Attention: TDR Forum Junkies 
Superdawg
TDR MEMBER
I was lucky to get my family together and spent a few days in Yosemite before Christmas. We were able to get a couple days hiking about eight miles each day. With a storm forecast coming in and not wanting to deal with potential snow or black ice in the early morning, we headed out just after dark on Dec. 23. I was pulling my 5th wheel for a combined weight of about 18k. Just before I headed into the Wawona tunnel, I lost 90% power. Fun fact: The tunnel has one lane each direction, is 4,233' long and is uphill the direction I was going. I was committed for the tunnel. I dropped to low 1 and floored it. I was barely able to reach 10mph, kicking out a bit of black smoke (understatement). No boost on the gauge. Parking brake off. After what seemed like a very long drive we made it out of the tunnel to a large turnout.
I grabbed a flashlight and began to look for issues. I checked all the boost lines and they appeared intact. Inspecting my Pacbrake PRXB, I noticed the air operated piston was extended which indicates the exhaust brake was activated (should only activate when off throttle in forward gears). My assumption is the electric solenoid failed, not releasing the air holding the piston extended. This left the butterfly valve in the exhaust closed, blocking off all but a small portion of the exhaust coming out of the engine. It was kinda hot after that run.
I released the air line at the solenoid which let the piston retract, opening the butterfly valve blocking the exhaust.
On the road again, sans Pacbrake, driving the mountain roads towards Oakhurst. After a couple miles of mountain roads, I heard a pop. Pulled over and checked the trailer tires. After I looked at one side, the obvious occurred to me and was confirmed by a look under the hood. My trusty Pelican flashlight that has been with me for 15 plus years died a glorious death. I had left it on top of the valve cover earlier to work on releasing the air line. After the short drive, it fell off, onto the hot exhaust manifold. Both lithium cells exploded, rendering my favorite light deceased. Forturnately, the engine compartment is mostly metal and survived just fine.
Today, I tested the solenoid and it (and piston) seemed to operate just fine. I replaced it anyway with a new solenoid and kept the old one in the truck for a spare. Maybe a glitchy solenoid, on it's way out? Maybe the piston jammed? I did notice the piston was installed with the air line facing down, making it impossible to lube with oil. I removed one side and spun the piston 180 degrees (air intake facing up) and lubed the orifice. Seems to work fine. Not even sure how long I have had the PRXB, maybe 15-20 years? Love it.
I grabbed a flashlight and began to look for issues. I checked all the boost lines and they appeared intact. Inspecting my Pacbrake PRXB, I noticed the air operated piston was extended which indicates the exhaust brake was activated (should only activate when off throttle in forward gears). My assumption is the electric solenoid failed, not releasing the air holding the piston extended. This left the butterfly valve in the exhaust closed, blocking off all but a small portion of the exhaust coming out of the engine. It was kinda hot after that run.
I released the air line at the solenoid which let the piston retract, opening the butterfly valve blocking the exhaust.
On the road again, sans Pacbrake, driving the mountain roads towards Oakhurst. After a couple miles of mountain roads, I heard a pop. Pulled over and checked the trailer tires. After I looked at one side, the obvious occurred to me and was confirmed by a look under the hood. My trusty Pelican flashlight that has been with me for 15 plus years died a glorious death. I had left it on top of the valve cover earlier to work on releasing the air line. After the short drive, it fell off, onto the hot exhaust manifold. Both lithium cells exploded, rendering my favorite light deceased. Forturnately, the engine compartment is mostly metal and survived just fine.
Today, I tested the solenoid and it (and piston) seemed to operate just fine. I replaced it anyway with a new solenoid and kept the old one in the truck for a spare. Maybe a glitchy solenoid, on it's way out? Maybe the piston jammed? I did notice the piston was installed with the air line facing down, making it impossible to lube with oil. I removed one side and spun the piston 180 degrees (air intake facing up) and lubed the orifice. Seems to work fine. Not even sure how long I have had the PRXB, maybe 15-20 years? Love it.
