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Diff lock vacuum pump
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Posted 10/31/2019 2:52 AM
vancouverChris
Member


Date registered: Feb 2019
Location: Vancouver
Vehicle(s): 2003 G500
Posts: 15

Diff lock vacuum pump

Im fairy new to my G500 and trying to understand the operation of the vacuum pump. My understanding is; when I have the diffs locked it is only designed to run intermittently to maintain a certain pressure. Despite it saying "Engine running, continuously" on page 9 of the link below.

http://fourbyfourclub.com/Manuals/W463249DiffLocks.pdf



My pump runs continuously, so its most likely the pressure switch within the pump that has failed?

Seeing as I didn't know any better, Ive done a fair amount of time with the diffs locked while off roading and the pump running continuously during my ownership of the vehicle in the last year. Could this have caused any damage/problems, anything that I should be concerned about. Is there anything I should look into?

Thanks
#241145
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Author
Posted 10/31/2019 6:55 AM
DUTCH
Administrator Doppelgänger




Date registered: Apr 2006
Location: US, GA, Atlanta
Vehicle(s): 2015 Audi Q7 3.0 TDI,2018 Sprinter
Posts: 9963
5000
RE: Diff lock vacuum pump

Mine runs continuously when the engine is running.



(DiffLockVacPump_DxO_DxO.jpg)



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Attachments DiffLockVacPump_DxO_DxO.jpg (181KB - 2 downloads)
#241146 - in reply to #241145
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Author
Posted 10/31/2019 11:22 AM
vancouverChris
Member


Date registered: Feb 2019
Location: Vancouver
Vehicle(s): 2003 G500
Posts: 15

RE: Diff lock vacuum pump

Ok, then Im confused.. I thought you stated differently in the post attached (post #17)

Do you mind clarifying?


https://www.benzworld.org/threads/intermittent-diff-lock-problem-03-...


"The electrical auxiliary vacuum pump supplies the differential lock system with vacuum if the prevailing intake pipe [manifold] vacuum is not sufficient so that the diff locks can be engaged.

The positive actuation of the vacuum pump takes place by actuating a diff lock switch via the control module and the time limit delay.

The negative actuation takes place via ground wherein it is not actuated via the diaphragm pressure switch until there there is a vacuum of less than 0.4 bar in supply pressure to the lock system.

When a lock has been selected and the diaphragm pressure switch has closed the negative contact at a vacuum of less than 0.4 bar, the electric motor in the vacuum pump runs and generates a vacuum in the lock system.

When a vacuum of greater than 0.6 bar is reached, the contact opens and the pump is switched off.

This can be repeated several times if several locks are actuated one after the other, or the vacuum in the lock system falls below 0.4 bar."

Edited by vancouverChris 10/31/2019 11:24 AM
#241148 - in reply to #241145
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Author
Posted 10/31/2019 3:04 PM
DUTCH
Administrator Doppelgänger




Date registered: Apr 2006
Location: US, GA, Atlanta
Vehicle(s): 2015 Audi Q7 3.0 TDI,2018 Sprinter
Posts: 9963
5000
RE: Diff lock vacuum pump

Better to go by what the official PDF or JPG file says. Don't go by something I maybe stated in error 15+ yrs ago.
#241150 - in reply to #241148
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Author
Posted 11/2/2019 12:27 AM
vancouverChris
Member


Date registered: Feb 2019
Location: Vancouver
Vehicle(s): 2003 G500
Posts: 15

RE: Diff lock vacuum pump

Well this sounds like good news!

Just to clarify, your pump runs continously from the time you hit your centre lock until you deactivate the locks.

#241154 - in reply to #241145
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Posted 11/2/2019 12:48 PM
AlanMcR
Expert




Date registered: Apr 2006
Location: US, CA, Los Altos
Vehicle(s): G300DT E300DT 230SL
Posts: 3500
2000
RE: Diff lock vacuum pump

That would imply a vacuum leak somewhere in the system. Or, alternatively, a bad vacuum pump.  It shoudl run for a while and then stop when the correct vacuum level has been established.
#241156 - in reply to #241154
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Posted 11/2/2019 1:07 PM
DUTCH
Administrator Doppelgänger




Date registered: Apr 2006
Location: US, GA, Atlanta
Vehicle(s): 2015 Audi Q7 3.0 TDI,2018 Sprinter
Posts: 9963
5000
RE: Diff lock vacuum pump

AlanMcR - 11/2/2019 12:48 PM

That would imply a vacuum leak somewhere in the system. Or, alternatively, a bad vacuum pump.  It shoudl run for a while and then stop when the correct vacuum level has been established.


When my engine is running, that pump runs continuously as is indicated on the posted PDF; and there are no leaks in my system.
#241159 - in reply to #241156
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Posted 11/2/2019 3:31 PM
paulunm
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Date registered: Jan 2015
Location: Los Angeles
Vehicle(s): 2000 G500
Posts: 124
100
Re: Diff lock vacuum pump

Not trying to add to confusion- but mine does not run continuously when the engine is running. It did when I had vacuum leaks.

I've heard of other trucks that do run continuously, and all three lockers indeed do engage (RED light illuminated)- so I'm not sure why some are different than others.
#241160 - in reply to #241159
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Posted 11/3/2019 12:21 PM
AlanMcR
Expert




Date registered: Apr 2006
Location: US, CA, Los Altos
Vehicle(s): G300DT E300DT 230SL
Posts: 3500
2000
Re: Diff lock vacuum pump

The pump should get power anytime a yellow light to is on.  However the internal shutoff should stop the pump whenever the target vacuum level is reached.  That can be due to intake vacuum or the action of the pump.  One of the first things to go seems to be that sensor, which is internal to the pump.
#241161 - in reply to #241160
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Posted 11/5/2019 8:56 PM
vancouverChris
Member


Date registered: Feb 2019
Location: Vancouver
Vehicle(s): 2003 G500
Posts: 15

RE: Diff lock vacuum pump

Is there any harm if it runs continuously? Should I be concerned about any damage, or inspect anything?

#241179 - in reply to #241145
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Posted 11/6/2019 2:19 PM
AlanMcR
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Date registered: Apr 2006
Location: US, CA, Los Altos
Vehicle(s): G300DT E300DT 230SL
Posts: 3500
2000
RE: Diff lock vacuum pump

vancouverChris - 11/5/2019 5:56 PM Is there any harm if it runs continuously? Should I be concerned about any damage, or inspect anything?

If it only runs when one or more lockers is selected, I wouldn't worry too much.  It will fail a bit earlier than usual.  If you have verified that there are no vacuum leaks in the system, then, in my opinion, the limit switch part has already quit. Might as well use the rest up too.

The only reason for the pump is that the gas models have weak vacuum whenever the throttle is opened.  The diesels have a much bigger, chain driven vacuum pump that runs all of the time.  It's real purpose is to provide vacuum to the brake booster.   

#241181 - in reply to #241179
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Posted 11/8/2019 1:39 AM
4x4abc



Date registered: Apr 2006
Location: La Paz, Baja California, Mexico
Vehicle(s): 02 G500
5000
RE: Diff lock vacuum pump

I have a modified switch set - I can select any locker at any time I like
with either front or rear locker selected (or both) the vacuum pump shuts off after a while
whenever the center diff is selected, the pump never turns off
#241186 - in reply to #241181
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Posted 11/10/2019 3:08 PM
W5YK
Extreme Veteran




Date registered: May 2006
Location: San Diego
Vehicle(s): 2002 G500, Unimog U2450,
Posts: 543
500
Re: Diff lock vacuum pump

If the engine is running, the vacuum pump runs continuously if any locker is selected.

If the engine is not running, then the vacuum pump runs if any locker is selected, and eventually it will stop when the vacuum switch senses good vacuum.

This is a handy way to check if you have a leak in your vacuum lines. Stop the engine, select a locker, see if the pump stops after about 30 seconds. If it doesn't, you have a leak. The more lockers you have on, the more lines are getting tested.

To test just the pump itself, take the hose off the end and stick a wet finger over the barb. The pump should stop (engine off for this test).

The difference in behavior between engine running and not running is not under computer control, since the vacuum switch is always in circuit. It has to do with the different vacuum level from the manifold keeping the sensor on. Not sure why some people are seeing their pumps shut off with the engine running. I suspect they have a bad check valve to the manifold.

Edited by W5YK 11/10/2019 3:15 PM
#241191 - in reply to #241145
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Posted 11/12/2019 3:27 PM
ewalberg
Expert




Date registered: Apr 2006
Location: Past: San Francisco. Present: Germany
Vehicle(s): 2000 g500
Posts: 1887
1000
RE: Diff lock vacuum pump

Interesting. I've got AlanMcR's original modification to the locker switch pack (allowing any order of locker selection). If I apply the front or rear switch, the pump never turns on, they will however engage if the vehicle is running/rolling/turning. If I select the middle diff, the pump immediately comes on. I don't think it turns off.
#241198 - in reply to #241186
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