WILLIAMS AIR THROTTLE, Loosing Air while driving?

scenicruiser997 · March 13, 2011, 02:25:21 PM

On our last trip out in the GM 4905, I noticed that as we were driving I would lose air from 120PSI down to about 90PSI then it would fill back up to 120PSI and repeat this cycle. It would take us 5-10 miles to drop the air to 90 PSI, before the governor would kick in and rebuild the air. When we pulled over and parked, and let the motor run with no throttle, the air would hold steady. Am I right, believing that the Air Throttle is what is leaking or could it be something else? Please let me know what you think. Aaron in Oklahoma

buswarrior · March 13, 2011, 04:19:20 PM

The difference between driving and parked is the parking brake circuit.

Engine off, aired up, chock the wheels and release the parking brake, your leak will present itself.

happy coaching!
buswarrior

gus · March 13, 2011, 06:25:29 PM

Makes sense to me. It leaks when driving and doesn't when parked with the engine running and the air throttle not being used.

An air throttle exhausts air every time you let up on it so it uses a lot of air underway unless you don't move it at all.

Try moving the air throttle in and out when parked and watch the air pressure.

If you have spring or DD3 brakes the hold off cans can be leaking. Easy to tell, just don't use the parking brake when parked to see if the air pressure holds. If it leaks, set the parking brake to see if it stops leaking.

buswarrior · March 13, 2011, 06:32:12 PM

Air throttle uses only enough air to fill the diaphragm/piston down the back and that's it.

No ongoing consumption, unless it leaks, or unless you lift your foot on and off it. If it leaked that much, it would be torn wide open, and then some.

Let us know about the parking circuit test.

happy coaching!
buswarrior

scenicruiser997 · March 13, 2011, 08:10:55 PM

Just took the air throttle off bus and cleaned it up. O-rings looked good, just had a lot of black goop inside the unit. Now I'm having a really hard time lining up the Air lines to reinstall the throttle. I will try the parking brake as soon as I can get the @#*$ air lines back on the throttle. Thank you guys, for the help!!!

scenicruiser997 · March 14, 2011, 07:33:03 AM

Well I got big problems. After 2 hours inside the compartment under the driver's seat, I got the Air lines hooked back up. But now when I rev up the engine, I get air blowing out the exhaust port, and can see the pressure dropping fast. So I guess when I pulled the air throttle apart and cleaned it in the parts washer, I must have put something backwards when I rebuilt the throttle. Buswarrior, said that it should only exhaust only when I release the throttle. Also, Buswarrior, you were right. I built up air then shut off the engine, and released the parking brake and YES, I could hear air coming out by the passenger rear tire area.
Now I have two things to fix.

buswarrior · March 14, 2011, 06:34:16 PM

Yup, the life of a busnut...

The stuff I try to fix, won't, the stuff I leave alone, breaks...

Chin up, you'll get it sorted out!

happy coaching!
buswarrior

gus · March 15, 2011, 07:48:07 PM

Reusing O rings is almost always a bad idea no matter how good they look - that has been my experience and it took me a while to catch on since they always looked so good.

Using parts washer solvents is also a bad idea if it included the old O rings.

The new O rings should also be lubed with some kind of inert lubricant depending on use.

It is also very easy to replace air cylinder parts in reverse - don't ask me how I became an expert on this!!