air brakes not releasing

[richardkillmon]

Hello again,

Every once in while my brakes won't release.
1976 MCI 5B
I have had mechanics look at them and have no results.
I have things changed as requested and good for awhile and then in comes back.
If I have the air built up and release the them multiple times and finally they work.
Today I tired for over 45 minutes with no luck.
Any suggestion on how to narrow down the issue?

Thanks

Rick

[Lifes2short4nofun]

I have had the same issue on my 72 5B a few times.  I just pump the brakes a few times after I release the parking brake and they free up.   Hopefully someone knows what the issue is.

[lostagain]

You may know this already, but in case you don't:

Press the brake pedal lightly and hold it lightly. Push the push/pull button, and then do a full brake application (like push the pedal to the floor). This brake application has to be at a higher pressure than the pressure the park brakes were applied at. In theory they only apply at 80 psi or so because there is a pressure regulator to take care of that, so your service brake application will be higher (between 90 cut in and 120 psi cut out) to release them. Build your air pressure to cut out (110, 120 psi) before you try releasing to maximize your chances. If that doesn't work, maybe the regulator is bad. Maybe the DD3 brake chambers need to be taken off, disassembled, cleaned and rebuilt with new diaphrams, and greased. That is not really difficult to do as long as the housing aren't rusted to rat s*it. If they are rotten, you need new ones. While the wheels are off, look at all the brake components to make sure everything is as it should be. Do you have a maintenance manual? A parts manual?

Good luck.

JC

[richardkillmon]

Thanks for the information.
I don't have a maintenance manual or parts.
Is there a link you can send me?

Thanks

Rick

[buswarrior]

Sticking brakes is a lack of maintenance or lack of use issue.

Manuals come up periodically on all the buy/sell sites, craigslist, kijiji, ebay, etc. As well as the bus sites, here at BCM, over at BNO, busgreasemonkey, etc.

You need 3. Parts Manual, Maintenance Manual, Operator's Manual.

Often overlooked in DD3 brake system woes is the inversion valve. It controls everything, and never gets changed out by anyone until it's too late...

It is a wear item, any new-to-the-busnut coach with an unknown aged inversion valve, should be changed out as a matter of preventive maintenance, and then it's done.

The airlines probably are rusted solid, just cut 'em to get it all out of there, and LABEL BOTH PIECES, so you can take them to a shop and have replacements made up while you wait.

Take careful note of the orientation of the inversion valve and airline routing, as you will see, getting all those airlines back where they belong, after it has all been removed some days before...

Pictures and more pictures, you will put those airlines on in the wrong place...

Use anti-seize on all mating surfaces and threads, so you don't ruin another set of air lines down the road when a chamber needs replaced...

Happy coaching!
Buswarrior

[Oonrahnjay]

Sticking brakes is a lack of maintenance or lack of use issue.  ...
Buswarrior

       With all due respect to the OP, it appears to me that it's more than that.  The OP clearly doesn't understand the operation of DD3 brakes and how they work.  His *first* priority is to understand the function of the pressure and release cycle -- if you don't know the release procedure, you can have wonderful, clean, new parts for all the system and still have problems.
       I think that you're right that this failure of brakes to release is a maintenance and lack of use issue, but having the properly maintained parts (or new ones if the old ones can't be repaired) must be linked to the OP learning how the system works and the importance of knowing how to operate it.

       Rick, I'm not criticising you.  You're at a point that we all were at -- some 50 years ago, some last week, we're all here together.   But you indicated that mechanics have "thrown parts at it" and things haven't improved.  It's important that you understand the suggestions about pressure, foot pedal procedure, and the other parts of the release cycle as well as understanding issues with the components in the system.
       The DD3 system is now nearing 35 or more years out of date.  Information is rare (the system was not mentioned in the Bendix Brake School that I took a couple of years ago) and parts are old and few mechanics are really up to date on how to work on them. 
       I don't have DD3 brakes (and if they had been on my bus when I bought it, I would have changed them out for a more modern spring brake system) so I can't comment on the subtleties of the release system, but I'd urge you to get as much background information on your system as possible and understand what's going on.  That's your first priority; when you are up on this, you'll be ready to tackle components in your system.  You'll also understand the info you receive from people here who deal with DD3 brakes everyday.
       Good luck, and best wishes for getting your brakes system working well.

[chessie4905]

Here:  http://www.bendix.com/en/servicessupport/documentlibrary/doclib_1.jsp

You need to download document SD-02-4600.   DD3 operation.

One thing to keep in mind is that the push- pull control controls the locking rollers inside the dd3. When button is pushed down in the brakes released position, a constant air supply is fed to the rollers(lock port) to keep them released while the coach is moving. Pulling up to park position applies pressure to rollers (lock port). You need to apply enough pressure to brake treadle to apply enough pressure to keep coach stationary. The rollers, now locked against the brake actuator rod keeps brakes applied regardless of air pressure in system. To release parking brakes, you need to depress parking brake button. Which releases pressure on the lock port. However the rollers are now wedged against chamber actuator rod and wont move till you apply the brake treadle to move the actuater rod enough to cause the rollers to release. Bendix specifies use full brake application pressure (120 psi) to insure rollers release. They also designed the dd3with a larger diaphragm on the parking release side to insure you can always release the parking brakes.
Reasons for issues getting parking brakes to release can be leakage at the seal at lock port piston. Leakage here can cause loss of sufficient pressure to release rollers properly. Also corrosion and lack of lubrication can also cause problems.
Brakes should also be in proper adjustment. If you have these issues, check the info on above pdf. Leaks at the slot on chamber or parking brakes not releasing properly indicate you need to remove and service the DD3 chambers. Btw, there is a grease fitting to provide lubrication to the rollers in the lock chamber. Don't go crazy with lubricant. Three pumps occasionally should do.

[eagle19952]

http://www.bendixvrc.com/itemDisplay.asp?documentID=2393

this url will auto down load

[richardkillmon]

Free at last
Free at last
Thank God almighty
Free at last.

Thank you all
They released after I tied your suggestions.
The links you guys sent - perfect.
Your help over this rebuild has been so much help.
I was worried today because I have the bus in a warehouse and no room to work on it.
I'm getting too cocky because I feel if I screw up you guys will save me.
Thanks for taking one less worry from me while trying to retire and drive the USA.

Rick

[dj]

Ill add my two cents worth here...I have a 102A3 and my brakes wouldnt release   made sure air was built up then release the brakes and stab the brake petal once and the would release ok.......did this usually after sitting a while.....I did change out the control valve as  some have said earlier. but some time it would do that   grease is your friend on bake systems tho keep everything lubed up and excersize the brakes regularly.  hope this helps

[buswarrior]

Making a full service brake application is part of proper DD3 release procedures...

Those who don't are playing with fire...

Dragging brakes due to an improper release procedure will ruin yer hobby...

You don't just punch the button and go...

Happy coaching!
Buswarrior