2004 Zetor 7341 trailer brakes

[Guineafowl]

These tractors have a valve to supply air from the compressor to a port on the back for trailer air brakes, in response to hydraulic pressure from the service brakes. I think the front brakes are somehow reliant on the air supply as well:

The hydraulic part was leaking, so he joined the blue pipes together, but this locked the front brakes up, so he released the brake unions and has been pottering about his smallholding with no brakes for ages. Retired farmer and neighbour I’m trying to help out.

We’d rather just bypass the valve, since he doesn’t need the trailer brakes, and replacements or even seal kits are stupidly expensive. It’s leaking air as well, which is needed for the 4wd and diff lock.

The problem is, the pipework is more complicated than in the diagram. One air port appears to have an air feed from the cylinder (on the other side), but is connected via a T piece that returns to the other side again, to a valve above the cylinder. The other air port goes to something that looks like a cylinder, which looks like it has a hydraulic master cylinder bolted to it. Hard to see.

The only other thing is, there’s no cable attached to that lever on the back.

 

[m_c]

The blue pipes shouldn't be joined together, they should just be blanked off.
Each pipe will be a feed from the individual side brakes, so the air valve still gets actuated when only one pedal is pressed.
Joining them is likely causing pressure to go where it shouldn't, and causing the front brakes to stick on.

And my head hurt trying to understand the air pipe routing.
I'm guessing by cylinder, you mean reservoir?

The routing could be some implementation of a parking brake, however the system could be adapted so it works in a fail safe manner, in that you need to apply pressure to release the brakes, not apply them.

How many trailer air connections are on the rear of the tractor?
To meet EU specs, service brake should work by applying pressure, whereas parking brake should work by releasing pressure, although truck trailer brakes don't typically have spring brake chambers, they rely on additional air reservoir(s) to activate standard brake chambers should parking brake pressure be lost.
It could be a variation of an old single line system, however given the age, if it had air brakes, I'd expect it to meet the full air brake spec

However, there are some variations in terms of agricultural use, especially if the tractor is not a full UK spec, so things might not work quite how you expect them to.

 

[Guineafowl]

The blue pipes shouldn't be joined together, they should just be blanked off.

Yes, sounds sensible. Will do.

And my head hurt trying to understand the air pipe routing.
I'm guessing by cylinder, you mean reservoir?

Mine too, and I can (sort of) see it in front of me. Yes, it’s some sort of reservoir with what looks like a brake cylinder mounted on the end. It’s hard to see, right under the cab, behind the tank, and covered in lots of shyte.

How many trailer air connections are on the rear of the tractor?

Two, one like a male hydraulic QR fitting, the other flatter with a screw thread. Only one connected to the valve above the main air reservoir. This is hard to see as there’s a big bird’s nest tucked in there that I think he wants to keep.