1997 1500, 5.9

I am having issues with a soft brake pedal. When I hit the brake pedal, I hear what sounds like a rush of air from the pedal area and I have little to no pedal resistance for what I would guess is about 75% of the pedal travel. Everything in my mind is telling me they need to be bled, but I have bled them multiple times and and I am not getting air out of the system any more. If I disconnect the hose off the booster, the pedal is hard. If the engine is not running, the pedal is hard.

I have replaced:
- Rear shoes and wheel cylinders.
- Adjusted rear brakes
- Front rotors and pads
- both front soft lines
- master cylinder

At times, not every time, the pedal, within the first 25-50% of travel, feels like it is catching on something, but i am not seeing anything around the pedal area that would be causing that. Maybe something with the rod between the booster and pedal? Either way, that shouldn't be causing my soft pedal.

The only thing I havent replaced is the booster itself, but as far as I know, a bad booster would only cause a hard pedal, not a soft pedal.

Any thoughts?

 

If seals in booster are bad, that would cause a soft petal

 

Could that be the air gushing sound I am hearing as well, or is that normal for a soft pedal?

 

I still don't see how a leaking booster would cause a soft pedal....

 

Did you bench bleed the master cylinder before installing it on the truck? If not, there is likely air still trapped in it causing your soft pedal.

 

Yes I did.

 

When you replaced the master cylinder, did you notice any brake fluid dripping off the back of the old master cylinder?

 

Nope, rusty, but bone dry.

 

What procedure are you using to bleed the brakes? Do you have someone working the pedal while you are bleeding each wheel? Are you bleeding the wheels starting with the wheel farthest away from the master cylinder (passenger side rear) and work back towards the closest to the master cylinder?

 

I have a hose attached to each bleeder screw. Hose runs to a bottle with fluid in the bottom couple inches. I crack the bleeder and pump the brakes slowly about 10 times and check the hose for bubbles. And keep doing that until I don't see bubbles anymore. The fluid in the bottom of the bottle keeps air from being sucked back in through the bleeder. I start at the right rear, move to the left rear, right fron, left front. I did that twice,making sure I wasn't running the MC dry.