Tandems on a scamp - Fiberglass RV


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Old 02-16-2007, 07:47 AM   #1
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Trailer: 1996 19 ft Scamp 19 ft 5th Wheel ('TOGETHERNEST' SLEEPS 8
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. This will be the year of the tandem axel conversion on my 1995 Scamp 5er as my axel needs some work, sagging, new tires and brake work. have done a lot of research and studied our pioneers [Merl} conversion. Now as I see it the original single axel design is fine. My problem is to get tires that are rated to carry 1500 # and still give a soft ride. Merl used another 3500 # unit and 4 6 ply tires with 50# of air. Now I have considerable on hand experience with torsion axels welded directly to the trailer frame And that set up does not perform well .On a segmented paved road where the segments are like waves on the water believe me this set up will almost tear your head off. And if you run over a 2 inch brick on the road that will be like running over 2 bricks My set up would be like running over 2 1 inch bricks. My design will have the 2 axels welded together with its own box frame with a hub ½ way between the 2 axels parallel to the axels., and hubs welded to the trailer frame with a pin through each pair on each side so that the axle and frame assy will be able to pivot at the center allowing either axle to go up or down. I will be using 13 inch tires simply as they will take less cutting for the wheel wells and have a lower profile. As it looks now I will be using 15 degree upward slung axels that will both be trailing.
I believe I have read all information on this site including Donna’s very complete interview with my good friend Merl And would like any input on this that any may have as the axels will be on order next week At a cost of about $900.
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Old 02-16-2007, 12:10 PM   #2
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Interesting. How do you limit movement of the double-axle frame? Presumably you have something that stops the forward axle from slamming into the underside of the main trailer frame when driving over a big bump that throws the forward axle upwards.

Andrew
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Old 02-16-2007, 12:38 PM   #3
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A couple of thoughts. Your experiance may be different.

1. When running tandem axles, torsion axles, will give a rough ride. My dad took his third Alpilite 5th wheel back to the factory because of this issue. His first two trailers had tandem axle leaf springs. He had the Service Manager ride in the back with him while another person drove the truck. The service manager agreed and replaced his torsion axles with leaf spring axles.

2. An up angle torsion axle will give a much harder ride then a down angle axle. To visualize this, think of the exaggeration of the situation. With the axle at the max up angle when you hit a bump, there is NO suspension left. To make the situation worse, the axle wants to swing in a forward direction fighting the direction of the trailer forward motion. When you have the max down angle and you hit a bump, the axle swings back and up as you move forward giving a very soft ride. It is much like the front end of the old VWs bugs. (note: this is hard to explain in just words)

I hope this makes sense.
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Old 02-16-2007, 01:46 PM   #4
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I believe that Mike's concern about tandem torsion axles results from their operation independent of each other - they do not load share. Tandem leaf-spring axles with an "equalizer" rocker between them do share (although not completely effectively).

I believe that Lyndon's proposed design is a load-sharing arrangement, addressing this concern - that's why running over a 2" brick is like running over two 1" bricks: as each tire hits the brick, it moves up 2", but at the pivot point halfway been the axles the axle assembly only moves up 1".

I get the general idea but I'm not at all clear on the details... at first I was picturing a walking beam on each side, with the beam's pivots on the spindles of a single torsion axle, but that's apparently not the plan. Instead of walking beams, there is a frame... but don't follow how the frame is suspended. Lyndon, if you would like to post or e-mail a rough sketch, I'm game for drawing it up a little more formally (albeit not likely to Andrew's standards!). Seeing the design might help all of us understand and put us in a better position to provide useful input.

I really don't think tires carrying 1500 pounds and providing a soft ride would be a problem, if enough clearance is allowed for sufficient tire diameter. As a result, I don't think the tandem conversion is necessary for this reason; nevertheless, it's certainly a valid option and I look forward to seeing more detail and hearing how the project goes.
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Old 02-16-2007, 01:50 PM   #5
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Quote:
Interesting. How do you limit movement of the double-axle frame? Presumably you have something that stops the forward axle from slamming into the underside of the main trailer frame when driving over a big bump that throws the forward axle upwards.

Andrew
the frame that holds the axels will have a 6 inch up and down movement and I will have hard rubber pads between the frame and the dolly Something of this sort should only be encountered at slow speeds sich as speed bumps.
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Old 02-17-2007, 06:46 AM   #6
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I can't offer much of anything other than what I posted on Merle's behalf. All I know is he's perfectly satisfied with the setup. I wonder if alot of that satisfaction is derived from the fact he ended up putting shocks on the axles? I'm certain it had to help. Imagine driving any kind of tug down the road with no shocks...talk about a headbanger. Merle is supposed to be doing a writeup on the shocks, complete with template and model numbers. I'll get in touch with him in a couple of weeks...and see how it's going.

Then too Lyndon, you'll notice in Merle's writeup, he put in a spacer between the frame and axle. Since he knew he had to cut the wheel well out to lengthen it, added a couple more inches to accomodate the 14" tires, didn't really create all that much more work to get bigger tires.

I don't know if you've spoken to Merle directly Lyndon, but if you send me a PM.....

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Old 02-17-2007, 08:01 AM   #7
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I get the general idea but I'm not at all clear on the details... at first I was picturing a walking beam on each side, with the beam's pivots on the spindles of a single torsion axle, but that's apparently not the plan. Instead of walking beams, there is a frame... but don't follow how the frame is suspended. Lyndon, if you would like to post or e-mail a rough sketch, I'm game for drawing it up a little more formally (albeit not likely to Andrew's standards!). [b]Seeing the design might help all of us understand and put us in a better position to provide useful input.

I really don't think tires carrying 1500 pounds and providing a soft ride would be a problem, if enough clearance is allowed for sufficient tire diameter. As a result, I don't think the tandem conversion is necessary for this reason; nevertheless, it's certainly a valid option and I look forward to seeing more detail and hearing how the project goes.
Not enough room for any bigger tires so I have 2 options go with tandems or cut out side of body and add flares And nothing is necessary but a guy has to have a reason to get up each day when you are way past 70 other than going to the bathroom.
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Old 02-17-2007, 06:47 PM   #8
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Slightly OffTopic, but a number of 5W owners on Yahoo Scampers have put shocks on their single axles and report good results -- Join the group and do a search of the archives for details like part numbers.
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Old 02-17-2007, 10:12 PM   #9
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Thanks, Lyndon - the drawing makes it all clear. I'll draw it up and post my version later, in case anyone is interested.

This configuration is like a walking beam setup, except that the beams don't join the axles directly, they join the crossmembers which carry the independent suspensions. A normal walking beam has the springs between the beam pivots and the frame rails; this one has the springs between the hubs and the ends of the walking beams. I guess Andrew understood this the first time...

Essentially, the beams do share load between the axle assemblies, and carry it all to one mounting point on each frame rail. Pivoting of the beams allows additional travel over bumps so the ride should be smoother, but do not allow both hubs on the same side to move in the same direction any more than they would without the beams, so the trailer doesn't lean any more in cornering than a conventional setup.
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Old 02-17-2007, 10:36 PM   #10
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Okay, Lyndon, you wanted input; here are some initial thoughts...

The frame consisting of axle assemblies and side beams will be prone to twist when one side hits a bump. If it doesn't twist, it will tend to affect the other side (I think undesirably), and if it does twist it means twisting the axle crosstubes/crossmembers; is that a good idea?

The side beams would be shorter and lighter if the front axle was setup leading. I don't like the idea of leading axles in general, but this might be the time to use them.

The frame pivot pins/bushings are shown 2" ahead of the midpoint between the hubs (not the torsion axle crosstubes... but that's already understood): why? This will put more load on the front axle, and if I were doing anything other than evenly split I would guess that rear-biased would be better for ride and load distribution during braking.

I think consideration should be given to lowering the pivot pins below the hub height (at normal load) so that the frame's stable position is level. Having the pivot even slightly above the hub produces a "jacking" effect in which any resistance applied horizontally to the front axle will tend to make the trailer ride up over the front wheels. Speaking of that... what is the plan for brakes - both axles?

The bump stops (hard rubber pads) could be much softer, so that if the axle frame pivots enough to reach the limit the hit wouldn't be so jarring; there are lots of cylindrical rubber parts available for exactly this purpose. They can even be mounted over the rods of shocks.

I think shocks are always a good idea, but especially in this case; movement of the individual suspension arms are damped somewhat by the inherent characteristics of the rubber, but nothing is damping the movement of the frame unless there are shocks. I would want four: one for each wheel. It would be easy to mount them between the side beams and the trailer frame rails, but they would need to mount the suspension arms to do the best possible damping job.
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Old 02-17-2007, 10:41 PM   #11
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Quote:
Not enough room for any bigger tires so I have 2 options go with tandems or cut out side of body and add flares And nothing is necessary but a guy has to have a reason to get up each day when you are way past 70 other than going to the bathroom.
Anything that makes getting up each day something to look forward to is worth doing.

I assume that cutting out the side of the body will be necessary for the tandem wheels, so bodywork is involved either way; I may have misunderstood the plan in this respect. The advantage I see in tandems is that the wheel housings and side openings don't have to be any taller than stock (just longer front-to-back), while a larger diameter tire would mean either a taller wheel well or lifting the trailer body higher from the road.
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Old 02-18-2007, 06:09 AM   #12
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My project has now come to a halt as tandems will not fit under a Scamp with a larger refrigerater Options would be moving back 10 inches , raising to no wheelwells, raising Fridg and eliminating upper cabinet, Smaller fridg none of these are doable! Thanks for the input and see you down the road The best plans of mice and men oft times go ary or some thing like that.
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