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themechanic
New Member

6 Posts
Posted - 08/12/2015 :  06:52:17 AM  Show Profile  Visit themechanic's Homepage  Reply with Quote
I am working on a 2007 thomas c-2 saf-t-liner. The parking brake will not release. When the parking brake button is pressed the air leaks from inside dash. We have replace the parking brake valve.

themechanic
New Member

6 Posts
Posted - 08/12/2015 :  07:27:56 AM  Show Profile  Visit themechanic's Homepage  Reply with Quote
on the previous issue the parking brake valve replacement did not help. brakes are still not releasing
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aaronwilmoth80911
Top Member

538 Posts
Posted - 08/12/2015 :  10:48:10 AM  Show Profile  Visit aaronwilmoth80911's Homepage  Reply with Quote
Sounds like a problem with an AMU. They are under the bus towards the rear axle. You will probably need to get an air and wiring diagram for your bus specifically to try and diagnose them.
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tigger2
Advanced Member

USA
469 Posts
Posted - 08/12/2015 :  10:53:47 AM  Show Profile  Click to see tigger2's MSN Messenger address  Reply with Quote
Are you holding full pressure on the foot valve while trying to release the parking brake? If this is a lift bus is the lift switch turned off?
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themechanic
New Member

6 Posts
Posted - 08/13/2015 :  11:17:01 AM  Show Profile  Visit themechanic's Homepage  Reply with Quote
Yes full pressure on the brake and the wheelchair lift is off
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tigger2
Advanced Member

USA
469 Posts
Posted - 08/13/2015 :  11:27:14 AM  Show Profile  Click to see tigger2's MSN Messenger address  Reply with Quote
Do the brake lights com on with the pedal and will the dash come alive with key off with brake activation? We have had bad brake light switches bad in the AMU, usually the first section on the drivers side. The interlock needs to see brake signal to release.
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themechanic
New Member

6 Posts
Posted - 08/14/2015 :  04:25:02 AM  Show Profile  Visit themechanic's Homepage  Reply with Quote
Okay I agree but what does the park brake AMU look like?
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aaronwilmoth80911
Top Member

538 Posts
Posted - 08/14/2015 :  12:29:52 PM  Show Profile  Visit aaronwilmoth80911's Homepage  Reply with Quote
Just do a Google search on "Thomas C2 AMU" and you will find images for them. There are probably about 5 of them sandwiched together in a block. You will have to have your VIN to get the correct one, as they all look very similar, but are ported differently.
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grandyc
Senior Member

United States
58 Posts
Posted - 08/17/2015 :  06:22:37 AM  Show Profile  Visit grandyc's Homepage  Reply with Quote
There is a check Valve that comes out the treddle valve. It seems to me i had this issue once and that was the problem.
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