3 link ladder arm

[rdc]

I'm trying to build a 3- link rear ladder arm.

I have looked at the arms on Collins, H&M,and the Gieser truggy.

Do you need to keep the shock mounts on a straight line between the front mount and the rear hiem??

Or will it work better if the shock mount holes are lower then the straight line ( centering the arm verticaly under load)??

I also would like to thank the people involved in the mild steel vs chromoly post --- I learned a bunch

This is a class site---------------

 

[FABRICATOR]

Dilfab,
A lot of trailing arms are designed with the shock/spring attachedment below the swivel center line. This is what keeps the arm from flopping from side to side. Some set ups use spacers or other apparatus, on one end only (usually the rear), to keep the trailing arm upright. Either way is OK.

Generally speaking there is always a positive load on the axle from the trailing arm. About the only exception to this is when using a bypass shock with strong rebound damping at the end of extension to avoid harsh "top out." If you go for the "floating" arm, with the low mounted shock/spring attachment, it's important that the shock absorber and spring be mounted at about the same level. Otherwise they can cause the arm to flop as they work against each other.

This does make the arm more complicated. You can make a dog leg arm and mount the shock/spring on top. Or a straight, boxed arm with a boxed mount that goes down inside from the top (most TT's). Or some make the arm out of multiple tubing so the shock/spring can go down into the lower inside section.

 

[rdc]

Thank You for the info:

I have built the arms with the shock mounts in line -- the front mounting point using a bushing system to hold it in a vertical plane.

The arm is 49" long with a 16" coilover at 34"--- I will get 23" of travel--- I have a 350lbs spring and a 500lbs spring the truck weighs 3640lbs dry.

I don't know the rear axle weigh---I'm guessing at 1500 lbs----

THE NEXT QUESTION IS----- will I need a torsion system?????---if so is there any torsion bar from an existing front-end I can retro-fit

into my frame building the new arms at around 18" long---- I have access to a VW torsion system and my frame is only 34" wide.

I have found the 3-link system hard to build but I have learned a lot --- the next will be better

thanks again

 

[FABRICATOR]

Dilfab,

Make sure your front bushing system for the arms allows plenty of (center line) rotation, otherwise something will break immediately and you may loose control of the vehicle. The leverage over the front mounts can be astronomical.

As always, what is the application here? By "torsion system" I assume you are referring to an anti-sway bar. If this is the case, the VW system would not seem advantageous. Anti-sway bars generally go from one wheel to the opposite wheel, not from each wheel to the frame. Wheel-to-frame systems require very long torsion bars and are tricky to make work with long travel. Conventional wheel-to-wheel systems do not interfere very much with suspending of the vehicle, and are very adaptable to long travel.

Unless you've really done your homework, it might be to your advantage to keep close to what is out there and already working. The more you deviate, the more you will have to learn. (some the hard way!)

 

[Greg]

I recently finished my 4-link and it leans like crazy when I turn (especially after I got the spool in) but it works great in the dirt. I dont have a sway bar and I just have to tell myself its not a street car. You'll get used to the feeling. If you do decide to instal a sway bar, keep in mind the location you mount it. Seems most trucks put way back for weight distribution but it shhould br put where the frame/cage is strongest.

Greg

 

[rdc]

I tried to respond earler but I must have lost it--- so If you got this---sorry

I would remove the center lockin point in the VW torsion and use the torsion assemply and bearings to rotate

up and down untill the body tries to roll. The question is will a torsion with 400lbs per side be enough to stop the body roll.

The length of the arms will be the thing to move to adjust the amount of load into the torsion bar.

I will let you know if this works----- or if it goes shooting through my fiberglass bed sides.

Could you explain the rotation center of the rear ladder arm-- are you talking-- twist of the arm

or the rotation through the wheel travel???

 

[FABRICATOR]

Dilfab,
I was talking of twist of the arms but at all extremes of wheel travel. Greg mentioned mounting the assembly at the strongest section of the frame. This is something you should try to do. If it is done right, you won't need the big heavy VW cross tube, but just a simple piece of 1-1/2 or 1-3/4 tube. Many applications use no cross tube at all, just some hefty mounts.

Sway-a way may have a torsion bar that you can use, but there also lots of stock car bars available from several suppliers. These come in all shapes and sizes and with steel or aluminum arms of various lengths. Some even supply the bushings and mounts. You can even get hollow bars if you want.
Have fun!

 

[rdc]

When i started building this suspension system i put hiems at both ends of the ladder arm.

The arm flopped to one side of the other, under just the static load of the truck--- my concern was at the extreme highest right wheel position

and lowest left wheel position I needed both hiems to keep from bending the mounts.

Then I looked at the pictures of most of the trucks--- they only used one big hiem in the rear.

I'm assuming this means the arm generally moves through a vertical plane with the maximum

high to low situation taken up by the rear heim. The shocks are my next concern--- if the arm is moving

vertically then hiems in the shocks should not be twisting much--- meaning you shouldn't need much room

in the arms---------- But I can't take a chance of bending the shock shaft--- so I have room for them to swing

on the heims.----------- I'm only talking 23" of vertical travel--- If I were pushing the limits at 35 or more

I would be very concerned.----------- I like the idea of using some mounts on the torsion bar--- I don't think

you could too much torsion with a small truck torsion bar in a full size truck.

I will be out trying to break something this week--- I have 40 acres to play on next to my house.

I will let you know________________ thanks Chuck for your GREAT input