First I had checked the vacuum was switching over at the solenoid which it was. What I hadn't checked was if the vacuum switched over completely or not.
I then jacked the rear wheels up, put the car in 4H and neutral and flipped the DL switch. I then turned the back wheels which did not engage the diff-lock and the wheels kept turning in the opposite direction to each other.
I then disconnected BOTH the pipes at the diff and applied vacuum to the engage side of the actuator (see fig A) and turned the wheels which then locked. I applied vacuum to the disengage side of the actuator which then disengaged the DL.
From this I was able to determine the problem was the vacuum solenoid (see fig B). This time I removed both tubes, felt for vacuum when the switch was at the off position, there was at the disengage side of the solenoid. Then switched to engaged and felt again. This time, there was vacuum at the engage and disengage side of the solenoid. I suspect this did not allow the actuator to disengage so that it could engage.
I took the solenoid out and tried to clean it as much as possible. I sprayed WD40 in the side which was faulty which pushed a lot of dirt/rust out if the solenoid. I repeated this a few times until there seemed to be no more dirt and left it overnight. The next day I repeated the process a few more times just to be sure. I then reinstalled the vacuum solenoid to test it. At first it was still pulling vacuum through both engage and disengage while the switch was on DL engage. I toggled the switch a few times which then checked again. Finally, there was no more vacuum from the disengage side when the DL switch was set to engage.
I have not yet tested if DL engages just because I had just finished it all this afternoon and don't have dirt nearby to test it on. I will post back here if I experience any further problems.
- fig A
- fig B
The TL;DR:
Make sure both solenoid ports have vacuum but only 1 at time. If both ports suck at any point try clean them out.
