Good Hard Brake Pedal (not running), Lot of Travel with Engine Running

[Fleetw00d]

1992 Accord LX coupe. When I got the car, the pedal went all the way to the floor. The master cylinder was almost empty and full of black "mud" at the bottom. installed the new looking (very clean housing and reservoir) from a 1991 LX sedan, bled all lines until clean fluid came out at each wheel. The pedal was still soft and had too much travel and the engine sped up when depressing the pedal.

Front pads didn't have a lot of material left, so I installed the loaded calipers from my wrecked 93 EX coupe with a lot of pad left. Rebled the system; still not happy with the pedal feel (long travel, but not continuously sinking).

I pulled the MC and realized there was still the old MC to booster seal in the booster and a new one on the MC. Removed the booster to try to check the position of the booster plunger vs. the depth of the plunger in the MC. Math worked out that there was about 0.050" clearance between the booster plunger and the MC piston; unlocked the booster rod and adjusted about 1/2 turn inward although it didn't seem to change the position of the plunger on the MC side. Adjusted the clevis to 4.6 inches per shop manual. Reinstalled everything (with only one good seal between the MC and booster), bled all four wheels (LR, RF, RR, LF); good clean air free fluid at all four wheels. With the engine not running, the pedal pumps up fairly high and hard; but when I started the engine and went to back out the driveway, the pedal travel increased considerably, but eventually stops (not sinking like MC is leaking). All the other threads I searched seemed to involve "sinking" pedals that indicated a MC leak. Should I have not messed with the booster?

Anyone have a cross section of the brake booster or taken one apart with pictures of the internals? I'd like to understand the internal workings better.

[accordztech]

Rear drums out of adjustment. Readjust them and you will gain that initial pedal feel.

[Fleetw00d]

I had the drums off to check the shoe thickness, they were worn but have some miles left. The drums dragged some coming off - so there isn't much adjustment range there, but I will give it a try.

[evil_demon_01]

The pedal goes hard after pumping it with the car off because the booster loses it's vacuum.
After that it is supposed to sink when you start the car - That shows that the booster is working properly.

If your unsure of how it "Should" feel, jump in another CB and try it just to confirm.

[Fleetw00d]

The pedal goes hard after pumping it with the car off because the booster loses it's vacuum.
After that it is supposed to sink when you start the car - That shows that the booster is working properly.

If your unsure of how it "Should" feel, jump in another CB and try it just to confirm.

I know how it should feel and react; I have four other Accords to compare it to. It shouldn't sink as much as it does. I won't get to mess with the rears until later this evening. There may be more of a lip on the drum (making it feel tight when trying to take it off) than it appeared.

Update June 21, 2013:

accordztech, thanks for the tip. I reversed the drums on the hub, ran two nuts down to hold them, then used a heavy duty Scotchbrite disk on my drill to simultaneously rotate the drum and knock down the slight raised edge. That gave me about a turn or so of adjustment on the auto adjusters and reduced the pedal travel with the car running.

So now that the pedal feels reasonable, I finally drove it more than around the block this evening, doesn't feel like I'm getting much braking from the rear, even yanking hard on the hand brake only. I went over the shoe surface with a wire brush and brake cleaner to remove any "glaze" when I had the drums off. I think I have a new set of shoes around, I may put them on for good measure. I should probably Scotchbrite the front rotors and pads to remove any glaze as well.

[1990[H]accordex]

I'm also having this issue fleetwood, my pedal will go to the floor on the first pump, second pump it's where I would consider (good brakes), i've replaced wheel cylinders, master cylinder, front driverside caliper, did the brake booster check (haynes book) and also adjusted rear shoes, and still no help.

[Fleetw00d]

I'm also having this issue fleetwood, my pedal will go to the floor on the first pump, second pump it's where I would consider (good brakes), i've replaced wheel cylinders, master cylinder, front driverside caliper, did the brake booster check (haynes book) and also adjusted rear shoes, and still no help.

Did you bleed all the brakes real well after installing all those parts? How did you adjust the rear shoes (slight drag when installing/removing the drums)? If there is a lip on the drums (like mine) then you get drag when installing/removing the drum, but there is more clearance once the drum is all the way on. If you really want to make sure the drums are cylindrical, take them to a shop and have them turned.

Or, you can spend a lot of time going back and forth. When you apply the brakes in reverse, the extra travel of too much clearance between the shoes and the drum position the self adjuster pawl above a notch on the adjusting screw star. When you apply the brakes going forward, it pulls the pawl down, rotating the screw. Once the clearance is correct, braking in reverse doesn't move the pawl far enough to engage the next notch (until the shoes wear enough to increase the clearance again).