Dump Air Bags or Not?

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Dump Air Bags or Not?

December 11, 2011, 12:23:37 pm

Our 1999 40ft U320 Foretravel is on a level site and we have high winds from time to time here in El Centro, CA

I wondered about the advisability of dumping HWH to trap the tire covers. Any structural downside?

best, paul

Re: Dump Air Bags or Not?

Reply #1 – December 11, 2011, 01:50:50 pm

I don't believe there is any structural downside if you dump the air bags. I do every time I store the coach w/o incident. Others may disagree.

Re: Dump or Not?

Reply #2 – December 11, 2011, 02:01:53 pm

No structural downside, but if you're in it, might notice more rocking. I've noticed that ours tends to rock more when down on the tires, probably due to no shock absorbing from the tires...

I just love the challenge of putting bungee cords on the back of the tire covers...

Re: Dump or Not?

Reply #3 – December 11, 2011, 02:04:48 pm

Quote from: Paul Smith – December 11, 2011, 12:23:37 pm

..................I wondered about the advisability of dumping HWH to trap the tire covers. Any structural downside?...............................

Paul,
As Peter says, others may have different opinions:

Not advised, at least in our vintage coach................I think later on FT modified the design to preclude the tires contacting the floor when the HWH is fully "Dumped".

First, depending on how level the site is, you can introduce a twist to the frame that, while not permanent, still isn't a natural suspension mode.

Second, you reduce the number of suspension points by one half (a tire or two to the flooring versus two air bags between designed suspension frame members at each corner).

Third, the suspension becomes the floor frame (if the tires are in contact with the floor). The NEW "bounciness" that you feel as you walk through the coach is the floor frame flexing (not the "tires flexing," as some owners believe).

Some owners have installed short spacers on the "frame buttons" to prevent the tires from contacting the floor of the coach, when the bags are fully deflated.
If you don't have these spacers, or even if you do, if your site isn't near level, you can place a very large strain on the flooring as the top of the tire comes into contact with floor. The flooring and floor frame have to flex and take on weight/deformation until the frame member buttons make contact. If the flooring is left with that strain on it for very long (many variables; tire diameter, levelness, moisture in the flooring material, temperature and amount of weight taken for instance), "something has to give". Usually the floor just takes on a slightly, but permanently bowed deformation but it can also lead to delamination of the plywood in the flooring. Then the upper (delaminated) plywood laminations take on a "mind of their own", swelling and bowing up in high humidity conditions (soft, bowed up spongy feeling to the floor, especially a carpeted floor) and then shrink (lay back down tight) when the humidity goes low again.
I don't think it's a good idea to ever let the coach sit "dumped" for very long, unless you verify the flooring's not resting on the tires. Just asking for problems if you do.
FWIW,
Neal

Re: Dump Air Bags or Not?

Reply #4 – December 11, 2011, 02:05:42 pm

Quote

I just love the challenge of putting bungee cords on the back of the tire covers...

I rigged a coat hanger with a small hook made with a needle nose pliers for this job.

Re: Dump Air Bags or Not?

Reply #5 – December 11, 2011, 02:08:46 pm

Quote from: Peter & Beth – December 11, 2011, 02:05:42 pm

Quote
I just love the challenge of putting bungee cords on the back of the tire covers...
I rigged a coat hanger with a small hook made with a needle nose pliers for this job.

We use our awning hook.

-M

Re: Dump Air Bags or Not?

Reply #6 – December 11, 2011, 02:39:59 pm

Neal,
I was under the impression that the air springs used in Foretravels have an internal bumper in them and while it looks like the full weight of the coach is on the tire, it's actually still resting on the internal bumper inside the air spring. I recall checking (with a magnet) to see if there was any steel tubing in the floor directly over the wheels and I recall not finding any. I can't imagine the floor being capable of carring the weight of the coach without some significant steel in place. The load per wheel is typically about 5000 lbs.

I routinely drop the coach when on a level pad. I drop the rear and then I drop the front down to a point where I know it's getting close. I then go out and check the height difference between the floor and wheel on each front wheel. My own criterial is about 3/4" delta maximum - which is the amount of twist that gets induced when I do finally drop the front.

Re: Dump Air Bags or Not?

Reply #7 – December 11, 2011, 04:00:03 pm

Quote from: JohnFitz – December 11, 2011, 02:39:59 pm

........................I was under the impression that the air springs used in Foretravels have an internal bumper in them and while it looks like the full weight of the coach is on the tire, it's actually still resting on the internal bumper inside the air spring. I recall checking (with a magnet) to see if there was any steel tubing in the floor directly over the wheels and I recall not finding any. I can't imagine the floor being capable of carring the weight of the coach without some significant steel in place. The load per wheel is typically about 5000 lbs...................................

John,
I'm sure that there are many more variables than I have included.
The air bags do have internal bumpers and (I think) both earlier and later years of FT have frame "Buttons" that are more "aggressive" (limit the travel sooner to stop frame travel before any (or much) deformation of the flooring occurs).
There was a period of time (1998's included, all models) when the suspension design tolerances were stacked such that floor contact routinely occurs before the frame "stop limit buttons" or the air bag bumper internal stops are reached. I have seen several Unicoachs in the model years '96 through 2000 that have slightly deformed floors and/or delaminated flooring. Generally not a problem unless one is taking out the carpeting and installing a solid floor surface. Then it will become a problem, cracking tiles or trying to lift the new flooring if the frame travel "stop limit buttons" are not reached before the tires start deforming the floor.
I felt that Paul should know another opinion to his question, since he is in the included time frame.
Beyond the '96 to 2000 time frame, I don't know if owners have seen the delaminated floors. I do know that some owners have had enough delamination to require the replacement of sections of the flooring plywood.
By the way, you are correct that there are no floor frame elements directly over the tire. I'm sure that is strictly intentional. And, the entire weight of the coach is not borne by the flooring members when my HWH is fully dumped. Far from it. The tire plus floor and frame members just have to deform (roughly a 1/4" to 5/16") until the air bag bumpers and/or the frame stop buttons take the weight, probably all three (tires + air bag bumpers + frame member stop limit buttons).
So, another question might be, is there any downside to increasing the frame travel stop limit button's height by 3/8" to 1/2", to make sure that the frame travel stop limit buttons are reached first, before the tires or air bag bumpers bottom out?
Many owners have done that but there must be a reason FT didn't.
Neal

Re: Dump Air Bags or Not?

Reply #8 – December 11, 2011, 04:32:17 pm

Well, at the end of the day this discussion prompted me to recall me we have honest to gosh ceramic tile everywhere but the bedroom. (Only $8K by FOT several years ago by previous owners.)

So I don't even want to think about cracking tiles.

I'll work on Plan B, err C now ;o)

best, paul

Re: Dump Air Bags or Not?

Reply #9 – December 11, 2011, 04:35:35 pm

So, does the leveling system work in such a way as to bottom out the suspension and perhaps do all the damage described as well?...When attempting to level the coach at extreme slopes?

Re: Dump Air Bags or Not?

Reply #10 – December 11, 2011, 04:43:07 pm

I'm not sure why it would not do "something" since I have run onto slopes that put the tire (apparently) tight up to the floor.

best, paul

Re: Dump Air Bags or Not?

Reply #11 – December 11, 2011, 05:09:49 pm

Quote from: Peter & Beth – December 11, 2011, 04:35:35 pm

So, does the leveling system work in such a way as to bottom out the suspension and perhaps do all the damage described as well?...When attempting to level the coach at extreme slopes?

Peter,
I'm not sure how much variance there is between coaches or between lengths of coaches, but I know my HWH will run the air bag(s) down to hard tire contact with the flooring, either way:

Select "Dump"..................OR..................

On an extreme slope, Select "Auto Level" (via two presses to the "Level Command") Then the "high ground" tire or tires will bottom out hard against the flooring, trying to achieve level.

On extreme slopes, I try to always recognize the bottoming, turn the HWH "Off", thus taking it out of "Auto Level", go to full "Raise", then level manually keeping the coach off the tires. Sometimes this requires involving the DW at the helm and me with the flashlight and sometimes it requires settling for less than perfectly level (or moving). I then "Lock" the HWH condition in place by just turning the ignition key off. Of course this gets cancelled automatically as soon as the ignition is turned on, for even a moment. Once "locked", the coach seems to never lose that setting or HWH condition (system still tight at this age -

).
FWIW,
Neal

Re: Dump Air Bags or Not?

Reply #12 – December 11, 2011, 05:14:17 pm

WHen you dump the air bags, the chassis sits on the bumpers where ever they are, no matter if it is level or not, no matter if the body is in a twist, just sits on the very bottom, as zero air in bags. Real simple and I agree, leave it on the air bags and level. SO what if it rocks rolls a little in high winds or earth quakes.
As usual FWIW

Re: Dump Air Bags or Not?

Reply #13 – December 11, 2011, 05:25:36 pm

Yes, I have observed that the HWH leveling routine is to lower the high sides or fore/aft first, then raise the lower members as appropriate. Therefore, it must be that the high side will always bottom in extreme slopes or even not so extreme so long as the HWH computer knows the coach is not level upon its first routine to lower the high end?

Re: Dump Air Bags or Not?

Reply #14 – December 11, 2011, 10:03:03 pm

I will dump mine if the spot is level. I can turn off the 12 volt pump too. I know that the wheels will touch but they are not carrying any real weight on the floor of the coach.

No issues in 10 years of doing it that way.

Re: Dump Air Bags or Not?

Reply #15 – December 11, 2011, 11:43:16 pm

Quote from: John S – December 11, 2011, 10:03:03 pm

.......................I know that the wheels will touch but they are not carrying any real weight on the floor of the coach.......................

Quote from: Dave M – December 11, 2011, 05:14:17 pm

..........................WHen you dump the air bags, the chassis sits on the bumpers where ever they are...............................

So Paul, Peter,
It's looks like in 2001, something may have changed. Either the air bag bumpers, or more likely, the "frame travel stop limit buttons" height was increased to prevent the tires from deforming the floor when the HWH air is dumped.
It would be interesting to see how the actual height dimensions compare ('96 thru 2000 vs. 2001 and up). Maybe that is the answer to my question;
"Is there any downside to increasing the frame travel stop limit button's height by 3/8" to 1/2", to make sure that the frame travel stop limit buttons are reached first, before the tires or air bag bumpers bottom out?"
Neal

Re: Dump Air Bags or Not?

Reply #16 – December 12, 2011, 09:42:01 am

Wednesday is the coach exercise day. So, I'll check then if the tires are exerting pressure on the floor. I've never noticed any floor bulging inside the coach, but, then again, I've never really paid close attention to this. I'll report back the results then.

Re: Dump Air Bags or Not?

Reply #17 – December 14, 2011, 04:47:31 pm

Well, the monthly coach exercise is over and the fuel tank is now full...$3.849/gal at the local Marathon dealer. Another very low milage year at 1434 total miles and an average 8.79 mpg mostly flat and warm days.

I inspected the coach for the areas affected by dumping the air bags while in storage. The tire is touching the bottom of the floor area as Neal Pillsbury had indicated. In my case, there appears to be no bowing of the floor material. I can't see any bulging from inside the coach for the front tire area. The duallies floor area is hidden by the closet and shower pan.

Re: Dump Air Bags or Not?

Reply #18 – December 15, 2011, 12:31:31 am

Quote from: Peter & Beth – December 14, 2011, 04:47:31 pm

...............I inspected the coach for the areas affected by dumping the air bags while in storage. The tire is touching the bottom of the floor area as Neal Pillsbury had indicated. In my case, there appears to be no bowing of the floor material. I can't see any bulging from inside the coach for the front tire area. The duallies floor area is hidden by the closet and shower pan.

Peter,
It's an imperfect measurement, but I have put a thin sheet of malleable metal on top of my tires, dumped the air and measured the deformation to determine just how much deformation is occurring (at least 1/4" to 7/16").
From outside the coach, when you run your hand across it, is the floor above your tire permanently deformed at all?
If it isn't, I'd be really curious to know the thickness of your "frame travel stop limit buttons".
I've been intending to build mine up but don't know by how much. I have no ideal how close those buttons come to "bottoming out" on potholes and bridge joints.
Neal

Re: Dump Air Bags or Not?

Reply #19 – December 15, 2011, 01:19:43 am

From the look of things from underneath, the tires appear to bottom out while driving as evidenced by the tire scrapes having removed some of the "undercoat" material covering the bottom of the coach floor. But no major damage to the material so far.

Re: Dump Air Bags or Not?

Reply #20 – April 12, 2012, 04:00:02 pm

Ok, a quick question regarding Air Bag dumping. Do most folks "lower" their coach before leveling so that the first step into the coach is not a huge step? I've been dumping the air, not completely, before I level. I don't dump the bags to empty, but enough to make the step up not so large.

If folks do this, how do you stop the "Air dump" mid stream? I've been using the HWH reset to do this. Good? Bad?

Thoughts?

Re: Dump Air Bags or Not?

Reply #21 – April 12, 2012, 04:11:00 pm

Our present practice is to: 1) use automatic leveling until HWH is "happy"; 2) cycle HWH to manual leveling mode; 3) tweak leveling using bubble levels mounted in cockpit; 4) set HWH to automatic; 5) shut down engine.

Re: Dump Air Bags or Not?

Reply #22 – April 12, 2012, 07:27:34 pm

In 02 they added the bump stops and the coach can not touch the bottom on the tires. I have a few tire marks from bottoming out. There is no deformation noticeable either. I dump in many places first especially if I am going to be in a campground for a while. If I am just leveling for the night, I do not bother dumping. Dumping to first means that you will have one point on the tire somewhere and that enhances the stability.

Re: Dump Air Bags or Not?

Reply #23 – April 12, 2012, 08:12:27 pm

When I am on A level spot I may let the coach all the way down . When in our garage , I always let it all the way down . I notice that after about 20 or so days, it's down anyway. Brad Metzger

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