I know this topic has been discussed before, but searching for a solution. I bought the SSBC A153 disc brake conversion kit w/master cylinder for my 340 Duster equipped with 10" brakes, 5x4" BC. The main reason I bought it is I like the fact they are using USA made 4-piston calipers and they fit my 14" Rallye wheels. Lots of little problems with the kit that should have been worked out when they designed it, like:

-studs for 5x4 were not installed in rotors and not in box. They sent replacements that didn't fit, so I bought my own.
-brake hoses don't fit the bracket on the frame unless they are modified.
-Castle nut for the spindle too tall to insert cotter pin. Reused old shorter nut from drum package.

For a more stock looking conversion, I elected to use a Right-Stuff disc/drum proportioning valve/block for 69-74 A-bodies. This is a non-power 10" drum/drum setup converted to a non-power disc/drum setup, as designed specifically for this kit.

After sorting out these issues, got the brakes installed and went for a test drive. Stops worse than my drum brakes. Did some research on these kits a found that SSBC supplies 1-1/32" bore master cylinder which is too large for this system. Suggestions were to go to a 15/16" bore, which I did and braking is better, but probably still worse than the drums and I can't lock them up.

I've been working on cars and brake systems for over 45 years and have done a few disc brake conversions, but this one is giving a me a fit.

Master cylinder was bench bled. Brake hoses are clear and not blocked (fluid flows freely when bled). Pedal is firm and pedal ratio is the same as manual drums. It just doesn't stop like it should. I wanted to measure the disc brake line pressure, but the bleeder is very long and my adapter fitting didn't fit so I'll have to find the right fitting. One thing I read was someone with a similar problem thought the rear brakes were engaging before the fronts built up enough pressure to apply fully. Sound plausible? Switch to cermanic pads for better performance?

Sorry for the long rant. Frustrated. Looking for suggestions.

ceramic pads aren't going to help your problem.

no apology needed for the rant, sometimes we need to vent! I ain't up on hem too much but as you know there's been a ton of issues with SSBC. you might get a 3000 psi gauge (they're cheap) & see what you get at the calipers. that would point you back upstream or right there

SSBC sux

Period.

Your best bet would have been to send that junk back before you installed it, but too late.

Pedal ratio is the same as the drum setup is part of the problem. Your drums were self energizing and don't need as much pressure from your foot for a given braking force. Discs are not self energizing so you need more pedal effort, smaller M/C bore (with corresponding increase in pedal travel), or a booster.

video quality is meh, but the explanation is good and it also explains why the shoe linings are different and where they need to go.

self energizing brakes

That exact scenario was going on with another members SSBC kit in a B body.
He used the pressure gauge and could see the system just wouldn’t generate enough pressure to the calipers.
The problem turned out to be the adjustable proportioning valve.
He had it set to recommended starting point(1/2 way?), and once it shut the flow off to the rear, the pedal wouldn’t travel anymore, so it wouldn’t generate any more pressure to the calipers.
The first “test” after that discovery was to back off the proportioning valve all the way, which allowed increased line pressure both front and rear, and breaking was greatly improved.

He was told that it was “impossible” that the proportioning valve adjustment would have any affect on the front brake line pressure.
But with the P-valve set to half way the most pressure he could get on the gauge at the caliper, using both feet and giving it all he had on the pedal was 600psi.
With the P-valve backed off it was 1200psi.

Before I went any further I’d figure out a way to get a gauge fitting in there if I were you, and see what the pressure is at the caliper.

Fast68plymouth is right. You really need to know the pressure at the calipers in order to diagnose your problem.

Here's a link for a pressure gauge that you can use to measure the pressure. The gauge screws into the bleeder valve and is read directly off the gauge.

https://www.summitracing.com/parts/ssb-a1704

Hope this helps.

Thanks for the replies. I have the gauges, just need the right fitting to fit their caliper. As for the proportioning valve, I asked if I could use the OEM disc/drum type in lieu of the adjustable one and they said yes (its a cleaner installation), but I may have to go back to the drum type and install the adjustable valve. But, I'll check pressures first.

As mentioned the First step is to establish what pressure you are able to generate. I prefer to start at the master first and then proceed to the caliper as air in between or a bad master can have you chasing your tail. I like to see 1800 PSI or so in a hard panic stop. There are a ton of variables involved but I have found that number to be a good reference point for a standard type system.

If the pressures are good your next step is pad compound. We have had to go to a more aggressive pad compound on more than one of SSBC's systems. Hawk brakes is a good place to start. BTW We call them "rotor eaters" LOL

Their tech support leaves a lot to be desired, typical response is you have air in the system, Then after providing them with measured numbers at the master, caliper and pad (their head spins) they then ask how did you measure the numbers, With Gauges

Their response then is, Your the only one that has had this problem, SURE

Keep us posted

I've had my SSBC kit on my Charger since 2005. Initially I too complained about the increased pedal effort to try and get the thing to stop with the A body disc master they supplied.
Ran it like that for 2 seasons. Got frustrated and bought the correct Bendix booster & disc brake master. Night & day difference.

Send it back and use the stock factory stuff, like most people would suggest

So the prob with their kit is the master and or the booster?

Ok, I figure this out. Before I installed this kit I asked SSBC if I could use the stock Disc/Drum proportioning valve, and they said yes. I wanted to use this becuase it is a cleaner installation and you don't have to try and fit the adjustable valve in-line with the rear brakeline. I did drop the master cylinder size from what they provided (1-1/32") to 15/16" and brake performance was better, but not ot my liking. I was finally able to measure caliper pressure (the calipers have a very long bleeder valve; needed a special fitting) and caliper pressure was only about 600 psi with my wife pressing on the pedal. I swapped in the drum distribution block and installed the adjustable proportioning valve and with the valve adjusted to the halfway point, brake performance was better, but still not completely happy with it. Pressure was up to 750 psi. Limiting the flow to the rear brakes, pressure is now up to 1000-1100 psi and the car stops like it should.

I did check the service manual and it appears the 4-piston caliper brakes use a drum distribution block with a separate proportioning valve, compared to the one-piece Disc/Drum distribution block/proportioning valve that I got from RightStuff. I think the latter may have been used on the single piston caliper cars where the valving is different from the 4-piston caliper brakes. I like the SSBC kit because they are using the original style calipers, they own the rights to produce it and wheel fitment isn't and issue. Anyway, I'm happy with the brakes, but I'll probably keep the 15/16" master cylinder for better pedal feel.

Thanks for the replies and help with this problem.

You swapped the prop valve & with the smaller MC all is good now?

Yes. Need to do some more road tests. May go back to the bigger master cylinder if lockup is a problem.

Did you adjust the prop valve in or out to get the higher pressure to the calipers?

Have you tested the pressure at the rear brakes to see what the pressure there is now?

Counterclockwise (out) to get higher pressure. Haven't measured rear pressure.