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Help with leak between primary and secondary tank needed

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Hello fellow Monaco-ers,

I'm hoping someone can help me identify the type and make of the four circled air components in the first photo . The photo is taken from below looking up and towards the back of my 36'  1996 Dynasty baron.

I am trying to diagnose an airleak between the primary and secondary air tanks. It currently fails an inspection test wherby one tank is drained of air and a check is made if the other tank keeps air pressure. The test fails no matter if the primary tank (at the rear of RV) or secondary tank (at the front) is drained.  Always both tanks loose pressure. I have already replaced the two–way check valve. It  seemed the obvious  culprit as it connects the primary and secondary air systems. Unfortunately, no change. It could ofcourse be the two check valves between the wet tank and the primary and secondary tanks but then they must both have failed for this problem to occur. Not sure how likely that is.

On the second photo one can see a green tube used to drain the air of the primary tank via an unused connection of what I think is a Service brake relay valve. It looks like I have two of those next to each other. Not sure why as I have only one rear axle with therefore two breaks. The component on the left is probably the relay valve for the spring brakes. The two main air lines coming from it each go to a spring brake chamber (not on photo) . The component on the right I can not identify at all. Having looked at some youtube instruction films (bendix) it could be a spring brake modulator valve but I realy don't know. On the second photo this valve can be seen from the side (component towards bottom of photo)

If I knew which  components these are I could try and diagnose the problem futher by clamping some lines shut and see if the problem goes away. But if someone has another idea about what the problem might be or a good way to diagnose it I would be very thankfull. I forgot to say that this Monaco lives in the Netherlands and expert help on US air systems is a very hard to come by....

A long story but maybe some of you has some ideas on the subject.

Kind regards,


photo 1 - rear air components.jpg

photo 2  - Connected air drain during test.jpg


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If you dump the air from only your wet tank will the primary and secondary tanks hold air?

In the downloads section there are a number of manuals covering the air brake system.  Here is a link that will get you to a number of manuals and a copy on the Bendix manual in case you don't already have a copy.


Bendix Air Brake Handbook - BW5057_online.pdf

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Thanx Frank. There are some documents I didn't have yet. I will try draining the wet tank as soon as I can. It should give me an answer to the question if the check valves are both OK or not. Should have tested that before but was convinced that the two-way-check-valve was at fault.... I'll let you know.

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I have a 95 Dynasty with exactly the same problem. I to have gone through the air system and come up with the following conclusion. The spring brake relay valve ( the one on the left in your picture) is fed blended air from both the front and rear air tanks. This is to prevent the spring brake from applying if one tank was to loose air pressure. There is a shuttle valve in the sp br relay that achieves this purpose. If you drain the air system, remove the front and rear brake lines from the sp br valve and cap them. Build up air and drain either front or rear tank and see if the other tank holds. These shuttle valves can gum up and stick. 
The valve on the right in your picture is the inversion valve (spring brake modulator valve).

I have the air system schematics for the 96 Dynasty on my other computer that I could send you if required. 

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Hello Dennis,

Thank you very much for your reply. This could really help me further. The schematics of the air system would be great. Currently I am constantly second guessing the connections and function of components. Please mail me the file(s) at erwin.schreutelkamp@gmail.com

 I performed the test today as suggested by Frank to drain the wet tank with the whole system at 120psi. Both the primary and secondary tank loose pressure quickly at the same rate. That would suggest that both one-way check valves between the wet tank and other tanks are stuck open. I'll try and remove one soon to see if it's working. I have to tread carefully as I can not buy any parts here. Everything has to be shipped from the US. Very time consuming and also expensive (cost of every part is at least trippled). Thank you both so far and I will keep posting my findings!


Edited by Columbus
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