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00 g500
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Discussion Starter #1
O.K. the premise:

I think it's been suggested that a particular failure mode of the diff lock system (sucking hydrolic fluid into bad places) is the result of the vacuum pump not turning off (as it is supposed to) after reaching a set vacuum pressure, therefore over sucking if you will. Mine appears to stay on indefinitely. It's also been mentioned that fixing the switch that turns it off isn't much help becuase it doesn't last very long and your back to full on vacuum pump.

Oh yeah, and the purpose of the vacuum pump is to boost the vacuum pressure to help engage the diff locks. But the 300gdt (turbo diesels) doesn't use any vacuum pump because diesels have lots of system vacuum pressure.

Next, i have my diff locks re-wired so i can activate in any order. The vacuum pump, however, only comes on with the center. THis has turned out not a problem, becuase as it was speculated, there's enough system vacuum pressure in the g500's that the front and rear engage fine without the aid of the vacuum pump. IN fact its my preferrence now becuase then i don't have to listen to the noisy pump nor fear the vacuum pump over sucking. Perhaps the vacuum pump system was designed with small gas motors in mind such that the vacuum pump is unnecessary for the bigger g500's and ofcourse the diesels.

The question:

Is it possible that i don't need the vacuum pump for the center too? Or does the center lock require something more? Could i cut out the vacuum pump from the system entirely (with a switch for example) and avoid any failure modes associated over vacuuming the locker system... and have a quieter locker system.

Thanks ahead of time.
 

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96 G300DT
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I'm pretty sure that the center locker doesn't need any more vacuum that the others.

re: the pump running on .. check to see if you have a leak in the vacuum system. Pretty common given the shear number of valves and junctions in the system.
 

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2000 G500 NMLE
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Pump Running On

AlanMcR - 2/16/2005 9:50 PM

I'm pretty sure that the center locker doesn't need any more vacuum that the others.

re: the pump running on .. check to see if you have a leak in the vacuum system. Pretty common given the shear number of valves and junctions in the system.
For some reason (?heat? - ?made in USA?) these pumps seem to lose their internal shut off pressure switch and continue to run on after the correct vacuum is achieved.

I put a new one on a year ago. When new, it shut off when the proper vacuum was achieved. It now runs on and there are no leaks in the system.
 

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2000 G500L, 1968 SWISS Mog
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246 Posts
RE: Pump Running On

I didn't know that the pump is supposed to be off when the pressure is reached at certain point. Mine keeps running. I thought it's normal...

So, what could be the reason for pump to be running all the time?
Vacuume leak? Vacuume pump's internal shut off switch as Dutch experienced?

Yasu
 

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96 G300DT
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RE: Pump Running On

I'm of the opinion that the whole vacuum pump idea is overkill. Even the gas engines should provide plenty of vacuum for locker operation. Unless, of course, you have the trottle wide open for a long time. The system should have a vacuum reservoir that holds the highest vacuum achieved by the intake manifold. In the kind of conditions that one uses lockers the throttle will rarely be wide open. High throttle would be a recipe for snapped parts.
 

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1992 300 GDL
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Manifold vacuum-Diesels vs petrols

There is a difference between the intake manifold vacumms on diesels and petrols. A petrol speed is controlled by a flap in the manifold to restrict the air flow thus (when it is not fully opened) causing a vacuum between the flap and head.Ideal for taking a vacuum to the brake booster and diff locks. A diesel does not have the flap it's speed is controlled by fuel quantity available ,the fuel pump/accelerator. Therefore there is no vacuum in the manifold. In a turbo diesel there is actually positive pressure in the manifold . Therefore, diesels need a separate vacuum pump.
There are variations to diesel engines and some do have a flap as part of the system but I've never been sure what part it plays.
The early petrol 463s did not have a vacuum pump, they used the manifold vacuum to operate the brakes and diff locks. They had a big reservoir build into the front cross member. Do the newer ones still have that?
My vacuum pump is mounted on the front of my engine and runs all the time. I'm not familiar with the electric ones which are fitted to the Gs which you guys are talking about. I thought that vacuum pumps just reached a certain vacuum and then held it at that point, are you saying that the electric ones keep on increasing the vacuum. Couldn't this damage the diaphram in the brake booster?
 

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RE: Manifold vacuum-Diesels vs petrols

Roly - 2/17/2005 5:25 PM

I thought that vacuum pumps just reached a certain vacuum and then held it at that point, are you saying that the electric ones keep on increasing the vacuum. Couldn't this damage the diaphram in the brake booster?
Separate circuits for the diff locks and brake booster, although they're connected through one way valves.

The electric pumps which have lost their auto cutoff do finally reach a steady state vacuum which is 2X-3X what it is supposed to be; and I think that shortens the life of the diff lock intensifiers.
 

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Eliminating the Pump

ewalberg - 2/16/2005 8:24 PM



The question:

Is it possible that i don't need the vacuum pump for the center too? Or does the center lock require something more? Could i cut out the vacuum pump from the system entirely (with a switch for example) and avoid any failure modes associated over vacuuming the locker system... and have a quieter locker system.

Thanks ahead of time.
There's a simple plug connector on the pump. Remove it to disable the pump and see how the system works.
 

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G320 & E500
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I have been told that there is an additional purpose for the pump. If the engine stalls, the pump will run for up to 30 seconds to maintain the locks until you can restart the engine.

I would purchase a cheap vaccuum gauge and check your vaccuum on those lines.

I am one of those people who had to replace several valves and one intensifier.When the intensifier went bad, it pulled brake fluid through the lines. That is probably what killed the valves.
If you are getting any hint of fluid in those lines. DO NOT ENGAGE THE FRONT OR REAR LOCKS! Find out which is leaking and have it replaced. (If I remember, they cost ~$180)
The transfer case uses vaccuum only and does not require brake fluid.
 
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