Brake issue

[vkjar]

Ok so I just had my rover in the shop getting some work done before winter really sets in while I was out of town working.

The master brake cylinder was replaced.

Having picked up and drove the truck around town for a day or two. the pressure started building in the brake system and the pedal was becoming very hard with little movement. Parked the truck to pick up some stuff from NAPA. upon leaving the brakes were fully engaged, the pedal was rock hard with no movement. the only way I could get out of the parking lot was relieve some of the pressure by bleeding off some break fluid.
I then had to do this again just to get home in a Walmart lot as the pressure was building up again.

back to the shop it went figuring it was something blocking the fluid in the MC

picked it up the shop said everything looked good in the MC, bleed everything again and the truck drove great for a few more days till today when the pressure built back up again.

a new MC is on the way

OK so could there be any other causes for this or is it just a faulty MC?

any suggestions would be helpful thanks

[SafeAirOne]

Sometimes little nuggets of rubber from the inside of the flex lines can come off and lodge in an orifice in the system and act like a check valve, allowing fluid to push past in one direction, but block fluid return in the other direction.

[carl k]

If the master cylinder pushrod is adjusted too far in, it doesn't allow the fluid to flow back into the master when you take your foot off the pedal. You might slack off the pushrod and see if that eliminates the problem.

Carl K.

[bpj911]

master cylinder

I have had both masters i replaced not work with the way the pushrod was adjusted when i removed it. Both didn't release properly. I would suspect that is your issue since you just had the master replaced. It's a simple adjustment to back off the lock nut and give it a bit more play. I have also experienced what safeairone said before though and that's a possibility of course though since you just had your master done it seems the problem might be over there. At my house I have found that the last thing i fixed is usually the issue...

[vkjar]

I had figured it was something blocking the MC causing the issue. but nothing was found. I will look at the push rod.

it is just odd that everything works great and then all of a sudden the brakes pressurize and lock up.

thanks for the info.