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Unimog U1200 full ag specs, CLK500
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72 Posts
Discussion Starter #1
I have a problem on my U1200. Brake pressure is going up on only one system. After cleaning out some of the air valves in the system, I found that the red trailer brake connection actually releases air. Once I plugged that red trailer connector everything appeared to work.
Is it normal that the trailer connectors must be plugged or do I still have a different problem?
THANKS
Johannes
 

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1980 U1000 Turbo...
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1,522 Posts
My U1000 will pressurise the red glad hand/ palm coupling all the time regardless of pedal position. If the palm coupling leaks, you'll see a split in the gauges as you try to get pressure back up.the yellow coupling should only be pressurised ]when the pedal is pressed. I used the red coupling for tyre inflation/ air tools as it flows far faster than the factory tyre inflation/test point thingy.also handy for reseating beads.
 

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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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4,967 Posts
Normal, a few threads ago we here in the US found that the yellow glad hand was pressurized full time. In fact that is the one I use for airing up tires.

The red one has two airlines going to it and the yellow hand only has one airline
 

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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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4,967 Posts
That's exactly what I have. It's just that your Yellow one faded to white.
 

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1991 U1550L37, 2019 G550
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2,015 Posts
Must have been yellow. On German trucks only red and yellow or black for the old single line brakes.
 

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1991 U1550L37, 2019 G550
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2,015 Posts
In real use they get replaced every few years. Light pink and dirty white is the color on my mog too.
 

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1980 U1000 Turbo...
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1,522 Posts
Ok. Looking at the back of the truck from the rear. Right hand side is the red palm coupling, and is the one I use for air tools etc. Single pipe to it. Left hand side, yellow palm coupling. Single pipe to that.
 

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1991 U1550L37, 2019 G550
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2,015 Posts
Ok. Looking at the back of the truck from the rear. Right hand side is the red palm coupling, and is the one I use for air tools etc. Single pipe to it. Left hand side, yellow palm coupling. Single pipe to that.
Yep, red is supply = always under pressure; yellow is control = under pressure when braking
 

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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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4,967 Posts
Question, will both be charged when the park break is on? Again, I use the yellow on the left side of the truck to run air tools and air up tires.
 

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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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4,967 Posts
Lots of others here have reported the same function as mine. And my truck is pretty much unmolested. I'm only the second owner since it was discharged from the military.
 

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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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4,967 Posts
Just went out and tested my truck.

When parked with the park brake on, I have pressure on both glads. But, when I disengage the park brake, only the red glad has pressure and the left yellow glad has zero. Now it all makes since.
 

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1980 U1000 Turbo...
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1,522 Posts
Just went out and tested my truck.

When parked with the park brake on, I have pressure on both glads. But, when I disengage the park brake, only the red glad has pressure and the left yellow glad has zero. Now it all makes since.
That would make perfect sense and explain our differences!
I was told when I first got the truck that the red one was the one to use, and have never tried the yellow one for that purpose!
 
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