Tandem pins will not retract, lack of air pressure?

I know this post is old but I have an issue to where I pull the knob out, pins will retract in but knob won’t lock and pins slide back out. Someone has to hold it out while tandems slide, then they release and pins lock back in place.

 

Just wedge something in next to the valve to hold it out
A Philips screwdriver might work.

 

sorry I should have clarified, I was called out to this job and they’re just having me replace the valve.

 

I have had this happen to me, but only when I forget to pull the brake valves in the truck. I was taught to set the trailer brakes by pulling the yellow knob inside the truck and then go pull the knob next to the trailer tandems. Maybe that is what you are doing and still having the problem. I'm not sure.

 

The yellow knob on the dash applies the parking brakes in the tractor. You want to pull the red knob on the dash for the trailer brakes.

I agree with you though about air still being supplied to the trailer. That’s how they are designed to work, that way when you release the trailer spring brakes to go down the road the pins (should) automatically lock.

 

Oftentimes you need to charge the air in the trailer for a few minutes first to fill that air tank. First thing I do when hooking a trailer, as soon as the lines are hooked up, i push in the red knob to charge the trailer while I crank up the landing gear and do the walk-around stuff. This builds up the air, but it sounds like your valve may be bad if that doesn't work.

 

You need to hold the knob in the out position with vicegrips. Then slide tandems and remove the vicegrips when done. Use that method until you can have the assembly replaced.

 

Won't do any good if there is insufficient air to actuate the mechanism. If there is enough air, then that would work.

 

A new emergency valve on the trailer is what you seek.

When you pull the red knob in the cab, the spring brake side on the trailer is venting too slow or not at all. That's why the slider pin release won't stay out.

 

Reread the post I was replying to. He said the pin retracts the pins but will not remain out. I gave him a way to hold it out while sliding.