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Author Topic: help with air brake problem  (Read 1578 times)
thomasinnv
Derrick Thomas
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« on: September 24, 2011, 10:08:40 PM »

A friend of mine has a motor home that is around 5 or so years old, a 39' fleetwood on a freightliner chasis, air suspension and air brakes. It has set for a couple years un moved and when he tried to move it today he has an air problem. The air builds to 120 just fine, but when you press on the brake pedal the front and rear air gauge drops like a rock. same thing if you try to release the parking brakes, drops like a rock and you hear a massive amount of air under the rig. was fine when it was driven in and parked there a year or two ago. is there some type of main valve under there somewhere that is causing this? what say the experts?
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wal1809
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« Reply #1 on: September 25, 2011, 03:18:15 AM »

First question is where is the air coming from specifically when you hear it?
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« Reply #2 on: September 25, 2011, 04:07:58 AM »

Sure sounds like bad diaphragms in the brake chambers.
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Jon Wehrenberg
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« Reply #3 on: September 25, 2011, 05:15:21 AM »

What you have described is 2 different leaks.

WHen you try to release the parking  brakes and it leaks that is "Emergency air".

When you depress the brake pedal that is "Service Air" that is leaking.

Tough to diagnose from here it would be pure guess. You need to get under there and identify where its coming from.

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zubzub
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« Reply #4 on: September 25, 2011, 06:20:11 AM »

WAG is the air relays are wonky....if you are lucky tapping on them etc might help...also a little oil if you crack a line.  Seems to me the relays could easily get a little corrosion/sticky sitting for a couple of years, and the relays are probably similar for the emerge brake and service...actually could be just one combined anti compounding valve... which would explain the identical symptoms....WAG. 
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luvrbus
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« Reply #5 on: September 25, 2011, 06:25:09 AM »

It has a dual air system and mice love the the plastic lines and those have a lot of the push in type fitting with plastic lines

good luck
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thomasinnv
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« Reply #6 on: September 25, 2011, 07:04:57 AM »

not sure I will have time today, but sometime in the next day or two I will go over to his place and crawl under there and see where the air is coming out of.
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belfert
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« Reply #7 on: September 25, 2011, 07:21:44 AM »

Just as with a bus be sure to block it up while under there.  A motorhome can kill you just as dead as a bus.  I've seen motorhomes that get pretty low with the air dumped.
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« Reply #8 on: September 25, 2011, 04:23:54 PM »

This info may be dated, but then again, so am I!  Grin

When trucks started using spring parking brakes as opposed to air parking brakes (which would eventually leak off & release the brakes), they started having massive brake component failures. Come to find out if the service brakes were applied while the parking brakes were applied, the combination on the two would put way more force on the brake assembly than it was designed to handle & it something would fail. Soon all systems were equipped with a protection valve which would not allow air pressure to be applied to the service brakes if the parking brakes were applied. If the diaphragm(s) in that valve fail, all air pressure will exit if you try to disengage the parking brakes OR if you try to apply the service brakes.

I seem to remember the valve in question has 5 or 6 connections and is usually located in such a way that the entire vehicle has to be disassembled to replace it....... DAMHIK!  Angry

This valve may have been replaced with some electronic device in newer trucks, I don't know.

TOM
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« Reply #9 on: September 25, 2011, 05:27:27 PM »

An anti-compounding valve is just a relay valve with a double check valve as part of the assembly.  Not all that complicated.

http://www.zafr.com/trucktcom/brakes_compounding.htm

http://www.anythingtruck.com/Merchant2/merchant.mv?Category_Code=HTP-AIRB&Product_Code=060-289714N&Screen=PROD
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« Reply #10 on: September 25, 2011, 06:29:07 PM »

It is because both the service and the parking brake drain air fast when applied, that I suspect the anti compounding relay/valve.  Also it is a good way to lose air fast, as opposed to a small leak in a diaphram.
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luvrbus
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« Reply #11 on: September 25, 2011, 06:56:05 PM »

The anti compound feature on a  R-14-R-16 works after the spring brakes are released could be the QR feature but I think he he has bad lines on the front and a rear with that being a dual air system.

Derrick will get her done he has a set of Jakes and blower seals here he need to install while I watch  LOL

good luck  
« Last Edit: September 25, 2011, 07:04:05 PM by luvrbus » Logged

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thomasinnv
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« Reply #12 on: September 25, 2011, 09:40:55 PM »

I'm gonna try to get a look at her tomorrow. I will be setting up the gospel tent in the AM, but might have some time tomorrow afternoon to get a gander under neath. Good thing about the freightliner chassis is that even with all the air dumped I can still almost sit up underneath it. lots of room to crawl around.

Clifford, when I get there to do the jakes and seals I need your set of eyeballs. I am still fighting a major oil leakage problem. I have already replaced just about every oil seal, hose and gasket short of ripping off the heads. I have catch cans so it's not the air box drains, we will talk in a few weeks.
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There are three kinds of people in this world....those that make things happen, those that watch things happen, and those that just wonder what the heck is happening. Which one are you?

1977 MCI Crusader MC-8
8V71N/740
95% converted (they're never really done, are they?)
AndyG
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« Reply #13 on: September 26, 2011, 07:05:12 AM »

Don't forget to chock the wheels just in case the brakes decide to release while you are under the coach. 
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thomasinnv
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« Reply #14 on: September 26, 2011, 02:54:15 PM »

got under there today and took a gander. Seems that something has chewed through the big air brake lines that attach to the valve just in front of the rear axle.
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There are three kinds of people in this world....those that make things happen, those that watch things happen, and those that just wonder what the heck is happening. Which one are you?

1977 MCI Crusader MC-8
8V71N/740
95% converted (they're never really done, are they?)
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