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Tires, Wheels, Brakes, Steering and Suspensions Discussion of preventative/corrective maintenance and other technical issues regarding your coach's Tires, Wheels, Brakes, Steering and Suspensions and related components.

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  #1  
Old 10-23-2019
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Kiwi3 Kiwi3 is offline
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Lightbulb Randy's Suspension Mods (WOG 2019)

I just wanted to try to capture some of what Randy was talking about at WOG 2019 on his suspension modifications to improve the handling of his coach. I hope he'll correct any errors that I post here and hopefully he will snap some pictures when he has time. If you have other ideas, lets keep it rolling here.

1. Shock modification: Adding a second set of shock mounts to the Drive and Tag axles. Randy has tried this and said that it helps stop the porpoising that many of the coaches have on rough roads. He welded the mounts on. I don't remember if he said where he sourced the mounts from. He used the identical shocks that are on the Drive and Tag axles. There was some discussion on having shocks tested on a shock dyno. Maybe there is a better shock than the Konis that will fit the mounts?

2. Air bag modification: For LX and LXI with the smaller air bags he recommended upgrading them to the larger size bags to improve suspension spring.

3. Tag axle air modification: The Tag axle only has one dump valve located on a 4-way connector which feeds airbags on both sides of the coach. When cornering the coach leans out of the turn which compresses the outside airbag forcing the air into the inside airbag resulting in more lean out of the turn. While the Drive axle will try to compensate for this it doesn't have enough control input. Randy has tried connecting the Tag axle airbags to the Drive axle airbags which would put them inline with the height control valves for cornering leveling. This works but causes the loss of dumping just the Tag axle for tight turning. Randy said that he was thinking about keeping the Tag axle airbags on their own circuit but adding a second dump valve to isolate the left and right sides from each other.

4. Dump valves & Height Control valves modification: To make servicing easier, Randy relocated the valves to the wheel wells outside the frame. He did have to make some extension links for the HC valves. Added bonus is that it makes inspection and service much easier on the valves (cleaning mud daubers out of the vent ports...).

5. Front suspension modification: Nothing firm, but some discussion on disconnecting the front sway bar as it is very firm. Also discussed some ideas on possibly adding a second dump valve similar to the discussion on the Tag axle.
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  #2  
Old 10-23-2019
ChrisRasman ChrisRasman is offline
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Very interesting.
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  #3  
Old 10-23-2019
al perna al perna is offline
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Nice work Bruce. I will add that after 40k miles with the stableizing bar , and 130k with it off there were differences .
Without the bar removed the ride is stiff and more stable in the turn .You feel the slightest of bumps in the road . The force will carry across the entire front end.

With the bar removed , the ride is loose and the force does not carry as much across the front end. But the turn are loose and you experience more lean without the bar . Just my experience and non technical wording .
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  #4  
Old 10-23-2019
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SNOWBIRD SNOWBIRD is offline
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I like the way the coach drives with the stabilizer bar. It feels more like a sports car when cornering and has no lean when a big rig passes. Its so much better than our Prevost XL that felt like riding a marshmallow. If that's what you like, then go for it. I will say, however, that my favorite was the ride of our old Eagle bus with the Torsilastic suspension.



Maybe after driving Jeeps for years, I'm just used to some bumps.
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  #5  
Old 10-24-2019
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Quote:
Originally Posted by Kiwi3 View Post

3. Tag axle air modification: The Tag axle only has one dump valve located on a 4-way connector which feeds airbags on both sides of the coach. When cornering the coach leans out of the turn which compresses the outside airbag forcing the air into the inside airbag resulting in more lean out of the turn. While the Drive axle will try to compensate for this it doesn't have enough control input. Randy has tried connecting the Tag axle airbags to the Drive axle airbags which would put them inline with the height control valves for cornering leveling. This works but causes the loss of dumping just the Tag axle for tight turning. Randy said that he was thinking about keeping the Tag axle airbags on their own circuit but adding a second dump valve to isolate the left and right sides from each other.
Here's a shot at what having the drive and tag bags for each side work in unison but still be able to dump the tag w/o dumping the drives also.

The key to this design is as Randy suggested - use a separate dump valve for each tag. However, when you do that you now create a similar issue as mentioned above - you can't dump just the tags - because the drive bags will try and dump through the tag dump valves.

To solve that, I'm thinking that a couple of hi-flow clippard (normally open) valves would shut when dumping the tags.

On-the-other-hand, if the dump valve inlet port closes automatically when control (pilot) air is present - then the tag isolation clippards wouldn't be needed.

No idea if this would actually work, kind of seems like it might ...

New stuff is in red.

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  #6  
Old 10-25-2019
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Default easier version

After thinking about this more, I'm pretty sure the dump valves close their inlet port when control (pilot) air is present - so the tag isolation clippards mentioned above wouldn't be needed. So this becomes simply adding a second (tag) dump valve and reworking the plumbing (again, as Randy first mentioned).

The only issue I see is you couldn't plumb the air supply to the tags through the pressure regulator - which is uni-directional - as it won't let the air flow out of the bags and exhaust via the HCV exhaust port under normal drive mode operation. Maybe there's some fancy bi-directional pressure regulator valve that would work.

Given in this setup there would be no pressure regulator for the tag bags - and they would run at the same pressure as the drive bags this might induce other handling issues - and increase the loading on the steer axle (lever/fulcrum).

Simplified version (note no pressure regulators on tag).

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  #7  
Old 10-25-2019
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Randy Dupree Randy Dupree is offline
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Clint,i did not reply last night because it was late and i was tired,i needed to think about your drawing.
But your last email is dead on target,no Clippard valves required.
FYI,the 2001 and i'm thing 02,and 03 have the tag bags connceted to the drive bags with no regulator on the tag,the tag pressure will run high,about 90psi.
And i think the tag gauge will show pressure the way your last drawing is drawn.
I will let you know!


I just looked closer at your drawing,the clippard valves are not needed,but after another quart of coffee i will be sure.
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  #8  
Old 10-25-2019
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Might be of interest... How MCI plumbs their drive and tag axles with an overflow valve.
MAINTENANCE MATTERS - WEIGHT GAIN: Handling Setra's suspension, tag-axle load shift

Do you think it would be possible to not have the HCV for the Tag axles but keep the two dump valves? That should allow you to keep the Tag axle pressure regulator inline and keep the air pressure constant in the left/right tag air bags while cornering? Be gentle I'm learning. I just worry about transferring to much weight to the front axle via high tag axle air bag pressure.
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  #9  
Old 10-26-2019
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Quote:
Originally Posted by Randy Dupree View Post
Clint,i did not reply last night because it was late and i was tired,i needed to think about your drawing.
But your last email is dead on target,no Clippard valves required.
FYI,the 2001 and i'm thing 02,and 03 have the tag bags connceted to the drive bags with no regulator on the tag,the tag pressure will run high,about 90psi.
And i think the tag gauge will show pressure the way your last drawing is drawn.
I will let you know!


I just looked closer at your drawing,the clippard valves are not needed,but after another quart of coffee i will be sure.
@Randy, are the 01-03 LXI's able to dump just their tags?


Quote:
Originally Posted by Kiwi3
Might be of interest... How MCI plumbs their drive and tag axles with an overflow valve.
MAINTENANCE MATTERS - WEIGHT GAIN: Handling Setra's suspension, tag-axle load shift
@Bruce, interesting setup, but seems to do the same thing as a bird does when dumping the tag - but for a different reason. They highlight the need to add weight to the drive axle for traction - we tend to focus on improved tight turning performance. Looks like their tags work in unison with the drive bags.

Something interesting about the MCI design, it has a built-in safeguard for drive axle overload (100PSI in this setup). Birds don't have that - not sure if that's super important or not, but apparently MCI thought it was on the Setra coach. Oh, ...and it re-inflates the tag above 18MPH ... nice to have.
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  #10  
Old 10-26-2019
Jim Brookshire Jim Brookshire is offline
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My 2001 LXI can dump just the tag. Switch and gage, but no regulator. Gets the air from the drive axle.
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