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4-link

rdc

- users no longer part of the rdc family -
i am building a 4-link for my 1988 toyota, and i was just wondering if anyone could give me any useful tips? i am planning on using a 1 1/8" rod end on each trailing arm, with 1 3/4" tubing, (braced and boxed in), on the upper links i am using 3/4" rods, with 1 1/4" tubing. does this all sound right? Also, how long should i make the trailing arms? i am going to make the upper links 3/4 of what the trailing arms are. And lastly, how can i find out how high on the frame i should mount the trailing arms and upper links? should i just tack a bolt on and cycle the suspension until i get a good pinion angle? any help would be greatly appreciated. thanks
 

Kritter

Krittro Campbell
Sounds like you may be in a little over your head? Good luck though. I would say trial and error is your best bet or find one that works and copy it.

Kris

When in doubt, GAS IT!
 

ntsqd

Well-Known Member
The 4 links I've delt with in the past (drags, not OR applications) had the baseline instant center (IC) set at the flywheel surface on the crank centerline at static ride height. From there the IC was adjusted to get the bite desired. I'm curious if this also applies to OR vehicles since where the IC is determines how much front end lift you get under acceleration.

From there I'd say you have to decide if you want constant pinion angle or equal UJ operating angles. Then you can sort out what the lengths are and where the pivot points need to be.

"Teach you all I know and you're still stupid"
-- Howdy Lee
 

Flea

Well-Known Member
hey i was wondering if you could explain baseline instant center and how this effects front end lift. is it possible to relate this to leaf springs with some sort of traction bar steup?

GOD BLESS AMERICA! and hopefully my poor truck too.
 

BradM

Well-Known Member
There are a few thing you have to bear in mind. The location of the IC in relation to the CG effects the anti-squat or how much the rear of the truck squats on acceleration. Obviously the IC moves as the suspension travels. Start with Thom's suggestion at ride height and you will be in the ball park. Also you have to consider the amount of driveline plunge. You should be able to cut it down to about 1/2" or less. That effects the wear of the splines on the yoke. Also, the length and vertical position of your top arm effect the pinion angle change. The shorter the top arm, the more pinion angle change. You will have to pay attention to how much angle your u-joints can handle.

I suggest that you do a lot of drawing first. If you don't have a decent CAD program do it on paper or build a scale model out of cardboard. That will allow you to move pivot points around and change the length of the bars without cutting any metal. Perhaps you need to do a little reading first. Look for Chassis Engineering by Herb Adams for a quick, east to read overview. For more detail, read Tune to Win by Carroll Smith. Do your homework before you build.

If you want more details, email me.



Build 'em light, wind 'em tight
 

FABRICATOR

Well-Known Member
There's the key word "homework!"

<font color=orange>The best ideas are the ones that look obvious to the casual observer.</font color=orange>
 

ntsqd

Well-Known Member
You can just take the approximation that the location I described is the Center of Gravity (CG), or you can spend some time with some scales and figure it out. More often than not my approximation location is really close.
How it relates to traction bars and leaf springs I haven't a clue. What type of traction bar design will greatly affect things. How I can't tell you because I don't know. I would have to start pulling books out and looking things up. The Herb Adams book Brad suggested is a good place to start. And there's nothing like reading Mr. Smith, who is as much of a character in person as he is to read, to get your juices flowing. I recommend all of his titles: "Engineer to Win", "Prepare to Win", "Tune to Win" as already mentioned, and "Screw to Win".....er that's what he wanted to call it, the publisher titled it "Nuts, Bolts, Fasteners & Plumbing."
And while we're on the books subject, one of the best explainations of how to use a shear-moment diagram for figuring out things like lower 4 link arms that have a coil-over attached to them is in M.M. Smith's "Trailers; How to Design and Build, vol. 2: Structure". I got my copy from Northern Tool.

"Teach you all I know and you're still stupid"
-- Howdy Lee
 

Flea

Well-Known Member
thanks ntsqd,

i never new there were so many books out there i could use to help me. i'll be checking those out.

GOD BLESS AMERICA! and hopefully my poor truck too.
 
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