question Zetor Proxima 6441 Brake issue?

[cowboyhan]

Hi!
I have an '05 Proxima 6441. The brakes have gotten very bad. The left brake will not even build pressure when pumped, and the right brake requires several (2-4) pumps before it engages.
I cannot locate any external leaks anywhere in the system. Also the brake fluid level has not changed since I replaced it and bled the system per Zetor instructions 1.5 months ago(first attempt at addressing issue).
I replaced both slave cylinders about 6 years ago.
I'm thinking the masters must be the culprit, but hate to buy the parts and do the labor without some real knowledge. Is it possible that faulty master cylinders could create some sort of a bypass situation resulting in an inability to build pressure when brake pedal is applied?

 

[ixer0]

It sounds like the master cyls.
Before you change them I would check the brakes are adjusted correctly, make sure the master cyl push rods are adjusted correctly and bleed them up as per the book and see how long they last.
Mike

 

[cowboyhan]

It sounds like the master cyls.
Before you change them I would check the brakes are adjusted correctly, make sure the master cyl push rods are adjusted correctly and bleed them up as per the book and see how long they last.
Mike

Thank you sir! I will read up on push rods before asking for more detail. I appreciate the insight.

 

[ixer0]

Push rods need just a tiny bit of play, with pedals locked together.

 

[cowboyhan]

Push rods need just a tiny bit of play, with pedals locked together.

Thanks to you both for your insight. I checked the free play. Definitely not the culprit. For the time being, both brakes will get some pressure after being pumped repeatedly, but lose it as soon as released.
Gonna swap out the masters.
For learning's sake: When the masters go bad like this, is it possible that there is a bypass sort of situation? As I noted originally, no external leaks showing and no real loss of fluid happening.
Also it looks as though it got wet around the masters at some point as there is some dust collection surrounding that area where they mount to the firewall, but nothing wet now.
Thanks for the education!

 

[cowboyhan]

Just an update in case anyone else encounters these issues. I followed the instructions in the manual for adjusting the brakes as well as the push rods on the master cylinders and it solved my problems! I don't know enough to explain it, but my brakes have been solid for over a week now.
I did have to fiddle with the push rod adjustments a few times to get things consistent, but now it looks as though I'll be returning the master cylinders I ordered.
The symptoms were consistent with master cylinder failure (the brakes had to be pumped to build pressure and would lose all pressure within seconds of being released), but there were no leaks and I was not losing brake fluid.
Thanks Mike (ixer0) for answering and for getting me thinking before I just swapped out parts. I appreciate the help !

 

[ixer0]

Thanks for letting us know and glad youre sorted. I