Started with a soft brake pedal, so I checked for leaks, none. I installed new front pads, bleed the brakes worked ok, then developed a soft pedal again. So I changed the master cylinder. Sam out come, an eventual soft pedal again. Bleed it a few time with a soft pedal again. NOw bleeding seems to work for a while and then the pedal goes to the floor after 50 miles of use.

It almost seems as if the brake fluid is not getting into the master cylinder from the rreservor. Allthough I obviously use alot of fluid when I bleed the brakes.

Any Hlep?

 

Try rebuilding yor calipers and cylinders they are probably bad.
What type of truck do you have?

 

I'm sure you probably have already done this, but check and dbl-check the tightness of the connections. Sounds like there is a slow small leak somewhere in the system. Are you losing any fluid each time you check the reservoir level?

 

The master is not completely dry on the outside. Although the reservoir seems to be full. Can air be getting ito the system from a very small leak? MIke

 

Just a different thought, may not be useful, but I've has sports cars (old) where the brake fluid at the calipers would overheat and boil and cause soft pedal. Had to bled afterwards to get the feel back again. The same might conceivably also happen if your brake line is getting too hot from something like the exhaust. Did you recently remove a heat shield or install headers, anything like that?

 

Nothing really changed for heat to the brake system. Now the calipers and wheels cylinders are old, but there are no leaks down there. The hose from ther brake fluid reservoir to the master cylinder seem to leak a bit. But the reseervoir shows no drop in fluid level. So if it is leaking there, it was not alot. I just tightened the hose clamps and will bleed the brakes again.

 

If a hose "leaks a bit" it will let air in. Also a component might not leak fluid but could allow air into the system. I just spent 6 days trying to bleed a system with a defective new caliper.

 

The brakes on my 97 were the same way. Finally, I had the rear wheel cylinders replaced. Stops great now...well, as great as one can expect with 285's. (especially when it came stock with 225's!)

 

I tightened up the hose from the brake fluid reservoir to the master cylinder, and bleed the brakes again. this time i did the pass rear first, like someone suggested. I pumped alot of fluid through to make sure I got all the air(especially if my leak was at the master cylinder). Brakes are firm again, they are usually better after a bleed. Now we will see if it holds. Thx for your help. Mike