Project Spec-V: Part 24: Setting up the Chassis
9/19/2007
The sophisticated suspension in our Time Attack car required special attention to proper installation. Unfortunately a proper setup is what many enthusiasts ignore when setting up their car suspension. Many enthusiasts do not realize that the setup makes as much difference as a shiny new set of coilovers.
Set up for the suspension consists of several steps. These steps are; initial rough alignment, corner balancing, setting camber and caster, and setting the toe. On our car the rough adjustment is difficult since the rear suspension is not adjustable at all. On a Sentra the rear suspension is a twist beam axle. Although it seems like an unsophisticated beam axle, it is actually a semi-independent rear suspension with an integral rear anti-sway bar built into it.
The beam is designed to twist allowing both rear wheels to have a large degree of independent movement. There is also a built-in torsion tube inside the beam which acts like an anti-sway bar. The whole assembly is welded together. Unfortunately Nissan has built this rear beam with a large amount of toe-in from the factory. We have measured as much as ¼” of rear toe-in on Nissan beams. Nissan probably adds this large amount of toe-in an attempt to eliminate over steer. For the high performance enthusiast this means that the car is doomed to under steer unless this toe can be removed.
To do this difficult task, we asked Darren Nishimura of West End Alignment for help. Darren in one of the best chassis set up guys in town and has developed techniques for eliminating the toe-in from beam axle equipped Nissans.
The most important tool for removing the toe-in from the beam is these simple fixtures that Darren fabricated. One piece supports the inner torsion tube and takes the force to bend the beam from a hydraulic jack. The other pieces are inserted into the beam to support the outer walls and prevent them from crushing. These pieces allow the entire beam to be bent together as a unit.
With the fixtures in place, a sturdy iron rail is chained to the beam and a hydraulic bottle jack is placed between the beam and the rail. The bottle jack is set so it pushes between the rail and the beam.
The rail is exceedingly sturdy so it won’t bend, only the axle does.
Darren applies pressure with the jack and bends the beam outward eliminating the toe-in.
Darren continuously checks the tow-in with a trammel bar during the process to make sure that the axle will not be over bent.
After bending the axle, Darren sets the camber, toe and caster for the front suspension. We set the caster at 3 degrees positive with 4 degrees negative camber and 1/8” toe out.
After Darren worked his magic, we sent our car over to Steve Mitchell at M-Workz. Steve’s first steps were to set up his floor levelers so he could precisely corner balance and align our car. Floor levelers are aluminum platforms that have adjustable legs so they can be set to be exactly flat and level with each other. First, Steve set a surface plate in the center of the floor and leveled that using a spirit level. Once the surface plate was level, Steve used it to calibrate his camber gauge and as a platform for a laser pointer. 
The laser was beamed to a scale sitting on each floor leveler, one for each wheel and the heights set so all 4 levelers were exactly the same height. 
When setting corner weights 1/16 of an inch makes a difference so this step is very important. Many chassis shops skip this step.
The levelers each contain an electronic scale so when the car is lowered down onto the levelers, the weight at each corner can be measured. 180 pounds of weight was placed in the driver’s seat and the car weighed. 
It weighed in at 2,640 pounds with the drivers weight and fuel. Now the corner weights could be set.
When setting corner weights, it is important to get the diagonal cross weights of the chassis equal. Of course you cannot get equal weights to each wheel because of the offset of the driver’s weight. Equalizing the cross weights ensures that the cars under steer/over steer balance will be the same when turning from left to right. The corner weights are leveled by adjusting the ride height of each corner of the suspension independently. Steve uses a computer program to tell him about how much to adjust each spring collar to equalize the cross weights.
After the corner weights are set, the car is fixed with Smart Strings which provide a datum point from which the toe of the car can be measured accurately for each wheel.
George measures and adjusts camber and caster with this electronic gauge. It is accurate to a 10th of a degree.
Steve measures the distance from the rim to the Smart String with a precision machinist rule, doing this he can set the toe to within 1/64”. With our chassis set up, we are another step closer to the track!