LXI SUSPENSION ISSUE

[cmillsap]

Here’s a schematic for the steerable tag controls. I’m at a loss to understand why Al’s tag air pressure is set so high. On my previous LXi with a steerable tag I did increase the tag air pressure from 55 psi to 70 psi to take some of the load off the drive axles. If I remember correctly that increased the tag load from 10500psi to 11500 psi and decreased the drive axle pressure by almost the same amount. It also increased the steer axle pressure from 13000 to 13600 or there about. It looks like Al’s steer axle pressure at 16000psi is the result of the high tag axle pressure. Since the drive axle is presently at 21000 psi with no bike load, I would drop the tag air pressure to allow the drive to carry more weight. David, on your #2 weight calcs above (with bike) I don’t understand why the drive axle weight load would increase over 2000 #s and the tag axle weight load stay static??

[davidbrady]

Thanks for the diagram Chuck. Funny thing though - I don't see a pressure regulator to set the tag axle pressure, do you? In fact, the whole system is different from my fixed tag. Notice how the left tag axle air springs are tied to the left drive air springs and likewise for the right. On my LXi the tag air bags are tied together like the steer axle. If I'm reading the diagram correctly, it looks like tag pressure isn't adjustable on this schematic and air delivery is regulated by the height control valves on each side. This is how SpongeBob is set up.

Regarding the extra weight calculations for when the bike is on board, I made a huge assumption, and that assumption is that the tag air is plumbed the same as my LXi; i.e., a pressure regulator sets the tag air spring pressure. If that's the case, then regardless of load applied, the spring pressure is determined by the regulator which means the tag load has to stay constant with or without the bike. But, all that goes out the window with this new air diagram.

In short, the 1500 lb bike shifts the CG from 15.33' to 16' behind the steer axle. If the tag load stays constant at 13K lb (but this is no longer true), then the remaining weight is divided by the drive and steer as shown: the drive gains 2800 lbs and the steer loses 1300 lb such that the net difference is the weight of the bike, or 1500 lb.

Do you see a pressure regulator for the tag air springs in your schematic?

BTW, my #1 calcs aren't Al's true weights. Those numbers are a guess at what a typical 43' slide equipped LXi would come in at per axle. (I had to start somewhere)!

[cmillsap]

(10-20-2014 21:02)davidbrady Wrote:  Thanks for the diagram Chuck. Funny thing though - I don't see a pressure regulator to set the tag axle pressure, do you? In fact, the whole system is different from my fixed tag. Notice how the left tag axle air springs are tied to the left drive air springs and likewise for the right. On my LXi the tag air bags are tied together like the steer axle. If I'm reading the diagram correctly, it looks like tag pressure isn't adjustable on this schematic and air delivery is regulated by the height control valves on each side. This is how SpongeBob is set up.

Regarding the extra weight calculations for when the bike is on board, I made a huge assumption, and that assumption is that the tag air is plumbed the same as my LXi; i.e., a pressure regulator sets the tag air spring pressure. If that's the case, then regardless of load applied, the spring pressure is determined by the regulator which means the tag load has to stay constant with or without the bike. But, all that goes out the window with this new air diagram.

In short, the 1500 lb bike shifts the CG from 15.33' to 16' behind the steer axle. If the tag load stays constant at 13K lb (but this is no longer true), then the remaining weight is divided by the drive and steer as shown: the drive gains 2800 lbs and the steer loses 1300 lb such that the net difference is the weight of the bike, or 1500 lb.

Do you see a pressure regulator for the tag air springs in your schematic?

BTW, my #1 calcs aren't Al's true weights. Those numbers are a guess at what a typical 43' slide equipped LXi would come in at per axle. (I had to start somewhere)!

David,

I believe all steerable tag equipped WLs had the tag pressure pre set at the factory and there was only a connector block located center of the tag axle and hidden under the foam insulation. When I increased the air pressure on my steerable tag, I had to replace that connector block with a regulator valve. I would make a guess that all steerable tag equipped buses were set at around 55 psi depending on what the weight distribution dictated. Although I doubt that BB weighed the individual axles on each new bus. They probably assumed that around 55 psi would distribute the weight load pretty close.

Sorry, I just assumed you had the actual weight of Al's bus. Al should weigh his bus so we can see how 100psi onthe tag affects his axle weights.

[davidbrady]

Chuck,

I like the plumbing on your schematic much better than what I had on my LXi. With this scheme we have 3 bags per side leveling the coach and we have more roll resistance offered by the tag axle, plus it auto adjusts to increases in tongue weight proportionally distributing tongue weight to both drive and tag axles. Seems superior in all respects. I wonder why BB ditched this approach in favor of the tag axles tied together and supplied by a regulator. Could be they did it to have better control of steer axle weights. As coaches got heavier the tag air regulator made shifting weight on/off the steer axle easier.

I'm convinced more than ever, given this new air schematic, that Al's issues are HCV or Panhard rod related.

I added your diagram to our Document Library:
WanderlodgeGurus->Document Library->Models->LXi->Suspension->Steerable Tag Air Schematic.pdf

[cmillsap]

(10-20-2014 21:46)davidbrady Wrote:  Chuck,

I like the plumbing on your schematic much better than what I had on my LXi. With this scheme we have 3 bags per side leveling the coach and we have more roll resistance offered by the tag axle, plus it auto adjusts to increases in tongue weight proportionally distributing tongue weight to both drive and tag axles. Seems superior in all respects. I wonder why BB ditched this approach in favor of the tag axles tied together and supplied by a regulator. Could be they did it to have better control of steer axle weights. As coaches got heavier the tag air regulator made shifting weight on/off the steer axle easier.

I'm convinced more than ever, given this new air schematic, that Al's issues are HCV or Panhard rod related.

I added your diagram to our Document Library:
WanderlodgeGurus->Document Library->Models->LXi->Suspension->Steerable Tag Air Schematic.pdf

David,

I am still mystified as to why Al's tag axle pressure is set so high. When he gets each axle weighed, it will shed some light on how the axle weights are affected by that extremely high tag axle pressure. It may be causing some of the problem. BTY, I'm wondering how Al's tag pressure got to 100 psi. Maybe the PO replaced the pre set relief valve (center connector block) with an adjustable regulator valve.

[davidbrady]

Chuck,

We may have to wait for Al to chime in here to confirm his tag axle air pressure gauge reading. I'm not following where you would plumb the pressure regulator; give me a schematic item number if you can Chuck.

The charts for his drive axle bags (Goodyear 1R11-152) show a requirement of 90 psi for a load of 5805 lbs per spring (23,220 lb total) at a design height of 8 inches. If his bus is plumbed per your schematic without any changes that would place the same psi, 90, on his tag axle air springs. This means that the proportion of load split between the axles was chosen by BB when they selected the tag axle air springs. Here's what we have recorded as the air spring for the steerable tag axle: Firestone: W01-358-9387

[cmillsap]

(10-20-2014 23:17)davidbrady Wrote:  Chuck,

We may have to wait for Al to chime in here to confirm his tag axle air pressure gauge reading. I'm not following where you would plumb the pressure regulator; give me a schematic item number if you can Chuck.

The charts for his drive axle bags (Goodyear 1R11-152) show a requirement of 90 psi for a load of 5805 lbs per spring (23,220 lb total) at a design height of 8 inches. If his bus is plumbed per your schematic without any changes that would place the same psi, 90, on his tag axle air springs. This means that the proportion of load split between the axles was chosen by BB when they selected the tag axle air springs. Here's what we have recorded as the air spring for the steerable tag axle: Firestone: W01-358-9387

David,
I do see what you ment. I looked the schematic over pretty throughly and I do not see a pressure reduction valve that is located between the tag and drive air susp system. Could be that the schematic is obsolete or not the correct diagram. I do know that there was a tag pressure reduction valve located on the rear center of the tag axle on my steerable tag equipped LXi. The reduction pressure was pre set at 55 psi and was non adjustable. It had to be original equipment by BB as it was burried under the foam insulation and hard to find. Rick at CoachWorx did the changeover for me. If I remember correctly there were just the three lines connected to it. They were the supply line & right & left lines running across tag axle to the air bags. I think the steerable tag air pressure should run approx the same air pressures as a fixed tag at about 50 to 70 psi but I'm not sure. I have not heard of anyone running 100 psi on their tag axle. Except Al of course

It's entirely possible that valve was bad on my bus and was originally set at100psi. But wouldn't that be higher than the rest of the air suspension system? Why have a reduction valve there unless it was to run the tag at less psi than the drive and steer axles?

[patticake]

Maybe I'm missing something here, but I don't understand what the tag axle pressure has to do with a sideward movement in turns. Please explain.

[al perna]

Hello ,

on the trip from Josams North to Pa we had a tag Pressure of 70 lbs Plus . Had same pressure from Pa to Chicago a few weeks back .

Had the ability to climb under the bus and found the curb side HCV had slid down , adjusted it to the same measurement of the drive side ( unable to measure bag height, no room ) pressure returned to 70 on trip back to Pa , but the drop on turns began .

[davidbrady]

Attaboy Al, get those HCV's fixed. I think that's where your issues lie. Chuck and I have shown that your bus has enough capacity to hoist its ass end. BTW, is your compressor cycling between 100 and 125 psi?

Steve, it's an effort in understanding how the tag is plumbed, whether it auto adjusts to increases in load or requires one to crawl under to tweak a pressure regulator, and understanding the roll resistance it offers. As you know, these heavy coaches need the help of the tag to get the bus off the ground. I've made the mistake before of assuming what's true about one LXi is true about them all! The steer tag is very different so I need to be very careful over what I claim about it.