1969 Roadrunner 4-wheel disc brake conversion - weak brakes

[biomedtechguy]

The only non-power brakes I've driven are the manual 4-wheel drums on my '66 VW Bug. However, that is a far cry from the system you are installing. There definitely is a more mechanical-feeling connection with the VW's manual brakes than the other cars I've driven.

Oh I have 6 years experience driving my Roadrunner that I am writing about with manual brakes. The first modification I made was a "Right Stuff"/Dr. Diff front drum to disc brakes conversion, BUT they have never been right for more than a few days or a week at a time. I've had a number of "ah-HA!" moments where a part or hose section or fitting was discovered and replaced and I just knew that was what was causing trouble all along...and then as always, soft pedal, pedal moving closer to the floor, and unreliable braking.
The master cylinder round plastic caps on the system Cass aka Dr. Diff sold me HAVE ALWAYS LEAKED, and he even sent out a pair of thicker caps that we thought may have fixed the problem, but NO.
The last time I thought a major problem was discovered, the hose that goes on the rear axle and has the metal junction block was the suspected culprit, I had it replaced and the lines bled again. Went and picked up my car and the pedal was high and stiff. I thought I had finally got it fixed, but over the next week, every day it got worse and worse.
So there won't be ANY part, piece, hose, or tubing from my existing system remaining in my car when the Wilwood goes in, and I expect it to be the PERFECT braking system.

 

[rdbird9]

Well it turns out the master cylinder pushrod needed quite a bit of adjustment (about 2 turns out) and the brakes feel a ton better. The pedal pressure point is much higher now and it stops much quicker when you really stomp it. I wouldn't call this totally solved but probably like 80-85% of where I feel it should be. I still want to get the car up in the air and look for the shuttle valve chtampa referenced above. Also I noticed while I was driving the car during the pushrod adjusting procedure that the idle was too high at a tick over 1000 rpms in drive when warm. The car is new to me and I guess in all the excitement of driving it I never noticed the high idle. I adjusted it down to around 750 in drive warm, which also requires less pedal effort to hold at a stop.

 

[70chall440]

I have done several of these and what I have discovered is that a single diaphragm booster will work usually but it comes down to the MC bore sized and the combination valve (aka proportioning valve). I use a 15/16" bore MC and a combination valve designed for a disc/disc setup.

 

[chtampa]

Well it turns out the master cylinder pushrod needed quite a bit of adjustment (about 2 turns out) and the brakes feel a ton better. The pedal pressure point is much higher now and it stops much quicker when you really stomp it. I wouldn't call this totally solved but probably like 80-85% of where I feel it should be. I still want to get the car up in the air and look for the shuttle valve chtampa referenced above. Also I noticed while I was driving the car during the pushrod adjusting procedure that the idle was too high at a tick over 1000 rpms in drive when warm. The car is new to me and I guess in all the excitement of driving it I never noticed the high idle. I adjusted it down to around 750 in drive warm, which also requires less pedal effort to hold at a stop.

The shuttle valve is inside the distribution valve.