3/4 Link

JrSyko

Jerry Maguire
What is the main difference between a 3 link and a 4 link? I know the physical difference but why do some trucks run a 3 link and some a 4 link? I have noticed that most prerunners run a 3 link while race trucks run a 4 link. Is this accurate?

See ya in the dirt!
 

partybarge_pilot

Well-Known Member
4 link offers more strength ( multiple load paths) and adjustability. But tends to give you axle wrap on articulation due to theoretical pivot point being behind the lower one's.
3 link, no weird articulation problems, only one load path at rear, less adjustability, less parts to replace.
 

Donahoe

Well-Known Member
Damm good Answer

NEVER LIFT!!!!!
 

Dylan

Well-Known Member
The theoretical pivot point your talking about is used for determining your roll axis. As far as axle rap goes the distance between the upper and lower links that’s needed for resisting torque is the actual distance on the housing. A 4 link that is not properly designed (to shallow of an angle between the upper links) can actually be weaker than the 3 link version. Id say it’s a toss up, you can make either one work really well or really bad and dangerous. Unfortunately I’ve seen a lot more bad link systems out there than good ones.
 
If were talking about a 4-link that is built to suit the frame rails of a stock truck frame. It can get pretty narrow at the forward end of the upper link V. One of the many pluses of a 4-link is to load the heims in the proper direction instead of side loading the heim like on the 3-link. Whether you mount the heim vertically or horizontally your link is still only as strong as that single rod end shaft or side loaded ball.

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partybarge_pilot

Well-Known Member
The theoretical point I was refering to was not for the roll center. If you draw an imaginary line down the top to links on a 4 link the intersection is somewhere behind the pumpkin. Depending on how far your pivots are apart this can be quite allot. This results in the axle twisting as it articulates. This isn't really noticeable when driving, just one of those preferance things. Even more fun is the rear steer effect from a 4/3 link. Really noticeable at high speed on the street. Almost like a forklift!
 

Dylan

Well-Known Member
yah thats called a lateral constraint point and along with the lateral constraint point formed by the lower arms you can determine roll steer (over steer or under steer, hopefully understeer)
Dylan
 

ntsqd

Well-Known Member
The other advantage/hidden trap a 4 link offers over a 3 link is that you can make the roll center change height relative to the axle CL thru the motion range. A 3 link's roll center has a fixed height.

TS

"It only seems kinky the first time"
-- Bumpersticker seen in Lost Wages
 
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