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Old 02-13-2017, 07:47 AM   #1
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Conversion of spring to air ride suspension

Has anyone every heard of someone converting the spring suspension in a school bus to an air suspension?

I know nothing about large vehicle suspension systems, so any thoughts or suggestions would be great. Thanks!

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Old 02-13-2017, 08:12 AM   #2
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I haven't. What would be the purpose of doing such a thing? It sounds like a pain, but that's usually my reaction to stuff involving large, heavy objects like leaf springs.

If you're just looking to even out the ride, a set of "helper" air springs, in addition to the leaves, might be what you're looking for. Many RVs use that configuration. The air bags are just there to provide softness to the upper range and let the driver level the vehicle better.
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Old 02-13-2017, 08:20 AM   #3
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Originally Posted by ourmefa View Post
Has anyone every heard of someone converting the spring suspension in a school bus to an air suspension?

I know nothing about large vehicle suspension systems, so any thoughts or suggestions would be great. Thanks!
It can be done, but you'll spend a lot.
Lots of school buses out there are equipped with air ride. Its totally worth it to find one that is. I've gotten lucky on both mine and they ride great. The shorty even has an air seat.
Kubla's BB has air ride on all four corners. That's gotta ride real nice!
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Old 02-13-2017, 08:21 AM   #4
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I haven't. What would be the purpose of doing such a thing? It sounds like a pain, but that's usually my reaction to stuff involving large, heavy objects like leaf springs.

If you're just looking to even out the ride, a set of "helper" air springs, in addition to the leaves, might be what you're looking for. Many RVs use that configuration. The air bags are just there to provide softness to the upper range and let the driver level the vehicle better.
Yes, the idea would be to help avoid some of the bounce that happens with spring suspension and also help with leveling the bus when needed. I have not heard about "helper" air springs - I will have to look into this.

My thought is that for some bus manufactures, the rear suspension seems to be an option. Once we have purchased our bus, I considered that maybe robbing the air suspension from a salvage bus and installing it on our bus might be a possible solution?

Thanks for the assist!
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Old 02-13-2017, 08:24 AM   #5
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Originally Posted by ourmefa View Post
Has anyone every heard of someone converting the spring suspension in a school bus to an air suspension?

I know nothing about large vehicle suspension systems, so any thoughts or suggestions would be great. Thanks!
It is possible, some work, but doable. Leaf springs do 2 things- they absorb the bumps, of course, but they also locate the axle. That means, they keep the axle right where it needs to be.

Air bags handle the bumps great, but they are just rubber bags of air- your axle would wrap on acceleration or shear on braking. You would have to add control arms to keep the forward/rear placement of the axle. Then you need to be concerned about the side to side movement of the axle, you'd need all this to be able to move without impingement. You'd need a small air compressor.




Hepler bags are much simpler.
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Old 02-13-2017, 12:29 PM   #6
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I have no real knowledge in the area but I can share something that I have observed others do with success trying to smooth the ride of heavily sprung trucks.

They installed GOOD shocks all of the way around. Removed one or two leaves from each leaf spring and added air bags between the axle and frame at each corner.

I am sure that there is some math to be figured out as far as how many pieces to remove and what size airbags to add. Do we have an engineer in the house???
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Old 02-13-2017, 12:32 PM   #7
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It is possible, some work, but doable. Leaf springs do 2 things- they absorb the bumps, of course, but they also locate the axle. That means, they keep the axle right where it needs to be.

Air bags handle the bumps great, but they are just rubber bags of air- your axle would wrap on acceleration or shear on braking. You would have to add control arms to keep the forward/rear placement of the axle. Then you need to be concerned about the side to side movement of the axle, you'd need all this to be able to move without impingement. You'd need a small air compressor.

Hepler bags are much simpler.
Great information! I just learned something about axles that I did not know. I guess I should take some time to investigate this more. Thank you!
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Old 02-13-2017, 12:33 PM   #8
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I have no real knowledge in the area but I can share something that I have observed others do with success trying to smooth the ride of heavily sprung trucks.

They installed GOOD shocks all of the way around. Removed one or two leaves from each leaf spring and added air bags between the axle and frame at each corner.

I am sure that there is some math to be figured out as far as how many pieces to remove and what size airbags to add. Do we have an engineer in the house???
This sounds like the best of both worlds! I will definitely look at this! I like the idea of shocks, as they are what will help the bus the most when we are not up on jacks!
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Old 02-13-2017, 02:41 PM   #9
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Can't give you a formula, but skoolies are sprung for their max gross with a full load of passengers and are typically WAY too stiff for any RV type build.

I can tell you I cut the rear spring rate in half on my 1.5 ton shorty and it is fine. I did add good shocks in back as the original chassis had none.

Any competent spring company can tell you what spring rate you need if you can give them the final front & rear axle weights. Talk to Eaton Detroit. They have been in the biz for over a hundred years and are great to work with.
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Old 02-13-2017, 02:57 PM   #10
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Actually a fellow Skoolie who lives just a few miles from me just had his converted, I'll text him later to find out what kind of cost was involved.
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Old 02-13-2017, 04:34 PM   #11
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This has been discussed around here before.

You would need the axle (the housing, anyway) with the suspension, since the brackets are suspension-specific and welded to the housing.

Way to go might be to cut the frame on the donor and bring the whole thing home. Then you could accurately drill the new holes to match the old frame.

The donor would likely be a single-axle highway tractor, since these are readily available.

I would love to do it, having driven air ride cross country for 27 years.
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Old 02-13-2017, 04:43 PM   #12
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Hi. I am also considering adding a HELPER air pack to the front of my TC1000. It has rear bags already, and an air seat. Id like to smooth out the front a bit, and maybe raise it a little. Also, I know they are not as Heavy Duty as the bags, but has anyone been known to add Air SHOCKS instead. I know some add 1500 or so lbs of capacity, and handle 150 psi..
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Old 02-13-2017, 09:53 PM   #13
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Ok he got back to me,, $10,000.00

That included everything , housing axles ring & piñon, bags
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Old 02-13-2017, 10:14 PM   #14
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It's not done a lot, but people do swap air suspensions onto medium duty trucks. Junkyard parts and lots of DIY seems to be the norm.

Here's one:

$300 rear air suspension - Diesel Forum - TheDieselStop.com
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Old 02-13-2017, 11:08 PM   #15
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Ok he got back to me,, $10,000.00

That included everything , housing axles ring & piñon, bags
"Everything"? Now I'm puzzled. Because…



…For Ten Grand, you can buy THIS complete air ride suspension, and he’ll throw in the rest of the 1995 Freightliner with Cummins M11 and 10-speed and you can drive it home. And you can do that almost THREE TIMES for Ten Grand. Price: $3,400. Los Angeles.






And if that one is not shiny enough, you can drive your choice of THESE air ride suspensions home with the rest of the 2005 Volvo attached, 365 horsepower humming, and still have $500 left over for the celebration. Price: $9,500. Dallas.
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Old 02-13-2017, 11:27 PM   #16
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There's labor in there too he paid a shop to install it. I'm just repeating what I was told
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Old 02-13-2017, 11:51 PM   #17
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Yes, of course. Maybe 30 or 40 man-hours at $180 or some such -- wild guess example.

I do understand that not everyone considers it a pleasant hobby to transplant major assemblies from one frame to another.

It just "hurts" to see it, when some of us would drive that Freightliner home for $3,400 and have the M11, RTO 10, and complete air suspension installed in the bus over a few weekends.
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Old 02-14-2017, 12:04 AM   #18
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You could get away with the existing axle. If you look, most of the suspension components are bolted on w/ U bolts. May have to torch a flat here or there, but is doable.

This company is supposed to be the cat's pajamas. Looks bolt-on, few mag drill holes in the side of frame. NEVER drill on top or bottom ledge of frame, nor weld to frame.

Hendrickson Comfort Aire


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Old 02-14-2017, 12:26 AM   #19
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As in the video of the "little" Ford, the track rod must be attached to a bracket that is welded to the housing.

And I like the idea of having the donor frame (or section thereof) as a template for drilling all the new holes correctly.

I used to drive Kenworths with "8 bag" suspension. That would be "4 bag" for a single drive axle. With that arrangement, ALL the truck's weight rides on air bags. The rods that hold the axles in correct position carry no weight.

Rode wonderfully. A few drivers opined that the locator rods were a tad inadequate and allowed the axles to shift around a bit. I suspect that was only runaway opinionism -- voicing an opinion for the sake of sounding wise and important.

8-bags also have two height valves -- one on each side, not connected. That completely eliminates leaning to one side in a long curve and in crosswind. No reason not to use two on any suspension.
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Old 02-14-2017, 12:47 AM   #20
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... the track rod must be attached to a bracket that is welded to the housing.

And I like the idea of having the donor frame (or section thereof) as a template for drilling all the new holes correctly.
The track rod in the picture above is attached to the cantilever, that is bolted to axle. other end goes inside frame rail. No weld needed.

2nd leveler might be nice, easy diy addition.
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