air bag replacement - dual convoluted or rolling lobe?

[bevans6]

One of the jobs I'll have to do sometime next year is update the air bags on the MCI MC-5C.  At least one is almost new, the rest could be original!  As an Arizona bus the air beams seem quite solid, and the current system is stock and  holds air pretty well.  Would I be best served by replacing with the stock design dual convoluted air springs with the same system, or would I get better ride and over-the-road performance from installing a rolling lobe upgrade kit and blocking off the air beams?  Would it make any sense or be a reasonable plan to just change the front suspension to rolling lobe (either as a long term solution or as an interim step if I do the front and rear at different times) and leave the rear dual convolute?  As a description, what is the major difference in ride and performance generally between the two setups?  I know modern buses use rolling lobe - was that for cost savings, maintenance issues with air beams, or are they just better all round?

My complaint with the current ride is that it is harsh over rough pavement, really crashes and bangs over pavement transitions and small potholes.

Edit for Tom:  I am indeed running corrected air pressures, per Firestone's data sheet, 85 psi front  and 80 psi rear.  You are correct since that cured or dramatically improved a lot of ride and handling issues compared to 105 psi all round when I got the bus!

Thanks, Brian

[TomC]

Which ever way you go you should choose one or the other, but don't mix the two since the two different styles of air bags might have different frequency of rebound creating a wierd bouncing sensation (for instance-typically double convoluted bags react faster, so you'd bounce faster in front, and slower in the back with rolling lobe). Double convoluted bags with sound air beams are perfectly fine-after all they have worked well for how many years now?  Rolling lobe are nice, but I think you're under estimating the amount of work to mount different air bags-to select the correct bags with enough travel, diameter, compressed stop bumper, etc.

As to your ride complaint, it sounds more to me that you have the tires at a too high inflation rate.  Just because it says 110psi on the side of the tire, doesn't mean you should be running it at that inflation.  The best thing to do is to go weigh your bus in full tank traveling mode-weighing the front and rear axles separately.  Then simply look up on line at your tires manufacturers site, and pull up the inflation table for your size of tire.  I bet you'll find you can reduce your tire inflation quite a bit-creating that better ride you're expecting.  For example, I have 11R-24.5 16 ply Michelin XZE on both front and rear.  They say 120psi max front, 110psi max rear.  But I weigh in at 10,500lbs front and 20,500lbs rear, which works out to be around 85psi.  I run 90psi all around and the bus rides very well.  My transit also has double convoluted bags, but with aluminum cans on top of each air bag instead of the air beams.  I replaced all 8 of the bags with no regrets.  Good Luck, TomC 

[Tenor]

Brian,
I have the stock beams and bags on my MCI 7.  I run 100psi in my tires and I find the ride comfortably firm, but not jarring.  Since your beams are good (and you can do all new bags and hardware from Mohawk for under 1K) why re-invent the wheel?  Good luck!

Glenn

[Len Silva]

If your airbeams are good, I would stick with the factory air bags. Since you have addressed tire pressure, next is shocks and radius arm bushings, front and rear, as well as making sure everything is well greased. Any or all of those things will make for a harsh ride.

[bevans6]

Thanks guys.  I have put new shocks on, even though the old were fine after I got them off, just nasty looking...    the radius arm bushings all look good as well, and I had them inspected by a suspension specialist place that also checked my alignment.  The panhard rod bushings are nice yellow nylon, so they have been upgraded.  It's entirely possible the harsh ride over sharp ripples and bumps is all in my mind and the bus is perfect - how would I know, the last bus I drove was an International schoolbus in 1977!  And my region is not known for having smooth roads - frost can kill a fresh paving job in two or three years up here!  I will no doubt stick with stock as long as the beams are good.

Brian

[zubzub]

In the old car world nylon bushings are known to give a harsher ride.  Pretty sure the same applies to buses.

[Chopper Scott]

As I had an air beam start leaking last summer that I repaired and after seeing the condition of most of the present air bags I decided to go with the rolling lobed air bags. I started on the project this afternoon. It really isn't that hard to change but I have a welding shop and am used to this type of work. We are in a blizzard right now so working on the bus in a nice warm shop with little interuptions is great timing!

[rv_safetyman]

I have read Jack Conrad's article on the conversion to rolling diaphragm springs and it does not look too bad.

When I converted my truck conversion to air springs, I put a large air tank in the spring system to smooth out the ride.  This is the same principle as the air beams - larger volume to reduce the "spring rate".  I used one tank connected to the two springs.  The tank was your typical truck air tank.  In the plumbing process, I put solenoid valves right at each air spring.  When I needed better cornering, I would close the valves so that the air springs were isolated and only had the volume in the bag - higher spring rate.  Worked pretty good.  You folks with air springs could think about this option. 

Jim

[bevans6]

If you could do a before and after comparo of the rolling lobes vs the stock system, that's the information I'm after.  Capped off rolling lobes vs stock air bags with stock airbeams, what is the qualitative difference is the question!

where can I find Jack's article?  It might have just the information I am looking for!

Brian

[zubzub]

Glad to hear your enjoying yourself in your nice warm shop.  My shop is bigger than yours but hard to heat.

I am interested in your air beam to rolling lobe conversion.  I figure when the time comes that's what I will do so some pics and explanations would be great.  

[rv_safetyman]

Brian, Jack's article appeared in Bus Conversion Magazine 2-3 years ago.  Good article as I recall. 

Perhaps Jack can tell us which issue and maybe you can get a copy.

Jim

[Chopper Scott]

Looks rather cool ZubZub!!! Changing the bags is really pretty simple but like everything on a bus, bigger. Getting the bus jacked up and blocked up basically took as much time as getting the bags changed. Each old spring has 8 bolts on top and bottom. The nuts on mine were brass actually and the bottom ones all came off with an impact. The tops ones all wanted to spin and there isn't no way to actually hold them so I grabbed the torch and more or less melted them off. A little chisel work broke the old bags loose and out they came. I let the suspension down as far as it would go to put the new bags in and it took a bit of work to get them in but nothing real hard. Then tighten them up and redo the airlines and you're on the downhill side. The kits come complete from Mohawk with all you need, less airlines etc, and fit well. I still have to do the rears so I hope I haven't jinxed myself!!!

[zubzub]

Just a follow up question re the rolling lobes from Mohawk.  Seems to me truck trailer rolling lobes springs come with a block off plate already as trailers do not have air beams.  Would it not make more sense to just source RL springs of the correct size and install them where the convoluted springs used to be.  I.E. why go with Mohawk special bus stuff when off the shelf trailer RL springs (and presumably mounting hardware) are available?
Don't want to seem to cheap (though I am) but as I'm in Canada ordering from Mohawk et all is big $$$for shipping/duty/brokerage fees.

[JohnEd]

I don't know what Jack's article says but in my mind the issue was visited and the results were:  Stock system w beams was noticeably superior.  Next came rolling lobes.  Last was stock bag without air beams.

I was visiting with David down at S Orygun Diesel and he showed me a bus for sale.  He had had the bus in for service a year prior and it left in good shape.  He told me that it needed tires all the way around as the guy obviously had bought "Log Truck tires" and the bus now rode abusively hard.  My meager understanding is that those heavy duty truck tires are also made for off road with rocks and lumber mixed in the muck.  I know from experience that car tires can have widely varying levels of comfort in ride.  And it isn't just plys....there are different rubber compositions that give better wear or traction or heat rejection not to mention construction variables.  Do those city tires that will stand up to a curb once in awhile ride differently than higher speed rated and more efficient highway tires?

What tires do you have, make and model?  Any body else getting comfy ride from that product?  Air pressure should do wonders but that naysayer seems to disprove that if his 7 does well at your pressure but his bus is much heavier.....no? 

Nylon bushings are a terrible idea on any car I have done that to that was used for street....way rough and brackets also fail due to their increased loading from impact. 

I hope you keep us updated.  Glad you did the shocks as they are the most probable culprit right after you verify that the tires are, in fact, inflated.

My Lex rode like a log truck and I learned that my springs were completely sacked.  1 inch of travel and it ricocheted off of everything.  It took new springs AND shocks to get her back stock plus for a P Sport.  You have an adjustable ride height air suspension and I wonder that the ride height has been lowered to reduce your travel.

Keep us informed of what you verify....so far it is shocks and bushings, right?

John

[Tenor]

Zubzub,
I was told by the rep at Mohawk that their engineers designed the plate system for air beams 20 some years ago, and I wonder if someone in Canada has the parts to do it to avoid the shipping hassles.  Since I can't see Brian's info while posting, are you in Canada too?  Since these coaches were made in Canada, isn't there an easy way to get the original equipment there?  Obviously (being a troll from Lower Michigan), I need some "edumacation" about the great white north.

Glenn