Air pressure gage on dash.

[Chaz]

Well, now that I am into the air thing on my bus, I was wondering if the air pressure gage on the dash would tell what a person could rule in or rule out on finding a leak in the system. 
  The green arrow (primary reservoir) goes down the quickest. Is that any kind of a tell-tale sign on where to look for a leak? I know there are a few possible culprits, I was just trying to eliminate what I could.

   Thanx guys,
       Chaz

[HB of CJ]

I don't know.  Perhaps others will share the probablilities.  My '74 Crown developed a bad leak in the foot treddle valve on the brake pedal.  Would drain the air in only a couple of hours.  I fixed it (I hope!) by manually working the treddle a couple of hundred times, along with some WD40.  Apparently (?) the seals just needed some exercise.  A rebuild here is certainly planned.

Earlier slow leaks (2 to 3 days) were tracked down the old fashioned way borrowing a directional audio mike and headphones from a scientist/mechanic friend and crawling up and under the coach checking out each individual brake assembly.  Found a pin hole in a air line going to a rear brake can.  Hope this helps and Happy New Year! and all that stuff. 

[Ncbob]

From my discussions with many bus owners the majority will maintain some degree of pressure for up to 3 day...mine does but it gradually goes to zero. While at this point the suspension isn't leaking down I wouldn't expect the brake system to hold pressure for too long.

Bob

[buswarrior]

Hello Chaz.

With two needles, you have one each to the two halves of the dual brake circuits.

So, if one goes down quicker than the other, your bigger leak is in the related circuit. You've got it right.

Please note, on a modern dual circuit plumbed bus (post 1975) with a twin needle gauge, the gauge on the instrument panel is only indicating the brake circuit pressures, found in the two service tanks beyond the check valves. It does not indicate what is in the accessory circuits (suspension, wipers, shutters, etc) or the wet tank after a time of shut down.

happy coaching!
buswarrior

[Chaz]

Thanx Buswarrior.
  But I must say, I'm not following you too well. I guess it may again be time for the book. But the book did say one needle was primary reservoir and the other was secondary. Hmmmmmm...
   Chaz

[FloridaCliff]

Chaz,

BW is right on the mark with the two tanks.

As an additional option, I am going to add a gauge for my accessory tank when I get up front.

As I resolved all of my air leaks etc, it would have been nice to see whats going on there too.

As an example:  When I would stop at a location for a quick pit stop, my air would leak down on the gauge to say 60lbs, on both needles, and stay there.  What was happening was that I had a leak in my accessory tank system that would bleed off quickly down to zero, I would then have to wait until the whole system reached at least 90lbs to release the park brake. A real pain.  With the Accessory tank gauge I would have noticed this sooner.  Of course now experience warns me!

Fixed the leak source and everything is great.

Its really worth it to track down all those pesky leaks, My rear bags are still up after almost 45 days, the front seems to leak down slowly with all the going in and out after its shut down.

Best of Luck

Cliff

[Dallas]

Cliff and Chaz,

You might as well add an air brake application gauge while your at it.

You could use a single needle air pressure gauge and hook it directly to an outfeed on your treadle valve. This gauge can tell you a number of interesting things, such as, under certain circumstances, how well you overall brake system is adjusted, (The more out of adjustment the brakes are, the more pressure on the treadle you'll have to use to get the same stopping power, even a 5 psi difference will show up on the gauge.), it will also let you know when your brakes are getting warm and starting to fade from heat, (for the same reasons as the out of adjustment brake does.. it takes more air pressure to get the same stopping ability). Another added plus is that if you have a leaking service diaphragm, the gauge can tell you this by the way it acts when you apply the brakes.

If you want to be really fancy, use a dual needle gauge and hook one needle to the front brakes and the other needle to the rear brakes, this way you can get a better idea where each set needs work and in what way.

I use to put the dual reading gauge on each of my trucks and lowered my over all brake replacement costs by probably 20%. That isn't much over the life of a semi truck, but every penny saved was a plus.

Dallas