November 6, 2002

Tightening up the suspension

The suspension of a car moves to absorb the bumps. This movement allows the wheels to remain in constant contact with the road. If a car had a solid suspension including metal wheels (since rubber tires flex to absorb bumps), the whole corner of the car would leap into the air every time it hit a bump. This would make driving down the road a series of exciting moments, as different corners of the car would stop accelerating, braking, or turning at random moments.

A suspension is very useful in helping the car maneuver. It also has the pleasant side effect of cushioning the people in the car from bumps.

On a street car, the suspension pivot points use a metal bushing held in place by a rubber bushing. This is an excellent design for the street since rubber absorbs vibration and lasts a very long time without maintenance. There are some negatives. Since the rubber bushing has 'give', it does not positively locate the pivot point. That means when you turn, the rubber bushing moves a little. This slows the reaction of the suspension and changes the arc of movement of the suspension. This means the car does not react right away and it does not react exactly the same way each time. These are bad characteristics for a race car. On a race car when you turn the wheel, you want the car to turn now! It is also important that every time you turn the wheel, the car turns (handles) exactly the same way.

To change the Electric Imp from its street car origins, we want to replace the bushings with spherical bearings. A spherical bearing is basically a ball bearing held captive by a ring. The front and rear of the ball bearing have been machined flat and a hole drilled through the center of the sphere. The spherical bearings will allow the suspension to move with the minimum resistance and the minimum slop.

Here is a picture of the stock suspension end (left) and a spherical bearing (right).
On the stock suspension, there is a metal spool that the bolt goes through located by a rubber bushing.
On the spherical bearing, the central metal spool can twist and turn freely, but always around the same static center defined by the arc of the sphere shape of the outside of the spool.
rubber bushing vs. spherical bearing
Let's start with a look at the rear suspension. The entire rear cross member was actually held in position using rubber bushings. This meant that the whole car's body could move in relationship to the rear suspension.
In this picture, we have already punched out the cross member's rubber bushing and replaced them with aluminum bushings (1 & 2).

The lower arms have four rubber bushings (at 3, 4, 5, 6), two are out of the frame (5 & 6). The trailing arm has two: One at the body (7) and the other at the upright (8).

Rubber bearing locations

Here is the rear upright removed. This is the bushing label 8 in the previous picture.

rear upright with rubber bushing

To replace the rubber bushing in the rear upright, we must press in a spherical bearing and machine in grooves to take lock rings.

spherical bearing in rear upright
The trailing arm is cut and a threaded spool welded on to take a rod end. Modified trailing arms

Close up of welding.

close up of welding

We also strengthen the welds on the stock piece to prevent flexing.

grind and add welds

Installed with two metal spacers, the trailing arm and it's # 7 suspension point now looks like this.

replacing # 7 rubber bushing
Here is the end result. Notice that the rear cross member has been replaced, so 1 (out of sight) and 2 are metal bushings.

The stock lower arms have been replace by a tube with rod ends in each end (3,4,5, 6 is blocked from view). This also allows us to easily change the length of the lower arm to improve suspension geometry. The rear of the trailing arm is # 8.

revised rear suspension

In the front, we replaced the stock lower A-arm with a lighter after market aluminum piece. The Front A-arms rear bushing looked like this.

Old Front A-arm rear bushing
We replaced it with a MRT part that changes the angle of the lower A-arm in a way that is suppose to improve the front suspension geometry.

It comes with a neoprene bushing which we decided to keep due to the difficulty of machining a new one.


On the front of the A-arm, we were able to punch out the front bushing and replace it with a spherical bearing.

bearing in front A-arm
Two custom spacers keep it located and not binding. spacers for A-arm
A-arm ready to go on. A-arm ready to go on
We also replace the stock steering arm with a rod end. stock steering arm vs. rod end
The end result. Only the ball joints have not been changed. revised front suspension


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