swingarm & motorcycle spring-shock suspension

[Bob Hammond]

Hello,

I've been noodling around with the idea of building a camper or a base camp chuckwagon, using this chassis that I built in 1985 in my mother-in-law's basement (later re that). It started as kit like the HF 40x48, but it is pre-Harbor Freight from Kmart. I put a longer 2.5 x 2.5 tongue to accommodate a Sunfish sailboat, but the leaf suspension was beating the hull, and so I made this suspension from perforated tube and motorcycle shocks (currently from a 750cc bike?). The sailboat rode on it like it was a pillow. After the Sunfish was donated to the Boy Scouts, it served as a utility trailer for very light loads, and for HS homecoming parade floats. Now it's decision time, after a refurb job on the paint, wheelbearings & wheels, coupler.

Does anybody have a guess as to how much weight this thing might safely bear? On the table for tongue load strength, I estimate about 750 lbs. The frame and suspension are in very good condition w/o rust or leaks from the shocks. Should I go to my hardware store and borrow 500-800 lbs of bagged cement or gravel, and go for a bumpy test drive? I'm planning to put a bicycle rack on the tongue, ahead of any box.

My biggest concern, is that the spring-shocks will fail. They are mounted on an incline, instead of vertically. Since the springs bear load largely in compression and support only a little bit when bending, I'm worried that piston rods of the shocks will bend. Any opinions about that?

[Bob Hammond]

I forgot to mention that the first version used much smaller spring-shocks, from a 350-500cc bike. One of them broke at the eye at the frame, when the Lady-wife loaded the trailer with a >lot< of topsoil, about a cubic yard as I recall.

[angib]

I don't see any problem with the shocks surviving like that - assuming the pivots at each end are free to turn.

The geometry of the axle and trailing arms is 'interesting' and I think the axle has a carrying capacity of about 1.5 times the shocks themselves. The laden weight on the rear wheel of a 750cc motorcycle is probably at least 600 pounds (200-300 pounds of bike plus 300-400 pounds of load) and your two springs/shocks are what supports one bike rear wheel, so at a rough guess I'd say the springs/shocks are good for around 900 pounds.

The wheels/tires look like 12 inch items, so a pair of them can carry that weight easily.

Looks like you've got a good frame for a lightweight teardrop - the only issue is the deck height which seems pretty high.

[Bob Hammond]

Thanks for the lookover.

On the old 8" tires, the trailer tracked straight with very little bounce as observed by someone in a car following me.

When I made it, I didn't do a engineering analysis. I figured that the load would bear on both the square tube and the shock (mostly on the tube), and that the shock would be compressed and dampen when a bump or pothole was encountered.

The shocks are free to pivot on 1/2" & 5/8" bolts (fine thread w/ locknuts). The rubber bushings are in good condition, and greased with waterproof axle grease on the pivot bolts. There is no/minimal sideplay on the pivots because I shimmed them with (greased) fender washers. The axle U-bolts were custom-made by a truck suspension repair shop near Philly (Chester Spring Co.)

Originally, I was only going to put a deck on it to pitch a tent on it. I was going to make the deck to fold with hinges, made from two sheets of plywood, and with polyurethane foam mats for insulation and comfort under the tent. Now I think maybe I'll build a cabin, or I'll put at least a chuckwagon box on it. Another alternative would be this:

http://books.google.com/books?id=P9gDAA ... &q&f=false

[pchast]

As a rule of thumb a 'yard' of dirt or stone is considered to be
close or equal to 1 ton or 2000 lbs. Of course it varies quite a
little due to the type and density of the material. If your bagged
soil was wet you could have exceeded that weight.

Are you sure it was a full yard?

[Bob Hammond]

It's been ten years or so, but it was a lot of dirt, or maybe it was peatmoss. I was not amused at all. Luckily, she was only two blocks from home when the shock broke. So i dragged it slowly home with the tire rubbing the fender. That was interesting and stinky.

Then there was the day when she loaded the '93 Ranger with pea stone. The rear end was bottomed out, but she made it home, and the truck still runs.

[pchast]

Amazing.