I'm having some problems...

My brakes were in pretty bad shape (excessive pedal travel and the spongy feel) so having "addressed" the problem, I'm in even worse shape than before. Here's the order of events and symptoms:

- Replaced original bleeders with speed bleeders on all four wheels (rear drums, front disks)

- Bled the system (alone, which is the purpose of speed bleeders). No air left, as far as I can tell. Clean fluid flows immediately after cracking any of the four bleeders.

At this point, the pedal is stiff (feels perfect) with the engine off, but goes straight to the floor with almost zero resistance or pressure while the engine is running. The brakes do "work" in the sense that once the pedal reaches the floor, the truck comes to a complete, sudden, jarring stop.

- I re-bled the system... Perfect, but no difference.

Upon further inspection, I found that the brake booster check valve was loose and in poor shape.

- Replaced the brake booster check valve. Engine runs better, but no change to the brakes

- Noticed a "wooshing" sound at the fire wall each time the brakes were applied. Found that the noise was coming from the boot surrounding the input shaft of the brake booster (I don't know what the boot is actually called)

- Decided to replace the whole brake booster (only the booster)

- The master cylinder - which is only 2 years old - was secured with a bungy during the booster replacement. No damage to it or brake lines, system was never opened.

- Replacing the brake booster made no difference. No matter how much I fiddled with the length of the push rod, no difference was made.

- Today, I re-bled the system AGAIN, just to be sure. Looks pretty darn good.

That's about where I'm at now. I'm thinking the problem was the master cylinder the whole time. I'm going to replace it tomorrow morning but I wanted to see if anyone had any advice or knowledge to share at this point.

Thanks!

1976 F150. 300 i6. 2wd.

 

I'm also thinking that I may have pushed the pedal to far at some point during the initial bleed and damaged further damaged the MC. ??

 

It sounds like the master should be next. A spongy brake is a symptom of master problems. When bleeding, the master can stroke more than normal. If there is rust or crud inside the cylinder the extra stroke can find it and finish it off.

 

Make sure your wheel cylinders are leaking... But the MC sounds like the culprit. Make sure the new/ reman comes with the bench bleed kit and "bench" bleed it and not on the truck. You shouldn't have to adjust the push rod...