Project Hellraiser 4

Page 6


Previous Update

This part of the project seems to start and stop at a moments notice.  Typically when you get to the point where you need to add tubing, mount links, coilovers and a rear seat you quickly discover each item is interrelated and how you mount or position it will effect the other parts.  So you end up having to slowly piece it together like a puzzle, thinking thru each step before proceeding to the next and only tacking things in place (because things can and will need to change). Luckily this week had a holiday in the middle of it so I had an extra work day to get some stuff done.

First up was installing some bigger ducting for my spot cooler.  I ran some 10" insulated ducting from the exhaust port to the outside vent. Most of the stuff I did on the 4th did not require ventilation so the cooler actually kept the garage to a chilly 80 degrees until around 2 o'clock.  For reference it got to 116 outside that day. Since I took this picture I routed the other cool air duct across the garage over towards my tool box/drill press area.   

Before it got too hot I decided to get my grinding out of the way early on the 4th so I could start up the cooler.  I ground all the upper link mount remnants off of the frame and finished cleaning up the rear axle housing.  This took a couple hours and by the time I was done I was a few shades darker.

With the grinding done I could set the new rear axle truss on the rear axle.  At this point I fired up the cooler and decided to do something that would allow me to close the garage door and escape the heat.

After discovering my transmission cross member bolts had worked loose I decided it was time to make a support for the transfer case.  First a template was created and the plate cut out with the plasma cutter.

I intended to grab 3 of the rear output mounting holes with the plate, then tie it to the frame via a pair of spring bushings.  Obviously everything had to be bolt on to allow removal so that is what drove me to this design.  If you have an Atlas or Stak there are a few places that make a clamp that grabs the rear output, you then just have to attach the clamp to the frame via some bushing.  I wanted to use something similar but the rear output on my 300 is tapered and I had no solid mounting points overhead or under to attach the clamp to the frame.

Once the mounting holes were transferred to the new plat I put a 90 degree bend in it and added a gusset top the top and bottom of the bend (only the top gusset is shown above).

Next I mounted pair of spring bushings/DOM tubes to the frame, ran a pair of 1.00 x .120 wall arms out to the t-case plate and then welded some tabs to the end of the arms to allow me to bolt the arms to the t-case plate.  Lastly I tied the arms together with a plate.  The big hole in the tie plate is for filler access, the other holes were dimpled to make the plate rigid. I actually finished this project up by Thursday night (painted and bolted it on).

All during the week at lunchtime I was using the machines at work to make/modify parts.  Since I am upsizing my rod ends this go around I needed to shorten my front lower links and re-tap them for a 7/8-14 thread.  I did this by hanging the link over the end of the mill and adjusting the head to reach.  I will be using this size link for the front lowers, and all the rear links.

I also worked on my V 2.0 dimple die station which came about after I bent the first one trying to dimple some steel (which I knew I shouldn't have tried but....).  Anyway, I decided to build one beefy enough to eliminate the need for an H frame press since garage floor space is in short supply. This time I dug into my good steel pile and made the spine from 3" diameter, .312 wall DOM tubing.  The gussets were made from 1.50 x .250 DOM that came from an old suspension link and were positioned to maximize the throat on the press station.  The base was 4 x 2 x .250 wall tubing which has a brace under the spine and jack to keep it from crushing in. I plan on adding one more brace where the lower diagonal meets the horizontal where the anvil is mounted.

Here's the press in action, dimpling the braces that will get mounted to the press.  Without the gussets there is a slight deflection when dimpling 14 gauge steel but nothing that would lead to premature failure. I also added die storage along the back of the spine.

The press nearly done, now it just needs a coat of paint.

Back to the main project.  On Saturday I had some extra hands in the form of my Dad so while I assembled the rest of the rear truss and did the final welding he worked on making some tabs for the upper links.

I had made some temporary link from 1.00 x .120 tubing and some old 3/4" rod ends to locate the rear axle to my estimated wheelbase of 111 inches. As mentioned previously these are 37" long links, (with 3/4 rod ends) the same as the front.  Since the 7/8 rod ends are slightly longer the final links will be .875 shorter to accommodate the larger rod ends.

By Sunday we had the upper link mounts tacked in place at both ends.

I started on a cross member which will mount in from of the rod ends to allow for a tab to get the rod end bolts in double shear. My Dad was working on some gussets for the axle end tabs.

By 2pm on Sunday we had the cross member in, the gussets ready to be dimpled and tacked to the link mounts and had bent what I will call the floor hoop. I guessed at how much link clearance I would need between the floor hoop and upper links and still need to cycle the suspension to see if I can optimize seat room.  As is this height on the floor hoop gives me 40" of headroom for the rear seat passengers. More would be better but that will work if it has to.

Ok, so you may be wondering why I am re-arranging the rear links. My reasons are:

1.  I needed longer links anyways to accommodate the wheelbase stretch.

2. I wanted all the links to be the same length.

3. The new rear axle truss may also serve as a mount for my swaybar.

4.  I wanted to tweak the suspension characteristics bit.

Here's what I had.  The upper links had to be shorter than the lowers due to the position of the old cross member.  I was also locked in to the shallow upper link angles due to me re-using the existing truss that was on my rear axle when I bought it.  Due to the offset differential I could only move the passenger side mount in so far before the link would hit the differential on articulation.  the new truss is taller so I can move the upper link mounts as close as possible, picking up triangulation.

Here's the new setup.  The taller link truss on the axle buys me a higher roll center  (and lower anti-squat since the lowers don't move) and moving the link mounts closer together on the truss cut down on the roll steer when the axle articulates. The new, higher mounting position on the frame for the upper links also raises the roll center  and a combination of the increased triangulation of the uppers and their angle relative to the lowers moves the instant center further out in front of the rig. Confused?  So was I and really the only way to get a handle on things is to plug in some numbers and try moving stuff around as each variable has direct and indirect effects on the whole system.

If I want to get back to what I had before (or really close) I can move my upper rinks at the axle end up a hole (roughly 1.5" higher) and have nearly the same characteristics as my original suspension with the exception of a higher roll center.

IMO you can have the luxury of tweaking you suspension via the calculator only on your second go around since there are no perfect numbers for every possible rig/weight/terrain combination. Once you have a suspension design under your belt you'll have a better idea of what you like or didn't like and can fine tune from there.  I know from my perspective I like lower anti-squat numbers, minimal the roll steer of the rear axle and the instant center out in front of the rig and low to keep the front tire from lifting on smaller climbs.

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