Won't air

[Tikvah]

Maybe I'm confused, what is a DD3?

[luvrbus]

The DD3's are the brake chambers on the rear axle they have 3 air lines going to each one

[Tikvah]

Oh, that is not what I thought.  If it has three lines, how do I pinch one off?   Which one?
If there is a leak between the chambers, wouldn't it leak both directions?  I only get bleed-back when in park.  Since we fixed the treadle valve everything is fine when the park brake is released.

Won't be able to test anything else until we get the inverter valve back in place.  The MCI manual says to clean and service the inverter valve every 50,000 miles.  My guess is that it has never been serviced.

[luvrbus]

Take 3 pairs of vise grips to crimp the lines one side at a time ,a trick I use is slide a piece of pipe over the jaws on the vise grips that protects the rubber line from tearing and gives you a better seal

I think you are in the wrong place with working on the inversion valve those are open you have a DD3 problem I believe I have been wrong before tho       


good luck

[bevans6]

DD3 brake cannisters have three air lines going to them, and two chambers.  The air line closest to the push-rod end is the push-rod lock.  With no air pressure it locks the push-rod out to hold the brakes on, with air pressure applied it unlocks the push-rod and lets it operate normally in and out.  The middle air line is the service or main brake chamber.  Air goes there when the pedal is applied and forces the push rod out to operate the brakes normally.  The third air line closest to the back of the chamber is the parking/emergency chamber.  Air goes in there when the parking brake is applied to push out the push-rod and apply the brake.  What is a common cause of DD3 issues is a hole or leak in the parking brake diaphragm lets air leak into the main chamber when the parking brake is applied.  That air has to come out somewhere - it goes backwards to the R-8 valve, and from there can go to the E-6 foot valve and come out the exhaust port.  The first clue that this is what is happening is the air leaks out and makes a noise when the parking brake is on and there is air pressure in the parking brake section of the DD3.  The second clue is that with the parking brake applied and the noise/air leaking out, if you clamp off the center/main air line, the noise stops quickly, or if you clamp off the parking brake line the noise slows down and stops when all the air in the parking brake chamber leaks out.

The inversion valve is what sends air to the locking port and the parking brake port.  It's fed through an 85 psi pressure limiter, and is under the control of the parking brake push/pull valve.  If the push/pull valve is set to parking brake on, the inversion valve dumps air from the locking port to zero so the locking port can lock the push-rod out, and it sends 85 psi to the parking brake chamber of the DD3 to push the pushrod out and apply the brake.  If the parking brake push/pull valve is set to release the parking brake, the inversion valve flips over and sends 85 psi air to the locking port to let the push-rod unlock, and dumps air from the parking brake chamber to release the brakes.  You do a 100 psi brake application to fully release the brakes because the push-rod has to move out a tiny distance to let the locks actually release from the push-rod.

That's DD-3 and inversion valve 101...  

Brian

[luvrbus]

Both the DD3 and spring brakes use a inversion valve but work the opposite I am taking it for granted he has DD3 springs either way it has to have a signal to work 

[Dave5Cs]

Do you have an air dryer if so there is a check valve inside it if its an AD-2 if AD-9 with the screw on cartridge there is one on the out going line that if stuck open would let air go back instead of building or holding it. It is in the big nut looking thing coming out at the top of it. By the inversion valve there should be a double check valve also.

http://www.anythingtruck.com/category/htp-brake-air-valves.html
Above link will help you identify parts in the air system. HTH

Is air still coming out the peddle valve

Dave5Cs

[Tikvah]

The third air line closest to the back of the chamber is the parking/emergency chamber.  Air goes in there when the parking brake is applied to push out the push-rod and apply the brake. 


Is this accurate?
Air normally releases the brakes? ?  ?

[bevans6]

Tikvah, it takes three things to release the parking brake.  It takes air pressure at the locking port (closest to the push-rod end), it takes zero air pressure at the parking brake port (the back of the cannister) then it takes a pressure application at the service brake port (the middle port).  So the inversion valve sends air to the locking port and exhausts it from the parking brake port to release the brakes.

You have applying the parking brake right - the inversion valve sends air to the parking brake port to extend the push rod, and takes in away from the locking port so it can lock the extended push-rod.

Brian

[luvrbus]

Ok Dave what was the fix ? don't leave us wondering 

[Tikvah]

No answer yet.  We have driven the bus to Grayling and the problem persists.  We did find a leak in what we think is a shuttle valve attached to the inverter valve.  However, even though that shuttle valve leaked, and has been replaced, I still have air coming from my treadle valve while in park.
We have pinched the lines to the brake chambers without results.  My only guess it that it's a brake chamber and we simply can't pinch the lines well enough.
The coach can be driven, the air leak is not an issue when the park brake is not set.
I don't know what to do next, maybe take it to Brecheisen Diesel in Gaylord.  I hope to talk to them in a few days.

I can tell you that Greg, with Pacer Service Center in Muskegon has been the most helpful, kindhearted, and giving people we met in our time in that city.  He spend his whole weekend working on our bus, on his own time, just to be helpful.  We left almost in tears from our gratitude for his kindness.

[bevans6]

My next step, with what you have described, would be to remove the hoses from the service (middle) port on both DD3 chambers and put the parking brake on, and see if air came out.  Be aware that if you are driving the bus, if your parking brake diaphragms are indeed leaking you also have impaired emergency brake capability.  They are the exact same thing.

Brian

[Tikvah]

Are the brake chambers for the MCI-9 and my 102 A3 the same?
I see a pair on ebay