soft brakes - why?

[Mike Pearson]

I recently converted my 68 camaro from drum to disc. I used the Aerospace brakes. The pedal seems a little softer with the disc brakes than with the drums but the stopping power is amazing. All I have to do is rest my toe on the pedal and it stops great. On the first run i hit the pedal like I did when I had the drums on it. I had to put the car back in gear to drive to the end of the track. I used a similar master cylinder but did not use a porportioning valve. Follow the instructions on seating the pads. I took a couple of runs before the line lock held real good.

[Jeff Stout]

Does the car still have rubber lines at the calipers? Maybe they are expanding when pumped the first time. Just throwing an idea out there. Never mind reread your first post

[Kegracing]

Thanks again all for the help and suggestions. Worked all weekend and long hours, still have not had a chance to work on car.

Will let you all know what I find.

Ken

[nhramnl]

I learned this from Pustelny and it works every time. Fill the master cylinder, open the bleeders at all four corners and just let the car sit for a few hours. Obviously, check the master cylinder regularly, to make sure it doesn't go dry. The system will gravity-bleed just fine. To make absolutely sure you're done (though it is not necessary), close all four bleeders and put one pump on the brake pedal at each corner. You should get solid fluid, with no sputtering.

One other thing. the basic rule of master cylinder bore size says that too large a bore will make the pedal go too deep and the brakes will tend to feel spongy and too small a bore will make the pedal too hard and require a ton of pedal pressure.

[Bob Mulry]

Originally Posted by nhramnl

I learned this from Pustelny and it works every time. Fill the master cylinder, open the bleeders at all four corners and just let the car sit for a few hours. Obviously, check the master cylinder regularly, to make sure it doesn't go dry. The system will gravity-bleed just fine. To make absolutely sure you're done (though it is not necessary), close all four bleeders and put one pump on the brake pedal at each corner. You should get solid fluid, with no sputtering.

One other thing. the basic rule of master cylinder bore size says that too large a bore will make the pedal go too deep and the brakes will tend to feel spongy and too small a bore will make the pedal too hard and require a ton of pedal pressure.

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Good info except you got it backwards regarding the ratio of master cylinder size vs. wheel cylinder / caliper size.

The smaller the bore on the M/C the more PSI you generate within your brake system with all things equal. Now you with a small bore M/C you have HIGH PSI and LOW VOLUMN per pedal stroke.

With a large bore M/C, you have LOW PSI and HIGH VOLUMN.

Due to the large caliper bore size a small M/C might not apply the brakes fully with 1 (one) pump of the brake pedal.

A small bore M/C will feel softer than a large bore M/C due to the mechanical advantage of the small bore = higher line pressure.

A large bore M/C generates lower internal pressure and the pedal will feel harder because of the lower mechanical ratio.

Don't forget there is also a pedal ratio that can be used to your advantage but the same mechanical rules apply.......high multiplication = less M/C stroke...lower multiplication = more M/C stroke.

Just make sure that you have enough volumn to fill the calipers / wheel cylinders with 1 (one) pedal stroke.

With a high muliplication pedal ratio, a small bore M/C and large wheel cylinders we used to bend the backing plates in half prior to the use of trans brakes.......


Hope this helps,
Bob

[nhramnl]

Thanks for setting the record straight. When I wrote it, I spent 10 minutes re-reading it, thinking I might have gotten it backwards. Kinda like when you try to remember the old "set the intake lash when the exhaust is opening, set the exhaust lash when the intake is closing" thing.

[Kegracing]

First, thanks everyone! Jim and Mark, you were on the money. Amazing how much better it is after you get all the air out. I went back thru all the bleeders, and was just a little air at each bleeder screw.
Feels much better now. Have not had it out on the street(God bless my neighbors), its raining, but have a very good pedal now.

Ken

[Jim B]

Glad to hear the mechanical problem is solved...I wonder if your wife will get over Mother's Day as quickly?

[Kegracing]

she is still a little grouchy, but she did climb in and push the brakes for me today... fussed some, but did it!
I got a pretty good one, but dont tell her I said so

Ken

[danny waters sr]

Originally Posted by Kegracing

she is still a little grouchy, but she did climb in and push the brakes for me today... fussed some, but did it!
I got a pretty good one, but dont tell her I said so

Ken

Now get her to go to the track with you and do the fuel and tires and cooling ,while you ride around and socialize with fellow racers..lol