Any ideas?? Brake pedal is firm and near the top when truck is turned off but gets spongy and travels almost to the floor when engine is running.

 

Forgot to mention this is a 1999 4x4. Also, if I pump the pedal once when running the pedal travel decreases a bit.

 

your vaccum booster is probaly going out/ there has to be a leak in a brake line or booster unit. Also can you pump the pedal a few times after the truck is turned off before it gets to be hard to depress.

 

If it is a soft when the engine is running, but stiff when the engine is off, then the booster is doing its job which is to assist in actuating the master cylinder.

It is possible that the master cylinder has become worn or has a leaking seal. It is also possible that there is air in the system.

mikepro, in the future, please put your vehicle information into your signature and attach it to your posts. Also, the edit feature can be used to add more information to your post if another member has not yet replied.

 

After truck sat all night... Not running. pushed pedal all the way to the floor on first push. Second push pedal was right up and firm. No fluid leaks as floor is dry underneath. Note I unplugged the ABS unit a year ago after a third near miss. also changed out the line to the rear brakes a year ago after it rusted out. However pedal travel was fine until a couple days ago.

Okay, whatever it is it has to do with the rear brakes. Pulled out of the garage into snow and only the front brakes applied. The rear wheels were still turning in the snow. Has rear disc brakes so no adjustments that I know of.

 

You may have air in the rear lines. Try going through the bleed procedure again.

 

After bleeding and having to pull end cap off combination valve to manually reset it them rebleed from the master thru the abs unit I now have brakes but!!!! Way too much pedal travel. Looks like have to stock up on fluid and re do the bleed process from scratch to see if I can get more pedal,