Conversion to new mopar master cylinder question - please help!

[chargerfreak]

I'm installing a new lightweight Mopar master cylinder in my '71 Charger. I also purchased the 4 bolt to 2 bolt adapter and new pushrod, which was to long. I cut it down and now the brake pedal is sitting where it's supposed to, but there's a new issue.... Here's the question...With the master and pushrod installed when I push the pedal down it hits the firewall. Is this only because I don't have any line pressure because there's no brake fluid yet? I had assumed that the pushrod should bottom out in the master even without fluid pressure, before the pedal hits the firewall, but now I'm not sure. One thought that I had was that I needed to add an additional spacer so that the master would be farther away from the engine side of the firewall. I'm ready to start hooking up the lines, but as everything is custom because of a line lock and aftermarket proportioning valve I wanted to be certain before bending lines, especially if I'm going to need to add spacers. Any help from you knowledgable guys would be great! Thanks much.

[pishta]

Oops, Maybe you should not have cut it? It was just the straight rod with the eyelet on the pedal mount right? It is a 2 chamber M/C, does the pistons(s) uncover the inlet port when relaxed? as soon as the piston is past the inlet port, you should start building pressure. bench bleed the M/C and you should have some pressure, then install the lines and bleed from the bleeders with a vacuum source. The newer style might have been engineered with a lower pivot point on the pedal that would equate to a longer stroke. I have had an empty brake system pedal hit the floor too, Probably to prevent damage to the M/C piston or antipulse(?) valve at end of cylinder.

[cageman]

Hmm, I have never bought the expensive Mopar setup, but I have installed the alum plastic resevoir on almost all my vehicles and some of my friends too. I used the factory rod on all of them. Maybe the car is a power brake car, so that might be diff, as to where it mounts on the pedal. I just pulled the pedals out of a road runner and it had some weird pivot crap goin on, unlike all the manual brake cars I have.
I wouldnt worry about it bottoming out with no fluid in it. It needs the fluid to keep it from going all the way down. If you had a severe leak, then it would bottom out, but not with a properly functioning system.
I have gotten all of my resevours out of the junkyard, and I make my own 1/4 inch adapter and I use the stock rod, 5$ upgrade. It is a real good master.

[70AARCuda]

Your pedal goes to the floor as if you have no brakes...

Bench bleed the master cylinder before hooking it up to the rest of the system.

I did the same thing last week...new MP brake cylinder...adjustable pushrod too long...cut and rethreaded it...

[chargerfreak]

After some careful examination that's exactly what I did. Cut and re-thread.
Pedal sits where it should.....now to run and bend new lines. Thanks for the help guys.

[viper11]

hi guys
i am planning to upgrade to the alum master over winter but i have power brakes now
i want to swap to manual brakes to help route the turbo exhausts so heres my question: what size bore will work best with manual brakes and do i need anything other than the m/c and adapter??
this is on a 74 440 charger with front 12" and rear 11" disks with a adjustable prop valve
sorry for changing the subject
thanks jason

[chargerfreak]

Hey Jason. Yea, there are two bore sizes to choose from when buying the Mopar Performance Master Cylinder. You definitely want to go with the larger bore as it's specifically for cars over 2800 pounds. The part number is: DCC-5249271.