I'm currently running close to 4" of lift (hey, don't laugh, that's alot for a DSII-:flipoff2: ), and I want to make a set of corrected front radius arms. Nothing fancy, no three or four links. Just a drop-in replacement with the correct bend to bring my castor back to factory specs.

If possible I would also like to have a small bend inward to give more tire clearance so I can turn my steering stops back in. I read the previous thread about a 3-link on a Disco, and now realize that the stresses on a radius arm are tremendous.

Here's my question. What size and strength tubing do I need to use to replace my radius arms? I don't want to cut my factory arms because A: I want to be able to go back stock if necessary, and B: It's my daily driver so I want to build the replacements in my spare time so my vehicle isn't down. Any ideas?

Why not just get another stock set to play with? I have seen a few parting out dsII's out there.

Tom

The problem with modifying factory arms is when you add steel plate along the sides for strength, you make them even wider. This results in an even greater loss of turning radius. Right now with my 285's (again, no laughing!), I have them (my steering stops) cranked out pretty far, and miss the turning radius I used to have.

You could just plate the other 3 sides

Ron

Greg,

I don't think a single piece of tubing will do the trick for you. The get a large enough "area moment of inertia" to support the bending loads that the stock front radius arms supports would require a large diameter tube (which would give you more clearance problems with your tires). To support the bending moments, you would have to go to a two-tube design (upper and lower tube with some sort of web between them to transfer shear forces). This would require a new bracket system at the axle.

The three link works because the tubes are in comprssion and tension, not in bending.

Rich

Rich, so you are saying that to use tubing, I would need to go to a 4-link setup because of the forces? I was not wanting to get that involved. I may end up re-working some factory arms afterall.

Why not just talk to RoverTym or Rockware and see what they can think up? Prices are pretty reasonable for the quality they deliver, IMO.

Rich,

Your technical responses always amaze me. Just out of curiousity do you teach dynamic physics or something similar at the graduate level??? Or is it just a hobby that you apply your innate understanding of geometry and calc to? Maybe a structual engineer? Curious what your background is, it benifits the list a LOT!

Way

Greg,

Using a single tube to replace the radius arm would require a tube with more width than the stock arm. The stock arm acts like an I-beam. This is a very efficient strucuture for taking bending loads (i.e., those that occur when on the brakes). Tubes are better at taking forces along their axis (relative to their weight and size). Tubes could be used, it just would require some understanding of how the forces flow through the structure.

I simply heated my arms with a torch and bent them in a 10 ton press to increase caster. This approach was suggested in a LRM article years back. It takes a fairly high output torch.

Rich

Originally posted by Way
Rich,

Your technical responses always amaze me. Just out of curiousity do you teach dynamic physics or something similar at the graduate level??? Or is it just a hobby that you apply your innate understanding of geometry and calc to? Maybe a structual engineer? Curious what your background is, it benifits the list a LOT!

Way

i believe he holds a PhD in Mechanical Engineering and is a professor in the same at New Mexico State University in Las Cruces, correct? :D

Way,

I have a PhD in Mechanical Engineering, am a professor at New Mexico State University, have tought some courses on vehicle dynamics of high performance on and off-road vehicles (graduate and undergraduate levels), and use to be advisor to our Society of Automotive Engineers Mini-Baja team (that was back when our cars were amoung the fastest out there). I'm also a researcher, lots of publications and that sort of thing, and tend to think like a researcher. Trying to understand what makes a rock crawler crawl well has been a hobby of mine for a long time. I've been an off-roader since 1969 when I bought the series IIa. My involvement as the engineer for the first twist-off (read my technical report on this) was directly a result of my wanting to understand, from an engineering point of view, what works and what does not.

Presently, I am an Associate Dean and Director for Engineering Research at the University. However, despite all that education, what makes an off-road vehicle work is not clearly understood. There is absolutely no substitution for experience. This is why I get so excited when someone tries something new and reports characteristics of the results (such as the stuff that Sam has been doing).

Now you know why I cannot spell. I'm an engineer. Now the rest of you can flame me for be a useless egg-head:nuke:.

Rich

Instead of reworking the arms it might be easier to modify the axle mount.

On the front axle tube you would lower the front radius bush bolt hole. I would guess that you would need to lower it by almost 3/4in to restore your caster after your 4in lift. To do this would be as easy as welding a plate on the outside of the existing bracket so that you could redrill the hole at a lower position.

Another good side effect that could be gained by doing this is that by lowering the front bolts gives the radius arm more clearance away from the axle tube so that you could easily play around with a hinged arm setup by simply removing one of the front radius arm bolts and not have any modification at all.

If you did this on the rear then you could do the same there as well. And experiment with running a hinged arm front and rear without having to cut up an arm.

Guys here running nissans actually lower the front bold with a completely bolt on bracket but they use about 6-8 in lift and lower the bolt about 1.5inches do there is enough room for a bolt on mod.

Sam

Originally posted by rhills
Greg,

I don't think a single piece of tubing will do the trick for you. The get a large enough "area moment of inertia" to support the bending loads that the stock front radius arms supports would require a large diameter tube (which would give you more clearance problems with your tires). To support the bending moments, you would have to go to a two-tube design (upper and lower tube with some sort of web between them to transfer shear forces). This would require a new bracket system at the axle.

The three link works because the tubes are in comprssion and tension, not in bending.

Rich

Go 3 or 4 link and forget about it...Or just forget about it entirely and wheel the snot out of your rig with a big grin like Rich! :flipoff2:

BTW Rich, any progress on what your gonna' do to yours? Inquiring minds wana' know!

--D

Doug,

Presently, I have been designing the new bodywork and roll cage. Getting pretty close to the construction phase. Wasn't planning to extend the wheelbase till next year, but after going out with Lance this weekend (rode in his vehicle) and following someone else who just stretched his vehicle to 100", I'm having serious second thoughts about waiting that long. Huge improvement!

Rich

James Duff drop bracket (http://www.jamesduff.com/eb/traction.html)

here's a pic of a drop bracket that James Duff makes for early broncos, you could easily make something similar but the only downfall is the the bracket can get caught on stuff. I think the best alternative is to have the swivels re-indexed for proper castor.

OK guys, thanks for all of your input. You've given me a number of ideas to play with. I'll let you know what I come up with. Obviously a tubular arm is no longer an option. I could go to RTE, but I'd rather learn what can and can't be done myself and then do the work. That way I have an understanding of why the mods were done in the manner they were. Just trying to expand my knowledge a little, 'cause a little is all I can take.:)

Originally posted by rhills
Doug,

Presently, I have been designing the new bodywork and roll cage. Getting pretty close to the construction phase. Wasn't planning to extend the wheelbase till next year, but after going out with Lance this weekend (rode in his vehicle) and following someone else who just stretched his vehicle to 100", I'm having serious second thoughts about waiting that long. Huge improvement!

Rich

Awesome! Just what I LOVE to hear! BTW, I've been measuring the clearance I have under the frame rails (at the ride height that I'm settling on) and I'm at 23"....So I've shortened the wheel-base (yet again...Easy at this point!). I'm hanging right at 108" now. I just don't want to have horrendous break-over issues in Cruses...Even with the 42's, I want the ride height LOW (and stable) but still have the clearance under the rig the 42's deserve.

What's the frame rail distance (from bottom of FR to ground) you all have now? I'm up there! The drivers seat hit's me right about in the lower rib-cage...And I'm 6'5" tall.


-D

Doug,

I try to measure tonight. Off to Carlsbad NM this morning and don't know when I will return tonight. But I agree, break-over is a real issue in Las Cruces.

Any thoughts on how far the front axle can be moved forward without moving the steering box?

Rich

Originally posted by rhills
Doug,

I try to measure tonight. Off to Carlsbad NM this morning and don't know when I will return tonight. But I agree, break-over is a real issue in Las Cruces.

Any thoughts on how far the front axle can be moved forward without moving the steering box?

Rich

IMO, You can go forward about 2.5-3" without moving the box. You will of course have to re-bend the pitman arm (track) however to utilize the WELL designed PS box support/track-bar mount....It's been a while since I've looked at the Rover axle configuration under my truck, so the Rover bracketry (radius arms) might be a factor there...I just dunno' anymore...However the above dimensions would work for a 60/44. Then there is the issue of the frame mounted spring perches. I dunno' about an "easy" fix for that one...Hence the coil-overs (in the front) was the best option for me. My axle centerline is right at the trac-bar mount centerline...Forward about 7"...Hence my rear is back 8". Nice balance to factory v.s. full custom geometry.
I'm off to mount the JJ's on the rear lower links at the axle (just don't want a heim bind issue down the road. Now is the time for the articulation testing, while all is just tacked welded. If satisfied, will do the final burn-in this Sunday....

O'yea, Rich...One question. I'm considering moving the rear links out-board from parallel to the frame...I was thinking from a leverage perspective (and heim misalignment aspect) that moving them in a \__/ would be better for stresses and heim misalignment (maybe) during full droop stuff. Whatdaya' think? I see no issues (other than positive) with this configuration....Especially with a wide ass axle.

Originally posted by RockRover


Awesome! Just what I LOVE to hear! BTW, I've been measuring the clearance I have under the frame rails (at the ride height that I'm settling on) and I'm at 23"....So I've shortened the wheel-base (yet again...Easy at this point!). I'm hanging right at 108" now. I just don't want to have horrendous break-over issues in Cruses...Even with the 42's, I want the ride height LOW (and stable) but still have the clearance under the rig the 42's deserve.

What's the frame rail distance (from bottom of FR to ground) you all have now? I'm up there! The drivers seat hit's me right about in the lower rib-cage...And I'm 6'5" tall.


-D

DAMN you are low. Your gonna drag your shiat all over the place.

:flipoff2:

Nah joking. Just measured my frame clearance and its 19.5inches (this is with less than 3psi in the tyres)

And I got 27.5 clearance under my 2inch thick rock slider (the one under the door).

Sam

19.5 eh? That's right about were I'm gonna' be when I air um' down. Of course with the coil-overs I can adjust the ride height a couple of inches up or down if I really want.

Do you see any problem running rear trailing arms out from the frame about 10deg...Towards the ends of the axle? I can't see any problems other than I'm gonna' have to fab up 4 new axle/JJ mounts now! O'well...

--D

Doug,

I'm 16.5" to the frame. Now that the hard top is gone, I'm going to raise it maybe 2 inches. So we are in the ball park.

I don't see a problem with the trailing arms mounted wider on the axle than on the frame. This will actually give you a bit less roll steer (which is good).

Rich

Doug,

Run em straight cause its easier to do and when you go rear steer you wont have to redo the frame mounts. :flipoff2:

Either will do the job.

Sam

Thanks guy's...Didn't think of the roll-center improvement. Out they go!

Actually Sam, I thought I had my hands on another 60 out of a burned out Ford F350....Totally toasted...Down to the ground...When I stopped and looked at it it turned out to be 2wd! :( O'well...My rear steer axle WILL come...That's all phase III stuff anyway.

So 16.5 - 17.5 'ish' is around the stock ride height eh? So I'm only lifted about 7.5" (or so) inches with 16.5" more trac width...Good. THat's right in with the 2:1 priciple you taught me Rich...That is: 2" out for every 1" up on a D90 to retain factory CG. Hmmmmm. I might just lift her a couple more now!

Thanks guy's...Now off to the shop to burn in my rear links...All's coming together A-okay! Gotta' get a BUNCH done this weekend...Next weekend is slated for finishing the master-bath tile :rolleyes: Following weekend is either springing the rear or linking the front...Ahhhhh...Decisions decisions! :flipoff2:

--D

O'yea...Sorry Greg for stepping all over your original post! Should have started another thread :emb:

O'well...FAWK OFF NEWBIE! :flipoff2: ;)

--D

--D, no problem. As a newbie, I expect that kind of shit. :p Besides, I picked up a few things along the way. Here's a real newbi question. What does roll-center affect, and why is more better?