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Well, this was one of the final items in my laundry list of preventative maintenance and repairs for my 2005 G500 Grand Edition I acquired recently.
I purchased the G knowing the differential lockers were not functional. The truck has 69K miles and the previous owner never used them.
Prior to starting the vacuum system troubleshooting, I changed the TC fluid, front and rear diff fluid, and flushed and bled the hydraulics (also added braided extended locker lines as I added an ORC/Koni lift).
For the vacuum system, I first confirmed there was no vaccum being supplied to the center lock by pulling the hose at the TC and testing pressure. I used the diagrams from fourbyfourclub to check vacuum starting from the vacuum pump side. Confirmed manifold pressure, then worked my way to the reservoir in the FL wheel well and into the switchover valve block on the firewall, teeing off each segment and verifying vacuum. To my surprise, I discovered a leak at a the rubber Y connector located underneath the brake booster. This line comes from the reservoir/vacuum pump segment, feeds through the FL wheel well, and into the firewall area routed underneath the brake booster, (it's in an extremely confined space and hard to see). The small plastic connector in the rubber Y was split in half (labeled and circled, #510 in attached diagram).
After replacing this and verifying vacuum in the rest of the system, I took the truck out on a dirt road and tried to engage the lockers, and fortunately they all worked! Center, rear, and front! Engaged and disengaged without any problems. Super excited knowing these work and can't wait to exercise them on the trails!
Kudos to you! MBWorld should award half gallon jugs of Permatex Orange Pumice HandCleaner to G owners that DIY projects like yours! What's next?
Agree! I totally ran out and had to resort to spraying Simple Green on my hands at one point. I'll start a new thread on what's next, and perhaps a retroactive post of everything I've done since purchase.
The center is locked with vacuum, the front and rear use hydraulics, so try a fluid flush and bleed of the hydraulics if you have not already. You may not have any problems with vacuum if your center is locking.
As for the vacuum parts I used, here are links from fourbyfourclub:
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