PN A-Arm Front Suspension

Lap Fitting Ball Joints:


Due to the tight fit of the balls on the A-arm suspension, some parts may be too tight. Use "Mothers Mag and Aluminum" or other polish to lap fit the parts.

The A-Arm suspension set I had had a very tight fitting ball. In reality, the amount of tight fit is probably on the order of .0005" or so. But with such small precision parts, that will be enough to go from a free moving suspension to very tight. On the other hand, if parts were made looser, there could be quite a bit of slop in the suspension. It is better to have tighter parts, so you can lap fit them rather than to have too loose parts.

For very tight parts, here is a way to loosen them up.

Screw a wheel locknut or a regular nut to a M2X.4 screw. The long one that is supplied with the kit will work fine. I used two free running nuts tightened together to keep it from moving. Adjust the nut so that the screw does not protrude past the ball. This will keep the screw from scratching the suspension arm.

Apply Mothers polish to the ball, and work the ball in the suspension arm like a joy stick. This will not free up the suspension ball all the way, but it will get it to the ball park. This is only for the parts that are at the extreme end of tolerance stack up.

The ball I had also had a stubborn tight fit at a certain angle. Placing the king pin in a drill chuck with some metal polish, and few seconds of work loosened the suspension up all the way.

Final step:

This final step is important to achieve silk smooth suspension travel. When is done, suspension action will be smoother than anything mini-z has ever seen. It feels so smooth just to cycle the suspension up and down.

Apply polish to both balls on the king pin and on the upper ball. While holding the assembly together, cycle the suspension up and down. Position knuckle in different positions while cycling it. Cycle until it feels smooth. Wash polish off.



The best lubricant for the ball joint is probably Kyosho "King Pin Oil" It is a Fluorine lubricant that does not attract dirt.


The following is a spring chart that compares A-arm suspension springs with similar MR02 low down spring. The color order for A-arm spring is different than regular spring. The purple spring is the stock one that is included in the A-arm suspension kit. The only difference is the kit one is not painted. Notice that the spring for the A-arm suspension is overall stiffer than the standard spring used on MR02. The car tends to handle better with stiffer springs. In case you are wondering, you can easily swap in a MR02 spring to test out what happens with a softer spring. You will need to use a plastic wheel nut as a spacer to make up for the difference in spring length.






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