good pedal , brakes suck

[Ross50]

just bought this car . it has a disc/disc setup with power booster and what looks like a gm master . its frame mounted ,2 pound residual valves in the lines and no proportioning valve. the rear calipers have ford stamped on them and the fronts are jap. I have a decent pedal but the brakes wont lock up the tires. any ideas ?

[cffisher]

Welcome to CHR AIR in the system If you have or have access to a power bleeder that should do it for you

[Ross50]

Thanks. i've bleed the brakes with a mightyvac tool and the pedal seems good. I suppose there could still be air trapped .

[34_40]

Without knowing all the sizes.... it'll be a bit tough to determine if the components are sized correctly.

Caliper piston diameters? Master Cylinder bore diameter? If these are small or undersized.. or even the rotor, if it is to large for the caliper.. you might not be able to lock down a wheel.

But air trapped when the master is lower than the calipers is the most common complaint we hear about..

[Ross50]

Im thinking that the components are not compatable with each other. do you know what bore sizes work together ?

[Dave Severson]

Disc-Disc takes a different master cylinder then disc-drum, lots of folks ignore this when building a car figuring a master cylinder is a master cylinder. A proportioning valve is still the best way to be able to tune the brake bias from front to rear, Wilwood makes what's called a combination valve now. Used them on a few cars and IMO they are a super unit!

Could check some obvious things, are the front calipers being fed off the larger reservoir on the master cylinder? Are all the brake lines the same size, I've seen people mix and max sizes and use a bunch of hokey adapters, never gives good braking! As for bleeding, awhile back I got one of the new reverse bleeders----I'll never go back to the other style or trying to bleed with someone pumping the brakes and me cracking the bleeder! Also, look the lines over and make sure the routing is good, no pinched lines, and no big downhill loops in the line that go below the level of the master cylinder that will form an air trap you'll never get out of the system. With the brakes released, what is the clearance between the pads and the calipers? Some will also turn a rotor beyond it's prescribed limits in order to save a buck....

[34_40]

Random thoughts, In addition to what Dave said.. If there are 2 different sized reservoirs, then it's the wrong master as that is for a disc / drum setup. A disc/disc uses the same size reservoirs front and rear. Also the disc/disc should use the same size lines front and rear.

If I were you, I'd measure the piston size (O.D.) in the calipers and then call Wilwood and ask them for their opinion for a proper sized master cylinder. If the lines are mis-matched, change them as per whats required for the master..

If you are bleeding by pressing the pedal, do not pump the pedal more than 3 times and then crack the bleeder, pump 3 times then crack the bleeder, rinse and repeat as needed.. sitting there and pumping and pumping just forces the air into the fluid and defeats what you're doing. If you can borrow or rent a pressure bleeder, it can make your life much happier.

Also, what fluid are you using? DOT3? 4? 5? I'm in the minority and use DOT 5 silicone.. Love it and will never go back to 3 or 4... it's all in what you get used to.

[HWORRELL]

My first thought is Cheap front brake pads that the compound is to hard to grab the rotors. Seen it a million times.

[Ross50]

thanks for the ideas. found out the front calipers were not grabbing the rotors square . the inside was rubbing the bottom and the outside the top . reworked the caliper mounts and this helped but still not right . time to rethink this system.