I have searched other posts, but haven't found an answer to my problem.
Truck: 99 Dodge 2500, rear anti-lock only, 4x4, diesel.
I replaced some rusted out rear and front brake lines a month ago and bled the brake lines as best I could get. Got the pedal to what seemed normal, was a little spongy at first but things seemed good after a number of pumps and overnight. Took a trip longer than around town, 20-30 miles into it and could smell hot brakes (both front equal). Wheels also quite warm. Brake pedal seemed somewhat normal. Didn't have time to check it then, so it sat for a week or so. Brakes seemed normal around town again for a short while. Then, hopped into truck and brake pedal was high and only required very small amount of pressure to stop, brakes were dragging. My immediate thought was to replace the original rubber lines on the front. Thought it odd that both would break down at the exact same time. Replaced the drivers side first. Caliper still sticking some and dragging some. While front wheel was off, proceeded to remove caliper and as I usually do I slowly apply pressure from a c-clamp to push piston back. Piston was not going back as it would in the past, cracked the bleeder screw and then it went back, didn't push it all the way back, because I wasn't installing new pads this time around. Since the piston moved back, I figure the caliper clyinders are not sticking. Caliper slides were cleaned and smoothed out and lubed with never-seez. At this point I re-tried pushing the piston back again, still no go. I then started to crack the brake line fittings from the first one from the caliper up the the aluminum block with the switch/sensor and on to the master cylinder, all this with some pressure applied to the c-clamp. I had fluid squirting out of all the fittings (relieving the pressure). The only thing that seems to be stopping the fluid from getting back to the reservoir is the master cylinder. In all my previous brake jobs the fluid will go back to the reservoir when c-clamp pressure is applied slowly. Is it time for a new master cylinder or have I missed something? Thanks for reading and offering ideas!!

 

Yes, sounds like it could be the master cylinder, since you have already changed the front brake hoses and greased the caliper pivot points with anti-seize (I use brake caliper grease, but anti-seize should work as well). Change the master cylinder and flush the entire system with a good DOT4 rated brake fluid and you should be good to go.

 

Calipers im willing to bet.

 

Id also go with calipers. Cheaper to start there. A lot of stuff in between them and the MC. As in ABS system, proportioning valves and such. Doesn't take much rust/pitting/debris for a piston to stick.

 

If the dust seals on the calipers are breached/broken, I'd replace them. Otherwise, the master cylinder and fluid change are where I'd be going..

 

I am having a similar issue. I live in the mountains and when driving down hill on my way home a few weeks ago my front right break was smoking. I figured caliper was bad so I replaced it. Driving home the same way yesterday I now have both front breaks smoking and a really soft break pedal. If you allow them to cool down they work fine and the pedal is back to normal. I was thinking booster but I hate just throwing parts at my truck. Any thoughts?

 

master cylinder, or soft lines, or junk in the calipers. Booster won't cause them to stick.

 

Any way to test the m.c. To be sure?

 

No 100% way that I'm aware of..

 

Hey everyone! Thanks for the replies! Here is what I've done... Since I could get the back pressure to bleed off (with the C-clamp pressure applied) through all of the line connections back to th master cyl., I felt pretty confident that it must be the MC. Replaced it and everything seems to be working fine now. I think what happened is that when the brake lines blew out and through bleeding, the MC internals went all the way to the end, where they hadn't been in a long time and picked up debris, rust, sludge etc. and plugged up the return ports/path for the fluid to return. Those are my thoughts on what happened. Also, while replacing the MC I found two loose nuts on the power booster lines behind the MC that go to the PS pump, not sure why they weren't leaking PS fluid yet, but tightened them up by probably close to a half turn each. Good luck tylarkin, hope this helps.