Hi, can anybody help me with a problem with a 1999 Scania 144 530 tractor unit with disc brakes? When I apply the secondary brake I am getting a permanent leak from the exhaust port on the hand brake valve. As soon as I click onto the hand brake it goes. I have replaced the hand brake valve in the cab and also the hand brake relay valve underneath the battery box without any success. I am a bit suspicious of it being a brake chamber feeding it back up to the valve. Has anyone experienced this problem before that can advise me? Thanks John.
Your suspicion sounds pretty sensible to me, certainly often is the case when trailer valves are exhausting that the valve’s fine and the air’s coming back up from a chamber. Is there a brake test result disparity on the drive axle? - also have a look and see if either of the chambers have got the original chassis paint on. Unfortunately tractor unit chambers often not cheap.
The back axle has had 2 new brake chambers on it earlier in the year, when we brake tested it there was a difference between both readings and I have also fitted one new one onto the front axle, I have pinched up the secondary feed pipes on the rear chambers to stop anything coming back up but it is still has a serious leak.
The different readings will be down to one sides pads/disc being slightly more efficient than the other, maybe a caliper sticking slightly. Could it be sods law you have changed 3 out of the 4 chambers and the one left is at fault?? ( Assuming it has spring brakes on both axles ) I was going to suggest kinking the secondry feed pipe but you have done that already. Did it have the fault before you changed the rear chambers earlier in the year ■■
i have only just bought the truck recently and found the fault when i was checking it over for the mot i would think out of the 3 remaining its the old off side front i think i will take off pipes crimp up pipes and see what happens then
is the motor metallic blue?
when you have done all that with your chambers!! if that doesnt solve the return leak got to the back of your cab and check the fog and leccy plugs “not suzzies” has these plugs been moved or replaced “you wont no” as one of the wire in these plug sockets sometimes get put in the wrong location and for some reason it causes the air to go backward when pressing the brake/hand brake… like its a burst pipe i am sure its a white wire■■? but as normal as philberg will tell you i am wrong and talk donkey woolacks 
,
but it could be a chamber as they say… if this wire is wrong you get a good old whossssssssing sound tho!!
Sockets are wired up starting from top and going round clockwise, White ( earth ) , Black ( left tail ), Yellow ( left ind ) , Red ( brake ), Green ( right ind ), Brown ( right tail ) , Blue which is a spare and goes in middle.
Ive found some Scanias the yellow and green are the opposite way round.
As for them been wired up wrong and it backfeeds through handbrake who knows ■■?
philberg182:
Sockets are wired up starting from top and going round clockwise, White ( earth ) , Black ( left tail ), Yellow ( left ind ) , Red ( brake ), Green ( right ind ), Brown ( right tail ) , Blue which is a spare and goes in middle.Ive found some Scanias the yellow and green are the opposite way round.
As for them been wired up wrong and it backfeeds through handbrake who knows ■■?
Thats 
why your learning all my expertise ov the mighty scanias
the silver 144 one used to do it but it was more on the foot pedal it turned out it was a wire in the socket what was wrong A.
Yer you have found the yellow and blue to be opposites “lol” or should i say i found out that they were after you sent me on my way one sunday evening and everyone calling me a james hunt "what you mean i am one " for indicating wrong ways for two days
Your expertise lol, I’ve forgotten more
philberg182:
Your expertise lol, I’ve forgotten more
aaaahhhhhh, bless…
a lovers tiff
shuttlespanker:
philberg182:
Your expertise lol, I’ve forgotten moreaaaahhhhhh, bless…
a lovers tiff
And you go hook right off aswell
globby 480:
shuttlespanker:
philberg182:
Your expertise lol, I’ve forgotten moreaaaahhhhhh, bless…
a lovers tiff
And you go hook right off aswell
does that mean i can’t have any more when you get them?
shuttlespanker:
globby 480:
shuttlespanker:
philberg182:
Your expertise lol, I’ve forgotten moreaaaahhhhhh, bless…
a lovers tiff
And you go hook right off aswell
does that mean i can’t have any more when you get them?
I no what you do want in fact your a SYB come to think off it aswell jesus i am surrounded by these tight SYB