Working on my charger again trying to get the brakes to work better and looking for suggestions. I have converted the front from drum to early 80' diplomat front disc. The rear i used gm metric calipers and jeep rotors i believe. I have a universal master from summit with 7/8 bore. And a adjustable prop. Valve on the rears ne t to the master. I just cant seem to get a decent pedal, always low and kinda spongee. The cars runs almost 130 mph in the 1/4 and is kinda hard to slow down. Just trying to figure out which way to go. Thanks for any advice.

I guess you may be needing a larger bore master cylinder .
Probably 15/16 or 1



Tex

I should have said i have tried a larger bore master but that was off a 94 ram so i wasnt sure if the power master what the problem was so i switched to the small bore master with not a lot of change.

I keep thinking it is the master. Any suggestions on what work good with a setup like this?

Contact Dr. Diff. I ran a similar set up with his master and it worked great and was inexpensive.

https://www.doctordiff.com/

Sounds to me like you have air in the system. Your brake system sounds like a random collection of parts so first thing I'd check is to see if all of the bleeders are pointed up. If all of the bleeders are pointed up then bench bleed the master cylinder. Once all of the air is out of the MC then pressure bleed or vacuum bleed the calipers a few times. What are you using for brake fluid? Have you taken the brake lines off the MC and plugged the ports and checked what your pedal feels like? Have you installed a pressure gauge in the front and rear circuit to see what it says?

First thing is open up the prop valve all the way then bleed the
brakes again.. after bleeding try them again and see if the rears
lock up.. if they do adjust the prop.. a prop valve just slows down
the fluid so maybe you had your to tight and it was slow putting
on the rears.. prop valves should be open to bleed

As said confirm that the air is out of there then you will know if there is a proportioning problem (or not). I grab a helper & have him pump the pedal vigorously several times then on the next down stroke (with perfect timing) I open the bleeder which this helps get the agitated air out of there & in some cases the caliper needs to be pulled & tilted just right (in your hand/still connected) for the air to rise to the top. It like the air vent in the Egyptian pyramids, the air vent exit (bleeders) dont need to be exactly at 12 0'clock but where the passage meets the bore needs to be at or close to 12 0'clock. Put a block under the pedal so the cups dont go past their normal wear area & it helps him control the pedal movement better.

130 mph? Is this a drag race only car?

What does it matter brakes are brakes.. it a matter of hyd pressure

I have been using a pressure bleeder for the last couple years and it works great. I have always used the "pump and hold" method but since I got the pressure bleeder I don't need to bug anybody to help me bleed the brakes.
One other thing to look at is the rear caliper mounts. The caliper needs to be pressurized before you tack the bracket to the housing. Attach a dial indicator to the bracket and see if it moves when brake is applied.

Gus

FWIW, my drag car has the MC plumbed opposite of what I did with my street car. The street car has 4 wheel discs. On factory setups, the pedal feel is set by adjusting the REAR brakes. Not so in a drag car. Front runners don't stop nearly as well as slicks. Why would you put the brake bias to the front on a DRAG ONLY car? My street car , rear calipers have a bracket for the e-brake and when I first put them on, I didn't have the cable setup. Pedal feel was night and day after I installed the e-brake cable setup. Don't know about the OP's brakes. I would imagine his calipers are divorced from the e-brake.

Russell makes spring loaded bleeder valves that they describe as a one man brake bleeder. They are nice when it comes to stopping air from creeping back through the valves while bleeding. When used with a Mitty power bleeder, they work very well.

One of the problems with the factory style bleeder, is that air can seep past the threads while the valves are open for bleeding. I wrap several layers of Teflon tape on the bleeder threads to counter that air intrusion. It seems to be effective, as well.

A proportioning valve is a band-aid for improperly matched front and rear brakes. Caliper bore size, number of caliper bores and correct matching of front and rear caliper bores, plus the correct master cylinder sizing is critical to get the brakes properly biased. The clamping force of the front and rear calipers should be properly matched so they provide the proper level of front to rear bias without the need for a pressure reducing or proportioning valve to try and fix a mis-matched set of calipers.

Another brake system item that many are unfamiliar with is a hydraulic pressure shock reducer that cuts down the pressure spike of the fluid to the rear brakes and dramatically reduces rear wheel lock-up when the brake pedal is applied suddenly at speed. It doesn't reduce the line pressure, rather it just dampens the initial shock wave during high speed, spirited brake applications. It's well known on the racing circuit, but seldom mentioned hear.

I've found that back bleeding is the way to go, especially on stubborn systems. It consists of a large plastic syringe and short section of silicone tube that fits the bleeder screw tightly. Has the added benefit of making it a one man job. Since air wants by it's nature to travel upwards....

Sorry it has been so long since I got back to this thread. As far as air goes I think I have got all the air out of it. I had originally pressure bleed all the system and I went though last night and manually bleed all four corners and did get a couple small bubbles out of one of the fronts. I did talk to Dr Diff and he said the smaller bore master will give me a longer throw on the pedal but more pressure, The bigger bore master will give me less travel on the pedal but not as much pressure. As of now I have the small bore master on it which would make sense why I have a lower pedal. Maybe it is a 4000 lb car and has manual brakes so they just dont stop it good. I was maybe going to try a better pad to see if it would give me a little more power. Any recomendations on a good pad that has lots of stopping power? Thanks again for the info.