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rdauphinais

Can't find this air leak!

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So I bought a 89 midliner a couple weeks ago with a couple bad air brake fittings. Even though it had leak, it still built over 100psi. So I get new fittings, and replace the old ones with new ones, get it all together and go to test it. I can only build 10psi at half throttle, and as soon as I let off the gas it dropps to zero. I can't find any leaks or hear any. Nothing changed besides 4 new fittings. Any help is appreciated

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Those Renault compressors used on the engines can be troublesome in the valves. If you have an air dryer remove the inlet line from the compressor to it or the "wet" tank. You first need to ensure the air compressor is building airflow. Citing you are losing air very fast after limited build up of pressure, it may have exhaust valve(s) stuck open. In your wet tank if you have an open fitting that is plugged remove this and install a ball valve and air fitting. If not, remove the overpressure safety "pop off" valve and temporarily install an air fitting. Apply shop air to this and soap down the entire air system. With that massive of a leak you should hear air escaping with shop air connected.

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Or it could be just a bad air governor?

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1 hour ago, other dog said:

Or it could be just a bad air governor?

It could be and if a Bendix or Midland compressor, the first place to look. The Renault compressors were problematic, (IMO) and my reply is based upon past experience with them times about four trucks..... He has not responded with adequate information in which to offer effective t/s with yet, so staying generic. 

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Truck is a few miles away from me in a field so getting shop air there is almost out of the question. Just find it hard to believe that everything worked fine until I replaced 4 fittings and now it doesn't build hardly any pressure. I'll see what I can find later today, but I do t have hardly and experience with air brakes.

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Post up some photos of what you are working with. If the truck is a CS-300 series the air compressor is buried behind the turbocharger mounted low on the right side and the compressor is next to it. It is very difficult to see with the exhaust in place.

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I can easily see the air compressor right on the pass side of the motor in front of the turbo and behind the intake. I'll pull the exhaust line off and see if there is pressure coming out, I have a feeling there isn't.

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1 hour ago, rdauphinais said:

I can easily see the air compressor right on the pass side of the motor in front of the turbo and behind the intake. I'll pull the exhaust line off and see if there is pressure coming out, I have a feeling there isn't.

You don't have the engine I was thinking you did.

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Single long valve cover, or six individual ones?

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You have a different arrangement than three 89's and one 1992 CS-300P trucks I had if you can see the turbocharger, or air compressor. I had underbody exhaust however as they were rollback car carriers. The engine should be an E-3 @ 210hp if original to the chassis.

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