Hi everyone and thank you in advance for the help!

I've been driving for many years but I've done little on the maintenance side by way of brakes. I leave that to someone else. One of my coworkers encountered an anomaly with his trailer parking brakes. It's a newer trailer (within the last 4-5 years). It seems that they occasionally do not hold. It's an ABS system (obviously) but I don't know if that can be a factor. Service brakes are normal and the parking brakes have been normal to this point. One day he locked down the trailer only and it slowly started creeping backwards.

Any insight is appreciated in diagnosing this!

-Steve

First thing I would check is brake adjustment it could be a bad pod also is the brake pod damaged, bent, dinged, dented, etc?

Is it creeping forward because the air ride was lowered/deflated after the trailer brakes were set? That will cause "trailer creep".

They were supposed to have checked it when it was turned in. I have no way to check it now but we are still curious to any and all reasons for why this would happen. Thank You!

That was my first thought as well but it indeed went backwards. It's a spring ride wagon that was fully loaded and on pretty flat ground. I am curious however if the ABS systems of today are more complicated and present more opportunities for anomalies like this.

i bet one or more of the spring brakes chambers are broken and/or misadjusted brakes.

I doubt the ABS has anything to do with it, they're two separate systems. I'm wondering if the valve is failing, is there a big psshhhhh from the back of the trailer when the red button is pulled out?

After the trailer supply red button has been pulled (trailer park set). Chock the wheels. Go underneath and remove one of the Emergency/Park air connections from the spring brake chamber...cautiously. There should be NO air pressure in that line.