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General Discussion of preventative/corrective maintenance and other technical issues regarding your coach that are not covered in other Mechanic's Corner categories (ex. refrigerators, water heaters, and compressors).

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  #171  
Old 3 Weeks Ago
mhughes01's Avatar
mhughes01 mhughes01 is offline
Mike and Tracy
 
Join Date: Mar 2008
Location: Near Edmonton
Posts: 213
Default Hmmm

How high are you trying to raise it?

If I'm following you right, That's going to give you at most 6" of lift.

I suspect the plywood is going to crush a fair bit as well as you drive on it.

Maybe just me, but this does not sound remotely safe.

No way I would ever try and lift my bus in a campground. I've seen my Hwh sink a long ways into asphalt in a campground and those have big plates on them. I can imagine ramps, jacks and stands sinking at the worst possible time.

If something needs to be done on our coach on the road I find a heavy truck shop with a pit. If the coach isn't drivable, I'd call a wrecker with a low boy. I'm sure everyone has seen a greyhound on a low boy.

I have a pit at home expressly built into my shop when I had it built. But that's just for changing oil, grease and checking air lines, etc. No way I'd be under there removing wheels, etc.
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Mike and Tracy - near Edmonton, Alberta, Canada
1999 43 LXI, "Maddy" - 60 Series Detroit
FOR SALE, $65k U.S. OBO
2006 Jeep Liberty CRD (Diesel) or 2013 Jeep Rubicon 4 Down Toads; Sold Jetta, but it was an awesome toad.

Last edited by mhughes01; 3 Weeks Ago at 02:07 PM.
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  #172  
Old 3 Weeks Ago
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mhughes01 mhughes01 is offline
Mike and Tracy
 
Join Date: Mar 2008
Location: Near Edmonton
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Default This is why you take an air brake course if you own a bus!

Quote:
Originally Posted by Rick View Post
The parking brakes are applied by a big spring. The springs are inside the REAR brake pods. There is a huge difference in brake chambers front to rear. Any one can tell which is which just by looking. You do not want parking /emergency brakes on the steering axle. If you lost air pressure and the brakes locked up, how would you be able to steer to a safe stop.

Have you ever wondered why you have to build air pressure before you could release the parking brake? After you have air pressure and you push the parking knob in, air is supplied to the side of the brake chamber that compresses the spring. This in turn releases the brake. When you pull the knob out or your air pressure drops below 70-60 lbs that big spring overcomes the remaining air pressure and applies the brakes.

This could be a good topic for a tech session.
Our laws in Alberta require anyone driving an air brake equipped vehicle to take an air brake course and have a Q rating in their license.
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Mike and Tracy - near Edmonton, Alberta, Canada
1999 43 LXI, "Maddy" - 60 Series Detroit
FOR SALE, $65k U.S. OBO
2006 Jeep Liberty CRD (Diesel) or 2013 Jeep Rubicon 4 Down Toads; Sold Jetta, but it was an awesome toad.
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  #173  
Old 3 Weeks Ago
philipswanson philipswanson is offline
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Default

For your safety, plywood should never be used to support the coaches' weight. In time it will compress and become dangerous. But it's you life. You will never find a commercial RV business using plywood ramps.
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  #174  
Old 3 Weeks Ago
marvjeanm380 marvjeanm380 is offline
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My ramps are Glue Lams turned on the side. Many contractors are glad to give you their cut offs because they have less weight to take to the disposal site. They come in varying widths and are plenty strong.
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  #175  
Old 3 Weeks Ago
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CarneyRacing CarneyRacing is offline
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Quote:
Originally Posted by philipswanson View Post
For your safety, plywood should never be used to support the coaches' weight. In time it will compress and become dangerous. But it's you life. You will never find a commercial RV business using plywood ramps.
Okay, I have to draw objection here. People need to be a little more conscious of throwing out the gloom and doom saying "never" in some scenarios.

As with any jacking/lifting/ramping scenario, you need to be conscious of the base you are working on. You working on a pad of concrete or asphalt -- good base. Sand -- bad base, etc. Be smart about what you base is, because without a good base, your ramps will be placed in a bending load, and no ramps are really designed with this in mind. The case where the plywood would fail is when there is not a good base, which is a recipe for disaster with any ramp.

I agree that if someone wants to make jacks or ramps, they either need to really know what they are doing, or simply make them with ridiculous overkill.
The way it was posed from Pairodice, he is proposing to make a set of ramps that are solid laminated plywood 24" wide, wide enough to fully support both of the duals. Solid right? One sheet laminated on top of another? If I mis-understood this, please don't bother reading on.

Now lets look at laminated plywood. on the low end, plywood has a compressive strength of 4,000psi. And we will make some very conservative assumptions:
Axle weight:25,000 lbs
tire contact patch size:10"x11"
# of contact patches: 4
Given this info, the pressure loading on the ramps under the tires is 57psi. Which gives us a safety factor of over 70. Over SEVENTY. That safety factor is at least 10 times higher than the safety factor of the tires, the wheels, the suspension, axles frame, etc. Under this extremely low loading scenario, the only compression in the ramps will be if they weren't tightly glued together, and that would result in slight compression, but nowhere near failure. if a ramp is made of solid wood (not rotten), has a solid base underneath, and fully covers the tire's intended contact patch, it simply won't fail.

There could be a million reasons you don't see ramps like this in a commercial shop, but I can assure you that compressive strength is not one of them.
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1979 FC35 SB
250T, 4.33
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  #176  
Old 3 Weeks Ago
Jim Brookshire Jim Brookshire is offline
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Steve,
Don’t waste your words on posts by P. S. He only comes out of his hole to stir up trouble. Don’t bother to post informed information, he will not pay attention and the rest of us try to not pay attention to him.
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  #177  
Old 3 Weeks Ago
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Bill Pape Bill Pape is offline
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Play nice everyone, we won't close a safety thread.
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1988 FC, Silver Edition
Commerce, Michigan
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  #178  
Old 3 Weeks Ago
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brhodes brhodes is offline
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Coach Craft crew rolled my coach up their ramps made of 8 layers of 1x12 pine glued and screwed together and had no issues as they looked to have been well used.

I agree that the base you are setting up on is very important, no soft earth, gravel, etc. as concrete would be my preference only.

Just my 2¢
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  #179  
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philipswanson philipswanson is offline
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Quote:
Originally Posted by brhodes View Post
Coach Craft crew rolled my coach up their ramps made of 8 layers of 1x12 pine glued and screwed together and had no issues as they looked to have been well used.

Just my 2¢
Bet they wouldn't consider plywood.
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  #180  
Old 3 Weeks Ago
philipswanson philipswanson is offline
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Quote:
Originally Posted by Jim Brookshire View Post
Steve,
Don’t waste your words on posts by P. S. He only comes out of his hole to stir up trouble. Don’t bother to post informed information, he will not pay attention and the rest of us try to not pay attention to him.
Safety common sense benefits everybody. You can call that stirring up trouble or whatever you want. Sticks and Stones …………….……………………….
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