Hi
Tried a search which raised more questions than it answered.
It started coz I was looking for a good explanation of the functions of the air lines, preferably a block diragram. Still looking.
That search brought up a thread about split coupling.
A mention was made to novices. I assume that I’m not alone in that the training/test was merely a shove this in that.
Ok so air holds the brakes off.
I assume the brakes are held on by a spring and the air forces it open via a piston arrangement.
So putting the trailer brake on releases the piston. Is there any reservoir on the trailer?
The shunt button releases the brakes? So this means there must be a reservoir?
Split coupling… Putting the lines on first before securing the pin? Why do it?
What are the dangers? Could it be you do it if you’re only reversing?
On reading it says " risky…should only be used on a unit that is close coupled owing to a deep pin" (para). Do what?!
Can pushing the air line on release the brake on the trailer? Or will it release it if the handbrake is not applied. Thus the importance of the trailer brake.
Soz this is so long winded.
Cheers BB
Baby Bear:
Hi
Tried a search which raised more questions than it answered.
It started coz I was looking for a good explanation of the functions of the air lines, preferably a block diragram. Still looking.
That search brought up a thread about split coupling.
A mention was made to novices. I assume that I’m not alone in that the training/test was merely a shove this in that.
Ok so air holds the brakes off.
I assume the brakes are held on by a spring and the air forces it open via a piston arrangement.
So putting the trailer brake on releases the piston. Is there any reservoir on the trailer?
The shunt button releases the brakes? So this means there must be a reservoir?
Split coupling… Putting the lines on first before securing the pin? Why do it?
What are the dangers? Could it be you do it if you’re only reversing?
On reading it says " risky…should only be used on a unit that is close coupled owing to a deep pin" (para). Do what?!
Can pushing the air line on release the brake on the trailer? Or will it release it if the handbrake is not applied. Thus the importance of the trailer brake.
Soz this is so long winded.
Cheers BB
Ok so whats the question ■■
You have put info you found but cant forsure tell where your question is.
Baby Bear:
Hi
Tried a search which raised more questions than it answered.
It started coz I was looking for a good explanation of the functions of the air lines, preferably a block diragram. Still looking.
That search brought up a thread about split coupling.A mention was made to novices. I assume that I’m not alone in that the training/test was merely a shove this in that.
correct - in depth explanations of the workings are too much and an unnecessary filling of the trainees head - only the safety aspect needs to be doneOk so air holds the brakes off.
correctI assume the brakes are held on by a spring and the air forces it open via a piston arrangement.
I believe it is something like thatSo putting the trailer brake on releases the piston. Is there any reservoir on the trailer?
I think the reservior is reserved for the unit as I have never drained one on a trailerThe shunt button releases the brakes? So this means there must be a reservoir?
Too technical for meSplit coupling… Putting the lines on first before securing the pin? Why do it?
cannot get lines on after pin as there is no room to do so betwen unit and trailerWhat are the dangers?
forgetting any part of the procedure as, to most, this is not the usual way of couplingCould it be you do it if you’re only reversing?
if you mean coupling & uncoupling then it is done on both using the procedure in reverseOn reading it says " risky…should only be used on a unit that is close coupled owing to a deep pin" (para). Do what?!
A ‘deep pin’ is where the pin is located further towards the rear of the trailer as opposed to near the front - nearer to the front = more gap from unit to trailer when coupled upCan pushing the air line on release the brake on the trailer? Or will it release it if the handbrake is not applied. Thus the importance of the trailer brake.
You got it - very important is that trailer brake and unit handbrakeSoz this is so long winded.
no prob - I hope I got it all correct - if not I’m sure someone else will do soCheers BB
Sorry Nick it was all a question. Badly put together though
Cheers ROG been off to the link.
Does the trailer brake ever fail i.e would the check ever include a shunt?
Cheers BB
Baby Bear:
Sorry Nick it was all a question. Badly put together though
Cheers ROG been off to the link.
Does the trailer brake ever fail i.e would the check ever include a shunt?
Cheers BB
I’ve personally never known a trailer brake to fail.
Once the unit has connected with the pin on a couple up then 2 gentle short tugs forward to check that it is secure is a must - is that what you meant by a shunt 
I meant for the purpose of checking the trailer brake but I sort of answered my own question.
Cheers me dears
BB
Baby Bear:
I meant for the purpose of checking the trailer brake but I sort of answered my own question.
Cheers me dears
BB
Handy when you do that 
- just don’t argue with yourself…
… and lose 
But when I win the other me losses. So we call it a draw. 
Baby Bear:
Ok so air holds the brakes off.
Only down to a certain pressure, at which point they release again. That’s why it’s important to put the parkbrake on when you drop a trailer - even prolonged swaying in the wind can force the air out of the system on an air-sprung trailer, at which point anyone coming to couple up will just shove it backwards.
Pulling the parkbrake on will set the springbrakes as a backup. There is such a thing as an automatic springbrake system, most notably fitted on Fruehauf trailes, which applies the spring when you pull the red line, but I wouldn’t rely on it unless you are sure you know what you’re looking at.
It’s also illegal to park on a public road purely “on air”, so if you drop a trailer outside a customer then, again, make sure you pull that button. (Or ratchet the handle, although that’s rare now) It takes so little time and effort that it’s best just to make it a habit to do it every time.
(If you park on a road coupled up, don’t worry, the tractor unit will have a spring brake which keeps you legal, and comes on automatically with the handbrake.)
I assume the brakes are held on by a spring and the air forces it open via a piston arrangement.
Basically, yes, although there does reach a point, see above, where air alone will no longer hold the brakes on. You’ll have to get someone more mechanically minded than me to explain the ins-and-outs of it to you.
The “piston” bit basically involves each wheel having a “brake chamber”. This looks like a vaguely spherical metal block which is obviously bolted together in two halves. In between those halves is a diaphragm, and it’s that diaphragm which activates the brakes themselves. If you ever go to pick up a trailer and no matter how much air you rev in the brakes won’t come off, and there’s a loud, persistent hissing coming from behind one wheel, it’ll be the chamber that needs replacing. They bolt on and off quite simply and are replaced as whole units at the side of the road, so once you get a fitter out it’s a 20 minute job.
So putting the trailer brake on releases the piston.
Putting the trailer brake on activates the spring brake. It’s a seperate mechanism.
Is there any reservoir on the trailer?
Yes, trailers have their own tanks mounted on the chassis.
The shunt button releases the brakes? So this means there must be a reservoir?
Yes, but again only down to a certain pressure. This is where it gets confusing, because if the trailer has automatic spring brakes, the shunt button will not release them if the pressure is too low.
Split coupling… Putting the lines on first before securing the pin? Why do it?
Because it is fuel efficient to run with the trailer as close to the unit as possible, plus with a reefer (fridge trailer) the fridge unit will make the gap even smaller. If the gap is too small to physically fit yourself into in order to connect the lines, split coupling is the solution. ALWAYS PUT THE PARK BRAKE ON FIRST!!!
What are the dangers? Could it be you do it if you’re only reversing?
The big danger is that the trailer parkbrake isn’t on, so when you attach the red line the whole lot moves and you get crushed. Hence ALWAYS PUT THE PARK BRAKE ON FIRST!!! NO exceptions.
I don’t really understand what you mean with the second question…?
On reading it says " risky…should only be used on a unit that is close coupled owing to a deep pin" (para). Do what?!
Whether it’s risky or not is debateable. There’s no reason why it would be, done properly. The risks are all down to potential driver error. However, it is a faff, so only do it when you have to.
We used to have a load of trailers that, without going into unnecessary detail (unless you want me to) had the lines end up 2.5ft under the front of the box. Split coupling was one way of doing it…But if there was enough air in the trailer for the shunt button to work, we just used to tug-test, then drive forward and jacknife the unit 'round at 90 degrees to give better access. That will work with any close coupled trailer where the lines attach at a reachable level.
“Close-coupled” means the trailer, when coupled, is close to the back of the unit. A “Deep pin” refers to the position of the kingpin in relation to the headboard. If you look underneath, you’ll see it jutting down, and that some are further back than others. They can also be moved on some trailers, although that’s a workshop job.
If the pin is too deep for your fifth wheel and you try to couple, you’ll end up smashing your rear lights on the landing legs, and the back of your cab on the headboard, so if it’s an unfamiliar trailer CHECK. (I won’t get into sliding fifth wheels here, that’s a whole other thread) The best way to check is either by eye (with practice), by measuring (very grubby!), or by going back a little way and stopping to have a look before ramming it “home”.
Can pushing the air line on release the brake on the trailer? Or will it release it if the handbrake is not applied. Thus the importance of the trailer brake.
Basically, yes, if the handbrake isn’t on.
Soz this is so long winded.
Cheers BB
Not half as long-winded as my answer! 
Lucy:
Not half as long-winded as my answer!
You are female so that means you can answer more elequ elouq elekwant - oh [ZB] - BETTER than me 
Cheers Lucy
Took a bit of thinking about but got what you’re saying. That was my lack of knowledge not your explanation!
Cheers to all
BB
ROG:
[
I’ve personally never known a trailer brake to fail.
That’s because you are too young perhaps, it certainly wasn’t uncommon in the old days with ratchets.
The debate on the merits/dangers of split coupling has been argued both ways on here by experienced drivers. Myself I think it is so easy to become dangerous that it should only be done if there is absolutely no other way, not just for convenience.
Spardo:
ROG:
[
I’ve personally never known a trailer brake to fail.
That’s because you are too young perhaps,
The debate on the merits/dangers of split coupling has been argued both ways on here by experienced drivers. Myself I think it is so easy to become dangerous that it should only be done if there is absolutely no other way, not just for convenience.
You are right - I was forgetting about those [ZB] ratchet ones - and yes, I had probs with some of those