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Author Topic: Parking Brake Problem  (Read 1055 times)
Tikvah
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« on: June 09, 2014, 04:11:19 PM »

I pulled out of the campground a few days ago and thought it was odd that my parking brake didn't want to release.  I moved the bus forward and back, set the brake, released, the brake, and just played with it.  It seem to free up and I determined that I must have had some sticky brakes from sitting for a month.  The trip went well with no issues.  Then, a few day later, when I returned, I was backing into my space and stopped to check for trees, etc.  When I got back into the bus it wouldn't release again.  I again moved forward, back, set the brake, released the brake, and generally tried everything.  No luck.
I only had a couple feet to move, so I simply forced it.
Now I have to do something.
Yes, I had air pressure, about 110psi when I looked. 

I have a 1989 / 1990 MCI 102 A3 with the 6V92TA and Alison 740

I think that means I have the DD3 brake chambers.  At least I remember hearing that someplace.  Would it be the brake chambers, or could I have a brake shoe problem?  I hope I don't have to pull the wheels, I'm tight against a fence on one side. 

I'm not looking forward to crawling under, but I'll do what I must.  Any ideas?
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I couldn't repair my brakes, so I made my horn louder.
1989 MCI-102 A3
DD 6V92 Turbo, Alison
Tons of stuff to learn!
Started in Cheboygan, Michigan (near the Mackinaw Bridge).  Now home is anywhere we park
Dave5Cs
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1979 MCI MC5Cs 6V-71 HT-740 Allison, Roseville, CA




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« Reply #1 on: June 09, 2014, 06:18:22 PM »

Dave could be your inversion valve at the back axle well about in the middle or your relay valve. Have someone press on the brakes as you lay down at the back wheels and listen to see if it has a leak when pressed. If it does it is probably the Brake relay. It is the kind of round one by the back of the bay wall with brake lines going to it and out to the cans. The inversion has a bunch of lines going to it and a double check valve attached to it. It inverts when you have a leak and not enough air for your brakes to the emergency diaphragms of the cans.
If you have a bad push pull valve it will leak at it when you put it in the middle.

Try
http://www.anythingtruck.com/category/htp-brake-air-valves.html

« Last Edit: June 09, 2014, 06:20:15 PM by Dave5Cs » Logged

eagle19952
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« Reply #2 on: June 09, 2014, 07:35:54 PM »

When were they last greased ?
Were they applied with a full pedal actuation then set ?
Or do you apply them enough to hold and then set the park ?
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Donald PH
1978 Model 05 Eagle w/Torsilastic Suspension,8V71 NA, DDAllison on 24.5's 12kw Kubota.
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niles500
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« Reply #3 on: June 09, 2014, 09:11:17 PM »

please block the frame before you go under an aired up bus, sorry I had to say it, but......
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- Niles
krank
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« Reply #4 on: June 09, 2014, 10:24:19 PM »

Verify the pedal pivot is not starting to seize.
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Jim Eh.
1996 MC12
6V92TA / HT741D
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Winnipeg, MB.
Tikvah
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« Reply #5 on: June 10, 2014, 04:09:53 AM »

The inversion valve and the push-pull valve are both new last fall.

As to applying with the pedal at full actuation... I'm not aware that is necessary.  If the bus is rolling slightly and I pull the brake valve the bus stops with a sudden jerk. 

Never thought of the relay... actually didn't know there was a relay.
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I couldn't repair my brakes, so I made my horn louder.
1989 MCI-102 A3
DD 6V92 Turbo, Alison
Tons of stuff to learn!
Started in Cheboygan, Michigan (near the Mackinaw Bridge).  Now home is anywhere we park
gumpy
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« Reply #6 on: June 10, 2014, 05:19:33 AM »

Sounds like you may not be releasing them properly.

You must apply a full brake pedal application AFTER you push in the button. This allows the locking mechanism inside the chamber to release.

It could be that they need to be serviced and greased, too.

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Craig Shepard
Located in Minnesquito

http://bus.gumpydog.com - "Some Assembly Required"
eagle19952
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« Reply #7 on: June 10, 2014, 08:23:22 AM »

the reason I asked is that IF one was to apply a 100psi foot application (for instance if your brakes are out of adjustment and the s cam must travel further) to set the service brake, and you need a 100 psi application to release them, they may not have the travel within the DD3 to release.
 I may not be the best at putting my thought to paper/post.  Huh
I only apply as much foot brake as is needed to not roll then apply the park.
Sometimes that is none but never a full to the floor 100 psi application.
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Donald PH
1978 Model 05 Eagle w/Torsilastic Suspension,8V71 NA, DDAllison on 24.5's 12kw Kubota.
Wants Paint Smiley
Previously owned by Wee Willie Ent.
Tikvah
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« Reply #8 on: June 10, 2014, 06:30:37 PM »

I didn't expect that.  In the past I could release the brake and the bus would begin to roll freely without any brake pedal application.  I'm sure I have the DD3 chambers.
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I couldn't repair my brakes, so I made my horn louder.
1989 MCI-102 A3
DD 6V92 Turbo, Alison
Tons of stuff to learn!
Started in Cheboygan, Michigan (near the Mackinaw Bridge).  Now home is anywhere we park
luvrbus
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« Reply #9 on: June 10, 2014, 07:43:08 PM »

Could be your regulator has gone bad and allowing more than the regulated pressure of 85 lbs they are set to for applying the parking brake lots of DD3's will release without applying brake pedal pressure fwiw
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Tikvah
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« Reply #10 on: June 11, 2014, 05:17:44 AM »

The comments are appreciated, but not at all what I expected.  I guess I was thinking I needed to crawl under and pull the DD3 chambers off and rebuild them.  I'm not hearing that from anyone.  Am I wrong to think it would be directly related to the chambers?

As soon as the mosquitoes subside, I'll go looking for a relay under there.  I don't remember seeing one, but it should be an easy fix.  I don't understand what you think needs to be lubricated.  Can it be described?  what will the relay look like?  wires?  hoses?
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I couldn't repair my brakes, so I made my horn louder.
1989 MCI-102 A3
DD 6V92 Turbo, Alison
Tons of stuff to learn!
Started in Cheboygan, Michigan (near the Mackinaw Bridge).  Now home is anywhere we park
luvrbus
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« Reply #11 on: June 11, 2014, 05:30:53 AM »

Careful what you wish for sometimes the latch assembly is so rusted and gummed up they need to be remove to clean  Roll Eyes
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gumpy
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« Reply #12 on: June 11, 2014, 05:45:13 AM »

I was thinking there were grease zerks on the DD3 chambers for the latch assembly. But it's been awhile since I was under my own bus, so I may be mistaken.

I think you are probably on the right track thinking it's related to the DD3 chambers. But it could be as simple as lubrication, or proper application of foot pedal
upon releasing them. It's possible a diaphragm has developed a leak with is preventing one from releasing on it's own without the aid of the foot pedal.

I doubt it's a relay, but again, I could be wrong.


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Craig Shepard
Located in Minnesquito

http://bus.gumpydog.com - "Some Assembly Required"
luvrbus
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« Reply #13 on: June 11, 2014, 05:57:48 AM »

There are grease zerks on the DD3's I also doubt a relay problem
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eagle19952
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« Reply #14 on: June 11, 2014, 08:51:27 AM »

There are grease zerks on the DD3's I also doubt a relay problem


They are located here: tho covered with crap, you can see them, that are also left and right and there is an upside down that needs to be down to drain water and road krap.




On the left DD#:
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Donald PH
1978 Model 05 Eagle w/Torsilastic Suspension,8V71 NA, DDAllison on 24.5's 12kw Kubota.
Wants Paint Smiley
Previously owned by Wee Willie Ent.
eagle19952
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« Reply #15 on: June 11, 2014, 09:41:06 AM »

http://www.bendixvrc.com/itemDisplay.asp?documentID=4420

EVERY 3 MONTHS, 900 OPERATING HOURS, OR 25,000
MILES
When grease fitting is provided, grease with Lubriplate
“Aero” lubricant.
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Donald PH
1978 Model 05 Eagle w/Torsilastic Suspension,8V71 NA, DDAllison on 24.5's 12kw Kubota.
Wants Paint Smiley
Previously owned by Wee Willie Ent.
Tikvah
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« Reply #16 on: June 19, 2014, 09:35:32 AM »

There has been some discussion among friends as to the identification of my brake chambers.  Below are a few pictures.





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I couldn't repair my brakes, so I made my horn louder.
1989 MCI-102 A3
DD 6V92 Turbo, Alison
Tons of stuff to learn!
Started in Cheboygan, Michigan (near the Mackinaw Bridge).  Now home is anywhere we park
bevans6
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« Reply #17 on: June 19, 2014, 10:05:50 AM »

Those look like DD-3's to me.  MCI used nothing else until they stopped using them sometime in the 1990's I think.  If you set the parking brake with the push/pull valve you get (if the regulator is working) an 80 - 85 psi application to the parking brake chamber, which is the rear-most chamber.  That expands the parking brake diaphragm and pushes out the push rod while at the same time removing pressure from the locking section so the locks engage holding the push rod out.  If you then do a service brake application it puts air pressure into the service section (middle hose) and what you get is the average of the service brake pressure and the parking brake pressure based on the relative volumes of each chamber.  It might push the push-rod a tiny bit harder, but it's not the same as a full normal service brake application pressure.  DD-3's don't compound the parking and service brake pressure the way that spring brakes do.  Regardless it is poor practice to "set" the parking brake with a service brake application after the parking brake is applied (but I think we all do at some point).

As far as partial releases go, as soon as air is applied to the locking port the rollers are released.  If the pushrod hasn't relaxed due to air leaking out from the parking brake chamber the rod will just unlock and the brakes will release without a service brake application. That's because the locks don't actually lock onto the push-rod until it relaxes and moves back in to the chamber a tiny bit.  Normally a brake application is required.  The design is such that the pushrod pretty much will either lock or unlock, and being sticky won't cause a partial unlock or make the brakes drag.  If it didn't they would drag all the time.  There is a pretty big spring inside the DD-3 to force the pushrod back in, plus the shoe springs inside the brakes.  You do need to sparingly lube the locking section of the DD-3, but I don't look for it to cause a partial release of the parking brake unless the can is about shot.

Brian
« Last Edit: June 19, 2014, 10:21:05 AM by bevans6 » Logged

1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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