We have some old (2007) Schmitz fridge trailers and when we drop them we obviously put the trailer brake on but when pulling away from dropping one they can be dragged about 4 foot till the brake kicks in anybody know why please ? Obviously we lower the suspension on the unit when pulling away but why are they still able to move when all our other trailers stay put ?
What happens is when you drop the red line (without touching the trailer park brake knob) the trailer brakes lock on, using the air in the trailer reservoir, as if you had slammed the brakes on with the foot pedal.
What happens when you pull the park brake knob on the trailer is the air that holds the parking brakes springs off is released.
To prevent damage to the brakes from too much force the system will not allow both the spring and the regular brakes to act together. You will notice this effect if you pull the trailer knob whilst coupled and the handbrake is applied in the cab (although not with some Swedish units) and you won’t hear any air exhausted from the trailer.
It sounds like some problem with this. See if they move at all with the red line dropped but the trailer brake pushed in.
As I type this O.A.D king will be on google researching ,and after hours of research he will appear Friday to inform you that you are talking - - - - - !!! 
Obviously once again discredited, he will go off on a tangent and have a rant about something which has nothing at all to do with the thread 
I look forward to Friday 
Own Account Driver:
See if they move at all with the red line dropped but the trailer brake pushed in.
With the red airline disconnected the trailer doesn’t move but always had the trailer brake pulled out so can’t answer that part of the question. But it’s strange as it will let you drag the
trailer about 4 to 5 foot but no more. There’s talk of us having to choc them now to be safe when dropping them.
I don’t work on trailers and as a rule don’t get involved in stuff tat I cant give 100% answer on …O.A.D etc know more about trailers than me ,though it may be that the trailers are slow to exhaust the air that holds the spring brake in the off position.Possibly Quick Release Valve…Why it affects all the trailers I don’t know …Get one in to the workshop ,and stick gauges on the chambers and see if they are holding pressure
Sounds like they are not getting a roller brake test on PMI.
On some units you can push the handbrake down and the opposite way to release which sometimes exhausts air from the trailer. Can you try doing that before dropping and see if it makes any difference
norb:
I don’t work on trailers and as a rule don’t get involved in stuff tat I cant give 100% answer on …O.A.D etc know more about trailers than me ,though it may be that the trailers are slow to exhaust the air that holds the spring brake in the off position.Possibly Quick Release Valve…Why it affects all the trailers I don’t know …Get one in to the workshop ,and stick gauges on the chambers and see if they are holding pressure
I’m thinking along those lines. Generally trailer parking brakes often don’t exhaust as quickly as service brakes as it’s not that much of an issue for trailers as they will only be applied when the trailer’s dropped.
I wonder if there’s silencers on the exhausts that are all equally blocked with crap as they’re the same age.
I would try just disconnecting the lines and pulling out from under before setting the park brake on the trailer.
Own Account Driver:
I would try just disconnecting the lines and pulling out from under before setting the park brake on the trailer.
I’m surprised to see this advice from you. I did this once and only once - the old trailer I had used a shunt button which didn’t auto reset when you attached the red line. The result was that when I took the red line off and pulled the pin the trailer went for a wander on its own. Proper brown pant moment and something I’ll never repeat again.
On most Schmitz of that age will only have spring brakes on 2 axles , if the brake adjustment is out it may not hold the trailer
bald bloke:
We have some old (2007) Schmitz fridge trailers and when we drop them we obviously put the trailer brake on but when pulling away from dropping one they can be dragged about 4 foot till the brake kicks in anybody know why please ? Obviously we lower the suspension on the unit when pulling away but why are they still able to move when all our other trailers stay put ?
OLD 2007 that`s relatively new
m1cks:
Own Account Driver:
I would try just disconnecting the lines and pulling out from under before setting the park brake on the trailer.I’m surprised to see this advice from you. I did this once and only once - the old trailer I had used a shunt button which didn’t auto reset when you attached the red line. The result was that when I took the red line off and pulled the pin the trailer went for a wander on its own. Proper brown pant moment and something I’ll never repeat again.
It’s how Schmitz advise uncoupling. I suspect in some markets they may not fit hand valves at all.
The experience you describe though was a freak accident with a trailer that was unroadworthy. I would say check park and shunt are pulled out is a procedure best for before coupling. It’s a good practice uncoupling but, in this case it’s established there’s a problem with it.
If they all happen to have the factory original brake chambers on they may just need new spring brake chambers. New set of pads can sharpen up parking spring brake performance significantly also as the extra thickness means the spring doesn’t have to expand as much.
Thanks for all the replies next time I have a Schmitz I’ll have a play with it.