On my 01 1500 4x4, I am getting now and again loss of brakes, more often than not. If I drive down the road, my brakes will go completely to the floor and they will come back if I let up on them. Sometimes if I push them down right away again it will work fine then other times it will go back to the floor again. If I push the pedal down fast it will most of the time apply brake pressure and then once i let off it will start all over again.

I have replaced the master cylinder about a year ago. I wa having a somewhat similiar problem. I could pump the brakes then and they woudl build up and hold but if I was at a stoplight they would slowly bleed down. After replacing the master cylinder they worked fine. Now Im having this issue. My fluid is slowly going down as well but very minutely just below the line in almost a month of using it. I havent seen any wheel cylinders leaking on the back or calipers on front. No fluid on ground.

can someone help me with this. Im lost with it now. I dont know what to do change the master cylinder again or booster.

ALSO Is there any bigger brakes out there that you can upgrade to for my oversized tires. 315/75 16. I would like to make a little better braking. I have standard factory oem on there now.

 

If I understand correctly, the problem your having is that you loosing fluid? Is so, as a precaution, I'd change the wheel cylinders. There cheap, so why not. Then I'd bleed and re-bleed the brakes. It could be that you still have air in your lines. One way to check and see if you have a bad brake booster (which I doubt), is to pump the brakes with the key of and build up pressure. See if it holds that pressure. Then turn the truck on and the pedal should go to the ground. I've actually gotten 3 faulty rebuilt Cardon Master Cylinders in a row. Followed by 1 bad Dorman MC. Just my luck. My 2 Dorman works just fine. Look up 1 TON Wheel Cylinder mod...and welcome to the DF.

 

your original problem with the master cyl is the normal, classic failure, where the o-rings begin to allow pressure bypass, and pressure seeps away.
example - you hit the brakes and initially they are soft, but you pump them a couple of times and they firm up. also - sitting at a red light with your foot on the brake and the pressure slowly bleeds away. a couple of pumps firms them back up. also - no brake fluid is actually lost.

so - do you think this is the same thing, or are you actually losing fluid. as suggested, check capliers and cylinders for signs of leaking - black, excessive dust, or maybe even wet. maybe spray them off good with brake cleaner and recheck in a few days. i'm guess its possible for them to fail, but i've never replaced a brake booster...

also - just give them a good bleeding. that never hurts, unless you brake a bleeder.