Scarebird conversion still spongy?

[JLeather]

I've had the Scarebird kit on my truck for a couple hundred miles now and I can't get it where I want it in terms of pedal feel. Everything is new, I'm using all the recommended parts including the m/c. I've also put a new booster on the truck, new rear brakes/hardware, new lines, etc. The pedal feel is spongy and uncertain. I'm currently running an aftermarket drum/disc non-adjustable proportioning valve. I'm about to try a wilwood adjustable proportioning valve instead to see if maybe I'm putting too much to the rear brakes, but I don't think that will improve the pedal. Anyone been through something similar?

[Conrad]

I have the opposite - but obviously my setup is different.

I would guess there is air in the system. With the proportioning valve, it is very difficult to get air out of the rear system completely. I used my MityVac pump with a common bleeder setup to finally get the brakes bled completely. It was a PITA.

On mine, I have a dual-diaphragm booster, with not much pedal travel on my setup. I have braided lines, which make things 'harder' if you are looking for that feel. Though I am about the swap out the braided lines for regular lines when I swap in the dropped the axle. I will probably get custom braided lines when I figure out the length I need.

[JLeather]

What calipers are you running and what bore m/c?

[Conrad]

What calipers are you running and what bore m/c?

I bought a pair of GM NOS calipers off eBay. Track Hawk performance truck brake pads from Tire Rack. Super tight fit putting the calipers and pads on for the first time.

The booster/master combo is from Pirate Jack in Asheville. Booster is a dual 8” and MC is a tad over 1” bore. https://rover.ebay.com/rover/0/0/0?mpre ... 2166556364

I just saw that Pirate Jack is selling the “Ram Man” conversion now also https://rover.ebay.com/rover/0/0/0?mpre ... 3190621293

[JLeather]

I'm running the 8-lug setup so it uses 1994 Ram 2500 front calipers. Those would originally have had a 1 1/4" bore MC according to RockAuto. I'm running a 1 1/8" Disc/Drum MC from a 1972 D200 with power brakes, which should result in more pressure at the fronts at the expense of a slightly softer pedal. I pulled all the brakes apart this week and the rears were obviously working well, but the fronts seemed not to have been receiving much pressure. They were barely bedded in, with very little wear on either side of the front rotors. I'll re-bleed everything again, and then maybe try a different prop valve. Currently I'm running a GM-style aftermarket disc/drum prop valve. It was a major pain to bleed because it has that safety shuttle inside that kept trying to block off one brake or the other. I may change to a Wilwood adjustable prop valve without the shuttle if nothing else works.