Aftermarket Power Brake Problem

[NW Task Force]

I am running an aftermarket under-cab 7" power brake unit that uses the OEM style brake pedal lever that hinges forward and down (just like the stock brake and clutch pedal). I am running disc brakes at all 4 corners. Basically, my pedal does not return back up on its own after pressing the brake. It seems to stick in the partly applied position, therefore dragging the brakes. I can easily take the tip of my shoe and pull it back up and feel the brakes release all the way. Sometimes the pedal will return correctly on its own when I tap the pedal hard to the floor.........????? This brake booster unit is only 1yr old and I have tested it for vacuum (18 hg) and the pedal is hard when the engine is not running, when started it immediately moves down (seems correct). I did a little reading and it seems some hot rodders online do add on "brake pedal return springs" from time to time. This seems like a simple solution, but is it covering up a bigger problem? Anyone else experience this?

[Highsider]

For what it's worth...

http://67-72chevytrucks.com/vboard/s...d.php?t=631478

[DransportGarage]

Well, let me ask a few questions so we can get a better shot at your problem:

1) Did the pedal used to work correctly, or have you always had the problem?

2) How many miles/years are on the brake system since it was retrofitted to 4-wheel discs? (You partially answered this one. 1 year old.)

3) What brand is the pedal/master cylinder assembly, or where did it come from (Wilwood, CPP, Right Stuff, Inline Tube, etc.)?

4) Are you using 2-pound residual valves on both the front and back systems? (They are usually blue.)

5) Is the pedal shaft rubbing the floorboard sheet metal?

6) How much pedal travel do you have with the engine off?

7) Have you bled the system recently?

[NW Task Force]

1) Did the pedal used to work correctly, or have you always had the problem?
Used to work correctly, but returned slow...now it does not return and you have to tap the brake hard for it to bounce back up
2) How many miles/years are on the brake system since it was retrofitted to 4-wheel discs? (You partially answered this one. 1 year old.) Under 500 miles worth of driving
3) What brand is the pedal/master cylinder assembly, or where did it come from (Wilwood, CPP, Right Stuff, Inline Tube, etc.)? The brand is TOTAL COST INVOLVED ENGINEERING INC. I bought it through Zig's Street Rods

4) Are you using 2-pound residual valves on both the front and back systems? (They are usually blue.) Yes, I am running 2lb residual valves on both front & back systems

5) Is the pedal shaft rubbing the floorboard sheet metal? No, plenty of clearance

6) How much pedal travel do you have with the engine off? About 1/4" pedal free-play

7) Have you bled the system recently? No, last time I bled it was during completion of building the brake system, (last Spring)

[DransportGarage]

Well, those are the best possible answers to the questions I asked. My next step would be to call TCI and talk to them. At least they should be a stand-up company with reasonable tech support.

An exception to the quality of your answers might be #6). I understand the free play being 1/4", but what if you put 20 lb. force on it? If it's spongy after the free play you may want to re-bleed the system.

Some systems use either a long or short shaft into the master cylinder and some either use a spacer or no spacer, depending on the system. Go back to the TCI instructions to be sure you installed correctly. (This is probably not the problem since the system worked correctly for quite some time.)

Are you using silicone (DOT 5) fluid? That has less lubricity than DOT 3 or DOT 4, and it's possible you are getting some "sticktion" in the master cylinder itself. The only way to tell that I know of would be to remove the master and actuate it in a vise. If it doesn't return when you plunge it, it has a problem. A remote possibility is a broken internal spring as well, but I'm not an expert.

Personally, I don't think a helper spring would hurt a bit as long as it didn't make the pedal too stiff on the downstroke.

At least this will give your thread a bump so someone else can possibly offer a suggestion or two.

[dwcsr]

Originally Posted by NW Task Force

Sometimes the pedal will return correctly on its own when I tap the pedal hard to the floor.........????? This brake booster unit is only 1yr old and I have tested it for vacuum (18 hg) and the pedal is hard when the engine is not running, when started it immediately moves down (seems correct). I did a little reading and it seems some hot rodders online do add on "brake pedal return springs" from time to time. This seems like a simple solution, but is it covering up a bigger problem? Anyone else experience this?

The pedal is heavy and needs the spring it had originally.

[Joe Pass]

I had the same problem until I used the stock return spring and no more issues...I would have at least 3/4" free play on the pedal.

[Joe Pass]

And I also have rear disc drakes with 2lb residual valves

[NW Task Force]

Sounds like a return spring is the way to go. Where was the exact mounting of the spring, (for reference)?

[dwcsr]

The red is the spring the black is a rod. excuse the drawing

[Joe Pass]

It sounds like You have the same set up as mine and the stock location has been modified with the aftermarket booster/mc placement. I attached the spring to the casted swing arm (topside) http://67-72chevytrucks.com/gallery/...s/DSCN1842.JPG Just behind the brake switch wire is the casted tab to hook spring this picture doesn't really show the rear attachment,but it attaches to the pivot bolt end on the swing arm.http://67-72chevytrucks.com/gallery/...s/DSCN1844.JPG

[Joe Pass]

My truck is low and I can't get a good picture of the spring but I remember that I had attached it to the swing arm pivot bolt because the design deleted the stock rear attachment. The stock return spring is to long so I shortened it after I hooked it on with good tension, around the extra length on the pivot bolt end. You will get the idea once you hook the spring to the swing arm and pulled it back you might find the perfect location for attaching...good luck , Joe

[Highsider]

Been considering a screen door spring.

[DransportGarage]

Originally Posted by Highsider

Been considering a screen door spring.

If it's strong enough it will keep the bugs out...