Need some expert air bag leveling advice

[RichardEntrekin]

Scott,

I don't know one specific thing about your setup, so I'll put my fireproof unders on for the flaming.

On my coach, which I know is way different than yours, it takes around 60 psi to raise the coach of off dead flat. Do you know what that value is for your rig?

The point is this, the higher the air pressure in any air bag, the stiffer the spring rate. I have no doubt that if you are running 40 lbs in one side that it is mushy on that side and likely to sway.

The second thing is that you commented on lack of understanding of the tag pressure regulators. I would spend some time tracing that system, because if the assumption you made that the right and left tag were NOT independent is incorrect, then different tag pressures on each side could explain why you are seeing the side to side differences. Again, I don't know beans about your setup. But my tags are independent, and even though they appear to be connected to a common frame rail tank, that tank has a divider welded in the middle.

I could be all wrong, but this is easy to try. What happens if you set both tag regulators to the same pressure? Does that make a difference in the side to side pressures required to level the coach?

My apologies for offering advice on a system I have never seen, BUT the basic laws of physics still apply. The weight that an airbag supports is a straightforward calculation.   Divide the diameter of the airbag by 2, square that number, multiply by pi (3.14),multiply by the psi. For example an airbag of 6 inches in diameter running 50 psi will support 1413 pound   6/2 = 3, 3 X 3 X 3.14 = 28.26, 28.26 X 50 = 1413. The point is this, if you are truly running 80 psi on one side and 40 on the other, then the coach would have to be twice as heavy on the 80 psi side. We know that's not reality, so something else is going on.

[Jon]

If XX PSI brings the coach to the road or driving height it typically means the air bags are extended to about where they are going to have 3 or 4 inches of travel up and down. If you increase the pressure the bus will sit higher and the amount of travel up and down is going to change to where there is more travel down than up. Conversely if you do not bring the coach to the driving height by introducing less pressure than required the bags will provide a mushier ride and will bottom more easily and there will be more up travel available.

Ride height valves are the only way to assure the correct height and provide the ride and handling the designers wanted.

There is no way a driver can sense if the bus is too high or too low from the driver's seat, and either position, high or low has an impact on handling and driveability.

[daddysgirl]

The Warrior is right as is Jon. IMO, Those height valves are important. The bags are important. I have a spare set of both, just in case.
And from personal experience when I was a child..(behind a friends bus that wrecked as a result) if you play too much with the bags, it strains the bolts and the rubber. You do NOT want one of them to fail going down the road.

Thanks for the conversions Richard!

[Jeff Willard]

I'm not a Prevost or MCI guy and know nothing about them but...... the one question that should be answered is...... Do you think you're smarter than the guys that designed this system in the first place? If the answer is no, then fix it as it was designed. If you're trying to "fix" another problem, then design and build another system and leave what's there, as it was engineered.
I could probably hang this comment on the majority of threads on ALL of these boards. When I got started working on the Scenic's I quickly discovered that I spent far more time fixing and undoing other peoples "fixes" than actually repairing worn out parts and system.

[TomC]

I still have the stock, automatic leveling valves. I also have my own designed manual leveling system using the 3 points. I like not having to worry about leveling while driving, but able to level the bus in less than a minute. Also, have had a leveling valve go out (actually the connecting rod came loose) while driving. Simply threw the switch to manual, leveled it out and continued driving. Best of both worlds. Good Luck, TomC

[Scott & Heather]

I am totally game for going back to the leveling valves. They are still there. But the brackets the rod connects to are bent and look custom. One of them is actually rubbing the shock absorber. That has to be rectified before I re connect the leveling valves because they just aren't working right.


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[Rick 74 MC-8]

Scott

since you have to rebuild or replace that bracket anyway. Why not make the bracket so that you can move it from a remote location. Bob from Indiana did it. You still have leveling when parked just put it in a home position for traveling and ride height is automatically adjusted. Sean also did it with linear actuators very slick.

Rick

[Lin]

Rick, we did that using push/pull cables.  Similar to what Bob did, as I remember.  I am not sure how Scott is adjusting the air in the bags, but if it is a remote system, like on the dash, it would seem that he would be able to integrate that with the automatic ride height controls as others have done.

Air bag leveling is better than nothing but is limited to about a 6 inch differential from back wheels to front, that's a only about 1 inch per five foot of incline for a 40 foot bus.  I am happy that I have it, but I would be real happy if the tooth fairy installed a real leveling system for me.

[RichardEntrekin]

Scott,

If I have read this thread correctly, the initial reason you abandoned the height control valves was the side to side sway and mushy handling. Then, if you level the coach with your manual system by high inflation on the curb side and low inflation on the drivers side, it behaves in a similar fashion.

Then if you run higher pressures in the tags, you don't have to bias the side to side pressure with your manual system to get the coach to ride level.

I really think you need to dig into the pneumatic system for the tags. It could be you have unequal pressures from side to side on the tags, and regardless if you level the coach manually or allow HCV's to do it you have the mushy handling.

[Dave5Cs]

Agree with Richard. We have independent bag adjustment and don't have those problems at all. But we also don't have tag axle. So would seem that it may be your tag Axle has a problem. If you want both systems to work you could use the solenoids like Tom C did also.
Dave

[Scott & Heather]

Thanks Richard and Dave. This is exactly what I'm trying to diagnose. The issue isn't with ride height or even the leveling valves. I am essentially doing the same thing as the leveling valves but manually. And for those that think the leveling valves adjust for when you go around a turn etc, that's somewhat bunk. The 1/4" lines cannot allow enough air into the bags to adjust that quickly. Sorry, my 9 with factory leveling valves never adjusted very much around corners or turns. It just leaned. Plus, if your valves indeed did have the ability to adjust that quickly, you'd have an unlevel bus once the turn was completed and you were driving straight down the road. Manual control of the bags is actually pretty awesome. I have no desire to go back to leveling valves. I just need to sort out tag pressures cause that appears to be part of the issue. And frankly I get weary of hearing people say "if the MCI engineers designed it that way, then you'd better leave it that way unless you think you're smarter than the engineers" because frankly, yeah I have actually done away with a ton of stuff on both my buses that the "engineers" designed because it didn't fit my needs. My air door has the air shock removed because I wanted a normal door action with mere hinges. I moved my temp gauge because the engineers decided it was a good idea to put that down so low you can't hardly see it on the dash. I have electronic wipers because the engineers thought in 1992 that air wipers would be superior to electronic wipers that all the school buses and millions of cars and semi trucks had. I moved my air brake knob and transmission touchpad to the left side arm rest area because the engineers designed it to be on a pillar on the right side even thought I kept smacking that short differ with my calf getting in and out of the seat. I could go on and on. I like my manual leveling, and I have set the ride height per specs, but I think I have a tag that is helping the drivers side more than the passenger side and causing the slight lean so I'll need to sort that out.


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[gg04]

What it your front set at?  Different bus but my rr 54 lr 50 rf 42 lf 46 for factory ride height.  I'll drop it two inches for interstate highways.  Has worked for 17 years. rdw

[Dave5Cs]

Some adjust for the road crown of about 5 degrees that they use for road run off but we don't. 80 in the front and 75 in the back and good to go.

[sledhead]

on the M C I rear 42 lbs front 70 lbs and I too adjust for the crown in the road or a strong side winds when needed

and love the fact that I can control it right at the driver seat when driving

dave

[Scott & Heather]

Dave your C3 had 42 lbs in rear both sides and it didn't rock side to side? Wow.


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