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post #1 of (permalink) Old 11-02-1999, 05:52 PM Thread Starter
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AMC 20 Truss

This is the truss I am thinking about fabricating for my Model 20 rear axle (see attachment). It already
has an air locker, full floaters and disc brakes. There's no turning back now, I've already got too much
invested.

The green is flat stock. Plate gussets would be used between the axle and the outer truss members.
The vertical pieces (shown in detail view) would weld each side of the gusset and their ends would taper
to match the width of the outer truss members.

What do you think?


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post #2 of (permalink) Old 11-02-1999, 06:32 PM
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Re: AMC 20 Truss

Well it looks pretty good to me here but I have an opinion. (Who doesn't ?) The verticals (4)(shown in detail) seem to be placed so that they look good in the drawing and by this I mean look evenly spaced. I would place them all four closer to the center to take up the loads imposed by the "empty space". Look at it again and I think you will see what I mean. If not, let me know and I will breifly elucidate. (How's that for fifty cent words?)
sln

post #3 of (permalink) Old 11-02-1999, 07:01 PM Thread Starter
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Re: AMC 20 Truss

Actually, there isn't any "empty" space, it is filled with a full gusset between the upper and lower truss
flanges and the axle. I drew this up at lunch and could have been clearer. I had another that colored in
the spaces to show the gusset, but I couldn't get it to convert to a raster file correctly.

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post #4 of (permalink) Old 11-02-1999, 07:52 PM
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Re: AMC 20 Truss

I think your headed in the right direction....I am also planning a similar mod...but based on my last experience on some tough trails (translation, dents and scrapes on my axle) I am approaching it from a different view.
First...lets look at where the loads are. The greatest load is twisting created when under load. This action is seen as the diff trying to point up towards the floor...and is really seen on SOA as spring wrap. As long as the spring perches and tubes are welded, its not going anywhere.
The next worse force is when you park the pumpkin on a rock...now the weight of the jeep is sitting out there on those weak tubes....i.e., bent tubes.

One of the guys on our last outing had a truss that kept getting hung up on rocks....Based on that and what happend to mine, I plan on keeping the bottom portion as clean as possible and adding a skid plate to the pumpkin...the plate will need to go the back high enough so that the next time I'm sliding backwards and my gas tank slides off that big rock, the rock doesn't put its imprent on the cover. (yes...it trashed my gas tank shield...but don't worry, I just installed a new one that I made out of 10 gauge plate steel, it makes great place to jack the jeep up now). I want to weld a truss to the top portion of the axle....I'm actually thinking about making 2 triangular shaped pieces of plate steel and welding them at a 45 deg angle to the tubes...kinda like a V as viewed from the tube end. This will give the most ground clearance possible. My only other problem is how to attach the skid plate. Can't weld it because it has to be removeabe in order to remove the cover plate on the diff. While I am at it I am also going to reversed U-bolts and a different shock mount (yea, they got torn up too).

Maybe we should get someone to work this up on MCad and run a FEA on it. Then we can see where the real stress is.

Any other ideas?

84CJ7
post #5 of (permalink) Old 11-02-1999, 08:51 PM
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Re: AMC 20 Truss

I've been thinking about keeping the truss on top of the axle while still having a skid plate. I'm not sure how I'm going to do the truss yet, but for the slid plate I am planing to make a round ring to bolt onto the cover and rearend. Then I would weld a skid plate to it. When I need to get to the diff then I can unbolt it and the cover will come off with the same bolts. If this doesn't make sense then ask me and I'll try to explain it better.

Tim Springer
1980 CJ7
post #6 of (permalink) Old 11-02-1999, 10:33 PM
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Re: AMC 20 Truss

[img]/wwwthreads_images/icons/tongue.gif[/img] No sweat on the top-loader truss system. What you do is have an upside down shape like a crochet(crow-kay) wicket(does anyone still remember that game?). The ends set on the spring pads, and the truss crosses over the housing. You drop "suspenders to the housing right where the tubes go in. Force drives hub and wheel up....pivoting on the spring pad where the load resistance is located...the spring pad tilts and tries to let the center section bend to the ground, but the suspender system prevents it. The truss also has "section" front to back for resistance to bending in the horizontal.[img]/wwwthreads_images/icons/crazy.gif[/img]

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post #7 of (permalink) Old 11-02-1999, 10:37 PM
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Re: AMC 20 Truss

[img]/wwwthreads_images/icons/smile.gif[/img] The TAZ design is a good one. He wants to be sure that the attachment points of the truss are "buttoned" on in many small places and not few large ones...maybe a 3/8 of diameter tube segment with lots of small welds.[img]/wwwthreads_images/icons/wink.gif[/img]

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post #8 of (permalink) Old 11-03-1999, 11:09 AM
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Re: AMC 20 Truss

I really like the idea of attaching the skid plate using the diff cover bolts...very eloquent solution. You could use the diff cover as a templant to make the ring. However, I think I would cut the ring at the bottom...the plate needs to cover part of the back which would make it hard to get the bottom bolts out.

Still....one great idea.......


John......southern CA
84CJ7,3"lift,32"BFG
post #9 of (permalink) Old 11-03-1999, 02:02 PM
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Re: AMC 20 Truss

I have seen such a ring/skidplate for sale somewhere on the web in the last couple of weeks. Just looked quickly and I can't find it, but when I get a chance I'll look harder and find it and post the site.

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