Join Date: Oct 2006
Location: Clinton Township, MI
It has been a long time since I did a detailed study of the stock 4-link (AKA: quadra-bind) kinematics, but this is what I remember...
As the quadra-bind articulates the length of the upper arms needs to change. Since the arms themselves cannot change length, the "effective length" changes by having the soft rubber bushings deflect. When you switch to heim joints the bushings can no longer deflect and you actually increase the bind.
The reason that heim joints work in UCA's for drag race applications is because the UCA length does not need to change if the rear end stays parallel to the ground and body. When a drag car launches both sides of the rear end move together. In this application the heim joints actually help because they stop the rear end from deflecting and they transfer all of the energy to the body.
The problem is that in a road race or auto-cross situation the rear end does not stay parallel to the ground and body. As the car leans going around a corner one end moves up and the other moves down. This is when the "effective length" of the UCA's needs to change. Since the length is fixed you get "snap oversteer" or loss of traction.
The same general reason is why MM tells you that you need stock UCA's with rubber bushings if you plan to run their Panhard Bar with a quadra-bind set-up.
In short, those arms will work well for drag racing and they will be OK for the street, but you do not want them on a car that is going to push the limits while turning.
+ Jalape√Īo Red 1985 Mustang GT, 347 in^3, Canfield heads, 650DP, X-Celerator, & 1-3/4" LT's
+ Tremec 3550, D&D shifter, 3.73:1 gears, & TrueTrac differential
+ EVM watts & 3-link, Homemade LCA's, & Koni SA's
+ '00 Cobra R Brembos in front and SN95 Cobra rear brakes, R58 rims, & 275/40R17 Falkens