My park brake “yellow button” on the dash would leak some times until I turned it a little bit. I could make it leak by pushing the knob down or up or to the side. Very noticeable leak. I removed it, cleaned it, polished the inside, and greased it after replacing the very worn “O” ring. The easy job which only costs a few pennies because I carry a full “O” ring suitcase. Now I cannot even make it leak.
Dismantling requires forcing out a pressure pin (holds the yellow knob on the shaft) which I replaced with a stainless flush nut bolt for easy removal. Wyatt 1996 U320 40′
I had the same problem with my dash control park break leaking down overnight. I found your post on the “fix” and followed your instructions for removal. I also found a repair kit made by Haldex Midland part# 281126k – valve repair kit at Heavy Duty Truck Parts Online, Brake Parts, Light & Medium Duty Truck Parts, It has both “O” rings and the other parts for a complete rebuild. Easy to replace and reinstall and I believe it’s not leaking anymore. I did find another leak underneath by the steering column where the 60psi pressure switch is mounted to a “T” connection on the air lines. I tightened the small bolts where it connects to the “T” and I believe the leak is gone. It’s easy to get to and the photo shows where it is. Pierce Stewart told me that a leakdown of 10psi overnight is okay and hopefully this will do the trick.
I still need to get a stainless flush nut bolt for the knob to complete the job.
These kinds of DIY repairs build confidence in non-mechanics like me. Jerry and Cindy Maddux 1993 U300 36′