Improving brake balance/consistency

My 71 Ford Capri has a dual piston master cylinder which separately feed the front and rear brake systems. Front are disc and the rears are drum. I'm finding that the balance between my fronts and rears degrade during a race, especially at a tough track like Laguna Seca. My theory is that the fronts auto adjust but the rears get looser and looser as the pads wear. Since they are fed by different cylinders which are connected together, the pedal travel is the same (fronts are compressed) although the rears need more travel to compensate for the rear wear.

My thought is to connect the two cylinders together and feed the fronts and rears from a common reservoir. Of course, I'm aware that my pedal height will fall as the rear brakes wear and I could lose all my brakes if I have a single line failure either on the fronts or rears.

What do you guys (or gals) think?

Joe Craven
71 ITB Capri

Your theory on why your pedal gets worse during a race is correct. However, before you tie the front and rear together consider the following. Do you adjust/clean the rear brakes every time before going out on the track to minimize the problem? Is there another rear brake material that would wear better? (See other threads on brakes) Can you get some cooling air into the drums to help them wear better? (See Section 6B) Another trick, if you still have the parking brake, is to use it as an adjuster during the race. As the rears wear, set the parking brake a click or two. This will shorten the travel of the pedal. Ultimately, I would attempt to fix the problem, rapid wear of the rear brakes, as opposed to bandaging it.

Yes, brakes are adjusted between each session. I'm running Porterfield R4 compound pads and shoes. Brakes work fine at Infinion and Thunderhill raceways. Laguna Seca is so hard on the brakes that I wear between 20 to 25% of the pads and shoe material in one 30 minute race! By the end of the race, rear shoes are very worn to the point that I do not have anymore rear brakes. I thought about installing an e-brake, but the effort and weight are negatives. I recently purchased a set of custom green Carbotech rear shoes which I hear are more durable. However, they are supposed to expand as they heat up so I'll have to experiment with the optimum adjustment when I test them.

One issue that concerns me is that the bias is very dependent on how well I adjust the rear shoes before a session. If they are tied together, my brakes will work the same all the time unless my rear shoes get way out of adjustment.

Your comment about rear brake wear. Does the brake materials wear faster if they are allowed to run hotter? I run front ducting (have to at Laguna) but rears are naturally cooled.

Joe, sounds like you've been doing your homework. I think like most things, there is an optimum temperature a compound wants to work in. Too hot, and they will wear too fast,burn up the binding agents or glaze. Too cold, and they may still wear too fast and/or chew up the drums. (I use hawk blues on my FWD. On the track they work great, some rotor wear, but when the car is used on the dyno to slow down, they eat the front rotors.) Might want to hook a thermocouple or use temp sensitive paint to know what temperatures you're getting. I'm sure Larry at Carbotech would eat up the fact you have real data to help you choose a compound. A downside about tying the fronts and rears together is the fluid is going to take the path of least resistance. So as you push down the pedal, the front pads will touch the disc. However, not much force will be generated because now the fluid will want to flow to the rears because they have not contacted the drum. You will have to continue to push the pedal until the rears make contact, then your braking force will build. So your maximum braking application will continue to move later and later. (Hopfully this will not pump the resevoir dry.) With your current setup, the fronts are giving maximum braking all the time. You're just losing more and more of the rear. So in this instance, you are only delaying a percentage of your braking and of course you'll never lose all your brakes.

Joe-

My dad ran a Capri in ITA from 84 till early 90's (Its still in garage, as he can't let it go, he bought the car new in 73). He is always talking about brakes when we talk about it (reminise of the "good old days")...

I will talk to him and give you some of his feedback tomorrow.

Raymond

Back in the day dad ran Ferrodo brake pads and shoes (shoes were made for him). He had the 2.0L brake drums. He had a brake bias to the rear. He ducted air to the fronts with a modified baking plate that forced the air to cool both sides of the rotor. The entire system was eroquip or steel lines that ran through the car. He also used to "bake" the brake pads to outgas the pads to prevent green fade. He had a welded rear end (Spider gears) so it was constantly locked, not sure if that would help braking or not?

He suffers from "not remembering" so he can't remember if he adjusted the bias during the race or if the system was separate front to rear. He does remember that he had lots of problems with brakes and front wheel bearings.

My dad’s suggestion is to make sure you have new rear wheel cylinders (he changed his a lot because they hung up a lot). He also was constantly bleeding the system getting air out. The backing plates where the shoe sat was always kept clean and lubricated so the shoes would move freely. He does not have an opinion on your idea... he isn't sure if it would work or not. Unfortunately the brake system is not in our car as he sold all of it??? Why??? Who knows.

My opinion is that if you have not already tried a brake bias on the rear lines and adjusting it throughout the race (to increase pressure) then you should start there. On your warm up lap you should be able to find the correct settings to start the session/race and adjust from there.

Hope this sorta helps... If you want to chat with him send him an e-male to [email protected].

for your viewing pleasure here is a link to the old Capri... those were good old days... Corvairs, RX-3's, and the old Capri ruled ITA!!!

http://www.rstperformance.com/Index/capripictures.html

And yes those two kids are my bro and I J


Raymond

Raymond, great site, I especially loved the photos of the 73 ITA Capri. You guys have and still race a bunch of cars.

I used to run Ferrodo DS-11 front pads and those things lasted forever. They seem to be a very high temp pad and my brakes wouldn't work well until I got them good and hot. The material would probably work well for drum brakes. Any idea where I can get them made? I do have a set of Carbotech Green rear shoes which I will try at Laguna Seca with new rear wheel cylinders. Perhaps that'll be enough to solve my rear brake issues (crossing fingers)

I raced the Capri this weekend and although I beat my personal best at Infineon by 1 second, my goal is 2 which would be track record pace. I do have a rear proportioning valve installed and I was able to control the rear brakes. I kept adjusting it throughout the race, although I think that had more to do with brake temps than not. I ran a metallic set in the front which started to fade late in the race. I had to reduce rear brake as they started to lock as I pressed harder and harder on the pedal. I haven't looked at the brakes yet, curious to see how much the rears wore and what damage the overheated fronts sustained. I did back off the brakes for two laps and they came back for the balance of the race.

Next year I plan to bring out my 72 ITA Capri. I intend to apply everything I've learned with this ITB Capri to see how I'll fare with faster cars. From what I see out there, my Capri should be fast in a straight line with the deficits being the brakes and handling.

Joe Craven
37 ITB Capri
37 ITB VW GTI
probably 37 ITA Capri for '05