RE:Once I had an air line blow out and I lost so much pressure so quickly that by the time I got off the road and stopped, the engine would not shut down. I had to shut down using the rear engine panel shut-off switch. More on that some other time.

OK-- this is some other time

What are the problems of using air??

How does one shift with air?

Doug,

On full air controlled chassis like the Gillig, braking, shifting, suspension and some engine functions are all controlled by air pressure.

I was aware of most of these controls, but on my trip back home after purchasing the Barth in Naples, FL and heading for Massachussets, I learned a bit more.

There are two pressure guages in the dash which are feed directly with air lines. A line was rubbing where it went throught dash and looped down to the chassis in the front end. Well it finally blew just outside of Tampa on my trip home (Murphys Law). I knew right away that this was a big deal because I could see the air guages plunging downward quickly.

Fortunately, I75 had a wide shoulder where I was and a fairly flat grassy area beyond that. When you loose air pressure in a system with air brakes, the brakes go on as a safety feature. I think this is a function of some heavy springs being streched by air pressure to keep the brakes off. When you apply the brakes, you relieve some of this pressure and the brakes are applied relative to the pressure released. Loss of air pressure then effectively applies the brakes.

When you have a failure in an air line, you need to look for some place to pull off the road, or you will be stopped where ever the brakes lock. This is a somewhat simplistic explanation of this process.

What I found once I got off the road and was able to collect my thoughts was that I could not shift into neutral (no air pressure) and as a result, I could not shut down the engine. I sat there for a few minutes in a quandry, wathcing the transmission temp guage slowly climb.

Fortunately, I had taken home the engine/chassis manual one month earlier when I scoped out the Barth and gave my deposit. I did my homework and read the manual. Now I remembered that there was a remote access panel in the rear engine compartment with a manual shut off switch. I opened the compartment door and flipped the switch - the engine shut down and I smiled.

After several hours of frequent calls back and forth with the Good Sam ERS folks, I convinced them that I could not be towed, but needed a diesel mechanic to repair the air line. After three hours a mechanic showed up. He knew what he was doing. He disabled the "do not start in gear" function. I restarted the engine, he located the leak, I shut the engine down, he cut the line where it was worn through and spliced the line using an airline fitting. I started the engine again and let it idle.
The air pressure came up, I shifted it out of gear and I shut it down again. He re-enabled the "do not start function" and I was ready to go.

I paid him,and headed for home. I have never had another issue like this. To this point, the Barth has been well behaved and I am extremely happy with the entire coach. It rides and drives beautifully.

Having air vs mechanical/electrical functionality doesn't concern me. Both can fail and air is not less reliable than electric/ mechanical operation, perhaps even more reliable.

The bottom line is that a full blown diesel air chassis set-up is more complex and therefore more expensive to maintain. The flip side to this is that it is better built, heavier duty, safer and more substantial the other types of chassis.

I am sure that many others on the site can elaborate more deeply on this subject. Since I would like to know more about this myself, I hope they do.

Bill G

PS. How do you shift with air? I have a Stone-Bennett air shifter toggle switch on the dash. Toggle up once for DRIVE, up again for 3rd, again up again for 2nd etc. Toggling down shifts back to 3rd and then back to DRIVE and toggling again gets it into REVERSE. An input and output air line feed the back of the switch.

What are the problems with air? Air is only a different kind of energy to power a system. There are no specific problems, however, maintenance of the system (like most other things) is required. Purge the tanks regularly and check the moisture absorbent canister ocassionally.

quote:

Originally posted by Bill G:
...When you loose air pressure in a system with air brakes, the brakes go on as a safety feature. I think this is a function of some heavy springs being streched by air pressure to keep the brakes off.

This is mostly true. the way to say this would have been...I think this is a function of some heavy springs being COMPRESSED by air pressure to keep the brakes off.

quote:

Originally posted by Bill G:
When you apply the brakes, you relieve some of this pressure and the brakes are applied relative to the pressure released. Loss of air pressure then effectively applies the brakes.

This is false - The brakes will come on and go into a park position if you loose your air psi - they are called spring brakes but that only refers to the PARKING aspect of it.

Look at you front wheels, you will see what looks like half of a brake chamber - the front brake chamber is representative of what your foot brake does. You could loose all of your air and then jack up your front wheels and it will spin freely. Step on the brakes and the amount of pressure you apply to the pedal will push the push tube out to apply the brakes with air in the system.

If you pull your button out on the dash to park your coach the air bleeds out of the emergency side of the brake chamber and applies the brakes.

When you push the dash valve in, air goes into the parking side and COMPRESSES the parking brake spring.

When you look at a brake chamber on a drive wheel you will see 2 airlines going in. The end that's not mounted is the emergency, spring parking brake side. The side that is attached to the mount is your foot pedal side. Application of the foot pedal will send air to the service side and will apply your brakes. There are 2 sides to a spring brake chamber.


Figure 1 and 2 shows a front wheel - figure 3 shows what a parking brake chamber looks like.

View 4 shows what your brakes look like when you push your button in to release the parking brakes. View 5 shows what happens when you step on the foot pedal.

If you pulled the button out on the dash and set your parking brakes in view 5 you would see the big compressed spring push outwards and apply the brakes - that Grey air gap would be gone and it would move to the right. There is a second floating plunger in there.

More can be found here.

quote:

Originally posted by Bill G:
I am sure that many others on the site can elaborate more deeply on this subject. Since I would like to know more about this myself, I hope they do.

I hope that explains some of it.