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Excessive LEAN in curves while interstate driving?
It may be “normal” yet it seems when driving at interstate highway speeds, in curves, my 2006 year model H3-45 leans more than it should. Am currently in Angel Fire, New Mexico and spoke with an owner of a 2009 H3-45 who said his bus rides flat in curves, yet he said he installed Road King shocks some years ago which made a significant difference.
I have 18 month old red adjustable KONI shocks on the front and wonder if I were to re-adjust them to the middle or most firm setting if that might help. Anyone try this?
***My sway bar bushings look perfect and my A-arms and other wornout suspension parts were replaced about 18 months ago. Rear sway bar bushings good too, and new rear shocks were also installed 18 months ago.
I say my bus maybe just fine because I have not driven other H3 buses… THANK YOU for your thoughts… Jeff
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20 Replies
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It certainly wouldn’t hurt to bump the Koni’s to at least the middle setting.
How many miles on the shocks and other suspension updates?
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10,000 miles since all new shocks and new suspension parts.
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If you are speaking of long curves shocks may delay a lean by a few seconds if that, but it is the sway bars that determine how much lean you are going to get.
I am not familiar with the H enough to be certain, but I think your sway bars are attached at each end with links we have called “dog bones” because they look like dog bones. Within the links are urethane bushings and on my last two coaches they failed and I had to replace the bushings. I doubt if you can fail to notice a bad bushing because they bang and clatter a lot. But if a dog bone got loose or disconnected or its attach point has failed your coach is going to lean because there is nothing to prevent the lean.
Don’t waste your time or money thinking shocks are going to fix a lean in turns. First verify the sway bars are securely attached and all bushings in place. That is a 1 minute inspection.
If everything checks OK then the other potential problem is associated with the ride height valves. If your coach leans the valve on the side outside the curve is going to have the lever move to open the valve to deliver air to the air bags on that side to attempt to raise the coach. Conversely on the inside of the curve the lean will cause that side to rise and that will make the air bags on that side get their air dumped to lower the high side. Make sure you are not having air flow to or from the ride height valves restricted in some way.
If your coach has had moisture accumulate in the accessory system it is possible the ping tanks or air bags have water in them and that will definitely screw up the ability of the ride height valves to keep the bus level side to side. But the collected moisture has to be a lot so that might be a slim possibility.
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Ditto what Jon said, I would suspect ride rear height valve problems. I don’t remember the details, but I believe there were changes in the valves at some point going to a quicker response valve.
In a turn that you feel it’s leaning too much, watch your aux pressure gauge, it’s a good indication that the valve is working as air is being pumped to increase the bag pressures.
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Jeff be thankful you have a rear sway bar. My chassis was apparently ordered without that for some reason. I have compared what I have to those with one. The welded brackets on axletube that the brake chambers attach to have a provision for sway bar link attachment – which mine doesn’t have. Also the pad/attachment area welded to chassis on either side above axle isn’t there.
Looks like it could be doable, but a huge PIA to add for those reasons.
1999 XLV X-6872, liberty #440 -
I think what john said about ride height is correct,Because I think on newer coaches like yours they have ping tanks on each corner unlike mine, older coaches don’t have ping tanks so if mine leans it will come back up slowly, Yours I believe have ping tanks so their job is quick response to leans. Log on to Prevost website put in your Vin # and check out air system
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The ping tanks came with IFS. I believe that is when Prevost switched from the time delay ride height valves to the instant acting ride height valves.
But the bottom line is if the sway bars and their dog bones are all attached to their required positions then the coach is leaning as normal or there is an issue with ride height valves. All coaches are going to try to lean unless the curve in the road is banked like Daytona racetrack.
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Billy: I can’t fathom why someone would delete the rear sway bar if that is the standard for that shell. I can’t imagine why Prevost would allow that. I’d look into having that updated.
Jeff: 10,000 miles is too short of time for good shocks to go bad. I didn’t think to mention sway bars like the smart guys did. (Actually … I’ve become a little sensitive to stealing their thunder.)
Almost ALL the vehicles we drive today have sway bars (often called “anti-roll bars” because that is their function). But unless you’ve driven a race car, you don’t think about what they are doing for you as you go around a corner.
The “bar” actually can (should) twist as you go into and through a corner. The terms in racing are “big bar”, “small bar”, “hard bar”, and “soft bar”. A big bar will have little or no twist while a small bar will have quite a bit of twist. Prior to sway bars the manufacturers and racers used stiffer springs to control body roll in the corner. But for a passenger car the stiff springs gave a hard ride. Once sway bars were introduced the springs were softened to improve the ride.
The big thing set-up in handling for race cars today are: Soft springs (which allows the front to come down and shift weight to the front tires under heavy braking) and a “big bar” (to control the roll as the car enters and goes through the corner), and shocks with little compression resistance (lets the front end drop under heavy braking to shift weight to the front, easier to turn the car) and lots of rebound resistance (keeps the front planted and weight on the front tires as the car goes through the corners). You can see this especially at road courses at the end of a long (fast) straight going into a sharp (slow) corner. The front of the car can drop as much as two to four inches.
As you go into the turn the first line of defense as Jon said are the shocks, but they will slowly compress and rebound while you’re in the turn and just delay the roll. Almost immediately the sway bar should also come into play to resist the roll, and its resistance should likely be the same throughout the entire corner (unless the engineers have machined it so the resistance is progressive). Then the ride height valves will notice a change and one bag will get air and the other will drop air as the system works hard to maintain ride height.
I’ve had a occasion to drive a race car with both a small (soft) and a big (hard) bar during the same session, it was swapped out while I sat in the car. The difference was significant. Granted the soft bar should have had stiffer springs, but big bar made the car handle much better.
For Jeff … I’d have someone look (safely) to ensure the sway bar(s) is(are) properly hooked up, one of the links (dog bones) wasn’t unfastened or broken, or (very unlikely) the bar was broke. If you had that work done 10,000 miles ago, its possible that one of the fasteners has come undone and the bar isn’t doing anything for you.
I use mechanical locking nuts or Nylok nuts on the fasteners for the sway bars on the race cars. Many guys will use safety wire.
Only once have I driven a race car with the front sway bar unhooked. It did not end up well. I was so new to driving a race car that I couldn’t feel it was unhooked until it was too late and I was just a passenger along for an unplanned ride into the tire wall.
I should point out that if all the components of the front suspension of the coach are doing their respective jobs … while the coach is in the corner the outside front steer tire is getting a huge load.
Jeff, keep us posted.
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I cannot remember the web site otherwise I would post it, but one thing on it got my attention.
The web site reported test results for commercial buses that were tested in simulations to represent substantial miles of service. The test results showed chassis weak points, specifically the amount of flexing or damage resulting from the tests which were set up to duplicate thousands of miles of service.
On a Prevost the deflection of the chassis (twisting) was measured initially and had remained virtually unchanged for the duration of the test. That means we can jack our coaches up and support the entire weight of the chassis at three of the four chassis support points and the chassis will twist a couple of tenths of an inch. I made that up because I don’t remember the exact amount of twist but I bet I am close.
The weak points were interesting and one I remember is the sway bar attach points at the chassis failed during the test. The simulated mileage when that occurred was hundreds of thousands of miles but it did indicate that is an area to monitor during routine service. I cannot remember if the welds failed or the fasteners failed but as Dick mentions the sway bar plays the largest role in keeping the coach level during turns.
1999 XLV X-6872, liberty #440 -
If you want to see how well a Prevost chassis holds up under testing here is where you can learn all about it:
http://apps.altoonabustest.psu.edu/buses/reports/477.pdf?1499095116
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I’ve had the front sway bar attachment points tear out of the frame on my BMW track car.
BILLY: I believe 40′ coaches are either not equipped with rear bars or they may be optional. My 40′ Marathon did not have a rear bar.
I would strongly suggest the OP drive another H of similar vintage before spending any money.
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Dick – Marathon ordered the shell, 95 XL.
Joel – good to know there were other leaners built.
Sway bar appears to be avail according to parts manual. Not sure why ANY would be ordered without, unless for some strange reason on some specific chassis it wasn’t avail. This thing loves to lean.
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Good Evening and thank you ALL for your input! Please excuse my delayed reply…was due to the fact we were on the road all day traveling from Angel Fire, New Mexico to Lubbock, Texas.
My wife and I have been on the road since the second week of June and are now on the way home so I will definitely check all items mentioned very soon. I will report back if I find anything. Thank you again, Jeff
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Jeff, before you get home disconnect the toad and follow the bus and look at it as it goes around curves.
Take photos or find some way to quantify what you think is a leaning.
I have followed a lot of coaches over the years and while some slight leaning may occur I rarely saw one with what I would consider excessive leans. When I did see one lean too much it was typically an old coach that looked poorly maintained.
After you get a mental picture of how your coach leans or doesn’t in curves try to follow another coach like a Greyhound or other Prevost.
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On my last coach I also had excessive leaning . It turned out to be a broken Pan Hard . It is a bar that goes from pumpkin to chassis .
We think it happened while driving with a bad air spring in Ms on a bumpy road . This pan rod only sits 1″ above the drive axle .
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