Chassis

[PaulC]

I'm looking to build an 8x4 offroader and want some ideas on chassis strength. Best size steel, type of frame construction etc, etc, etc.

Cheers
Paul

[brian_nj2006]

What total weight are you looking at for the trailer? I built mine out of 2x2x 1/8 frame is 10x5 to the inside of the wheels with 1' extensions on the side. My trailer will be bigger than most here but I am 6'8" so I need it. Pic of frame is in my album

[mikeschn]

Paul,

I know Andrew will chip in... he's got a lot of prior thought into the chassis.

I know when I tried to compare steel to aluminum, I came away with steel being the winner.

What you really want to know is what the modulus of elasticity is for the various shapes you are talking about. You want the highest modulus of elasticity with the lightest weight. I'll bet a web search would get you started...

Mike...

[brian_nj2006]

For my next trailer. I think I will use "C" channel instead of square tube. I realy overbuilt the first one. I pulled a 1100 lb quad up on it and it didnt move! But then again my tow vehicles can handle the weight. But the next one will be smaller and for towing behind a jeep wrangler.

I would also like to do all my wall framing in alluminum tube welded all the way around next time to keep the weight down even further, and give it some flex when off road.

[Dave Nathanson]

I used 2" square tube with .090 wall for all except the tongue which is now much heavier (since that Baja trip). We've taken it all over the place, many places where no trailers belong, and the frame is handling it just fine. Anything thicker than .120 is probably just extra weight. Actually we got the .090 and (at first) I was sure it was way too light. That worried me to no end. Until we really tested it & it passed every time. So now I know that its strong enough for the TD frame. Um, but not for the tongue.

I've seen some people use their Jeep frames as a guide and build with thickwall 3"x2" square tube. It just gets too heavy to handle.

I did also add 1/2" square tube front to back to try & keep the frame from hanging up on rocks. No only is that working OK, but it also adds some strength & stiffness I guess. Anyway, don't over build! It will just make it heavy, hard to tow & hard to control. It would be nice occasionally to have a 2" receiver hitch on the back end of the TD. Maybe for a bike rack?

Don't forget the electric Brakes!

[PaulC]

Paul,

I know Andrew will chip in... he's got a lot of prior thought into the chassis.

I know when I tried to compare steel to aluminum, I came away with steel being the winner.

What you really want to know is what the modulus of elasticity is for the various shapes you are talking about. You want the highest modulus of elasticity with the lightest weight. I'll bet a web search would get you started...

Mike...

What!!!! Would you mind repeating that please Mike
Cheers
Paul

Yup, I'm Back

[jagular7]

Here is what I'm starting with. Military M101 3/4 ton trailer frame. I'll remove the axle, tires, and some of the suspension leafs. I prefer a td with a parking brake especially an offroad one. I'll probably be using a lt235 tire to keep the height of the trailer inline with the height of the Jeep.





Its a 'C' channel frame with a box tongue links. Only box crossmember is the one for the shocks.

[Dave Nathanson]

Hey, jagular7, that looks like a good sturdy chassis to start with. I do like the idea of the parking brake too. Really amazing that it such a rare feature!!! I've managed to get by with wheel chocks, but sometimes I wish I had a parking brake.

As an offroader, I feel that electric brakes are important too. Imagine this:

You're towing your trailer offroad, heading down a very long & steep hill. You are facing downhill, but not exactly straight downhill. You suddenly need to stop, and you hit the brakes. If the trailer doesn't help stop, it's going to apply all it's forces at an angle to the rear of your Jeep. This could turn your Jeep, pushing it a bit sideways. And that may not be desirable atall.

[jagular7]

Hey, jagular7, that looks like a good sturdy chassis to start with. I do like the idea of the parking brake too. Really amazing that it such a rare feature!!! I've managed to get by with wheel chocks, but sometimes I wish I had a parking brake.

As an offroader, I feel that electric brakes are important too. Imagine this:

You're towing your trailer offroad, heading down a very long & steep hill. You are facing downhill, but not exactly straight downhill. You suddenly need to stop, and you hit the brakes. If the trailer doesn't help stop, it's going to apply all it's forces at an angle to the rear of your Jeep. This could turn your Jeep, pushing it a bit sideways. And that may not be desirable atall.

From experience? I understand the need for such on the road with the large vast public about you and certain laws for weight, but offroad, never really thought about it to that extent. My speed on dirt roads is less than expected.

Would a hydraulic tongue brake setup be better than electric? Electric is a variable constant brake system and without noting, you could burn up the brakes correct? I've read where a diesel pusher was flat towing a trailer with an electrical brake system. He road the brakes down a hill and burned up the brakes, then burning the tire and having it blow on him. I think the picture is on here somewhere.

[Dave Nathanson]

I would never want a trailer brake that activates by backing up. I do that too often. Sometimes I've bitten off a little more than I can chew, and I need to take several tries at an offroad obstacle. Like sometimes a steep loose gravel hill qualifies in that category. Traction might be an issue, and the last thing I need is the trailer fighting me as I try to back down for another shot at it. It's kinda scary when you are offroading (even slow) and hit the brakes but the trailer pushes you.

My trailer is light enough (under 1500 lbs) that Calif law does not require brakes. But I'm always really glad to have them, both in town & offroad.

I've found the electric brakes to be predictable & work well for me. I have a low end Tekonsha brake controller that I mounted on top of my Jeep dashboard so it's sort of level & I can see the color indicator light. I don't know how anyone would burn up the electric brakes accidentally.

There is a light on the brake controller that changes colors: green means it's connected to the trailer. various shades of amber mean the brakes are partly applied, and red means full braking.

I also understand that there is probably no (reasonable) way to fit both a parking brake and electric service brakes into the same axle (but I wouldn't know) and you already have your military axle. So I don't mean to brow beat you about this. I'm just saying that I've found my elec brakes to be useful and good. I also go 4x4ing with a friend that has a military trailer and he does OK too. So it's not the end of the world either way.

[angib]

I also understand that there is probably no (reasonable) way to fit both a parking brake and electric service brakes into the same axle

Dexter offer electric brakes with a mechanical parking brake - go to page 9 of this 3500lb axle pdf. Whether they also offer an easy way of rigging up the cable to operate the parking brake, I don't know.

Dexter also offer hydraulic free-backing drum brakes, which is like what we use over here in Yurp (though with mechanical actuation) - the brakes don't operate when the wheels are rotating backwards, so you can freely reverse despite a surge coupler. They also offer hydraulic brakes with a parking feature, but probably not on the free-backing type!

Andrew

[M. Olsen]

On one of my last teardrop frames I used steel tube that was 1.5" wide by 2.5" tall and had a wall thickness of 0.083". This gives me about the same cross section as a 2x2 - 0.090" tube but it is stronger in the vertical plane where the spring forces are acting, if I understand things correctly. So for the same weight I believe that I end up with more strength where I need it. I ended up using 1-1/2" square tube with a 0.065" wall for the cross members under the floor.

I too would like to have a receiver off of the back. My first teardrop had one and it worked great for hauling a large bike rack. I imagine that It could come in handy too if you ended up in a tight spot and needed to pull the trailer from the back.

On another note, I can see another advantage of having electric brakes on a trailer axle. You can, on most brake controllers, manually apply the trailer brakes independent from the tow vehicles brakes. This might be helpfull if you are going down a steep hill. You can manually apply and use the trailer brakes to suplement the compression braking of the engine with out fear of locking up the tires on the tow vehicle and possibly entering a slide. Just random thoughts.

[jagular7]

Oh no, don't take that military trailer to be the kind of the original Jeep military trailer, M100/416. They are the 1/4 ton bucket trailers that were behind the flat fender Jeeps. It weighs in ~400#s empty.
The M101 is the next size larger trailer and was designed for the M37 and M715 trucks. It's a 3/4 ton label, but will handle over 3 tons offroad with the box on it. Its weighs ~1425#s empty. Its weight comes from the unsprung weight. I'd bet those drums weigh 100#s each. Wheel/tire 250#s.

I'll be removing all that, removing some of the leafs in the spring pack to lower it, add a braked 3500# axle, relocating it back another foot or more, and so on.