First unscrew and remove the chassis from the body. Then remove both of the rear tyres. Hold the slot car up so you have a good view of the rear rims and axle. Rotate the axle at a steady rate and look for any irregularities.
Grab each rim, gently try and rotate each rim in opposite directions. This will pick any loose rims on the axle, if you find a loose rim, it will need to be glued. Also check the rims for defects, especially for cracks in their hubs. ( This also can be fixed with a Brass or Plastic sleeve over the hub to prevent the crack from opening again).
Now Check how well the bearings are seated in their holders, by gently moving the axle up and down and side to side. It’s no big deal if they move a little, in most cases they can be effectively glued with Super Glue. Check for any slop between the axle and bearings. Some of the slot car manufacturers have oversized bearings; these may need to be addressed to achieve a tighter fitting bearing. If this is the case, then place a small amount of Super glue between the bushes and axle ( one at a time!! ). It is now vital that you put the rear tyres on a flat surface and move the car back and forth for a few minutes before the glue dries. Not doing this could see the glue drying and the axle locked. If this happens then NEVER try and put the car on the track or power supply as you will more often than not burn out the motor from the added strain. After a short while the wheels will become nice and free again Now without any slop, Just add a little oil to the bushes and your away and running.
You can now use a Craft Knife to remove any excess glue form the axle. The best and easiest method is put the car under power while holding the tip of the knife on the axle.
If you find High and Low spots on the rims, then they will need to be sanded flat. This can be done using a tyre truer or buy putting power to the car and placing it on a wooden block with sandpaper. This is the best way to achieve a nice and true rim. Vibrations should disappear once the rims is round and true. Now that the rims are true, It's time to place your Tyres back over the rims and start the sanding process all over again! After a little while you should notice no more Hopping.
Now testing your slot car you will need to accelerate down a long flat straight, looking for any hopping at the rear end. If you find that your slot car is still bouncing around, then the tyres are not sanded properly! Also you should note when cornering to check if the car slides well and the tyres are not grabbing. To eliminate this you will have to round of the outer edge of each tyre by using some sandpaper.
You will need a setup board for this, (Or find an old DVD cover and cut a slot in it). Now the main aim is to check the ride height of the guide and front wheels (tyres). The easiest way to get the most of the guide into the slot is to sand down the tyres to the right diameter. Although on some cars, this can result in a lot of sanding. Another method is to place a copper sleeve over the axle and to a set to a determined height.
If your going to sand the tyres down, you will need to do this at a slow speed.
If you find that your guide is to loose, Then apply some glue to the edge of the Guide hole and wait until dry. Now find a drill bit with the correct size you need and hand twist the guide hole to remove the unwanted glue. Replace the guide and add a little oil.
There are some slot car brands such as Ninco that have the Angle Winder setup. In these cases you need to brace the motor and back-end in order to prevent the crown gear moving away from the pinion when chassis twists under acceleration. Piano wire or a metal coat hanger are probably your best options. Simply bend the wire into a shape that runs from the top of rear axle mounts and across the front of the motor. Then carefully glue in place, being careful not to get any excess glue on the axle or in the bearings.
To get rid of that dreaded Noise, you will need some abrasive Toothpaste or some king of fine cutting compound. Just smear some paste onto the gear, and run the car slowly, for about 5 to 10 minutes while still applying the paste to gears. When you hear the gears starting to mesh without the noise, clean the paste from the gears, and then apply oil onto the gears.
What we like to do is to leave the car bodies loose on the chassis. To do this lightly sand or scrape with a hobby knife the outer areas of the body, where chassis touch. Also lightly sand the outer chassis to where they meet the body. Now find a drill bit that is one size larger than the original hole ( usually 3mm ) in the chassis where you removed the screws from and hand drill the holes to make them larger. This will allow for the screws to not bite onto the edge of the chassis hole. This setup can improve handling greatly.
There is not much we do here, except to add a little oil to both ends where the shaft extrude from the can. Also add a little Super glue to the engine mountings to stop the engine from shifting from side to side under acceleration.
The braid should always be kept clean. Get yourself some WD40 and a clean rag. Now spray the WD40 onto the rag and wipe the braids clean. As you will see that by doing this your car will achieve a much better contact.
We do not use any adhesives or WD40 to clean tyres. If you require to clean you tyres just use a little spit or water on a rag with your finger tips and rub tyres in both directions.
Always try and keep all of your broken wings and mirrors that you have lost while racing, so they can be re-glued for your next racing event. This way all cars will look like they should. ( not only this , but your cars will be worth more when selling in the future ).
All listings above are suggestions only. There may be other tuning and better methods available.