Take Death Trap to the next level (5 Viewers)

workingdog

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I'm putting a fairly built dana 60 and 14 bolt under my '68 fj40 along with an Atlas with drops to match. The 40 already has a 6.0 liter LS and 4L80e. To do that, I'm going to SOA the front and 4 link the rear. This is my first really big project, so this is about learning, not demonstrating. Here is on fj60 axles and 37's (at Rubicon Springs).

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So, what I'm sorting right now is locations and measurements.

Here's the front with OME springs flipped. Waiting on passenger side perch to attach to springs. I shortened the front hanger and set the rear hanger in the frame to reduce the SOA's overall lift.

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Here are the parts for the rear and what I'm working on now.

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I have a truss for this you can see lying on the floor I need to tack on for now.

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I've been told that lower link should be about wheel diameter. I'm going to run 40" KO3s (or Milestars). So, that makes the lower link 39" forward of the axle

If I set the upper link at 80% of lower link (31 or 32") then it looks like they will want to land right about at the rear of the Atlas (waiting on adapter to mount to 4l80e). So, that looks about perfect. If I need to get them longer (to maintain pinion angle), then I can 'adjust' the crossmember into the right spot and fudge the support for the back of the Atlas.

I have a support structure that was built to protect that trans pan and transfer case and support the back of the trans (at the atlas adapter). I'm going to reuse that by cutting the mounts for trans (which I'll move to center), torque bar (don't need) and transfer case skid (which gets superseded by new skid plate).

I'm going to buy the Goat Built rear atlas support and build a new cross member at the back of the Atlas to both support the back of the atlas and for the upper link mounts. And then tie that cross member back to the support structure for a more complete skid than I had before.

I think I'm going to shoot for 104" wheelbase. Still not sure what I'm going to do in the rear for springs- we had to shorted the axles so much that I don't think I can run coilovers outside - plus I'd like to avoid punching a hole in the rear wheel wells. So, I'm thinking I might end up with Jeep springs and shocks. But if I can find some short coilover that will fit, I'd like to do that.

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workingdog

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Okay, here's an update.

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tie rod and drag link shortened.

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Ruff Stuff 4 link kit arrived
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And here's the current calculator for the rear. I think this is pretty close. All the altitudes might change.


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workingdog

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Okay, the transfer case is back with new input shaft. and it's up and clocked to more or less home. Had to trim a the ribs on the underside. Can I clock it up a little more? Or is it good?


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So, this is the view of the from the front axle pinion.

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I've already moved the motor 1" towards passenger to more or less center line. I could move it another inch.
However, it looks pretty good to me, the things that look like hoses are the Atlas shifting cables.
 

Tank5

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I have never built a linked suspension like you are building, so I cannot help you with it. I am curious what the advantage is to going spring over in the front instead of linking it? My inexperience leads me to think leafs in the rear and links in the front would be better. I don’t know that that is the true though. Curious why you chose what you did.
 

workingdog

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I'm afraid my logic is going to disappoint. The front would take the axle with just a spring flip and move 2" forward without touching the spring mounts - I thought originally - I actually had to relieve the rear spring mount into the frame. To get the rear axle back, I was going to have to put all new spring mounts in and get new springs as well, so a 4 link is the same amount of work (more or less). Also, I'm a geek and I just like how 4 links work. Once this rig gets some time on it, we might link the front as well. I'm linking the front of my EV 45, so that will give me some experience with 3 link with panhard bar.
 

DangerNoodle

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I will say, I like my front links a ton. It made the ride so much better. SOA rear isn't as bad. I'd rather push the front forward father than the rear. Moving the rear isn't as hard. Plus, the front is much easier to install coilovers for. Rear would probably require coils to fit your requirements.

My logic is that the rear follows the front. Having more travel in the front allows for more fun, anyways. It also seems to limit how much wheel lift you get, which to me, is much scarier than having the rear move around.
 
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How did you set up the hardtop with no sides? I have an extra fiberglass top, and thought about doing something similar.
 

workingdog

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I built 2 plates, one for each side, that attach to 2 roll bar clamps (each) between the and C pillars of the roll bar. The plates sit right where the top of the sides would sit and the top bolts to the plates just like it bolts to the sides. the front attaches normal. Worked great, actually.
 

workingdog

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had to set the 40 down today to figure out where the front axle set at ride height. Had to set it on stands, level front to back and side to side and then my (200 lb) son climbed onto the front bumper and jumped up and down to get the front springs to settle. Took an hour and a half just to get to here.

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Interesting note, the shock that I thought was perfectly straight up and down is now slightly angled as the springs flattened and the shackle moved back. Good demonstration of how the axle moves as the leaf suspension works.



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We got the laser out, you can see it not quite set yet on the hub, and measured down from the frame at two spots so we could replicate ride height with the rear axle. It says 16 3/8 (which I changed to 16 and 5/8 because the laser was quarter high.


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Now, with the rear axle finally at ride height, I can set pinion, and then I can measure link lengths.

But first, I have to finish the support structure for the transmission and skid plates and frame side lower link mounts. This is the same support that was under the rig before. So happy I was able to reuse most of it. I had to add the back rib (no paint), but it saved a bunch of time. However last hole bolting it to the frame is now blind (they used the series of holes on the inside of the frame to locate the other mounting points). So I'm going to have to figure out how to make that work. Either thread the frame or figure out a weld-in threaded insert.


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I can also reuse the transmission mount that actually goes into the Adapter - which was a little wider, but an adapter plate and I think it's all going to work.

The back rib is also going to be the mounting point for the frame side lower link mounts. I'm going to get some truss mounts from WFO and use them upside down. Been very, very happy with the WFO mounts and hardware. Very well thought out. Using their truss mounts on this will save me a day of screwing around with tabs.

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When my new studs arrive Monday for the Atlas, it will go back in for what I hope is the final time.

QUESTION: When I took the previous adapter and transfer case out, the adapter was bolted to the transmission with nuts and no lock washers of any kind. And that's what it's on there with now. Is that correct? Seems a little sketchy. Not even the self locking nuts that AA uses on the transfer case side.

Then I can set pinion angle, measure link length and build some temp links and test cycle the rear axle.

I was told over the weekend I had no chance in hell of packaging coil overs. So, that's a dissapointment. So I'm looking at TJ coils and shocks as a solution.
 

workingdog

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Here is the spreadsheet with current values. All are tacked in except the lower links on frame cross member, I had it at 20", but moved it to 22" to improve the upslope of the lower link and squat improved. That angle really drives a lot. I'm happy with this right now.

I've got conduit in for the upper links. I'll get conduit in as soon as the lower link mounts arrive and then use the conduit to cycle the suspension.

Screenshot (2).jpg


Had the backing plates on the 14 bolt the wrong way, had no idea the emergency brake headed backwards. Didn't notice that when I took it apart. There's an hour of my life I won't get back fixing that.
 

workingdog

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So, all the rear links have arrived and are in. My first attempt at putting the lower links on the cross members was clearly wrong as soon as I put the EMT links on, so I flopped them. And the lower links are still a little shallow in angle. So I'm gong to raise the links at the crossmember a little more. I rotated the studs on the Atlas (had to weld nuts on the old studs to get them out) and it's in and clocked up. Did a little more clearancing under the tub.



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I am still really struggling with the coilover math and angle and position. I haven't 'groked' it all yet.
I'm pretty sure the coilovers will fit inside the frame rails. I need to build a cross member for them to sit on. And modify the axle mount I have to sit at the angle it needs to sit at.

I'm guessing I'm about 800 lbs at each rear corner. 4" of up travel. 6" of down travel. 800 divided by 6" gives me a spring rate of 133 lbs. But, I'm going to be at a significant angle, so I'm going to have to adjust that up to make up for the loss the angle creates. Not sure the exact angle yet.
 

cruisermatt

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I'm confused by your last statement. Dividing sprung weight weight by the amount of downtravel is not spring rate. Spring rate is a fixed value for a individual spring. SAE value for spring rate is lbs/inch so that is the amount of weight required to compress the spring 1".
If you are wanting to determine a good spring rate to start with then you would start with ride frequency and calculate spring rates based on your sprung weight.
This is a good article with the math but you are probably going to have a hard time finding this type of info for this type of vehicle... it sounds like you are really wanting to understand this stuff fundamentally which is awesome, but you will probably get best results mimicking what other guys run and is known to work well if that makes sense


once you get a estimate for a good base spring rate, figuring out how to account for that with a angled coilover is easy. It's just springrate/cos(angle). Figuring out the vertical component of the spring rate.
 
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workingdog

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That's just what the the video from filthy motor sports did. Take the inches of compression at right height and divided by the weight at the corner and that gives you the spring rate you need.
 

workingdog

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I posted these to the wrong thread yesterday.

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It's really coming along. Matt was amazing yesterday. I've got to get a picture of the crossmember/trans support/lower link landing. Amazing work to shoehorn it in there. If all goes well and the Four Wheel Parts gods are with us, we'll have it roll and maybe driving around later today.

Progress on the EV45 too. hopefully pictures of that later today.
 

cruisermatt

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Making lots of forwards progress. Today’s work, Suspension cycled for shock measurements, shock mounts done, temporary used 5125’s installed, frame side coil mounts done, brake lines done, axle and links installed for good, shorter oil filter installed to clear front DS, front axle, steering, etc all installed for hood, fluids topped off, hopefully driveshaft, rear springs and brake hoses in tomorrow and we’re driving. I’ll try to remember to get a pic of the installed crossmember/skid plate/link mount/trans mount I came up with, a lot of cutting and welding went into that

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