4104 air system

[Denny]

I have a annoying leak in my bus air system.  Normally the bus will go from 120 psi when I park it at night to 70 psi in the morning.  Now it is down to zero in the AM.  I have done all of the obvious stuff, soaping all of the visual fittings.  I actually bought a listening meter to listen for air leaking, but have not found the leak.  I have two questions.  1. how many tanks does the 4104 have.  I read something that said they should have 3 but I have 4.  Which is normal??  2. does anyone have or know where to get a schematic of the air system.  I would like to know where the air goes and which tanks fill first.   I am going to have to get deeply involved in this next month and would like as much info as possible before I start tearing things apart.

Thanks for you help
Denny

[zubzub]

my '04 has 3 rear wet tank at rear left, dry tank forward between front wheels, aux tank left front hatch.  Get a free download version of the parts manual, it will help locate things.

[RJ]

Denny -

Before you tear out all your hair over this, consider:

During the 15 years I worked at our local transit property, EVERY TIME we got a new bus order in (anywhere from 10 - 24 at a time), there would be BRAND NEW BUSES that would have zero air pressure after sitting overnight.  You'd walk out of the shop and look at them parked in the new delivery area, and there would always be several sitting cattywampus from the air leaking out of the suspension system.

Have you done a DOT air brake check on you coach?  If it passes ok, then the leaks you'll be chasing probably are not safety-related (leveling valves, windshield wiper controls, etc.)  If it doesn't pass, now you're into the more critical stuff, which is usually brake system related.

So do your DOT check first, then let us know the results.  Here's a good one, located near the bottom of the article.  It is geared to those coaches that are equipped with either DD3 or Spring brakes, but the basics are the same for your Johnson bar:

http://www.busnut.com/bbs/messages/12262/16203.html?1167072614

Oh, and if you don't have the shop manual already, get one!!!

FWIW & HTH. . .

[robertglines1]

When average temp drops 20 degrees mine leaks down almost twice as fast. Just  a expansion contraction fact of fittings/valves and air line material. In warmer climate it stays up longer.    Bob

[Denny]

Thanks for the info so far.  I haven't had time to do the DOT brake check check yet but that is a good place to start.  I am still wondering how many tanks I should have on the bus.  I have two in the back, each one behind the duals, and two in the front.  One in the drivers tool compartment and one behind the spare tire.  My bus also as spring brakes and an emergency air button on the dash that in case the air goes out of the brake system you can push it and get enough air to get the rig off the road.  Again, I haven't really gone past soaping the couplings yet so a lot is still to be determined.  I do have the original GMC bus manual and it does not give me a description of the entire air system.  My book does not even tell me how many tanks it is supposed to have.

Thanks
Denny

[zubzub]

I would guess the one behind your left dual (oops I mean right dual) is the emergency "extra get off the road air tank"  It would probably be plumbed in such a way as to be isolated from  loads in the main system but with a one way valve so it can be aired up from the main system.

[gus]

There is a drawing in the very front part of the brake section of your manual that shows the complete air system layout.

Unless there was a later model change (Mine is a '54) the tank on the right rear is an extra, can't imagine what for though because I ran mine a long time with the wet tank bypassed (Couldn't see the bypass connections).

The left rear tank is the wet tank, the front center is the dry tank and the left front is the Aux tank.

It is not the least bit unusual to lose all air press overnight although the air bags usually stay up much longer.

The windshield wiper controls are a common leak source. Try turning them all the way off (Park) against the spring and see if you hear any leaks. Sometimes they are only part-way closed and will leak. Sometimes they leak no matter where the knob is set! Sometimes it is easier just to install a shutoff valve on the wiper supply line!

[Denny]

Gus and all who responded - thanks for the info.  I found the diagram for the air system like Gus said in the brake section.  That info is going to be really useful when I get into this.  I think the curb side rear tank is the "emergency air" tank and will look at trying to isolate it to determine if that is a problem.  I also think the problem might be in the wipers.  They sometimes stop in between their cycle of changing directions.  Good place to look.  Thanks again to all who have responded and made suggestions.  Any other thoughts or ideas will be appreciated.

Denny

[buswarrior]

The exhaust of every air valve in the brake system.

Foot valve in the compartment under the driver, the relay valves somewhere in the rear axle cavity.

Sky is the limit for the modifications to your coach for the spring brake install, find the valving and check the exhausts.

Do this check in the three configurations: sitting parked, sitting with parking brake released, and sitting with parking brake released and brake pedal wedged to the floor.

A remote compressor and an airline to keep the coach aired up will help this be a more straight forward exercise.

All the usual safety cautions: don't go under the coach unless it is blocked to prevent air suspension and tire failure from killing you, and block the wheels to prevent it from rolling over you, into the neighbour's yard, the river, your own automobile...

It takes longer to prepare to do some maintenance, than it takes to do the maintenance.

Short cuts have killed busnuts, proudly take the time to do it safely.

Use the search, both here at BCM and over at BNO, to find reams of info on safety methods for keeping the coach up there, and space down here for you.

happy coaching!
buswarrior