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Message |
John Biundo (Jbiundo) (209.239.207.65)
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Votes: 0 (Vote!) | | Posted on Monday, November 05, 2001 - 1:22 am: | |
I had a brief side discussion under another thread over on the MAK board about this, and as a result, I'm convinced I don't fully understand this important topic.
I'm getting ready to remove the interior skin on my MC 9, which is considered structural. As such, it seems a good idea to block up the body beforehand. Question is, what's the right way to do this?
"Da book" (vaguely) identifies "coach jacking points" and "axle jacking points". I believe these are two different points, though the diagrams lack enough detail to be sure. Following is my interpration of the diagrams and text in da book. I'm not terribly confident I've got this right, so I'd appreciate expert opinion!
1. The axle jacking points are preferred for most jacking operations (e.g., tire changes). They are connected to the axle assembly, and therefore, indirectly to the chassis via the airbags.
2. The coach jacking points are connected directly to the chassis. The diagrams are pretty vague here. My interpretation is that these points, on an MC 9, are the large frame members that the radius rods attach to. These beams certainly look like they're very substantial frame members that are capable of supporting the weight of the coach. Significantly, these points do not connect to the air bags directly, and therefore can bear the entire weight of the coach without being affected by the air bags.
My conclusion: when the coach is blocked up from the coach jacking points (#2 above), the following is true:
- loss of air pressure in the air bags will NOT result in any change in the level of the coach
- this is a solid position of support from which it should be safe to remove the interior skin, raise the roof, or do any other structural work.
Comments, please!
Thanks in advance,
John |
John Biundo (Jbiundo) (209.239.207.65)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, November 05, 2001 - 1:27 am: | |
More questions:
Sorry, forgot to ask part two in my last post.
Assuming I've got the right understanding of how to block up, the next question is: how do I actually load the weight of the coach onto the blocks? In other words, is there a(n easy) way to depressurize the air bags, thereby lowering the chassis onto the blocks? I'm apparently blessed with relatively airtight bags, 'cause the level of my coach remains very constant over long periods of time. So the coach doesn't just "settle" onto the blocks.
Alternatively, should I build some blocks that incorporate some bottle jacks so that I can adjust the height of the blocks so that they begin to bear some of the weight of the coach?
Hope the question is clear... thanks again for any input.
John |
Russ Murray (Russearline) (172.182.193.18)
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Votes: 0 (Vote!) | | Posted on Monday, November 05, 2001 - 5:04 am: | |
Hi John, thats a tough one hopefully someone out there has a good answer. I would think that if you block the chassis (frame) that the air bags deflating would not have any impact. Check the operators manual about deflating the bags. Our 4905 has self deflating bags. They go down in about 4 days.
Russ |
Steve Gibbs (12.148.43.8)
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Votes: 0 (Vote!) | | Posted on Monday, November 05, 2001 - 1:25 pm: | |
John,
If all you are doing is removing the "stress panels" under the windows with the intention of reinstalling them I do not think you need to block the coach. I had no problems taking mine out to spray foam and then replacing them with the bus sitting on the tires. However, I did not attempt to drive the bus during this time as I was afraid some shifting could occur.
I have read several posts of other MCI owners removing and reinstalling the stress panels with no problem. One even drove his coach quite some distance with the panels removed.
Now, if you are planing on raising the roof or cutting in a side entry door, that is a bus of a different color. Although I do not have the answer to how to properly block for this, I'm reasonably certain that the coach body must be supported from more than four jacking points, axle or otherwise.
The roof, along with the side walls and tunnel, carries the body strength from the front to rear axles and taking off the roof could result in a sag.
Again, if you are just doing the side panels, no worries. The ceiling paneling is not structural as far as I know. |
Dale Leyten (216.23.152.10)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, November 05, 2001 - 2:16 pm: | |
In doing my 5A, I drove bus onto blocks that put the coach body at the height that I wanted for removing suspension, installed I-beam across coach jacking points and blocked into this position. After shut down of engine, I blocked diff also. air bags deflated, coach body remained in same position as jacking points of coach hold body, which is connected to diff by radius rods and air bags. Remove wheels, then diff. Been in same place 1-1/2 years, has not moved. I ensured that placement of coach blocking would have coach level side-to-side and end-to-end. Let the renovations begin. I am not doing a roof raise, or any panel cutting, but is sure nice to have a level floor to install cabinets, etc. . Good luck. |
Scott Whitney (63.151.69.220)
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Votes: 0 (Vote!) | | Posted on Monday, November 05, 2001 - 3:19 pm: | |
Hi John,
I think you are correctly understanding your coach suspension. It sounds to me like you have clearly identified the different jacking points - namely that jacking from the axle (as to change a tire) is entirely different than jacking the frame (as to relieve weight on the air bags) Unfortunately, I cannot help identify the exact points. Maybe someone with an MC9 and a digital camera can shoot you some quick pics?
It sounds to me like you either need to:
1) Get 4 seriously heavy duty bottle jacks and lift from the frame jacking points enough to take the weight off the bags. Do you have a concrete slab? If not, make sure you have a good piece of plywood under the jack. I heard a horror story of a bottle jack plunging 6 inches into the ground thru the asphalt. But even still, bottle jacks will leak down over time, so you are going to need some wood or metal blocks. I don't think you would want to leave it on bottle jacks long term.
or
2) Block the frame with solid chunks of wood until you are 100% sure that it will not come down on your head. Then find a way to relieve the air in the bags i.e. disconnecting an air line etc.
Or I suppose you could do #2 and just let the air leak out over time. I am sure eventually it would bleed out - but might take a few weeks or month. You could probably get to work removing panels without any fear of hurting anything. You can use large blocks of wood and then squares of plywood of different thickness to get it to the correct height.
I also have heard of people driving around with the panels removed but I don't know enough about MCIs to offer any advice on that one way or another.
Scott |
Tom Caffrey (Pvcces) (12.146.33.42)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, November 05, 2001 - 6:47 pm: | |
John, the way our air bag height control valves work, if you jack up the body an inch or so, the control valves will try to lower it, releasing the air in the airbags.
They're not smart enough to know that they should not release all the air; they only read body height relative to axle height, so they only need to be fooled into an attempt to lower the body.
One caveat; if you jack up only one jacking point, the other control valves will also be reading body to axle height, so it might be possible to cause one of them to try to readjust the height while you are jacking.
Be prepared to take all the weight on the blocks while you are jacking. Also, our coach uses three control valves in order avoid overloading any one corner.
When you try to jack up any one jacking point, consider how the ALL the control valves will be affected.
One trouble with four pick points on a rigid solid is if any one of those points does not carry its share of weight, all or most of the weight will be hanging on only two of the remaining pick points.
For this reason, it is generally safer to pick from three points because all of the points will carry a predictable share of the weight, and the two heaviest loaded will still have less than the two heaviest loaded if you pick with four points.
If you had uneven settling under your bus after it was blocked up, you could have most of the weight shifted to the two kitty-cornered blocks; whatever sets on the blocks is what the coach will feel.
You might well wind up with a twist in your coach if you don't check the loads on the blocks from time to time. You only need to check the easiest pair from side to side to prevent a twist.
If you give these ideas some thought, it should become clear to you what I am talking about. Many times, working construction, I saw people hook up four chains to a load, thinking that it was somehow safer, but it isn't.
Good luck!
Tom Caffrey PD4106-2576 |
Scott Whitney (63.151.69.220)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, November 05, 2001 - 7:20 pm: | |
Hey, I think Tom is on to something! Fooling the air bags into releasing air is probably a lot easier than the method I suggested in the other thread - disconnecting the control arms. Tom's way, you don't have to disconnect anything to get them to dump. Cool new trick . . .
My bus utilizes the three point system by having both pairs of front air bags connected to one ride-height valve in the center with a free flow btwn pairs.
Scott |
busmanted (207.12.173.89)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, November 05, 2001 - 8:00 pm: | |
Hi John, First, you cannot jack the bus up too much on the coach jack points as the airbags will not support the weight of the axles at all. Using bottle jacks is OK, but they could leak down. When I raised my roof, I blocked up the coach jack points so if I even got a flat tire it wouldn't matter. Then I blocked the body at three points on each side tightly so I would not get any sag anywhere before I cut any structual parts. I kept it this way until I finished all welding, cap installation and side skinning. luckily (unluckily actually) my coach leaks right down so blocking the coach jack points was easy without raising the bus. These jack points are too small to put a jack and blocks- you must choose one. Good luck, Ted |
Oaepalmer (Oaepalmer) (208.164.96.29)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, December 29, 2001 - 3:52 am: | |
Got any pix of your roof project while it was in progress or any sage advice, like where you got klekos cheap or where you obtained your skin? |
Stephen Fessenden (Sffess) (63.27.89.90)
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Votes: 0 (Vote!) | | Posted on Sunday, March 03, 2002 - 10:17 pm: | |
You can make blocks for blocking up you bus with a chainsaw and segments of tree trunk or heavy branches from tree trimming.
I was cleaning up a fallen tree and some other trees at my place and it was costing me to take the big pieces to the dump. I had been planning to get some blocks at a specialty lumber yard when it hit me. Each of those short tree trunk segments rady for disposal had a perfect block inside just waiting for a chainsaw to let it out. FREE OAK BLOCKS.
I have ordered a Haddon Lumbermaker to allow me to make more precise cuts. Search "Haddon Lumbermaker" to get to their website.
Look at what you are cutting though. One tree had drywood termites in it. So could untreated lumber. |
Dennis Gloe (Tontorod) (63.27.107.93)
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Votes: 0 (Vote!) | | Posted on Monday, March 04, 2002 - 4:30 pm: | |
Hey John,
You might also try railroad ties. I own a salvaged referigerated railroad box car and blocked it with rr ties. The cool thing is you generally can then use them on a project around the house.
Dennis |
John Biundo (Jbiundo) (64.175.37.67)
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Votes: 0 (Vote!) | | Posted on Tuesday, March 05, 2002 - 12:38 am: | |
Hi all,
Thanks for the suggestions. The original post was quite a while ago, so thought I'd report that I have my blocking situation well in hand. I actually used a combination of heavy duty rectancular steel tubing (4x6x1/2") - 6' long, running transversely under the front and rear frame jacking points, and a bunch of 2x6's, stacked in pyramids. Used various thickness plywood to shim it up. The rectangular tubing solved the problem of being able to both lift and support from the same point.
Also blocked at a bunch of points along the body and under the front and rear ends, using 4x4's and cedar shims. I just raised the roof, so I needed to block extensively.
Thanks,
john |
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