Poor Pedal on new system - what wrong?

[ChallengerGary]

Okay, on the 72 RR Clone I recently built and sold I installed an all new brake system - we're talking:  power booster, master cylinder, front calipers & pads, and rear wheel cylinders and shoes. I even installed a new distribution block on the rear end.  Well, before I sold the car I told the buyer that I tried bleeding the brakes but could not do it myself.   I had a buddy help me and got them to work but you had to pump the death out of them.  Basically, I told him up front it was not safe to drive yet.   I told him to give me few days to fix it before he came to get the car. Well, as luck would have it, he arranged for the car to be picked up within 2 days of this and I never got a chance to finish the brakes.  He tld me no big deal.  He's now go the car and says that they still cannot get the pedal to firm up. As best as we can tell there are no leaks in the system.  He's even installed another new master cylinder with the same results.  What gives?  Why can't we get these stupid brakes to work right?    

I am thinking maybe the proportioning valve is bad   HELP - I hate selling a car to someone that has problems and I've offered to help by either reimbursing him for expenses related to this or figuring out the problem and getting him the parts he needs.  He's very frustrated (understandably) and I would take the car back and give him a refund if I could but I can't.  Unfortunately, I've already given the money to my mortgage company (I was a little behind).

[422STROKER]

There is a procedure for resetting the prop valve in the Service manual.  Involves turning the car on for the light to come on and such.  I used this when I did mine and it seemed to work.  Also make sure the rear drums are adjusted properly. 

Tom

[Chryco Psycho]

possibly the bore on the new master is too small , the smaller bore will have a lot more travel & softer feel tyo it larger bore reduce the travel & go hard fast

[ChallengerGary]

 Chryco - How/Where do I get a larger bore master cylinder for him?  The one that is on there is the onky one listed for 72 Satellite Series in the O'Reilly's system.

[Bullitt-]

Are you bench bleeding the master cylinder before installing on the car?

[ChallengerGary]

Are you bench bleeding the master cylinder before installing on the car?

Yes, both were bench bled.

[Chryco Psycho]

There was a list in a Mopar mag a couple of years ago of most of the popular MC , I would try something like a New Yorker or Old truck with the cast master & measure the bore , a small change as little as 1/16 in bore diameter can make a huge difference

[ChallengerGary]

Chyrco - any idea what year New Yorker I should try?

[Chryco Psycho]

something in the 72-76 range , they all used the same master in those years

[422STROKER]

So 2 bad M/C's so far?,doesn't add up.  If You used the factory disc M/C then You should be fine.   Do you have enough vacuum?

Tom  

[ChallengerGary]

I just realized probably had a total brain fart when I installed the system.    I swapped 73-up A-Body spindles and calipers for the factory drum brakes and it probably requires a different master cylinder  

Someone please tell me I am right that I was wrong 

[ntstlgl1970]

Do you have to pump up the brakes with the engine off? or only when the engine is running? I would second bench bleeding the master if not done already. Also make sure the pushrod coming out of the brake booster isn't adjusted too long. If there is any preload on the master cylinder when you bolt it on, the pushrod is too long. This can cause the symptoms you are describing as well as the other things already mentioned.

[hemiken]

I just realized probably had a total brain fart when I installed the system.    I swapped 73-up A-Body spindles and calipers for the factory drum brakes and it probably requires a different master cylinder  

Someone please tell me I am right that I was wrong 

Hey Gary,

Yes............ You must change over to a disc brake Master as the drum Master will not work correctly as you already know.

[Chryco Psycho]

 

[Aussie Challenger]

   If you did use the drum master cylinder you should have a better pedal as it would hold pressure on the disc brakes ( not good though ). I have found that you need to come down at least 1/16" on the rear wheel cylinders when going to disc's, the proportioning valve is supposed to over come this problem but I have always reduced the rear cylinder size anyway.
  Is your power booster working correctly? I have had several situations where the booster was for a low vac. motor and therefore it supplied too much assist on a regular motor, the pedal went almost to the floor with engine running.
  Just another thought, have you got the calipers on the right sides, that is with the bleeder at the top?  Ask me how I know that one!!   
  Hope this can help..