Just did some work on truck-only 325,000 miles and still going strong! Replaced front wheel bearings, alternator and bled all brakes. Fluid in each line and no leaks. Brakes are spongy and sink, is it time for a master cylinder? If this is the case I would think I would see some leaks.

Any help appreciated!

Cheers

 

Yes most likely a bad master cylinder. Replace it. They leak internally.

 

Need more info to make a correct diagnosis. Why did you bleed the brakes? Was the pedal spongy before doing this? Are the rear brakes correctly adjusted? How's the e-brake? Tight, or does the e-brake pedal go all the way to the floor? The correct way to adjust rear brakes and the e-brake is to first loosen the e-brake cable adjustment, then adjust the rear brakes by turning the adjuster screw at the bottom of the assembly. You can do this throught the hole in the backing plate or with the drum off. After the rear brakes are properly adjusted (spins with the drum on, by hand, but not too tight) then the e-brake cable can be tightened back up until the e-brake pedal has good tension but not tight enough to pull the brake shoes when not engaged. As long as the drum still spins you are fine. Now you can try re-bleeding starting at the right rear then left rear then right front then left front. If you think the master cylinder has gone dry at some point, you might want to bleed the master cylinder first, by loosening the brake line fittings on the side of the master cylinder while a buddy presses the pedal. 2-3 squirts out of each fitting will do. Once the system has been adjusted and bled, you should have a good firm pedal. If the master cylinder is bad, the pedal will feel firm at first but will slowly sink all the way to the floor when pushed and held. This will be more obvious if you sit there with your foot on the pedal and then kinda vibrate yout foot slightly while pushing. If the pedal starts sinking to the floor, not just an inch, not just soft and spongy, all the way to the floor, the master cylinder is bad. A lot of times they will leak out the back of the cylinder and run down the booster but not always.
After all this, if the pedal is still "spongy", not sinking to the floor, put a clamp on the 3 brake hoses, one on back one on each of the front hoses. Press the pedal, if the pedal is rock hard, the master is good. If not the master is bad. If it's hard, while pressing, have someone take one of the fornt clamps off, the pedal will soften a bit, then take the other front clamp off, the pedal will soften a bit more, then the rear clamp. If you notice one clamp caused the pedal to fall more then the other's, that is the area to look. Might be that brake hose, or the caliper/wheel cylinder etc. Or you might even still have an air bubble in there somewhere that can only be forced out with a power bleeder.

Hope some of this helps

 

Thanks for help---Back brakes are fine--bled them, thought it might help-was changing front wheel bearings at the time, so it was no problem.

Shopping for master cylinder today and going to re-place-has original on it.
Have read about a sensor on rear end, but do not think that is a problem!

Again---Thanks

Cheers