I'm getting setup to get under my bus to grease, brake adjust, etc. I've read a lot of good threads on the subject but I'd like some more input.
I've kinda been debating how to support the rear of the bus. No concrete available for me so I'm stuck with asphalt or dirt/gravel. I was originally planning on building giant heavy ramps, but now I'm considering two other options.
1. 22-Ton Jack Stands (see attached) - These have 11"x11" base plates. I'm leaning towards this option because I need to do brakes, bearings and seals in the future. Would these sink into asphalt? Also, if I had to use them on dirt/gravel would 20"x20" 3/4 ply work safely?
2. Stack of 7 2x12s ~ 20" long - Basically make ramps without the ramp and add levels as I'm jacking the rear up.
What do you think about these ideas?
Also, If I lift the rear up do I need to chain up the tag axle beforehand or can it hang with only the drive axle supported?
IMO, those stands should work well. I use something similar, but I have a concrete bus pad. I also chock the front wheels. If you use the correct suspension points, I don't see why you should need to chain up the tag
When it comes to a bus, my experience is anything will sink into asphalt, including the tires, if the temp is on the warm side. I would just try to get the job done somewhat quickly, and use block floats like a crane truck does, usually 2' square by 3" thick, to spread the load. It depends a lot on the quality of the paving job. Usually a well founded dirt or gravel driveway can be more stable than asphalt, which technically remains plastic. If the bus runs, starting out with run-up blocks or ramps is a great idea. Jacking and blocking the bus is a serious business, but if you approach it with a serious intent it's not all that big a deal. Measure the clearance you have to work with when the bus is on the ground and the suspension is fully collapsed. Get a jack short enough to get under the jacking point with the bus fully down - I can't tell you how many times I merrily jack up the bus and then can't get it off the jack again because I've lost clearance with no air pressure...
Quote from: GnarlyBus on May 01, 2019, 10:08:02 PM
...Also, If I lift the rear up do I need to chain up the tag axle beforehand or can it hang with only the drive axle supported?
Does the manual say anything about letting the tag axle hang? GM doesn't recommend letting axles hang by the air bags - probably something similar in your book somewhere.
One thought about your plywood... Maybe consider using marine grade plywood so that it's not as prone to de-lamination when it gets moisture underneath it from laying on the ground/gravel. I'd also want something thicker than 3/4" - perhaps double that by gluing/screwing two pieces together.
You're on the right track as far as combinations of cribbing.
Note level ground and block the front wheels... no parking brake once the tires leave the ground
It is bad form to leave the tag axle hanging, it's only the shock holding it. If it breaks, the tag can swing as far as the tire lets it.
Knocks into cribbing, whacks you, upsets the coach, scares you real bad...
None of that gamble is required. Chain it up.
Happy coaching!
Buswarrior
Quote from: GnarlyBus on May 01, 2019, 10:08:02 PMWould these sink into asphalt? Also, if I had to use them on dirt/gravel would 20"x20" 3/4 ply work safely?
The stands look adequate but I wouldn't trust them on soft ground with a single layer of 3/4 plywood under them. I think they'd go right through the ply. I'd go with two layers of 3/4 plywood glue laminated or better still a plywood, lumber, plywood sandwich.
Quote from: bobofthenorth on May 03, 2019, 09:08:36 AMThe stands look adequate but I wouldn't trust them on soft ground with a single layer of 3/4 plywood under them. I think they'd go right through the ply. I'd go with two layers of 3/4 plywood glue laminated or better still a plywood, lumber, plywood sandwich.
Yep, and I'd go for at least a 1/8" sheet of aluminum laminated on top. Steel likes to slide of steel but not so much on aluminum. It would be kinda expensive (unless you happen to have some around) but not nearly as expensive as what it would cost your widow to have the bus lifted off you.
Hmmm. I went to the lumber yard and priced out Baltic Birch to make some 20"x20" plates with two layers glued together. It's about $65 for a 5x5 sheet of Baltic. Now I'm kinda reconsidering using 1/4" steel plates instead. Probably wouldn't be that much more expensive. Think 1/4" would do the trick on dirt?
How much stronger is 1/4" steel than Baltic double thick I wonder for this use.
For my work that I need to do under the bus, I'll be on asphalt.
For the work I need to do on the axles (wheel seals, brakes, etc.) I'll likely be on gravel or dirt. For this, I shouldn't need to get under the bus at all so I'm starting to think I should just crib it up with 4x4s or 4x6s real good.
Thanks for all the replies.
I would want 1/2" plate on dirt or asphalt.
1/4" is kinda weak for me...
Quote from: 6805eagleguy on May 03, 2019, 10:35:52 AM
I would want 1/2" plate on dirt or asphalt.
1/4" is kinda weak for me...
That's like 80 lbs!
Yes but 1/2" won't bend 1/4" will bend on soft ground IMHO
But then maybe everything I do is overkill :P
Is this heading in a bit of an excessive direction?
We're only holding up one end of a bus...?
happy coaching!
buswarrior
Yah I'm all for safety but it's starting to sound more like we're trying to bridge concrete with steel and park the bus on it. I really think the asphalt I'm gonna be on will be fine with the 11x11 foot pads of the jack stands. I figure I'll add some 3/4" ply to spread out the weight a bit.
The drive tires are about a 12"x24" footprint on each side. Seems like getting close to that would be sufficient.
I'll crib up under the frame as a secondary security.
I do appreciate the input. Reading old threads on this topic people have a tendency to "one up" on each other on safety until someone suggests a pit! Nobody mention railroad ties either or all heck will break loose! :)
A reasonable safety margin would be to expect one jackstand to hold up 20 tons. That's the full loaded weight of most buses so it should never go that high but with side loading and other odd things it really gives you about a 2:1 safety margin. (Expecting one stand to hold the full weight of one end is reasonable, rational and will probably happen.)
Can you simulate what 20 tons will do to your cribbing? Yes, if you have access to a hydraulic press. Worst case, the cribbing will be supported at opposite ends of the long axis. Will it support 20 tons that way? Then how much weight per sq. ft. will the ground support? You can find loading charts for concrete, asphalt, dirt, and probably gravel. Find a happy medium that allows a short span but gives adequate surface area, and then never, ever try to use it on wet ground.
Jim
Good food for thought. Only note is that most jack stands are spec'd as a pair. So 22 ton working load for the pair evenly distributed.
I think i have a plan now.
I use Cribbing, I have a stack of pressure treated 4x4x36 that I stack to support the bus.
I got the idea to use the Cribbing after watching a FEMA video about supporting damaged structures.
My usual method is to get the bus completely aired up, drive it up on the ramps and then crib it up under the jacking points and let it settle down on the cribbing.
The first time I did this, I was nervous about crawling under 26,000 pounds, so I let it sit for two days just to make sure before going under.
The one time I was not able to drive it up on the ramps, was when the air drier purge valve failed, and I could not get enough air pressure to release the brakes.
I used the 20-ton bottle jack and slowly jacked the bus up cribbing and jacking in stages until I was able to get under.
I was able to put 2 of the 4x4 side by side under the bottle jack to support it while jacking it higher, this could make a base for you to jack on.
Getting the bus up to work under usually takes me a few hours, I usually get it jacked up and cribbed on one day then do the work the next.
I keep the 4x4's stacked in one of the luggage bays, they come in useful for many things including leveling the bus in uneven campsites.
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fwww.peterbylt.com%2Fmci96a3%2Fcribing.jpg&hash=a41ab0a74d5d52dffe6c33d17b3869891a79114d)
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fwww.peterbylt.com%2Fmci96a3%2Fcribing1.jpg&hash=b31044643c685a95f3a0833b4ceaa92ca4708533)
Peter
Pit!
A few hours !? I drive my bus on 2 by lumber, then support the body with lumber stacked under the jack points. Takes me about 15 minutes max. Then I am rolling under with a creeper to do service.
JC
Quote from: peterbylt on May 03, 2019, 02:06:52 PM
I use Cribbing, I have a stack of pressure treated 4x4x36 that I stack to support the bus.
Your 4 X 4 stack makes me nervous, sad to say. Those are Treated Southern Pine, which are not particularly strong, especially with big knots in the middle of a span. I use 6 X 6 Treated, and I put them closer together when I use them. For the heaviest load I use pin style steel jack stands rated for 22 tons. The steel stands give you more working room, and have a welded-in platform base.
Quote from: DoubleEagle on May 03, 2019, 06:07:38 PM
For the heaviest load I use pin style steel jack stands rated for 22 tons. The steel stands give you more working room, and have a welded-in platform base.
Ever use them on asphalt or dirt/gravel?
On both, the base is very substantial. If I was on soft ground, I would add some thick plywood. Most of the time they are good by themselves. These are the ones I have: https://www.otctools.com/products/22-ton-capacity-jack-stands (https://www.otctools.com/products/22-ton-capacity-jack-stands)
Thank you! That's the info i was looking for. I think I'll go with those and make the double thick Baltic birch 1.5" pads for them as a precaution and prolly add some 4x4 cribbing as a precaution. Plus I'll leave the jacks under the jacking points tight.
Where's the best place for jack stands? Under the air bag beams or under the frame from that cribbed pic? I've attached a pic of the two spots being used i found on buses101.
Can't help you there, all I have are Eagles. When it comes to air bags, all I know is that they can suddenly deflate, so you have to be under something solid and appropriate. The MCI manuals should cover it.
I made some body blocks for the bump stops this week. Painted them yellow and am attaching rope handles.
Quote from: GnarlyBus on May 03, 2019, 07:41:52 PM
I made some body blocks for the bump stops this week. Painted them yellow and am attaching rope handles.
That is exactly what Big Transit uses here.
Looks great.
happy coaching!
buswarrior
Those look like an exceptionally good idea. Something I'll have to keep in mind.
Jim
I found that they are awkward to use. You have to crawl under the bus to put them on and off, while the bus is unsupported. I also have forgotten that they were there, and driven away... I prefer a stack of lumber I keep in the shop for under the jack points.
JC
strap handles on both sides of the wooden ramps, makes it a lot easier to get out
Quote from: buswarrior on May 04, 2019, 05:30:41 AM
That is exactly what Big Transit uses here.
I actually got the idea from you in an old thread. I remember the first time i heard about it i couldn't understand where the 4x4 was supposed to go until i saw this photo you posted. I'll add it to this thread for the next confused newbie. :)
Wow, blast from the past!
Thanks and you're welcome!
Happy coaching!
Buswarrior
I used a 4x4 that way and had it break in the middle of the night while we were sleeping. Sounded like a gunshot and thought that something ran into the bus when it dropped down the 4 inches. Made a different type out of steel pipe. :)
Whoa! We're all 4 corners blocked when it failed or just 1 or 2?
The wood being used needs to start out as good quality, and needs to stay that way.
Recovering used hardwood dunnage, hardwood skid materials, etc is one way to not spend money on store bought lumber. You'd be amazed at the quality lumber that is being used to prop up loads and then discarded.
If it has started to crack, it doesn't get used for cribbing/blocking purposes anymore.
There is no need to be scared of lumber.
happy coaching!
buswarrior
Do you crib or use jack stands for a backup if you are on ramps?
GM recommends using a piece of large pipe that will fit over the bumpers. About 10 or 10 1/2" . You raise coach with leveling bags and place pipes over bumpers. This is for replacing differential, but will work for other servicing. Shorter ones will probably be ok for other work.
Whatever you put into the axle bump stops, make sure it is loose fit...
The air suspension has to build back up to get off your prop, and depending on what you've been doing...
Be a whole new adventure if you can't get them out of there.
put them in place, then stabilize by letting some air out of the suspension, if it doesn't do it for you on its own.
happy coaching!
buswarrior
After raising coach by disconnecting levelling arm links and moving lever, you install spacer and move lever to lower coach down on spacers. The spacers should fit over the bumpers with some clearance. 1/4 to 1/2 inch.
Quote from: chessie4905 on May 05, 2019, 03:58:52 AM
After raising coach by disconnecting levelling arm links and moving lever, you install spacer and move lever to lower coach down on spacers. The spacers should fit over the bumpers with some clearance. 1/4 to 1/2 inch.
Sounds like this only works for someone with a pit. How else can you gain access to remove the links? Any suggestions for those working on a slab?
You block the suspension after you get it in the air.
Get coach in air
block suspension
do work
happy coaching!
buswarrior
Quote from: buswarrior on May 05, 2019, 06:14:36 AM
You block the suspension after you get it in the air.
Get coach in air
block suspension
do work
happy coaching!
buswarrior
I got that part. It sounded like chessie4905 was saying that you use the air system to get the bus elevated...
"After raising coach by disconnecting levelling arm links and moving lever"
If I could get to the leveling arms links to move the lever, I wouldn't need to raise the bus or be worried about blocking it.
Need a leveling/jacking system that bypasses the leveling valves it sounds like.
Jim
If you use enough of a ramp to safely get under, you have room to sit up in front and rear axle areas, although it is tight, especially if you are over 250 lbs. Then you can unhook links and manually operate levers. Make sure you have full air pressure so you don't run out halfway, and have spacers in hand. If you have axle blocked with wheels off, you can access them that way. I went down to shop and measured the bump stops in compressed condition (Bags deflated). Pipe for rear needs to be 4" id and front needs to be 3 3 /4" You only need 1 0 inch ones for back axle if you are removing differential. Rear can be 8" and fronts probably 6 inches. Use pipe, not tubing as it would collapse. A coach leveling system would make this much easier. Btw, release all pressure from bags after installing spacers and tie lever in a way that it doesn't try to again inflate bags until you are ready to do so.
Whats even better if you make 4 ramps. Put one in front of each tire and drive the coach up on to them all. Then you can air jack it up higher if you need to after chocking both sides of the other wheels. Block up or use stands accordingly.
The confusion...
Raising the body in relation to the axle makes more room to do work. In some cases, the work is impossible with the body at ride height, it needs to be higher.
This can be accomplished by jacking the bus high into the sky and lowering the axle, or by jacking part way to the sky, and manipulating the leveling valves to raise the body, and then blocking it way up there.
It is all this sort of preparation that takes time and physicality, such that there will not be much actual "work" accomplished, the first time you play this game.
A busnut typically runs out of cribbing, and has to go find more, gets the jack stuck someplace, has to go back and air up the coach over and over, find a step stool to climb into the coach, then has to put it back on the ground because the wheels won't loosen off... remove all the fasteners, muscle the wheels somewhere out of the way, fight with leveling valve rusted/seized pins...
The beer in the fridge is shrieking your name...
That's all for today...
Happy coaching!
Buswarrior
Yeah, and the beer is warm because you have no ac to plug into and generator isn't hooked up yet and all the ice in the cooler is now water, and you forgot to pick up more ice on the way to your conversion that is 20 miles from home because that is the only spot that you can keep it and work on it...
And don't forgot all the first aid stops, no more bandaids left, ripped 2 new holes in pants, promised significant other I'd be home 2 hours ago...
Jack needs more oil, won't make full height anymore, and 3 different guys in the storage yard asked if I was scrapping the tires....
And the grease gun got left at home...
Oh sure, buy a bus they said, it'll be fun.
And we wonder why so many coaches are poorly maintained?
Happy coaching!
Buswarrior
Y'all know that we're just a bunch of beginners, right??? (Except for Clifford - he probably has a set of these.)
Yeah - it's an amazing sight to see my whole bus lifted up by a set of these when I take it to Interstate. They can accomplish in one hour what would take me all day.
A couple more questions:
Is it ok to raise the front of the bus using a bottle jack centered on the axle? (seems ok)
Is it ok to lift the back of the bus using a bottle jack centered on the differential? (this one feels less ok)
Those stands work good I been using that style for years except mine are rated at 28 tons made in the USA
Late to game here: A lot of posted info is good! the soil under bus is sandy= prob 30 inch square pad /rock over sand I would treat like sand. high density (like yellow clay) can be supported by a 24 inch square pad..Also you need to use something other than pine. I use white oak 4by 6 x 30 inches long . Oak has a much higher compression factor. I have a heavy bus. base needs to be solid cover on first layer. because of compression load on up. FWIW I have a pit..stock you have 12 inches under jacking pad. experience 40 yrs as crane operator. chock lift block you only need one to fall to be fatal. Just food for thought. Look at a outrigger on crane most will have a layer of cribbing or be on solid base ( 6 inch concrete) Bob
Using those coach lifts are nice if you have the headroom in the shop. If they lift it by the tires, no good to service wheels. Plus they probably cost more than 10 grand, and finally, HF doesn't sell them...YET😏
Quote from: chessie4905 on May 07, 2019, 03:59:07 PM
Using those coach lifts are nice if you have the headroom in the shop. If they lift it by the tires, no good to service wheels. Plus they probably cost more than 10 grand, and finally, HF doesn't sell them...YET😏
Yep double the 10 grand plus a few extra,I was going to buy a set for Scottsdale but the city gave me a bad time about even installing doors then I don't like the floor space they take up either
Oh, but they ARE lovely to work on the wheel ends!
Raise coach, axle stands, lower coach onto stands, undo axle fastener, fine tune height, wheel the whole kit and kaboodle out on the lift.
No more oily sheet of metal and lying on the belly fine tuning a manual jack can to slide it out.
There are always used ones around, shops trade them in, shops go bankrupt, all depends on the busnut budget...
Happy coaching!
Buswarrior
A local vo-tech school got a set like those, but were able to be rolled out of the way when not in use. They never knew why they received them. Too big for the cars they worked on. They just sat gathering dust.
Boomer had a set for sale , you really need a dedicate shop bay for those with plug end most are 3 phase and heavy to roll around plus buses are mostly engine work 90 % of the time. A set would be nice right now I have a Eagle here at the shop he lost the drop box ,rear end gear, drive shaft,probably the flex plate and the 740 all at one shot big dollars to repair this one
Quote from: luvrbus on May 07, 2019, 06:31:39 PM
A set would be nice right now I have a Eagle here at the shop he lost the drop box ,rear end gear, drive shaft,probably the flex plate and the 740 all at one shot big dollars to repair this one
Ulp...
How did that happen? :-\
Quote from: 6805eagleguy on May 07, 2019, 07:21:04 PM
Ulp...
How did that happen? :-\
Looks like it started on the drop box or the pinion drive gear went first,the section between the drop box and differential is broken too I never saw that happen before but it is a mess he did a job on it and I feel bad for him ,he sucked it up and said fix it though he was keeping the bus and it is a nice Eagle
Quote from: GnarlyBus on May 07, 2019, 11:11:15 AM
A couple more questions:
Is it ok to raise the front of the bus using a bottle jack centered on the axle? (seems ok)
Is it ok to lift the back of the bus using a bottle jack centered on the differential? (this one feels less ok)
And if it happens to tip while balanced up there? What side forces are on the jack then, if it stays in place...?
Get short cuts right out of your head when it comes to lifting a vehicle.
The coach has manufacturer installed jacking points nearby to each wheel end.
That suggests the strategy to use is one corner at a time.
Happy coaching!
Buswarrior
Couldn't agree more. Too much weight involved to be taking chances with it. If that axle tips even a little bit that jack can shoot out of there like a rocket.
Jim
I wouldn't do with just the bottle jack with the standard round head but they sell a kit to use a bottle jack in the middle of a axle for the better brand of jacks for balancing the axle I have one for my Blackhawk 20 ton owned it for many years
Ok. I'll setup one jack on each side (was already gonna do this on the drive axle) and go slow. Thanks for the answer.
I was thinking that the jack points near the wheels were for a flare tire or when only one area needed lifting. But it isn't really stable to lift on the axle with a bottle jack's limited grip.
Oh yeah, did we forget to tell you?
It doesn't happen in one shot...
Lift, crib, lower to cribbing, crib the jack, lift, crib, lower to cribbing, crib the jack some more, etc...
A jack squat enough to perform under the jacking points at low tide needs 2 shots at it.
And then the wheels are seized to the drum... and down it all comes... again and again...
Happy coaching!
Buswarrior
Updating this thread now to show what we ended up doing. I try to finish threads I start.Hopefully it helps someone who reads this down the road.
We got the jacks, ramps and stands out to grease up the rear end of the bus yesterday. This was our first time lifting the back of the bus up and it went very well. I flipped the dash switch to drain the tag axle air then flipped the valves in the engine compartment to finish draining the tag airbags. Then I backed over two 2x12s and chained up the tag axles. I don't think the chains I've put together were the right size (none came with the bus) as they weren't tight when the bus was up.
We ran up on 2x12 treated ramps. Those were made from an 8' on each side. We normally a board of two for leveling when we're parked. Then we used two 20-ton HF air jacks to lift the bus using the jacking points. We placed the jacks on 12"x12" squares of 1/4" steel channel we'd painted blue with tractor paint to keep them from rusting. (they have 1" lips on two sides and are often used for stair tread in industrial applications but we found them in the steel yard scrap bin. These steel squares were on top of 16x24ish 3/4" plywood to help spread the weight because we were on asphalt. Once we got it up high enough we let the axle down on the ramps and the body rested on the 22-ton jack stands (I love those things). We kept most of the axle weight on the jacks. So we had a some redundancy in case one should fail.
Quote from: GnarlyBus on May 03, 2019, 12:01:46 PM
Yah I'm all for safety but it's starting to sound more like we're trying to bridge concrete with steel and park the bus on it. I really think the asphalt I'm gonna be on will be fine with the 11x11 foot pads of the jack stands. I
figure I'll add some 3/4" ply to spread out the weight a bit.
The drive tires are about a 12"x24" footprint on each side. Seems like getting close to that would be sufficient.
I'll crib up under the frame as a secondary security.
I do appreciate the input. Reading old threads on this topic people have a tendency to "one up" on each other on safety until someone suggests a pit! Nobody mention railroad ties either or all heck will break loose! :)
I know it's an older post, but whatever you do, never work under the bus or any vehicle with airbags unless you shore up the suspension between the body and running gear. Never trust those airbags or rely on them to hold the vehicle while physically under it.
Fancy way of saying safety first and always. Dirt can compact. Concrete can be too thin and crack badly then collapse. Wood can compress then fail. Even suspect cheapo foreign HD jack stands can suddenly fail.
What this all means is be very careful raising your Bus Conversion for ongoing fun easy doable maybe non expensive maintenance. I enjoy doing such. Others do not. Consider HD redundant supports systems. Be paranoid.
Do not forget to employ a dead level area. Gravity has a way of sucking over time. Have fun.
Quote from: HB of CJ on June 28, 2019, 12:39:12 PM
Fancy way of saying safety first and always. Dirt can compact. Concrete can be too thin and crack badly then collapse. Wood can compress then fail. Even suspect cheapo foreign HD jack stands can suddenly fail.
What this all means is be very careful raising your Bus Conversion for ongoing fun easy doable maybe non expensive maintenance. I enjoy doing such. Others do not. Consider HD redundant supports systems. Be paranoid.
Do not forget to employ a dead level area. Gravity has a way of sucking over time. Have fun.
It seems like extreme comments about safety and not keeping it all top of mind. Nothing like a close call first hand to internalize just how different a bus is than a car. The weight and mass differences make all these considerations that one never encounters when working on autos and light trucks. I seen it up close and far better to be scared and caution rather than unaware of the lurking danger.
Yah be safe people. Here's a few sketchy videos I've seen on youtube.
This guy has a cool scenicruiser that he was out there removing the engine by himself! I set the video to start about 20 seconds before it falls off the bottle jacks he was alternating from underneath to try to lift the bus.
https://youtu.be/LKUOl_I1Abc?t=2381
Here's another one from Bus Grease Monkey. I love Scott's videos. I'm pretty sure I've seen all of them. They keep getting better and better quality. I've learned a lot from them. This video is crazy though. I set it to start a minute before the bus tips to the side (for the first time!). Watch the whole thing or move to the 31 minute mark for more jacking and blocking. Scott pulls off some crazy stuff that I didn't even know was possible. At the end of the video he says it would've probably been easier to just pull the whole engine/trans combo.
https://youtu.be/le06HE3caGw?t=1482
These links are not meant to bash the content creators. Let's not start a shame party. They're examples of how quickly a bus can come down if you don't use the proper equipment. Be mindful of these when you plan how you'll lift your bus.
OK, consider this: If you had all the weight of the bus (40K lbs in this example) concentrated in one spot, a mere 1 degree angle in your jack off the vertical (in reference to gravity) would generate 700lbs of directional force. Half that is still 350 lbs.
So it's pretty safe to say that any time you jack the bus you are going to have hundreds of pounds of force trying to push it off your supports. If it moves any at all the angle will increase and the force will increase geometrically. If you look at a sine table that's pretty obvious.
Now then. Is your jacking point absolutely flat? Well it won't be once you start to lift the bus. Once again, that will generate side thrust.
Lifting heavy vehicles is all about controlling those side thrusts and they can't be taken lightly. (ha) That's why you chock the tires and build a wide base with your cribbing. It's not about the tire contact patch size, it's about controlling any and all lateral movement.
Jim
Years ago I built a pit to service our bulldozer. You know those concrete barricades you see at construction sites, the square ones that stack? Yeah, I bought three of those. Had to bring them home one at a time since they weigh 3,000lbs each. Used a spot where there was a drop off and used the dozer to cut a trench, position the blocks in a "U" shape, and then fill in around them so the approach was level. I was a little concerned about the blocks tipping in but it worked great and has been stable now for many years. Awhile back I poured a concrete floor in it and I had already put a steel plate to hold the dirt from falling away so I didn't even need a form.
Unfortunately I have an out-building in the way so getting the bus on it would be an adventure, not that it couldn't be done. I'd have to cut down the wild cherry trees on each side of it though. (btw the dozer is long gone) It is constructed so I could use the lower approach as a loading dock if I had to.
Jim
Jim,
Thanks for finding and posting a physics formula computation. From personal experience, there is a lasting image burned into my mind at the awesomeness and power of off center heavy weight in action. The bus was up on a bottle jack and being lowered. For some reason (no chock block and raised off ground on a very slight incline) the bus starting moving laterally forward. As it got off center hardly at all, it looked as if the bus literally jumped off the jack and lunged forward.
Off center 1, then 2, then 3 degrees, the lateral force increased so the jack became a lever and launched the bus off. It really did accelerate off, not a graceful slow tilt and drop.
Hoping not kicking a dead horse but just communicating a real wakeup call for those having plenty of passenger auto experience and now working on super heavy vehicles like buses.
Yeah, all that heavy stuff acts that way. Actually the light stuff does too but it's just not as scary. If your bumper jack starts to go you can grab it and pull it back. If you try that with your bus it won't make any difference and it could kill you.
In that video did you notice that the guy at one point had two blocks against each other about half way up his stack? It would have been just as easy to have spread them apart. He was creating multiple opportunities for the bus to move, and move it did. He's just lucky it didn't move with him under it. It seriously reminded me of those Third World videos where a guy has a truck tilted over and held up with a 2x4, working underneath it.
You guys called him Scott, I hope I'm not offending anyone on this board, but often there are only small differences between dangerous and safe and if you don't know what those are, then you are probably risking your life to try this.
Jim