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Pac Brake Problems…

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Hello everyone,

On my 2000 Dynasty, I have realized my Pac Brake is not working. It took me a while to realize it because the transmission would shift down and my silver leaf controller indicated the pac brake switch was on.

Anyway, I have verified the pac brake itself actually works; unplug the wire - put 12v to the connector (with air in the system) and it works. One wire is ground - The ground is good - I am just not getting the power. 

I looked in my wiring diagram (yes I know how lucky I am to have it), and on the “ABS/Transmission interface” page, it shows the pac brake foot switch - going to the transmission shifter plug harness and the Vehicle interface module (transmission).  Then coming out of the vehicle interface module a red wire goes to the pac brake relay 87.  

I cannot find that relay - it is not in either the front or rear bays… 

Does anyone know about that or other details I may have missed…

one other mystery (to me), The wiring diagram references a “engine retarder”. My engine (ISC-350hp) does not have an engine retarder built in - I have seen this relay in the rear elec box. But the diagram has this with the ABS stuff…



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I have a 2000 windsor, pac brake with footpedal.  Exhaust brake was working every now and then. I tested the foot switch with a test light, push down light comes on let off light goes out. Found the relay in the side dash cover,  left side of drivers seat. Tested that one and the two on the outside compartment drivers side. All tested good with a multi meter. Decided to test the foot switch again with a multi meter and the ohms was jumping all over the place. Replaced the foot switch with a toggle switch and it works perfect now, only couple 4 hour trips but it worked. 

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Our pac brake quit working also.  It was completely frozen open back in the engine bay.  Took it as far apart as possible cleaned it then lubbed (lubed) it with permatex anti-seize as it will remain as a lubricant up to 1400 degrees, much higher heat than the pac-brake special lube which breaks down at around 500 degrees.  Worked for a week or so then quit working.  Pulling my hair out and banging my head againt solid objects did not seem to make it work.  Checked for signal at pac-brake solenoid.  What?  No signal.  Tested foot switch and showed good.  Still no signal to pac-brake solenoid.  Started to trace wires from foot switch, thought they went through floor behind the switch mount.  Tore the plywood out to which the foot switch was mounted.  Did not go through the floor.  LO and BEHOLD, the spade connectors had come apart behind the mount.  Evidently they had come loose from someone pulling on wires in the left side console.  Connected them back together and did away with the foot switch and replaced with a rocker switch on the left console.  Working great ever since.  No more problems! Activate the switch whenever needed and pac-brake automatically kicks in when I take my foot off the acelerator.  Good luck and God Bless 

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