See Updated information on the late-2013 to early-2014 dynamics cart friction issue for a description of the issue that may require wheel replacement.

First we provide instructions for field replacement of Vernier dynamics cart axles (aka wheels) for standard and plunger carts. Encoder cart instructions are found after these instructions.

To replace an axle, perform the following steps. Use the 3/32 inch allen wrench included with your cart. You may want to also use a small flat-bladed screwdriver.

1. (plunger carts on plunger end only) Release the plunger so the spring is not under tension.
2. Use the 3/32 inch allen wrench to remove all four black screws from the cart end cap.
3. Pull the end cap off the cart. If there is a plunger, remove it with the end cap. Pull the plunger out of the center spring channel, leaving the spring in the channel. Keep the plunger and end cap together.
4. Push down on the axle with your thumb to take tension off of the two silver pins that keep the axle in place.
5. Remove the pins, keeping pressure on the axle. You may need to pry the pins out with a small screwdriver.
6. Gently release pressure on the axle so that the springs remain in place.
7. Remove and discard the bad axle assembly.
8. Insert the new axle assembly.
9. Push down on the axle and replace the two silver pins.
10. (plunger carts only) Insert the plunger into the center spring channel, through the middle of the coil spring.
11. Place the end cap on the end of the cart.
12. Secure the plastic end cap by tightening the two outside screws.
13. Replace the teardrop parts if you removed them, and tighten the two inner screws that hold the teardrop parts in place.

Test the axle to see that neither wheel rubs against the green cart frame. If one does, center the wheels in the frame by centering the axle. Retest.

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Carts with the additional Motion Encoder circuit board require a few additional steps to swap out the wheels. You will still need the 3/32 inch allen wrench included with your cart, as well as a small Philips screwdriver. You may also want to use a small flat-bladed screwdriver.

1. (plunger carts on plunger end only) Release the plunger so the spring is not under tension.
2. Use the 3/32 inch allen wrench to remove all four black screws from the cart end cap that does not have the power switch.
3. Pull the end cap off the cart. If there is a plunger, remove it with the end cap. Pull the plunger out of the center spring channel, leaving the spring in the channel. Keep the plunger and end cap together.
4. Use the 3/32 inch allen wrench to remove both black screws from the cart end cap that has the Motion Encoder Cart power switch.
5. Pull the end cap off the cart.
6. Push down on the axle with your thumb to take tension off of the two silver pins that keep the axle in place. Do not put any pressure on the circuit board or its components.
7. Remove the pins, keeping pressure on the axle. You may need to pry the pins out with a small screwdriver.
8. Gently release pressure on the axle so that the springs remain in place.
9. Remove and discard the bad axle assembly. Do not replace this axle assembly yet.
10. Loosen, but do not remove, the four Philips-head screws at the sides of the encoder baseplate. Do not adjust the pair of screws near the label.
11. Slide the encoder baseplate about 4 cm toward the power switch end.
12. Push down on the axle with your thumb to take tension off of the two silver pins that keep the axle in place.
13. Remove the pins, keeping pressure on the axle. You may need to pry the pins out with a small screwdriver.
14. Gently release pressure on the axle so that the springs remain in place.
15. Remove and discard the second bad axle assembly.
16. Insert the new axle assembly.
17. Push down on the axle and replace the two silver pins.
18. (plunger carts only) Insert the plunger into the center spring channel, through the middle of the coil spring.
19. Place the end cap on the end of the cart.
20. Secure the plastic end cap by tightening the two outside screws.
21. Replace the teardrop parts if you removed them, and tighten the two inner screws that hold the teardrop parts in place.
22. Slide the encoder baseplate back into its original position. Gently tighten the four screws.
23. Now insert the other new axle assembly at the power switch end.
24. Push down on the axle and replace the two silver pins.
25. Replace the end cap, taking care to put no pressure on the circuit board, switch, or LED.
26. Replace the two black hex screws.

Test the axle to see that neither wheel rubs against the green cart frame. If one does, center the wheels in the frame by centering the axle. Retest.

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