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Author Topic: First Problem with my Bus..  (Read 4382 times)
Highway Yacht
*****Jimmy*****
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« Reply #15 on: September 14, 2010, 03:55:25 AM »

Maybe it's just me, but I think if I parked my bus on an incline and it moved by itself, I wouldn't park it on the incline a second time without figuring out what the problem is and fixing it.



I know exactly what you mean, but I parked it there the 2nd time without a chock on purpose for testing purposes..... There is nothing that it can hit even if it rolled all the way down the incline... The incline only goes for like 200 feet then it would have to roll up another 400 foot hill and still wouldn't hit anything. I parked it there the second time on purpose and marked where my rear tire was just so I could make sure it DID in fact roll the first time. Believe me... I wouldn't park in anywhere else without chocking the tires now that I am sure something is going on.
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1979 MC-9  8V71-Turbo / HT740             * www.MciBusTalk.com *
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Highway Yacht
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« Reply #16 on: September 14, 2010, 04:03:18 AM »

Adjust your brakes and grease the DD-3 good then you will be fine,they get full of dirt and rust over the years and balls on the ratchets locks don't work to lock you probably just have one side holding



good luck

I've never attempted to adjust air brakes before and have no clue what a DD-3 is. Is this something that most anyone can learn to do by themself with a little instructions??? I've done all kinds of brake work on hydraulic brakes but never air brakes.
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1979 MC-9  8V71-Turbo / HT740             * www.MciBusTalk.com *
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Tenor
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« Reply #17 on: September 14, 2010, 04:45:47 AM »

DD3  is the name of the type of air brake systems most buses use.  Spring brakes are another.  The DD3 system uses valves and air to hold the parking brake on and they are designed to stay on whether or not you have air in the system.  We often refer to the brake cans on the drive axle as DD3's.  They are the only cans on the bus with parking brakes.  If you are mechanically inclined, then you probably have the skills to work on the system.  You need to block up the bus, and get in there with a grease gun and go to work.  The DD3 cans only get a little grease and I'll let someone else chime in there.  Do you have manuals?  If not, get some and get into a comfy chair! Grin  Then take the manual under the bus and get into a comfy creeper! Grin  NEVER go under a bus that isn't blocked up!  No air = no room for you! 

Glenn
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Glenn Williams
Lansing, MI
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1968 MCI 7 Ser. No. 7476 Unit No. 10056
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bevans6
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« Reply #18 on: September 14, 2010, 05:38:52 AM »

I would never try to service the rear brakes for the first time without a pit, or without taking the drive wheels off, one or the other.  It's hard to get in there.  You probably have automatic slack adjusters and I wouldn't try to adjust them on my own for the first time either - their ratchet mechanisms need to be adjusted and work properly or trouble down the road.

DD3's are simply the style of brake cannister on the rear drive wheels.  They work, as far as the parking brake is concerned, differently than other types of rear brakes, but if you don't know anything about air brakes that doesn't mean much to you.  the just have a locking clutch on the push-rod that when you apply the parking brake locks the push-rod out and on.  That locking mechanism is like a sprague clutch and uses little ball bearings and ramps to lock onto the push rod.  Once it is set, it should stay on regardless of anything.  It needs no air pressure at all to stay applied, you need at least 100 PSI to get it to disengage. 

What is probably happening is that the push-rod is slipping back, releasing the brakes, or the brakes are out of adjustment so you don't get full application when you apply the brakes.  Or you aren't setting the parking brake properly.  Or the parking brake diaphram on one or both of the brake cannisters is leaking and doesn't set the parking brake properly.  Or the 85 PSI parking brake air regulator isn't working right.  There are a lot of reasons why the parking brakes might not be working properly.

When you set the parking brake, are you just pulling up the knob or do you also give a big press on the brake pedal?

Brian
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« Reply #19 on: September 14, 2010, 06:02:55 AM »

Here is a pretty good link to dd3, from the source. good luck. Brians advice about getting it somewhere with a pit or well blocked is a great idea for the first time
http://www.bendixvrc.com/itemDisplay.asp?documentID=2393
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John O
Eastern Shore of Maryland.
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« Reply #20 on: September 14, 2010, 07:35:12 AM »

 Grin As I recall, Jim has a hole he dug recently that he can use as a pit  Grin  By the way, LOVE those trees!!!
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RJ
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« Reply #21 on: September 14, 2010, 10:10:07 PM »

Highway -

Before you spend a bunch of time/money on this, the problem may be in the way you're setting the brake.  DD3 must be set the correct way, or they don't hold well.

The correct procedure to set/release a DD3 is as follows:

Setting:

1. Position vehicle where you want it, lightly holding it in place with the service brakes.

2. Allow system air to build to governor cut-out (about 120 psi.)

3. With just enough of a service brake application to hold the vehicle, pull the parking brake.

4. Release service brake.  Bus should not move.


Releasing:

1. Start vehicle, allow air pressure to build to governor cut-out.

2. With foot resting on the service brake, push down on parking brake knob.

3. After pushing down parking brake knob, apply a FULL service brake application (all the way to floor) and hold for 3-5 seconds.

4. Release service brake.  Coach should roll.  If not, repeat steps 1 - 3.


DD3s are good brakes, but non-industry folk often have problems until they learn the system.  Even some industry folk don't understand what's going on - ask BK!

In your situation, after following the proper procedure, if the coach rolls, it's time to have a serious look at what's going on!

FWIW & HTH. . .

 Wink
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RJ Long
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« Reply #22 on: September 14, 2010, 10:18:42 PM »

RJ,
Thanks for the simple reminder that not all of us have been around these beasts for this application/disengaging of DD3's to be second nature!
Grin  BK  Grin
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Busted Knuckle aka Bryce Gaston
KY Lakeside Travel's Busted Knuckle Garage
Huntingdon, TN 12 minutes N of I-40 @ exit 108
www.kylakesidetravel.net

Grin Keep SMILING it makes people wonder what yer up to! Grin (at least thats what momma always told me! Grin)
Highway Yacht
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« Reply #23 on: September 15, 2010, 04:28:01 AM »

Highway -

Before you spend a bunch of time/money on this, the problem may be in the way you're setting the brake.  DD3 must be set the correct way, or they don't hold well.

The correct procedure to set/release a DD3 is as follows:

Setting:

1. Position vehicle where you want it, lightly holding it in place with the service brakes.

2. Allow system air to build to governor cut-out (about 120 psi.)

3. With just enough of a service brake application to hold the vehicle, pull the parking brake.

4. Release service brake.  Bus should not move.


Releasing:

1. Start vehicle, allow air pressure to build to governor cut-out.

2. With foot resting on the service brake, push down on parking brake knob.

3. After pushing down parking brake knob, apply a FULL service brake application (all the way to floor) and hold for 3-5 seconds.

4. Release service brake.  Coach should roll.  If not, repeat steps 1 - 3.


DD3s are good brakes, but non-industry folk often have problems until they learn the system.  Even some industry folk don't understand what's going on - ask BK!

In your situation, after following the proper procedure, if the coach rolls, it's time to have a serious look at what's going on!

FWIW & HTH. . .

 Wink

Thanks for this procedure. I'm not sure what the air pressure was when I set the parking brakes but will watch it closely the next time. I do know that the 2nd time it rolled I did not apply the service brake before setting the park brake. Reason being, I backed it up the incline... took my foot off of the service brake and let it slowly roll forward and then I pulled the park brake and it brought the bus to a sudden stop. I did it that way to make sure the park brake would stop the bus...and it did so very well.. The bus held there in the same spot for at least a few hours I know. I didn't notice it had rolled forward 12 feet until the next morning. I can't understand why it would roll just 12 feet and then stop while it is still on the incline. It looks like once the weight of the bus got it moving, it wouldn't stop until it reached the botton of the incline. I will do test #3 on it today using this procedure and report back here. I'm still going to take Clifford's advice and service the brakes anyways even if this procedure works since there is no tellings when it was last done, and I also need to learn how to do it.
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« Reply #24 on: September 15, 2010, 04:53:11 AM »

That tells me that your DD3 cannisters are not locking the push-rod out.  When you simply pull the parking brake knob out as you did, 85 psi of regulated air is applied to the parking brake section of the DD3 (which is separate from the service brake section) and air is removed from the locking port so that the locking mechanism can operate.  The 85 psi is applied from the emergency brake tank, which is separate from the service brake dry tank.  It will hold the parking brake  as long as it has air pressure, and then the locking mechanism is supposed to continue to hold the brake on.  It sounds to me like your brakes are applying fine, then as the pressure in the emergency brake tank bleeds off the push rod is released rather than held by the lock.

Which brings us full circle to Cliffords advice to service the DD3's and adjust the brakes.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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« Reply #25 on: September 15, 2010, 12:39:14 PM »

Hwyway, My MC-7 did pretty much the same thing to me while I was standing next to it. I put the parking brake on and went outside to unhook the toad when all of a suddenly the brake released and it started rolling backwards. I just about killed myself chasing the bus, jumping inside and applying the brakes. Pulled off the access road and back up the incline. I reset the parking brake and set there a minute to make sure it wouldn't roll, then back outside to unhook and it did it again. After I got home I replaced the parking brake push-pull and that fixed it. just a little bit scary!!!! Good luck with the fix.

Richard
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busshawg
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« Reply #26 on: September 15, 2010, 12:59:53 PM »

could be your drums have expanded from the heat and simply have too much diametre. I know the brakes should set up but it could be a contributing factor. Same thing happened to me only I was still in the bus when it started to roll. The only axle that is applied when applying the parking brake is your drive axle. I removed the wheels and drums. I found the rollers needed a very good cleaning. Also when you remove the drum and then brake shoes , it will allow you to turn the brake cams full circle, allowing the grease to penetrate all the way around the shaft. After cleaning greasing and over greasing, then cleaning , I put new drums on it works great. Something else to keep in mind is that the rollers only require a LITTLE grease. Mine were so over greased the shoes were very dirty and greasy. This alone will have allowed the bus to roll on an incline when teh brakes were applied. I think you should at least remove the drums and inspect. Don't just do a brake set up. You'll never look back and say, sure am glad I didn't inspect those brakes!

Grant
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Have Fun!!
Grant
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« Reply #27 on: September 15, 2010, 03:25:04 PM »

sorry, couldnt resist  Grin forward it to 4:30

RV (the movie) part 17 (ENDING)
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The Little GTO is a 102" wide and 40' long 1983 GMC RTS II and my name is Teresa in case I forgot to sign my post
Highway Yacht
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« Reply #28 on: September 15, 2010, 05:59:01 PM »

sorry, couldnt resist  Grin forward it to 4:30


YOU are just too CRAZY Teresa!!!!!!.. That was such a funny movie..
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1979 MC-9  8V71-Turbo / HT740             * www.MciBusTalk.com *
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Highway Yacht
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« Reply #29 on: September 15, 2010, 06:10:37 PM »

Ok...UPDATE!!!!.... I used the Park Brake Peocedure listed above earlier today and so far the bus hasn't moved any at all. I'll check on it again later tonight and also again tomorrow morning.  Also, I do have an air leak at the Duel Brake Application Valve located in the spare tire compartment. The air is coming out past the little plastic diaphragm at the bottom. I removed the lower half and played around with it a little and it does seem to not be leaking as bad but yet still leaks some air. I think the whole valve needs to be removed and cleaned and maybe replace all the orings.
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