air leaks and kits MC8

[bevans6]

The whole point of the QR1 is to exhaust air coming from the brake can if there is no delivery pressure to hold it closed so that the brakes release quickly after application.  Hence the advice to look for something wrong downsteam of the QR1 sending air back to it.

Good news on the pressure regulator, I have yet to rebuild my air cylinder but hopefully it won't be too much of an issue.

Brian

[rcbeam]

Brian:  Now that makes sense... finally one of the light bulbs in my brain just came on.  DUH... now I feel dumb.  So since air is leaking out the parking QR1 then the problem is probably the parking diaphragm in on of the rear cans.  If you're going to open on up should just change it all out and I did read in the book if you rebuild one then you should do the other on the same axle.

Is rebuilding one of these rocket science?  Anything I should know of be scared of?  Is the spring inside under a lot of pressure?

thx guys for your help.  Especially you, Brian.

[bevans6]

Lets review DD3 101 tomorrow.  Too much scallopini and red wine tonight...

Brian

[bevans6]

Here is my take on what might be happening.  I think I have the logic right, but like I always say air brake systems are bloody complicated!  I could well have this totally wrong, if so I hope someone points that out!  

The QR1 in the emergency brake circuit is designed to allow the air pressure in the emergency/parking brake chamber to release quickly when the brake is released.  Air flows through the QR to the inversion valve (via an 85 PSI pressure regulator, the same model as your buddy the pressure regulator on the belt tensioner, hence I carry a spare).  The inversion valve normally supplies air to the locking section (front air hose) on the DD3 and keeps air away from the parking brake section.  That keeps the shaft lock open, and lets the service chamber work.  When the parking brake is applied, the inversion valve switches, and sends air to the parking brake section (the rear port on the DD3) and takes air away from the locking section so it can lock the pushrod shaft in the extended position.

the only time you are supposed to get air exhausting from the QR1 is when the parking brake has just been released - air rushes out and lets the parking brake off.  If you are getting air at the exhaust of the QR1 when the parking brake has just been applied, then the QR1 is leaking pressure that it is supposed to be sending down to the inversion valve.  If you are getting air when the parking brake is off but the service brakes are applied, then air is leaking at the DD3 into the parking brake chamber from the service brake chamber.  Suspect a leak in the parking brake diaphragm on one of the DD3's.  If you are getting air exhausting at the QR1 when the parking brake is off and the service brakes are not applied, suspect the inversion valve - the only thing that has air pressure at that point is the locking port on the DD3, to keep the push-rod shaft lock disengaged - and it's not all that likely that air is going to leak past the locking section seal, into the main service chamber and then into the parking brake chamber to get to the QR1.

[rcbeam]

Brian:  I have looked at the diagrams and read the descriptions until I am dizzy.  My brain hurts.  I have read your explanation and it pretty much makes sense to me and I can follow it along with the diagrams.  The last time I aired it up, if the parking brake was ON, I had air leaking out of the QR1 at a steady rate.  If I released the parking brakes and they were OFF, then I had no leaking after everything settled.  I could not try the service brake.

I am going to air it up again Saturday and give all this another look and take specific notes.  Then I'll post back.  By opinion right now is that I have a parking brake diaphragm leaking and possibly a troublesome inversion valve.  It seems to be to be best to rebuild the inversion valve and the two rear brake cans and be done with it.  The diaphragms in the QR1 and pressure regulator were both hard and in bad shape, so I figure most of the other brake rubber parts are probably bad too.

[rcbeam]

I removed the parking brake QR1 valve again, and turned the diaphragm over and reinstalled it.  The QR1 still leaks a 'LITTLE' air when the parking brake is applied, but none when released.  Now I have since discovered that my push-pull valve is leaking out the bottom where the nut is when the PB is applied.  I called Luke today to order a new push-pull valve and was able to talk to one of the guys there about my leaking QR1 and he suggested that it is caused by the leaking push-pull valve.  He said replace that and then see what you have... so I ordered one from Luke.  We'll see hopefully by this weekend.