F700 lucas girling park brake issue
 

Hey all, working on an F700 with the infamous Lucas Girling brake system. my issue is the pump for the park brake will lock up intermittently when stepping on the brake pedal. this is whether you are driving or sitting in the shop. Tried it with park brakes released or set. when its NOT locking up, i can feel a slight pulse in the pedal every 20-30 seconds, when it does lock up, its right when the first pulse comes. Tried a new pump, but to no avail! I can get it to stop by releasing and setting the park brake in quick secession, but it will come back. I'm leaning towards the park brake valve, but wondering if it could also be a problem with the hydraulic relay valve there by the master cylinder?! Any help would be greatly appreciated, Thank you!

Welcome to FTE!

Follow the links in that thread for more background on the LG brakes. Sorry I can't point you more directly on this topic:

https://www.ford-trucks.com/forums/1...tom-truck.html

So, I was able to figure this out. It WAS the park brake valve. Decided to take it off and blew in the return(?) port of the valve and air would come out of the supply port. So, I'm guessing that when the park brakes were released, it would send pressure back through the supply line and would lock the pump up. Hope this helps anybody else that has this similar issue!