My son has a 71 Valiant that we converted to manual disc brakes including the following:

1) Swap to 4-piston KH setup
2) Replace metering block with later model having proportioning valve built in.
3) Replace master cylinder with new unit having 15/16" piston
4) Replace pushrod with adjustable unit
5) Bench bleed MS prior to install

The problem is that we cannot get rid of a spongy pedal. We've tried gravity bleeding, normal pedal bleeding, using a pump, etc., but it seems like air is still trapped somewhere.

Suggestions?

You got the calipers mounted correctly, with the bleeder screws at the top?
You still have air in the system, that's for certain.

Yes, both bleeders are up top. Definitely still has air. We can get the pedal to firm up with a couple pumps.

Also, forgot to add that this is a Manual (no booster) setup.

On a toughie (& this one sounds (very) close!) I cap the MC with a pair of brass plugs from the Edelman cabinet at your parts house (1/2-18 or 1/2-20 or 9/16-18 or 9/16-20 I cant remember which) & if the MC is good (& bled out) the pedal will be rock solid with virtually no travel then I hookup the frontmost port for the rear brakes & see it is still solid so far. What I would do on this one is unscrew the next to the firewall MC line for the front discs & cap that MC port & see if they (the rest of em) are solid.

Thanks! I have a set of those I used to bench bleed the MC, but I will try as you suggested to see if we can isolate the problem.

What brake fluid did you use? dot 3/4 or 5?

Rears still drum? Are they adjusted up?

Try this method.
At this point you have nothing to loose.
Worked for me a time or two, when i was professionally wrenching for a living, when i had a problem child in the brake system.

I call this method "reverse bleeding."

Let me explain what to do.

Get yourself one of these little "squirt cans" and put a length of rubber hose on the end of it.
Fill it up with brake fluid.
Take out some brake fluid from the reservoirs in the master cylinder.
Hook up the hose to the bleeder screw rt rear. lt rear, rt front, lt front, and squirt fluid into the system, back up into the master cylinder.
You are essentially forcing fluid and any air, back up into the highest point of the brake system, which now is the master cylinder, in the engine compartment.
Keep removing fluid out of the master cylinder, if you don't mind it overflowing all over the place.
Might just work for you, who knows, give it a try.

You appear to be right up the street from me in CH, as I'm on the Sunrise Blvd, side of Rancho.
Good luck.
Jim V.
hemi71x

Oh, one other thing to mention after i got done writing all of the above.
How are your rubber flex hoses on the rt, and lt, front, and the at the rear over the axle?


****Rears still drum? Are they adjusted up?****

As others have already stated, this is also very important.

^^^ Jimmy I'm gonna try that one of these days

That is the best and cheapest way.

If air in the system was the problem, more pumps wouldn't make the pedal firm. Sounds like your rears are way out of adjustment and using up the initial shot of fluid when the pedal is first depressed.

Thanks for all the input. To answer a couple questions:

- Using DOT 4 brake fluid (system was emptied out with new MC)
- Still have 8" drums in the rear
- Rear drums are adjusted to just touching the shoes

Jim- I really like the oil can idea. I will give that a try! I'm just off Sunrise @ Antelope

Looks like we have now solved the problem. As it turns out, there were 2 problems:

1) Rear brake not properly adjusted (not sure what happened as they were adjusted right after we installed the disk brakes)
2) The nut on the pushrod (brake pedal end) was too tight causing the pedal to stick high and low.

Thanks for all the help in solving this!