3 point suspension question

[rrliljedahl]

Last Jan, I hired someone to modify my 1 ton truck to carry a flat bed camper. 9 months later, my flatbed was still not complete! I have taken my truck back and am now trying to finish it myself.



The rear pivot mount looks complete and solid.
Others with more experience than me agree that he did a good job of welding this support.




My question concerns the 2 front mounts where there is a 7/8 x 4.5 x 2 inch piece of wood between the rails of the flatbed and the vertical support that was welded on the frame.



Is wood the best material for this weight bearing surface? (I project that the dry weight of this flatbed camper will be 2500 pounds). If not, what are the recommendations as to what I should replace it with?

Thank you to those who reply.

 

[proper4wd]

The wood should be fine - nearly all medium duty trucks have wood between the box and chassis. It provides some "give" and vibration dampening. Overall this looks like a high quality fab job.

 

[1stDeuce]

Yup, I'll second that the wood will be fine, and should prevent things from squeaking as the frame twists. (The front of the bed will need to shift just slightly to accommodate the twisting.) If it does give you any problems, a nice little block of HDPE would probably work too. The HD GM trucks don't twist much anyway compared to older or MD trucks.

Nice bed, by the way!!

 

[pugslyyy]

The front mounts look fine - but I'm questioning the rear pivot. Seems like you are asking a lot of those two pieces of aluminum square tube, how are they reinforced? What's to stop the bolt from collapsing the tubing?

 

[westyss]

The one thing that looks suspect from the pictures is the pivot mount itself, the pivot bolt that passes through the aluminum cross member should ride in a bushing of some sort in my opinion, it is focal point for all the weight of the camper and deck that will be working constantly and over time will work its way through the aluminum weakening it.
Now mostly I am assuming that the aluminum is not a thick walled beam but maybe 1/8" wall or 1/4"?
This goes along with what pugslyyy stated too, from what you estimate that the overall weight will be, add a BIG buffer as most everyone loads much more weight in the end.

 

[rrliljedahl]

To all
Thanks you for questioning the design of the rear pivot mount. I took off the nut and washer to discover that was a threaded rod running through the mount with no bushing.


With an 1/8 aluminum wall rubbings against the threads, enlargement of the hole was sure to happen.

The question is what would be the best way to handle it from here?

Advice is welcomed.

 

[java]

To all
Thanks you for questioning the design of the rear pivot mount. I took off the nut and washer to discover that was a threaded rod running through the mount with no bushing.
View attachment 255018

With an 1/8 aluminum wall rubbings against the threads, enlargement of the hole was sure to happen.

The question is what would be the best way to handle it from here?

Advice is welcomed.

Pop the rod out, drill the hole larger, weld a sleeve in to keep from crushing the tube (could probably get away without this, but makes it a fair bit stronger), install bushing of some sort to match the bolt diameter, and re-install the bolt.

 

[westyss]

To all
Thanks you for questioning the design of the rear pivot mount. I took off the nut and washer to discover that was a threaded rod running through the mount with no bushing.
View attachment 255018

With an 1/8 aluminum wall rubbings against the threads, enlargement of the hole was sure to happen.

The question is what would be the best way to handle it from here?

Advice is welcomed.

If you have access to a welder to weld a bushing in there, even a thicker aluminum tube that the bolt can pass through and ride on, having the two beams will displace the weight and should work. It is difficult to come up with something that will not react with the aluminum for this. If it was me I would weld a 1/4" walled aluminum tube onto the beams and find a non corrosive lube for the bolt, the bolt would be best to have only the threaded portion at the end and not inside the tube.

While welding a few runners welded north/south onto those main east/west beams would be a good idea, something that displaces the load outward from the pivot bolt, like a web, connecting the two main beams will add strength for all of it, like building a house and having the cross braces between floor joists.

 

[DiploStrat]

Contrarian View

Consider dumping the pivot design and going with a spring based, pull apart mount as used on the large Bimobil trucks and any number of Australian campers.

 

[rrliljedahl]

To all
Today we pulled the rear pivot mount apart and discovered that there was no bushing or sleeve in the 1/4 inch steel support. Just a hole large enough for the threaded rod to go thru. Luckily I found all if this out now rather than after I put the camper on and the aluminum bed fails.
Thanks again to everyone who noticed that and brought it to my attention.

 

[ersatzknarf]

Glad you thought to pull it apart to check. Please do not reuse the threaded rod and use a bolt with a long enough shoulder to do the job, if you decide to continue that route, and add the recommended bushes.

 

[pugslyyy]

I would always be nervous about that hole in the tubing - it weakens it right where it is seeing the most stress. The pivot should really be below the tube - or as Diplostrat suggests just go to spring mounts middle and rear.

 

[pappawheely]

I would use a bolt on pillow block in the rear if you are committed to the three point design.

http://www.northerntool.com/shop/to...i_sku=189779&gclid=CP-C58aS88ECFQhafgod3lEAMA

 

[rrliljedahl]

Modifications have been completed.

3/8 inch sleeves and 1/4 inch bronze bushings installed in the steel vertical support as well as the 2x4 box aluminum box.


1/4 inch vertical reinforcements on the 1/8 inch 2x4 inch aluminum box.


The 7/8 inch threaded rod replaced with a 7/8 inch grade 8 shoulder bolt.


1/4 inch bronze washer between the aluminum 2x4 box tubing and the steel vertical support.


Additional north/south horizontal support added between the 2 weight bearing east/ west 2x4 box beams.


Everything now welded into place.


Thanks for all the advice.

 

[pugslyyy]

Ah that looks like a much more solid approach - good job. I know what a PITA it is, but now is the time to make it right - you don't want to be wondering what's going on under there later.