brake issues

[fireguyfire]

Again troubleshooting my 68 power steering car after a full resto, and I still have ineffective braking. I still have the original power booster, and I have a brand new master that I bench bled myself. I converted the car to front discs (Wilwood) and a front disc brass proportioning valve block that mounts just under the master (nice system). I had almost no brakes when first tried, so I read threads here and adjusted the acorn nut on the end of the booster pushrod so that I now have obvious flow of fluid in the new master when the brake pedal is pushed to the 1/2" mark as recommended; SO I am happy that everything is right there.
The pedal feels normal and has vacuum assist (its not hard or soft) but I just have little braking; enough to hold the car at idle, but not enough to stop it when its moving. So my questions would be, what to do next. Should I rebleed the brake system? How can I tell if I have enough vacuum at the booster? Should I look at re adjusting the rear drums to make sure they are right?

[Ghoste]

It is a disc brake master correct?

[fireguyfire]

Yup; the whole system was a front disc brake conversion kit which included new front brake lines to bring the lines up to the bottom of the master, the master and the 1 piece brass block proportioning valve. The actual front disc set is a Wilwood set.

[Ghoste]

Does the Wilwood kit use a GM booster and master?

[fireguyfire]

So I have good vacuum at the booster with the engine at idle; I will put the gauge on it tomorrow, but I can tell its good.
Is there a way to confirm if the booster itself is working or faulty?

[Windsor]

Sounds exactly how my '40 was acting when I did my swap (took out old frame mounted single bore and put in a firewall mounted 7" booster with corvette dual master and firewall mounted pedal). Back brakes would hold the car at an idle, fronts were pointless, and didn't stop for squat.

[fireguyfire]

What did you do to fix it?

[Windsor]

Residual pressure valves.

[fireguyfire]

Can you enlighten me on where you put them, and what they do please?

[ACUDANUT]

Residual pressure valves.

Huh ?

[Cooter]

Residual pressure valves hold very small amount of pressure on rear drum brakes to keep pedal from feeling spongy. Most master cylinders already have them installed.

OP, I assume you have driven the car enough to 'seat' pads right?

[Windsor]

As Cooter said. They are mostly used for vehicles with the master below the wheel cylinders (frame mounted). However, they are also used on firewall mounted systems when the master is unable to move enough fluid to engage the brakes completely. On drum brakes, a 10lb RPV is used to help prevent air from being drawn in on release and allow for less fluid to be needed to engage. On disc brakes, a 2lb is usually used (though I do know some guys who run 10lb) to help keep the pads against the rotors.
Look up the specs on your master to find out if it came with them. If not, the RPV goes in the brake line, preferably as close to the master as you can to keep as much of the line under pressure as you can.

[Windsor]

Forgot to mention. There are types that thread into the master and there are inline types

[fireguyfire]

Okay; I am now thinking that I do have a vacuum problem, or at least a vacuum problem as well. I cannot get my headlight doors to operate even though I have a new can, headlight switch and have confirmed that the plumbing is correct. I know the actuators work as when I rebuilt the grill I could open and close them by sucking on the hose pretty easily. I also noticed that when I switch the setting from heat to defrost in the car, it does not change, and I seem to remember that some of the gates in the heating/cooling box were actuator activated as well. Seems like way too much of a coincidence to not be an issue.
Anyway, bought a vacuum gauge today and I am reading 7 at the PCV valve going into the brake booster, as well as 7 at the end of the larger line that supplies vacuum to the reservoir can.
Is this enough vacuum to work the actuators and the brake booster? If not, how do I fix this problem?
I did put a mild comp cam in my 383 and it has an Edelbrock performer carb on top, but in my research it seemed that these should not affect vacuum much at all.
Is there a way to put an outside source of vacuum into the headlight system to see if it works?

[Windsor]

Question. How is your pedal? I mean, is it soft, firm, does it feel soft for a portion of travel and then firm up?
Also, would I be correct in assuming that it is a tandem master cylinder with the rear port feeding the front brakes and the front port feeding the rear brakes.

[fireguyfire]

Kind of a cop out, but the pedal feels pretty normal; not hard or soft it is just that with the pedal fully depressed I have very little "bite". I adjusted the acorn nut on the booster so that I have obvious brake fluid flow in both resevoirs in 1/2" of pedal travel, or perhaps maybe even a little less so I know that is not my issue.
When depressing the pedal it even makes that "tchhhhh" sound like when you get a power assist. I am wondering if I have a bad brake line bleed, and I am also going to double check my rear drum settings. Failing that, the only other thing I can think of would be a faulty proportioning valve, which is brand new and built for this front disc conversion system.

[fireguyfire]

I think I may have figured out my problem; I set my timing with the vacuum hose connected to the distributor!! Tomorrow I will do it correct, pull and plug that line and set the timing to 7 1/2 degrees; hopefully I see a corresponding increase in my vacuum into the normal range!

[fireguyfire]

I now have a vacuum reading of 15; is this going to be enough to run my brake booster and headlight doors?

[Back N Black]

should have no problems with 15 vacuum

[fy469rtse]

How much free travel in pedal also, you adjusted the threaded ball that pushes master cylinder ? Also like cooter said brakes will be crap feel to them until pads run in,

[fireguyfire]

Okay; I have rebled the entire brake system and went through it with a fine toothed comb. Did get some more air out of the system, and I have confirmed everything is 100% plumbed correctly.
I now have brakes that function, but I have to really push hard to get them to work, and have a firm pedal. I am now thinking my power brake booster is the issue, as I have a vacuum reading of 15 going to the booster.
Is there a good way to test the power brake booster to for sure confirm it is not working? If it is not (which I now strongly suspect) can I get a new or refurbed one?

[fireguyfire]

Check that; took another vacuum reading after plugging off all discharges from the vacuum tree and I have a reading of 12; is this enough to run the power brake booster if it is functioning?

[fireguyfire]

figured out that I have enough vacuum to run my headlight doors which were not working either; plugged off all 3 leads off of the vacuum tree off of the intake manifold; took the line that feeds the headlight cannister and jumped it to the front "T" fittings and the headlight doors opened; switched it over to the actuator "T" that has the yellow stripe and they closed nicely too. I'm hoping if I have enough vacuum to run the headlight doors I will have enough to run the brake booster; opinions?

[hemi68charger]

vacuum of 12 should be fine too........ I have about 11/12 in the new Hemi I just put in the Daytona and it stops the car fine........

[fireguyfire]

What is the best way to test the power brake booster to see if it is working?

[tan top]

What is the best way to test the power brake booster to see if it is working?

get in the car , with the engine off , pump the brake pedal  5 or 6 times   , then with your foot still hard on the brake , start it up ! if booster is working correctly  brake pedal should sink a little 1/4 to 1/2 inch may be little bit more ,( its not set in stone ( lot of variables ) , but you should feel the pedal sink a little on start up ,

also nothing to do with the brake booster now , ive just learnt something new in this thread    
  I always thought only drum brake cars need a residual pressure valve , due to the drum springs retracting the wheel cylinder pistons , soon as brake pedal is released , & next time you press the brakes with out the valve the pedal will be momentarily spongy for one pumpish.  & discs never needed a residual valve only a brake proportioning valve