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RonF
Top Member
867 Posts |
 Posted - 12/03/2014 : 04:05:41 AM
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Never seen these before but I'm using logic to troubleshoot them. I have a bus that sometimes the foot brake is locking the rear chambers. I have taken both large lines off and they have air coming out of the lines without the brakes applied. I am tracing the lines to find the malfunctioning valve, haven't found it yet. I don't want to just start replacing stuff. I suspect it could be the foot valve but of course this is on a flat nose bus and getting to the lines are not easy. Any ideas?
Additionally I was told by the long time mechanic here there is a kit or parts you can order to change it over, anyone know of this? |
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slippert
Top Member
USA
630 Posts |
Posted - 12/03/2014 : 04:42:56 AM
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In what location is your foot valve mounted on firewall, or on floor? I have seen Semi trucks with valve mounted on floor that the plunger would get corroded and stick causing foot valve to hang up and keep brakes partialy applied... suppose that could happen if valve is mounted off floor too... but not as common as chemicals and dirt can't set on and around plate and plunger... the foot valve signals the relay valves for brakes to apply, if you have air coming out of service lines to chambers, it is coming from a relay valve mounted near that axle.... I would check at relay valve first...to see if signal line has pressure on it that should tell you if foot valve is sticking, if no air pressure coming from foot valve to signal relay to activate then relay valve could be malfunctioning...also you said the rears are hanging up so probably not foot valve as problem with that should keep both front and rear applied... this may not be alot of info but hope it helps ...
Bendix.com has some decent info online for trouble shooting air brake systems... |
Edited by - slippert on 12/03/2014 04:57:05 AM |
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RonF
Top Member
867 Posts |
Posted - 12/04/2014 : 04:51:24 AM
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| The foot valve is floor mounted and I am working on it in my "spare" time, haha, working my from the chambers forward. We shall see. |
US Army retired CMBT |
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Thomasbus24
Administrator
USA
4545 Posts |
Posted - 12/04/2014 : 05:44:27 AM
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Last time I had that (couple months ago) it was the treadle (pedal) valve. Of course it was a transit and there was nothing remotely easy about the job!!!!
There are repair kits that I know of, but it seems like you'd still have to remove the valve to do the job. Go new and forget it...nothing like having to do a job twice because an o-ring got nicked or something  |
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RonF
Top Member
867 Posts |
Posted - 12/08/2014 : 09:37:05 AM
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Problem found.
There is a balance valve on these older things and it appears it is not working. If you have the parking brake applied and put your foot on the break pedal and release the parking brake, the parking brake will release. However once you do that then you will get a constant supply of air to the chambers for the foot brake side of the balance valve. If you release the parking brake without putting your foot on the brake, all is well.
Once you have the brake in a lockup up state the only way to release them is to pump all the air out of the system build it back up, release the parking brake without touching the foot brake.
That's the good news.
The bad news is, the balance valve is no longer in existence and you have to retro-fit the rear brake system with the modern R-12, QR-1,30/30 chambers, slack adjusters, and maybe the chamber mounts. You got to remove a few air lines, plug some ports and all is well. |
US Army retired CMBT |
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Thomasbus24
Administrator
USA
4545 Posts |
Posted - 12/08/2014 : 11:48:12 AM
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| Thanks for the update. How old a bus is this? |
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RonF
Top Member
867 Posts |
Posted - 12/09/2014 : 05:11:08 AM
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| 1994 Bluebird all American 72 passenger TC 2000 |
US Army retired CMBT |
Edited by - RonF on 12/09/2014 05:11:34 AM |
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Mechan1c
Top Member
USA
853 Posts |
Posted - 12/09/2014 : 09:36:24 AM
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| Do you have the OE p/n for the valve you need? If it's a Bendix part someone's brake supplier might have one? You never know... |
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RonF
Top Member
867 Posts |
Posted - 12/10/2014 : 03:56:44 AM
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| It's a bluebird part with a bluebird part number. Already tried Bendix and Haladex. It's an ITI company and the valve is no longer made. |
US Army retired CMBT |
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Air-Mech brakes
