MiN - 9/21/2011 8:29 AM

I've just finished doing a B service on the G55 with the addition of replacing the front CVs, bearings, seals and discs (lovely job) - got the CVs from Eurotruck at a significant saving on the full axle shaft. There had been an intermittant problem with the rear diff lock not engaging swiflty and then dropping out after a few moments. Doing the service gave me the chance to investigate, thinking it may be a fluid or vacuum leak problem.

With the rear axle on stands I turned the ignition on, but without starting the engine, and pressed the centre and rear locker switches expecting to hear the hum of the pump. Nothing. Checked the connections and checked the voltage to the pump and all was ok. Simple conclusion was that it was the pump. Tried a direct connection and again nothing. Disconnected it and took it off and pulled it apart and could do nothing or see nothing to fix.

The solution, obviously, was to order a pump and I managed to get the only one currently in the country. Suffice it to say, the new one worked and the diff locks engaged faultlessly. Why am I making a deal of this? Well, the pump on my 12 year old G500 with 400,100km has never ceased to work and has been used a lot more than the 6 year old 150,000km G55's. Part number for the G55 and G500 is 463 550 01 83. A Hella part made in the US.

4x4abc - 9/21/2011 10:57 AM

Karl,

why not share the source for the little inexpensive pump with us?
would love to get one before mine fails

fernweh - 9/21/2011 3:48 PM

Here's the info:

http://www.sparkfun.com/products/10398

djdinaz - 9/21/2011 5:06 PM

The one on the truck looks very similar to the Hella H81953021 (a picture is in this PDF: http://www.kartek.com/Media/Catalogs/2011/HellaElectricsCatalog11.p... on page 77). It has an operating range of -25 to +96 C, and can be had online for under 80.

djdinaz - 9/21/2011 6:17 PM

http://www.discountfleetsupply.com/helh81953021.html is the first place I saw it w/ a price.

DUTCH - 9/21/2011 2:39 PM



Looks identical to mine. Can you reference an on line source for the "under 80"price?

fernweh - 9/21/2011 5:14 PM

Anybody can confirm, that the vacuum pump runs all the time when the center diff lock is active, is there a pressure switch built-in?

Karl

W5YK - 9/21/2011 8:13 PM



Karl - that is correct, if the engine is running.
If the engine is turned off, the pump will stop after 30 seconds or so.
There is a pressure switch built in. But with the engine running, you never get there.
The vacuum pump is wired in parallel with the center locker air solenoid, there is no separate pin for it on the switch pack.
The 30 second delay after engine off comes from the switch pack I think, not from the pressure switch. Not certain, will check.

shochu - 9/21/2011 7:37 PM
now i kind of wished for the basic cable & hydraulic system of the 460
although i suppose the cable too could snap, as my even bigger handbrake cable snapped a while back

4x4abc - 9/21/2011 9:30 PM

I though along Richard's lines - pump runs when the engine is on and the center diff is locked
wanted to confirm it an hour ago

surprise - my pump is dead as well
more surprise - all diffs locks as they should

engine vacuum?
meaning the pump is not really needed?

Razon - 9/22/2011 1:00 AM

Also, if you could find a more robust design (piston type for example). Rubber membrane just isn't meant to last, but you probably won't be able to beat the cost. (they did the same with the vacuum pumps on the early diesels...first they used membrane type, then they upgraded to piston type)

Also, as a "backup" you guys could run a line from the intake manifold to the pump with an inline check valve (one way valve) (use T connectors at both ends. If you would go the extra lenght to install a vacuum reservoir, you would probably rarely ever need the pump.

Edit: Harald mentioned the same thing while I was writing the reply....maybe it's allready done like that from the factory. Doesn't the manual show a vacuum diagram?