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· Senior Member
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Discussion Starter · #1 ·
Well, I posted this once before, but was recent enough the thread was lost in the mess.

OK, here's the deal. The dump valve was replaced last year (by someone else, so I don't know what they did), but things haven't been right since. The bag fill like they are supposed to, but, don't unload the air bags like they should. The valve exhausts air, but the suspension doesn't come down like it should. Just likes to drain the air tanks.

Switching the air flow on the "in" and exhaust ports doesn't help. Not sure if swapping the long screws to turn it 90* in the bracket will work or not? Taking the other one apart, I don't think so.

The new valve is no different.

Any ideas?

'95 Mack CH613. Almost 1 million miles on it.
 

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Discussion Starter · #3 ·
Oops. Misspoke. The LEVELING valve was replaced. It is a Hendrickson brand valve. Don't have the p/n handy. If I had a working camera, I'd take a few pics. SUPPOSED to be the right valve, per the VIN. They've been wrong before.

The dump valve is still the original, as far as I know.
 

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Discussion Starter · #4 ·
Leveling valve looks like this one-

 

· Dents..it's a work truck.
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i dont believe thats the correct valve,dont look like the one i use on my macks.
 

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Discussion Starter · #7 ·
So the bags only inflate and will never deflate?
More or less, ya. We have to use the dump valve when unloading grain, same as on the trailer.
 

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Discussion Starter · #8 ·
I suspect it might have been one like this-


But, it has been long enough, I don't remember for sure. Either way, in theory, it should still work, but IDK. :confused: :confused:
 

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Discussion Starter · #10 ·
The one we have reacts plenty fast. It just empties the air tanks, NOT the air bags like it is supposed to. :bang:
 

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What part number / kind dump valve? Is it after the leveling valve or do you have a dump built into the leveling valve?
 

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Discussion Starter · #13 · (Edited)
The leveling valve is the problem, not the dump valve. The dump is before the leveling valve.

I posted a pic of it on the previous page. Don't have a p/n handy. It is a Hendrickson valve.

I did slip the arm off of the valve and flip it 180* to see if reversing the flow would change anything, but nope. So I put it back the way it was.
 

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Does your dump valve look like this?
If so, it must be plumbed in AFTER the ride height valve, or it will cause exactly the problem you are describing i.e. it must be between the ride height valve and all of the air bags. switching ports on the dump valve would also cause the same problem. Not running all of the air bags through the dump valve could also cause this problem.



The leveling valve is the problem, not the dump valve. The dump is before the leveling valve.

.
 

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Discussion Starter · #15 ·
I'd take a pic, IF I had a camera, but I don't. :(

I don't think that valve looks like what we have, but I'll have to take a peek at it the next time I see the truck. Might be a few days.
 

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Does the valve look like this?
http://shop.easternmarine.com/images/product/thumbnails/sm_8651.jpg
If so, it goes after the leveling valve. Only valves I have used were pilot dumps and went between leveling valve and bags. Dumps the air out of the bags and blocks off the output from the leveling valve so it doesn't just vent. If this style was hooked up backwards I guess it would dump the leveling valve and not the bags thus emptying the tank.
 
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