Parking brake release problem

[tanman496]

I have a GMC H8H649 And I live in NY its alittle cold here today around low 40,s anyhow i seen whats its like to start a dd  8V71 When it a little cold guess i will need a block heater if i decide to start it over the winter. OK back to my post after starting the bus I let it build up air preasure and went to release the parking  brake and when i did it started to make this ear piercing noise and now it wont build air preasure to release the parking brake. The ear piercing noise persists and when i push on the parking brake  switch it feels like there is air preasure at it and no matter what i do i cant get it to release the air at the parking brakes.

[tanman496]

I think something is sticking does anyone have any idea's what to do??

[Dave5Cs]

If you have an air dryer, it sounds like it is stuck open, so won't build air and the noise is the air blowing through and out the bottom.

Dave5Cs

[Lin]

I can not specifically say what the problem is, but if your gauge is not showing any air pressure and the brakes are not releasing, either the compressor has totally failed or the air is being pumped out somewhere big time.  A leak of the magnitude should not be hard to find.  The engine noise may hinder your search but may not.  Do you have an electric compressor you could use?  First, it would tell you if the compressor is your problem and second, it would make your search for the breech more peaceful.  I would be sure to chock the wheels before starting any exploration.

[bevans6]

What kind of parking brake do you have, DD3 or spring brake?

Brian

[Oonrahnjay]

What kind of parking brake do you have, DD3 or spring brake?    Brian 

     Yes, tell us that -- and fer Pete's sake -- tell us where the "ear piercing noise" is coming from!

[luvrbus]

Sounds to me like a drain valve or safety release valve has popped or maybe a o-ring in the parking valve, his bus model has the DD-3 brakes

good luck

[tanman496]

I believe my bus has the DD3 Brakes but i am not sure what that means.And the noise is coming from either between the rear wheels or near the drivers side rear wheel its hard to tell cause its that noisy

[luvrbus]

You blew a diaphragm or a relay then

[tanman496]

I guess you could say its more of a whistling noise but very loud

[bevans6]

Probably the 85 psi regulator.  When it fails the air rushing out the tiny drain hole is ear-splitting.  That happened to me a while ago.

When you push in the valve to release the parking brake, air is sent from the push/pull valve to the 85 psi regulator and then to the inversion valve.  The inversion valve releases the air from the parking brake section of the DD3 and applies air pressure to the shaft lock section, releasing the shaft lock.  You then apply the service brakes to push the shaft out a bit, which releases the rollers and allows the shaft to move, releasing the brake.  Just an opinion, but if you are going to drive and maintain a bus, you need to know this stuff cold.

Brian

[luvrbus]

You may need to ask the GM guys but I don't think the 4905 same as your bus has that 85 lb regulator GM and Eagles are a little different than the MCI

good luck

[bevans6]

If that's true then I do apologize.  I recall some talk about the regulator from a GM guy some time ago, but I don't really know that bus at all.  I thought the 85 psi regulated air to the inversion valve was a Bendix design thing, not a bus manufacturer thing.

Brian

[luvrbus]

Not all buses have the Bendix system you see on some Eagles a separate tank between the rear wheels the tank is regulated at 85 lbs by a large regulator from the main tank for just the DD-3 nothing is really standard on a bus lol MCI does a good job at it though   

It really makes you sad now when we in America don't even own Bendix any longer Honeywell sold it off to the German Brake people Knorr/Bremse in 2002 shame to see a intuition here since the 20's gone

[Dave5Cs]

if you can use a good spray bottle with soap and water in it. Set it to spray a long shot and spray all valves under there that you can see. Back it up on ramps if you can. You should see some bubbles fast. If it is a regulator I just bought one for 76.00 retails 114.00.
relay valve cost me 57.00, retail 100.04
Capital City Clutch and Brake Inc. in West Sacramento, CA

Dave5Cs