Cut and turn project

Around new years I dove into a cut and turn d35 project. I set my goals: 4" added spring height for 6" of lift, and strategic bracing to make the beams stronger. I want to run 35's when all is said and done. I did a bunch of research and looked at alot of set ups. I decided against relocating the lower balljoint, as no-oone could tell for sure how far you can push the bj out without binding the shafts at full lock and popping off thurst washers and c-clips. 3" inches was the suggested maximum.

I decided, like a few others, to make my modfications inboard of the diff. I made some calculations, and determined by trgi I would need to build 7.66* of camber correction into the beams for 4" of spring, 6" lift. I made a vertical cut almost all the way through the beam and spread it to a distance I calculated, making a triangular gap. I used 3/16 plate to fill the gaps I'd made, added a couple "trusses", and burned it all together with a hobart 140.

Here are some pictures of my results:

vertical cut beside diff




Filled gap, trussed






Fast forward 6 months and more research. Most setups look more "bent" than mine. I busted out the tape measure and calculator again, and sure enough my gap was off by .37 inches Here comes the old addage "measure twice cut once", but in my case it's "measure twice weld once"

I now have a cut and turn for 2.3" of spring, not the 4" I had planned for. So now i'm looking at my options. I can cut it up and start all over again. This would allow me to add a plate to the front of the beam as most guys do, and I probably should do. I'dd have to scrap my trusses and build new ones.

I can also run it as is with a 1.7" spacer, I will require a 1" spacer anyway with the coils I've got on hand. However, my alignment cam would be maxxed out. I could plate the inside of the beam. I could also push out the lower bj.

Looking for constructive input from those who may know better than me. I don't want to debate BJ vs C&T, please, as this is the route I've decided to go for reasons that appeal to me. I wheel tight trails and spend a good amount of time at full lock. I'm in no rush to finish this project, as I'm without a license for two years. I want a strong, safe and well performing setup. I'm planning on adding 44 outers, and maybe heim steering, but thats a whole 'nother thread.

EDIT: for anybody whose interested in this, for the drivers side D35 beam, every inch of additional spring height requires 1.9 degrees of camber correction. Thats additonal SPRING length, not LIFT height. It will be different (more correctionper inch req'd) for the shorter passenger beam, i'll post that spec when i tackle the p.s.

I'd probably just cut the beam again and open the gap up a little more, then plate it in again. Won't look real pretty, but should be fine from a strength standpoint if done properly.

You mentioned wheeling tight trails and being at full-lock a lot though... Do you actually need modded beams for that? (THE benefit of modded beams is greater clearance for landing jumps and other high-speed uses, which doesn't sound like would be the case here)

I suppose I don't really need a cut and turn. I like the custom aspect of it as well as the cost effectiveness. I shouldn't have much more into this setup when all is sadi and done as I would installing a conventional drop bracket lift. It provides a good entry point into some basic suspension design for me. I'm an engineering student, and its pretty cool to me to practice some of what I've learned in a medium I really enjoy, wheeling my ranger. I wonder why specs such as camber change per inch of lift for each of the beams aren't readily available for determining just how much spacer one can run with x degree alginment bushings. And what effect that budget boost will have on your caster, and how that will be lessend with an extended RA. I will gain a deeper knowledge of this suspension with this project, and some decent fab experience. I plan to share what I learn along the way. I'm pretty embarassed I miscalculated that, as its pretty simple math. I'll probably do as you suggested.

Well, I'll learn from your mistakes. And hopefully from when you do it right the first time too.
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Richard

Ok, cool deal, though the modded beams aren't without a couple drawbacks (which is why I asked). Sounds like you're mainly in it for the learning experience.

As for the camber specs (spacer/spring length vs. degrees of correction), it varies a bit depending on whether you have extended radius arms on it or not.
With stock radius arms, the suspension axes for both sides are actually symmetrical with each other (the same amount of coil spacer thickness/spring length change will cause the same amount of camber & caster change on either side). Extended arms changes it's geometry a bit however, the passengerside's camber curve sharpens ever so slightly, and the driverside broadens a hair (this comes from the front-to-rear mounting of the axle's pivot points relative to each other, combined with the beams being different lengths). Fortunately it's not enough of a difference to be noticeable in normal driving (the benefits of the extended arms far outweigh this particular drawback), though if you really wanted to, moving the passengerside beam's pivot rearward a couple inches could restore symmetry to it's geometry (something I have not bothered doing on mine).

I can see how caster would be affected the same for each beam because of equal length radius arms (both sides same length). You probably have examined this further than I have, but it appears to me that the shorter p.s. beam will undergo more camber change.

How have you "dug deeper" into the geometry of this thing? I'm not being critical, I just want to learn.

Draw a line from each side's pivot bushing to the radius arm bushing. You'll see both lines (axes) will be on the same angle relative to each other even though the beams are different lengths. These axis angles don't change an equal amount as you extend the radius arms however (and is why the camber curves will be a hair different after putting ext. arms on).

This diagram should help to visualize it:
http://img.photobucket.com/albums/v173/sfr4x4/ttbsymetry.jpg

Red = axis of suspension movement
Blue = distance from axis to spring
Green = distance from axis to tire.

that drawing explains it perfectly (with no words necessary), this is a cool project, ill be watching!

Cool, that diagram helps, thanks. I was thinking there must be an axis of rotation for the whole deal. The arc of travel is created by the line segment from the axis to the tire center, and the tangent on that arc would be the resultant angle (comprised of) of camber and caster change.

I reallly wish I had a bare frame, even just from the trans x-member forward to play with, it is harder to make sense of any of this or get certain measurements with beams on your garage floor.

I'm probably overthinking this whole deal, but I dont have much else to do