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Old 11-12-2018, 01:59 PM   #1
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Location: Livonia, Mi.
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Excessive air pressure build up/brakes/air ride

Hello ,

need a little help. 2003 phaeton 330 cat, on our way back from Cali ( live in michigan) i noticed that both air psi gauges would go to about 145/150 psi. on accel only i would hear a hissing noise coming from up front between the seats. ( it is throttle related) looking under the coach this is where the 2 air tanks sit along with the valves. so something is releasing the excessive air build up at 150 psi.
so the question is what controls the air psi and thoughts on failed part?

i never had any issues with air ride and or brakes but i know it to much. looking under the coach i cant see any witness marks from any air escaping


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Old 11-12-2018, 05:52 PM   #2
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Probably the governor that regulates the air compressor is stuck on. Excess pressure will pop open the safety overpressure relief valve.

Been through all the continental states and provinces. Rinse and repeat. Present coach 2018 VTDP 3407.
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Old 11-12-2018, 06:17 PM   #3
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The governor controls the air pressure.

It gets its air signal from an air tank thru a thin, 1/4 line. If that line is leaking, the governor will not work. It could be hard to hear because the small tank it connects to will drain quickly and has no gauge.

You need to get the pressure up, shut down the engine, and quickly listen for any leak before the tank drains.

If the line is good, then you should change the governor. They are adjustable but when they go way off, its broken inside or jambed up. Replace it for $30.

Here is a picture of it. The second picture is it mounted to a Cat engine, air compressor.

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Old 11-12-2018, 08:14 PM   #4
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Thanks for the reply's! Twinboat thanks for the pic. i will check it out

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Old 11-13-2018, 09:09 AM   #5
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It might be tight quarters to replace it. Also be sure to check on the exact part number. I found mine to be a little more than 30 and was 50. Also had a hard time removing the one of the two bolts that attach it to the compressor. Was corroded inside the governor. Be sure to mark the two small lines which connect to it also. you don't want to mix them up. I had to remove a trans cooler line to the radiator to get access. The bolts use an allen head tool. also toque to the spec when installing and I used never seize to help in the future.
Be sure to clean the surfaces and install new gaskets.

You may have to transfer some of the plugs on the governor. pay particular attention to which holes are used and which are plugged when installing the new device.
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air, brake, brakes

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