oTruck brakes

[Furniss]

Truck seems to be building excess pressure in brakes, builds up to 12bar and then blows and sees to leak off down to about 9 when it triggers compressor again, seems like a sticking regulator/unloader ?
pretty sure it used to hold a steady 10 ish unless lots of demand.
is it servicable, clean it etc - I have no experience with them.
there seems to be a bit of oil about, perhaps an odd spot on mudguard i havent noticed before...

 

[V8Druid]

Truck seems to be building excess pressure in brakes, builds up to 12bar and then blows and sees to leak off down to about 9 when it triggers compressor again, seems like a sticking regulator/unloader ?
pretty sure it used to hold a steady 10 ish unless lots of demand.
is it servicable, clean it etc - I have no experience with them.
there seems to be a bit of oil about, perhaps an odd spot on mudguard i havent noticed before... View attachment 82904

don't recognise the 'shape' of that, but the unloader valves I am familiar with (trucks and cranes) were usually rebuildable/cleanable - generally though it was cheaper to buy a new unit than faff with a rebuild kit and time to do it
that looks to be a drier and unloader - tried changing the filter ?

 

[Furniss]

don't recognise the 'shape' of that, but the unloader valves I am familiar with (trucks and cranes) were usually rebuildable/cleanable - generally though it was cheaper to buy a new unit than faff with a rebuild kit and time to do it
that looks to be a drier and unloader - tried changing the filter ?

changed it myself in 2023 - the garage who serviced truck and sorted adblue didnt do it this time
i have a filter on order

 

[hiluxman]

So it's constantly building air and blowing off?

Let it blow off and switch it off see if you can hear an air leak. Also knock the park brake off, I had similar and it was an air leak on the park brake side but it'll not show with the brake on.

 

[Furniss]

Its had an occasional leak on the park brake side up in cab - goes for weeks and is fine then an odd day or 2 hear it.
but dont think this is related tbh - it suddenly started building excessive pressure, i took this off to clean it out as it was completely choked as you can see, this being choked may of led to s**t getting in maybe ?

anyhow to test i left it off and let it build pressure and blow off, after blow off you could feel and hear steady continuing air flow under this, i guess that should shut off completely after blowing off but like I said i have no experience with this setup.

 

[hiluxman]

Its had an occasional leak on the park brake side up in cab - goes for weeks and is fine then an odd day or 2 hear it.
but dont think this is related tbh - it suddenly started building excessive pressure, i took this off to clean it out as it was completely choked as you can see, this being choked may of led to s**t getting in maybe ?View attachment 82938 anyhow to test i left it off and let it build pressure and blow off, after blow off you could feel and hear steady continuing air flow under this, i guess that should shut off completely after blowing off but like I said i have no experience with this setup.

On occasion I hear a very faint air leak from the apu when switched off like you've described. But only rarely and its nothing that'd cause the pressure drops your seeing.

Also as you, I'm not mega clued up on them. Fortunately lad who inspects my truck is.