Parking Brake Problem

Tikvah · 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?

Dave5Cs · 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

eagle19952 · 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 ?

niles500 · 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......

Jim Eh. · June 09, 2014, 10:24:19 PM

Verify the pedal pivot is not starting to seize.

Tikvah · 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.

gumpy · 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.

eagle19952 · 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.

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.

Tikvah · 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.

luvrbus · 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

Tikvah · 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?

luvrbus · 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

gumpy · 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.

luvrbus · June 11, 2014, 05:57:48 AM

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

eagle19952 · June 11, 2014, 08:51:27 AM

Quote from: luvrbus on June 11, 2014, 05:57:48 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#: