Let's talk non-steerable Tag Axles

[RussWhite]

While parked in the lot at the American Museum of Science and Engineering at Oak Ridge Tennessee I observed a Prevost tour bus making turns with his tag axle wheels completely off the pavement.

I don't think my axle will do that, but I do have a three position switch with some control of how air to added and released from the air bags between the tag axle and the chassis frame.

I have had a brief discussion of the switch with a tech at the factory and read the owner's manual, but would like to have the thoughts of other forum members on how they use their tag axle switch. The manual suggested the down position to dump the air and get extra weight and traction on the drive axle. The tech suggested using the top position in conjunction with the HWH "raise" button for increased suspension clearance in very low speed situations. How do you folks use yours? How do you know the center position puts the right amount of air in the bags?

Thanks, Russ

[Wally Arntzen]

When backing up to turn around I always dump the air for the tag and it allows you to turn sharper, reduce the wear on the tag tires and not damage the lateral shock that is above the tag system under the coach. When I got my coach my friend who runs a bus repair garage discovered that the shock was bad and we replaced it.
He made it clear to me that you should always dump the air when backing up if in a turning situation, making sharp turns at low speeds or when in slippery conditions and you need all of the weight on the drive tires.
Prevots do lift up but dumping the air as the Newells do is the same result.

[afrench45]

When I put my coach in reverse, the back end lowers and dumps the air from the tag. Maybe yours automatically does it like mine?

[fulltiming]

The Prevost use a very LARGE spring to physically lift the tag off of the ground. The Newell doesn't do that. However, as others have pointed out, dumping the air out of the tag will a) decrease turning radius and b) reduce the wear and tear on the tag axle and tag tires.

The 3 position switch includes normal, dump and add air to try to get the drive axle under 20K.

[Richard and Rhonda]

Russ,

To your original questions.

One, I have not been able to figure out which position the switch needs to be in to put more weight on the drive wheels. My coach appears to do the same thing in both the up and down positions. I have wondered if I needed to put in in leveling mode when using the switch. I will try that next.

About the issue of how air pressure is controlled in the tag bags. There are two answers I know of. The first is that on some coaches Newell used two "six packs" of HWH pressue solenoids in the back. The six pack for the tag has a pressure regulator on the air feed into it. That regulator controls the pressure in the tags. The second answer is that on some coaches, mine for example, only one six pack was used. The air pressure in the drive bags is the same as the tag bags.

[RussWhite]

I need to learn a lot more about what is going on - and soon. Today I followed the advice to dump the tag bags when I put her in reverse to back into my camp site. Fortunately I had someone back there watching and he said, whoa! your hitch is almost on the ground. So I went back and sure enough, I had maybe a inch and a half between the hitch and the road. See picture attached. It was going to be a fairly straight backup from there so I went from dumping the tag to the other extreme and got some additional clearance. I then started backing into the site which has a downward sloping entrance to a level site. As I was directed in my helper watched closely and stopped me when the hitch touch the concrete of the site. At that point I had the raise request flashing and the tag in the full bag position. I went to fast idle and waited and there seemed to be conflicting things going on. Both rear axle ride height valves where exhausting. So what keeps the two systems ( ride height and leveling ) from fighting each other. I had told the leveling system via the HWH panel I wanted "raise", but it seemed the ride height wanted to put the coach at normal travel height. The ride height valve seems like a pretty simple device in that it has a rod connected to the axle and tries to exhaust the air when the distance is too great, and add air when the distance is too close. Is there anything that should take it out of action if I try to override with the HWH "raise all" button? Some boards under the tag axle tires and I made it without scraping my new concrete. All suggestions appreciated. Is there any way to check that my ride height is correct? I "touched" something in the middle of the bus as I slowly creeped across some railroad tracks. I had stopped and hit the raise button, but almost immediately a car pulled up behind me and I just hate to inconvenience someone else, so I slowly moved on. I have not found any damage from the slight interference.

[fulltiming]

Russ, I don't know if the measurements are different on a 1999 coach but on the early 1990's Newells, ride height should be 12" from the ground to the bottom of the square tubing just up inside the sidewall of the coach just behind the front wheel well and just in front of the rear wheel well. The travel height valve linkages are adjustable and that is what you will need to do if you have significantly less ground clearance. For more information see http://www.newellclassic.com/forum/showthread.php?t=389

With the long wheelbase of the Newell, it is possible to drag high center. I have had several occasions where I had to press and hold the RAISE button to get the coach up as high as possible to avoid dragging the center of the coach. Make sure you do not attempt to move the coach more than about 5 mph when using the DUMP or RAISE buttons. Be particularly careful when using the DUMP button. The rear wheel flares will rub on the rear drive tires and the front tires will be severely limited in turning radius before the tires begin to rub so if you really want the front down low keep the front wheels pointed straight ahead. Also remember that the dump and raise takes place slowly. To expedite the process, put the coach in neutral, hit the fast idle switch and let the engine driven air compressor have a fighting chance to put some air into those air bags. You really need to keep the air pressure at or above 80-90 psi to get the lift to occur during a reasonable time.

If anyone is interested in me uploading and posting a link to the HWH Air Leveling System Manual from 1999, let me know.

[rheavn]

Russ,
Just to verify, the ride height measurements on a '99 chassis are 12" on the front & rear, measured as Michael stated. I have noticed that the HWH system on my Newell compared to my previous coach is much slower to adjust. Michael had posted a "how to adjust ride height" post some time back that I found very helpful when I adjusted mine.

[RussWhite]

Thanks folks. It all makes sense and I want to get some real data just as soon as I get organized from moving. One really needs to have some idea of just how long to wait before assuming the requested raise or lower is complete. Since there is no feedback I will just do some tests and post the results. I did learn when trying to back into my sloped sight that the Allison just blinks at me and will not engage a gear if the tag axle is in the bags full position. Returning the switch to center position allows the Allison to shift. Since the bleeding is probably as slow as the filling if I do the move just as soon as I return the switch to center position I still get some benefit from filling the tag axle bags as an increase in ground clearance. It sure would be helpful if the response was much quicker than it seems to be. The air lines look small and are probably a major contributor to the slow response.

[fulltiming]

Compared to the Prevost, the lowering of the coach or the dumping of the tag is agonizingly slow.

John, if you are reading this, can you or Karl provide the logic for the slow airbag (particularly the tag) air discharge rate? I suspect there is a reason as there is with the other things that Newell does.

[rheavn]

Russ,
This may give you a place to start & compare. I had my coach low & level in my shop. I started the coach & ran it in normal idle for 3 minutes & then placed it in fast idle. It took 4 minutes to totally air up the coach. After 5 minutes the front was at ride height. It took almost ten minutes before the rear was at ride height.

Hope this info is helpful....................

[Wally Arntzen]

Michael, on my 88 I hold 40 pounds of air in the tag as informed by Newell. Mine dumps quite fast but it probably is a different system that you have.

[RussWhite]

Thanks Steve,

That is sooooo slow! It makes it almost impossible to make a height change in response to changing road conditions unless you have a place to pull over and wait. I have contacted HWH about a system they install called Active_Air. It is supposed to be very quick, but I don't know if they will do it on an older Newell. I'll let the group know what I learn.

Russ

[Richard and Rhonda]

I am not sure we are talking apples and oranges. I agree that if I have the bus sitting on the stops and I have to air up from it sitting flat that it can take up to ten minutes. HOWEVER, if I am sitting level, and have the engine on fast idle, I can raise the bus to the top of the bags in about two minutes.

Based on my interpretation of the gauges, I reckon it takes about 85 to 90 psi to float the bus at the ride height, by the time I have about 105 psi in the bags the bus will be at the top of the suspension travel.

That explains the difference in the inflation times. To go from sitting flat to ride height requires that I build from zero to about 90 psi in all the tanks and bags. To go from ride height to the top of the suspension only requires that I go from 90 to 105.

I hope that was clear.

One thing that may be counterintuitive is that you really don't want a fast response in the ride height leveling system when you are going down the road. You really don't want the suspension jacking up and down with every irregularity in the road. In fact most ride height valves have some sort of restriction in them to slow the response down. On the other hand I can certainly appreciate the need to raise the coach quickly to go over obstacles or clear tight approach angles.

[express1]

Yes Richard we know about quick response to road condition.....Creed.
Have a safe and newelly trip east.