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  #1  
Old 01-10-2005, 11:39 PM
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How to disassemble aux water pump-part 1

First, this is not extensive - but it should help- for an electrical problem. A coolant leak is a different story, but I'll have to cover that another time. I found my aux water pump to be non-operational. Infinite resistance as measured with an ohmmeter. I made a quick test rig to put 12V to it and got nothing also. I clipped off the plugs for the aux water pump and the monovalve from my parts car. I extended one lead only on each one, so they could be attached directly from the battery to the device. Because 1 leg is short (and my SD has the battery right next to it) it's impossible to hook it up wrong. When the devices are operating properly, it's easy to both feel and hear them work.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Last edited by Pete Burton; 01-11-2005 at 07:54 AM. Reason: added info
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  #2  
Old 01-10-2005, 11:47 PM
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So I removed the aux water pump and monovalve TOGETHER. I removed the 4 screws to the heat shield in the center and then the shield for better access. Then, I disconnected 2 hoses from the monovalve at the firewall, Hose from the aux pump back to the engine pump (at the aux pump) and the little hose from the monovalve to the windshield surface heater (some of you won't have this). Disconnect plugs to both units, remove 4 screws (2 holding each unit) and lift out. It's a little tight, but it goes, really, it's not too bad!
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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.
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  #3  
Old 01-10-2005, 11:54 PM
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Remove the 2 slotted screws at the end of the motor. Now, here's the trick! Apply a bit of penetrant to the space where the white plastic that holds the wiring meets the main body of the motor. Make scratch marks on the outside so it goes back together the same way. Use a knife or knives to get this started, rock back and forth and make a gap. Keep the white plastic in place against the part of the motor that leads to the water pump. Gradually, you will get about 3/16" to 1/4" space and you will be able to lift the magnets and housing free of the rotor. Continue to go slowly, and leave the magnets exactly where they are in the housing, there is no need to move them. They want to stay where they are anyway, but if you do remove them from the housing, you have to figure out how the clips hold them in.
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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Last edited by Pete Burton; 01-13-2005 at 08:26 AM. Reason: important note
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  #4  
Old 01-10-2005, 11:55 PM
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See the greenish, oxidized copper crud? That's easily brushed away. The commutator can be cleaned with an eraser, scotchbrite, a tiny screwdriver, piece of very fine sandpaper, etc. The lines on the commutator can be cleaned out with a wire, a toothpick or the like. Excercise the brushes and make sure that they are not cracked or super worn down. The springs should still push down on them with a bit to spare. I really don't think any thing is gained by disassembling any further. But, now is the time to see if this will work. Put your meter on the 2 leads and move the rotor. You should have continuity, probably several ohms at least. If so, reassemble the motor and put 12V to it. Mine ran straight off and pulled about 0.3 amp at no load. Reverse procedure to install back in car. Hope this helps!
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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Last edited by Pete Burton; 01-11-2005 at 12:19 AM.
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  #5  
Old 01-11-2005, 01:46 PM
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Bump Up
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  #6  
Old 01-11-2005, 03:30 PM
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Pete,

This is a very nice write up. I was wondering whether the failures out there were mechanical from the internal impeller OR as you have shown, electrical.

Anyone else have experience replacing these motors? I know they can get noisy but can they stop pumping with the electrical motor still running?
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  #7  
Old 01-11-2005, 04:14 PM
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I tried taking mine apart last year................was a lost cause screws broke....etc.......in my case it was so much scrap.
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  #8  
Old 01-11-2005, 04:26 PM
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Now I know what i will be doing tonight

I pulled 4 of them at a yard--everyone was Bad (didn't work)--but I will settle for 1 of 4...
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  #9  
Old 01-11-2005, 04:36 PM
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Oh, BTW even though my post dealt with the electrical portion of the unit, it's probably a good idea to check the pump side for leaks. After I had disassembled the pump side (with those teeny little snap rings) and reassembled, I pressure tested it by filling the pump side with water and pressurizing to about 20 psi. If you just do the motor side and you know there was no leak before you started there would be no need. But if you've pulled one from a boneyard, it wouldn't hurt to check. Just takes a minute.
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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.
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  #10  
Old 01-13-2005, 08:28 AM
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I added another note (about the magnets). Has this helped anyone yet? Seems like the season to notice that the pump may not be working.
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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.
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  #11  
Old 01-13-2005, 08:47 AM
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I am sure it has helped or will help someone in the future.

Mine was too far gone to save...............I tried.
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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche
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  #12  
Old 01-13-2005, 01:48 PM
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hey, at least you tried. I often try when I'm not sure if it will work, because if I try and fail, I still learn something and I feel much better about buying a new whatever. Gee, maybe I should have tried to fix my pistons!
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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.
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  #13  
Old 01-13-2005, 01:51 PM
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Quote:
Originally Posted by Pete Burton
hey, at least you tried. I often try when I'm not sure if it will work, because if I try and fail, I still learn something and I feel much better about buying a new whatever. Gee, maybe I should have tried to fix my pistons!
If its hosed and doesn't work......you replace it.....if you screw it up worse trying to fix it what happens? you replace it......

Never hurt to try and yes you do learn something.....and best case.....you fix it.
__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche
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  #14  
Old 01-15-2005, 09:22 PM
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I've had one bad motor which turned out to be stuck brushes. Pull the motor apart as shown then give each brush a little shot of WD-40 to free them up. The windings should not be black but a nice copper color. The rotor laminations should be smooth. Turn the rotor a few times to seat them and it should rotate when connected to a battery. Note that for correct rotation, the black wire is + and the brown wire is -. Pressure testing the pump is a good idea since leaks can occur around the pump shaft seal.
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  #15  
Old 01-15-2005, 09:45 PM
Brandon314159
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Quote:
Originally Posted by boneheaddoctor
I am sure it has helped or will help someone in the future.

Mine was too far gone to save...............I tried.
Were you using your icons sense of care when it comes to "repairing"

I just had to mention it even though I know you have the patience

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