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unimog 406 1970
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Discussion Starter #1
restoring a 1970 u406 cant get air system to build pressure..checked everything in the circuit ..what to troubleshoot??
 

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85' U1300L Holset Turbo VA A/C, 66' Propane 404.1 rock mog, 1975 416 Doka, G500, Volvo C303
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Since you are restoring it I assume you have check or replaced the air tanks? My 416 had a hole in the main tank big enough to put my fist through. Couldn’t see it or hear it.
 

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1988 U1300L RW1 Working gears Dual Tanks AC Rigged for Camping Plus: 91 F250 HD 4x4
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171 Posts
restoring a 1970 u406 cant get air system to build pressure..checked everything in the circuit ..what to troubleshoot??
You should review this thread carefully and in the entirety:


Jason F2 had a bit of an epic, in what turned out to be a very small but very annoying cause/ problem. Not that this will be your answer, but I would strongly suggest a methodical approach, starting with the origins of the airflow. You assert that the compressor is fine. On what basis (test or observation) do you make that determination? Next in line is the pressure regulator/ unloader (which was Jason's root problem), and then down the " chain of command" of the air system. Failure to build pressure, barring (pun ??) the absence of loud air noises, would suggest that the issue is very early on in the system. With perseverance you should prevail. Don't hesitate to ask further questions, and keep us posted as to results.
 

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1987 Unimog SEE
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Some have mentioned to remove a drain plug in the air tank and add a fitting that allows you to pressurize the system from another tank, which may allow you to hear any leaks. Pumps create Flow while the load determines the pressure. I second the methodical approach mentioned above.
 

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unimog 406 1970
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Discussion Starter #5
thanks
Since you are restoring it I assume you have check or replaced the air tanks? My 416 had a hole in the main tank big enough to put my fist through. Couldn’t see it or hear it.
a lot i lldo check the tank carefully
 

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unimog 406 1970
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Discussion Starter #6
Since you are restoring it I assume you have check or replaced the air tanks? My 416 had a hole in the main tank big enough to put my fist through. Couldn’t see it or hear it.
Thanks a lot
 

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unimog 406 1970
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Discussion Starter #7
You should review this thread carefully and in the entirety:


Jason F2 had a bit of an epic, in what turned out to be a very small but very annoying cause/ problem. Not that this will be your answer, but I would strongly suggest a methodical approach, starting with the origins of the airflow. You assert that the compressor is fine. On what basis (test or observation) do you make that determination? Next in line is the pressure regulator/ unloader (which was Jason's root problem), and then down the " chain of command" of the air system. Failure to build pressure, barring (pun ??) the absence of loud air noises, would suggest that the issue is very early on in the system. With perseverance you should prevail. Don't hesitate to ask further questions, and keep us posted as to results.
Thanks for advice..patience and scrutinity.. i ve followed the system and cant see where the problem is or hear any leaks..i ll keep on checking and keep posting ..thanks again
 

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85' U1300L Holset Turbo VA A/C, 66' Propane 404.1 rock mog, 1975 416 Doka, G500, Volvo C303
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4,997 Posts
Just FYI, my system was basically silent in terms of rushing air. Unless you get some
appreciable air pressure you will never hear the air rushing out.
 

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unimog 406 1970
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Discussion Starter #9
You should review this thread carefully and in the entirety:


Jason F2 had a bit of an epic, in what turned out to be a very small but very annoying cause/ problem. Not that this will be your answer, but I would strongly suggest a methodical approach, starting with the origins of the airflow. You assert that the compressor is fine. On what basis (test or observation) do you make that determination? Next in line is the pressure regulator/ unloader (which was Jason's root problem), and then down the " chain of command" of the air system. Failure to build pressure, barring (pun ??) the absence of loud air noises, would suggest that the issue is very early on in the system. With perseverance you should prevail. Don't hesitate to ask further questions, and keep us posted as to results.
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20200114_130954.jpg 20200114_130624.jpg
 

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1988 U1300L RW1 Working gears Dual Tanks AC Rigged for Camping Plus: 91 F250 HD 4x4
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171 Posts
that hole there can be the problem..
I think this is basically the same problem that I recently diagnosed on my 1988 truck, with dual range (9.3 bar / 7 bar outputs) regulator, part of the trailer brake option.


Just bubbling away: 18 bar to 5 bar, overnight, consistently. The bubble is from the cavity on the atmospheric side of the piston, the seal is obviously failing. No repair kits available anymore, the new replacement just arrived from MEREX yesterday ($- ouch!).

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