Leveling System



Since the summer of 2005, the bus has been functional for camping, including a bath, kitchen, and sleeping areas. They're not complete, nor are they pretty, but we've been using it a lot. We've been to Alaska, Florida, and out to Colorado and Wyoming many times. We don't mind that it's not finished, and in some ways, it makes it easier not having it all nice and pretty.

One of the biggest problems we have, though, is getting a level spot to park for the night. It seems no matter where you are, there isn't anyplace ready made for the coach with a level spot. The Wal-Mart parking lots we sometimes stay in are all sloped for drainage. Many of the camp grounds we've used even leave a lot to be desired when it comes to level pads. And where we go camping in Wyoming, while having the appearances of level, requires a hole on one side for the tires, and several blocks on the other, and still it's not quite there.

Having the coach unlevel wouldn't seem like a big deal, and for the most part, it's not. The bus has to be really out of level for it to be a problem with sleeping, and even cooking. The biggest problem is getting the shower to drain.

The MC9 floor has a natural slope of about 3 inches from rear to front. Not sure why this was done, but it's there. When I installed the shower, I used that natural slope to my advantage by placing the shower drain at the front of the shower floor. The idea is that if the coach is level front to rear, then the shower will naturally drain towards the front simply by the slope of the floor. I also sloped the forward corners so that water on the sides would also drain towards the center, and ultimately into the drain. This has worked well, other than it's nearly impossible to get the coach level without significant work placing blocks under the wheels. Even if you do get it nice and level, by morning, something in the air suspension has usually leaked off enough to throw it all out of level, anyway.

So, I've been planning on adding a manual leveling system for several years, and finally, I decided it was time. I've always known I would use the coach air bags for leveling, and my intentions have always been to figure out a way to retain the original height control valves for traveling. It's only been recently, though, that I actually was able to figure out how to do all this and get it done at a cost I could afford.

I've gone through several iterations of design of the leveling system. Some of my initial ideas used 3-way air solenoid valves that could be used to add or remove air from the individual bags. I was unable to find any of these valves that I could afford, and so started looking at designs which use two separate valves; one for putting air into the system, and one for letting it out. I bought a couple different types of solenoid valves for this purpose, but found that they would not hold pressure when there was a significant imbalance on either side of the valve. So, I'd decided to try a different approach, and purchased some cheap air regulators from Harbor Freight. The idea was that I could use the regulator adjustment to dial in the proper pressure to get the bags to the proper height, and the regulator would maintain that same pressure in each leveling bag as long as I had air pressure to feed it. I planned to use a small oilless pump to maintain pressure, with possibly the addition of a small air reservoir. I then found some Humphrey solenoid valves, which I could use to isolate the suspension system from the auto height control valves. They are stainless steel, and are well made. They have 24v coils, and will hold pressure which significant differential pressure between the two sides.

I continued to plan for the leveling system using the small regulators. I was having a problem figuring out how to mount the regulators so that the gauges would be visible, and the control knob would be accessible. I wanted them mounted in the dash, but just couldn't figure out a good way to mount them. I finally realized this just wasn't going to work well, and began rethinking the whole concept. I kept coming back to the original idea of using two solenoid valves to raise or lower the air bags and I finally determined that the Humphrey valves would work for this. My located and purchased more of the Humphrey valves, and began assembling all the components.

The coach leveling system is a 3-point system as provided by the original height control valves. The rear driver's axle had two valves, which control each side. The two sides of the front air bags are tied together and use a single height control valve. The three point system prevents racking of the coach frame which could occur if the two sides of the front axle were separately controlled. Note that the height control valves do not provide leveling of the bus, but rather provide a specific height of the coach body above the axle assembly. If the coach is on unlevel ground, it will still be unlevel inside, but the height of the coach body above the axles will be constant.

The leveling system I designed would retain the original 3-point system, as well as the original height control valves for use while traveling. Obviously, to effect manual leveling, I would need to bypass these automatic valves, or they would simply interfere with the leveling system. After careful thought, I determined that electronic solenoid valves could be used to isolate the height control valves from the air beams and air bags. The valves would be installed between the height control valve and the air beam. In order to conserve power when boondocking, I decided to install the solenoid valves such that the automatic height control valves would normally be isolated, and therefore would need to be energized to re-engage the automatic system for traveling. This way, power would not be expended while the coach is sitting level in a camping spot and the automatic valves cannot interfere with the coach leveling. For manually raising and lowering each leveling point, I would need 2 separate valves on each leveling point. One valve would allow air into the air beams, and the other would allow it to be expelled. So, each leveling point in the system would require 3 separate solenoid valves.

The Humphrey solenoid valves I used have 3 ports on them. One is a common port, and the other two are normally closed (supply), and normally open (or exhaust). They are designed to supply air to some type of air actuated device through the normally closed port when energized, and then exhaust that air through the normally open port when de-energized. There is no OFF position or in between state. The common port is internally connected to one of ports at all times, depending on whether the coil is energized or not. This is why two separate solenoid valves are needed to effect raising or lowering the system.

So, the concept of manual leveling is that the auto/manual valve should be set to the normally closed position, and then air is added/expelled to/from the leveling point through the raise or lower valves, to change the height of the leveling point. Each leveling point will provide approximately 6 inches of vertical movement. between

I installed 3 solenoid valves for the front axle suspension system in the cubby hole compartment located at the top of the stairs under the co-pilot seat. Plastic DOT air lines were routed through the floor into the spare tire compartment, and then through the rear bulkhead to the location of the front height control valve. The airline that connected the control valve to the air beams was removed, and replaced with the two plastic DOT air lines. The line coming from the height control valve was routed to the input side of the auto/manual selection solenoid valve. The line going into the air beams was connected to the output side of this solenoid. The normally open port on the auto/manual solenoid valve was plugged.

For the raise/lower solenoid valves, I connected them such that when energized, air flows into the common port of the raise solenoid valve and out the normally closed port. It then passes through the normally open port of the lower solenoid valve (which is not energized) and out through the common port. The output from the common port of the lower solenoid valve is Tee'd into the line that runs from the auto/manual valve to the air beams. The normally closed port on the lower solenoid valve is open to atmosphere. This port is used to exhaust air from the air beams when the valve is energized.

I then installed switches in the dash to controll the electronic valves. I installed a SPDT switch for control of the auto/manual valve and three mom-on/off/mom-on switches to control each leveling point valve set. When the auto/manual switch is in the up position, the auto leveling is engaged, and the coach height control valves are active. When in the down position, the manual system is enabled, and power is provided to the three switches which control the leveling point valve sets. When the auto/manual switch is in the center off position, neither the automatic or manual leveling system are active, and the suspension will remain static. When manual leveling is selected, the leveling switches are energized. Pressing the momentary-on leveling switch to the up position activates the raise solenoid valve of the selected leveling point set, which allows air into the air beam and causes the coach height to raise at that leveling point. Pressing the switch down acitvates the lower solenoid of the selected leveling point valve set, which exhausts air from the air beam, causing the coach height to lower. When leveling is complete, the auto/manual switch is returned to the center off position, which cuts power to the leveling switches, conserving power, and keeping them from accidentally being activated. The two extra switches (with the orange lenses) are for a small air compressor I will be installing in the rear bay. It will be used for airing up the bus system, or for adding air directly to the leveling sytem for adjustments.

The auto/manual switch I installed came with 2 incandescent indicator lights inside. Actuators with lenses can be installed on it to show the lights. Unfortunately, the switches are designed for 12 volts, and my leveling sustem is designed for 24 volts. I feared if I connected the lights to 24 volts they would be short lived, so I opened the switch, removed the bulbs, and replaced them with LEDs and 1500 ohm resistors suitable for operating on 24 volts. This worked well, except that the LEDs kept burning out. More on this a little further down...

When I installed the electronic solenoid valves for the rear leveling points, I combined both left and right side valve sets into a single manifold of solenoid valves, connected in the middle by a brass Tee. The valves were connected together using brass nipples and Tees. This allowed me to minimize the number of air line fittings needed to connect everything.

The air lines between the height control valves and the air beams were removed and replaced with plastic DOT line, as was done in the front system. The air supply for the manual leveling system was routed from the engine compartment, above the rear differential, and through the rear bay bulkhead, along with the lines from the height control valves. These lines were connected into the manifold of solenoid valves. Finally, a small cheap regulator was added to the air supply line, which will regulate the maximum pressure used for manual leveling. I set the regulator to 90 PSI.

And finally, I bought a little trailer tongue level and attached it to the dash. I set the bus level using a small spirit level, and calibrated the dash level. Now, I can watch the bubbles on the dash as I set the level switches, and know when the bus is relatively level.

So, that's my leveling system. At the time of writing this, I've had it installed for a few weeks, and have used it a couple times. When I took the bus to dump the holding tank, I stopped next to the dump station, raised the right rear corner, lowered the left rear corner and front end, and dumped the tank. Everything in the tank naturally ran to the front left corner of the tank where the dump valve is attached, and completely drained the tank. When I got home, I repeated the leveling sequence, and drained the fresh water tank completely, in preparation for winterizing the bus. It worked out really well. After winterizing, I leveled the bus and turned off the switches. It's been holding level now for several days, so I'm calling this one a success for the time being. The true test will be when I take the bus camping again next summer in the mountains of Wyoming.

Oh, yeah, the LEDs...

The LEDs in the auto/manual selection switch kept burning out, after I initially installed them. I went through 4 LEDs before I finally realized that the solenoid coils were producing a back EMF current that was blowing the LEDs. I installed diodes on the output lines from the switch, and cured the problem. I'll probably wire in some diodes across the individual solenoid coils, too, to ensure a path for the back EMF to dissipate. For now, though, I've had no further problems with the LEDs


Tips and Tricks