Redbull Addict - 10/5/2011 1:39 AM

I was casually following this thread but this past weekend on a trip to the sierras, I noticed that my rear and front lockers took noticeable longer to engage and on one occasion unlocked. I actually replaced my vacuum pump a few months ago. I also noticed that the lid for the hydraulic reservoir holding the brake fluid was cracked with a 2mm gap all around. The fluid looks dark.

Redbull Addict - 10/5/2011 8:27 PM

Thanks for the pdf, Dutch!

Yea, the dealer had a new cap in stock, now I just need to figure out whether to do it myself (I'll need the equipment) or take to a mechanic.

W5YK - 10/6/2011 5:45 AM

I had the same thing with my filler cap - a nice crack all the way round almost. I wonder why that happens?
In a pinch, you can use a normal german brake filler cap like any VW/Merc and others use.

fernweh - 10/30/2011 6:24 PM

A diff lock vacuum system update.


Karl

DUTCH - 10/30/2011 3:48 PM



Sehr gut, mein Herr!

fernweh - 10/30/2011 7:20 PM


Just in case nobody knows how the system is supposed to work, I have printed that page, where it reads: pumps runs, until vacuum reaches approx 550 mbar.

Karl

DUTCH - 10/30/2011 5:10 PM



Only when the engine is not running. When the engine is running, the pump runs continuously. Stupid, but that's the way it is designed.

W5YK - 10/30/2011 6:38 PM

Karl, I had the same check valve go bad on my G500. I could not get the hoses off it, so I bought new hoses and new check valve. Those check valves do not like getting dust and dirt in them, which is exactly what they receive if there is a leak somewhere, sucking all the available dirt into the system.

Mercedes says in one of those slides that the pump runs continuously with the engine running. I think they must have selected the pressure switch setting at a point where the engine never makes that much vacuum when running, but the little pump can make it if the engine is stopped. As you said, the power is always supplied to that little pump (if center locker selected) regardless of engine running or not. There is no logic in the switch pack for this, just the pressure switch.

I will stop before I get confused. I wish they had made it simpler.

fernweh - 10/30/2011 9:11 PM



I'm so very sorry, but that isn't correct.

Karl

DUTCH - 10/31/2011 4:43 AM



MB, apparently, seems to disagree with you. Seems strange, but that's what they describe. See attached.

fernweh - 10/31/2011 9:41 AM

Interestingly, the vacuum pump ON & OFF cycling because of the pressure switch, would only occur when the engine is off, but ignition is on and the center diff lock switch has been activated.

Roly - 10/31/2011 11:23 AM

Karl,
When you connect the second pipe to the white connector on the vacuum pump and the engine is running , the vacuum in the pressure switch is "reduced " to that of the engine which is not sufficient to turn off the pump. And the engine will never make enough vacuum to switch it off, thus it runs always with engine on.
On my 1999 the white line to the engine is not connected at the factory, so the pump switches off.
Pleased that you have found you leak.

4x4abc - 10/2/2011 7:00 PM

HELH81953021 arrived!

Looks identical to the original Hella pump. Only the electrical connectors are 2 instead of 3. Its missing any Hella labeling (could it be a China knockoff?)

But anyway, it works just fine for $76!