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Old 08-27-2016, 01:36 PM   #15
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Here is my theory of whats wrong.

1, You are adjusting your brakes by turning the jacked up wheel and backing them off until there is no drag. That is probably leaving to much travel in the chamber rod. Remember 1" is the proper travel

The proper procedure is to tighten the slacks until they don't move, turning them the correct way will lock the wheel. Then back them off about 1/4 turn. Take a bar and see if you can move the slack adjuster away from the chamber 3/4 inch.

That all the movement you want, prying by hand.

2. A suspect that with the brakes out of adjustment, you are depleting your tank air, when you apply the brakes. That's why you get a 90 psi reading.

I'm also curious if you did this test with the parking brake on. If you did, the inversion or anti-componding valve may also directed some of the air to the spring chambers while holding down the pedal, using more of your tank capacity.

The anti-componding valve is there to protect from componding service and spring brake pressure at the same time.
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Old 08-27-2016, 07:39 PM   #16
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twin boat... one of the tests of the air brake system is an engine off test of the ability of the brake system to support at least 5 complete stops ...... this is a timed test event to be sure that there is capacity in the system (tanks) to fully stop the vehicle many times without the engine running and of course if the air compressor is not running... this provides enough air to stop the vehicle safely in the event of an air compressor failure... or the engine stops running...

This timed event is so that you can safely stop the truck/coach with the service brakes before the pressure drops below the magic 60-65 psi and the e-brake/parking brake switch pops and sets those brakes....

Remember that with the parking brake set.... the s-cam is engaged with the mechanical spring in the brake chamber... since pressing the service brake (brake pedal) and having the parking brake chamber engaged (air removed for this chamber) there is enough mechanical advantage if these 2 systems functioned at the same time to mechanically damage parts of an air brake system... so the valving (compound valve) on an air brake system won't let you apply the brakes when the e-brake is set... well you can press the brake pedal but air IS NOT applied to the spring brake... yes you can sometimes hear air moving when you press the service brake pedal.... but valving (compound valve) is preventing that air pressure from adding to the pressure of the spring in the service chamber....

During e-brake application... the spring in the chamber has fully extended the shaft, and the slack has applied pressure to the s-cam and the shoes are pressed against the drum...

Please remember that most stops are completed with simple applications of the brake pedal and can be obtained with about 20 psi of pressure at the spring brake... its only those fast, panic stops that require more than 20 psi of pressure... the brake system has, when functioning correctly a huge safety factor..
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Old 08-28-2016, 11:11 AM   #17
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There is a lot of great advice here and what we have learned is the air brake system has a lot of unique process that do not apply same as hydrolic systems.

The op sounds like they have a good skill set but they are trying things that are changing the system design instead of locating the simple fault.

We did same with a stupid shifting problem but that was a stupid time...

OP needs to stop and take the unit to a certified place and take along all of the harvested materials and leave their pride and ego at home.

Air brakes are complicated systems and pedal pressure is not direct like in an auto so it could be a simple adjustment or a faulty valve

Something the experts have changed so many times they know what to look for first.

The op may have introduced problems that need to be corrected as well.
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Old 08-28-2016, 12:44 PM   #18
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OP, there's a lot of information in this thread, and a lot of it is VERY incorrect.
Please take the coach to a semi truck/trailer/independent/dealer that does a lot of air brake work. They'll have certified technician that can inspect your system and advise from there.
You sound like you have enough experience to communicate with them and understand what they find.
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Old 08-28-2016, 10:00 PM   #19
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Quote:
Originally Posted by mackwrench View Post
OP, there's a lot of information in this thread, and a lot of it is VERY incorrect.
Please take the coach to a semi truck/trailer/independent/dealer that does a lot of air brake work. They'll have certified technician that can inspect your system and advise from there.
You sound like you have enough experience to communicate with them and understand what they find.
While reading all the replies I was hoping you would join the thread. I've learned a lot from your posts about air brakes.
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Old 08-29-2016, 09:11 AM   #20
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Originally Posted by Ray,IN View Post
While reading all the replies I was hoping you would join the thread. I've learned a lot from your posts about air brakes.
I'm flattered.....I'm all for giving good sound advice when I know I can see the problem from my keyboard.

Air brakes, while not very complicated, have there own set of issues that sometimes only a professional eye can spot.
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Old 08-29-2016, 09:12 AM   #21
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Originally Posted by TQ60 View Post
There is a lot of great advice here and what we have learned is the air brake system has a lot of unique process that do not apply same as hydrolic systems.

The op sounds like they have a good skill set but they are trying things that are changing the system design instead of locating the simple fault.

We did same with a stupid shifting problem but that was a stupid time...

OP needs to stop and take the unit to a certified place and take along all of the harvested materials and leave their pride and ego at home.

Air brakes are complicated systems and pedal pressure is not direct like in an auto so it could be a simple adjustment or a faulty valve

Something the experts have changed so many times they know what to look for first.

The op may have introduced problems that need to be corrected as well.

Best post on this thread.
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Old 08-30-2016, 04:13 PM   #22
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I would check that the pins on the rear slack adjusters are not frozen in place. The pins at the turn buckle at the end of the rods.
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