have not put the body on and are able to redrill the footbox. This modification will allow the use of the less expensive master cylinder.

If you are looking to perform this on a completed car, your only alternative may be the 15/16" MC, and performing the modifications I did on our street car using the Dog Leg mod, Lower Pivot hole, and an aprox 6.5:1 pedal ratio.

I would be interested in hear from those who have tried this. Send your thoughts to david.j.borden@att.net

David Borden