I pulled the rear tire off my bike and a little silver clip fell out of the rear brake caliper. where does it go?

Hello Dale, this is an easy job on your bike. Use a flat head screw driver and remove the brake pad cover...it will pop off.
Remove the hairpin type clips off of the ends of the brake pad pins.... Use pliers & pull the brake pad pins out from the front of the rear brake caliper....Clean the rear brake caliper's piston with brake cleaner. Use a rag and wipe it clean...Reinsert the old brake pads into the caliper. Place a pry bar between the brake pads, then push the inner piston into the caliper body, this will allow room to install new pads.... Remove the old brake pads...Coat the brake pad pins and the new brake pads metal back plates with high-temperature grease.

Slip the new brake pads into the rear brake caliper, then push the brake pad pins halfway into the caliper. Slip the spring clips into place between the brake pads and the brake pad pins. Push the brake pad pins completely through the rear brake caliper. Push the hairpin clips back into the brake pad pin tips. Snap the brake pad cover onto the top of the rear brake caliper....

Pump the rear brake pedal until the pedal feels firm, indicating that the brake pads have closed around the brake rotor...No bleeding will be needed because the system was never opened - That's all there is to it...i hope this information is helpful & good luck with your bike.

Just follow this instructions:

1 Unbolt the brake caliper from the front fork or rear swingarm, using a socket wrench. Use a 14-mm hex socket to unscrew the front caliper bolts, and a 6-mm Allen socket for the rear caliper.
2 Slide the caliper off the brake rotor. Suspend the caliper from the handlebars or frame, if needed, using a bungee cord.
3 Pull the hair clip pin out of the brake pad's retaining pin on the outside face of the caliper using a pair of needle-nose pliers. Push the retaining pin out of the back of the caliper with your finger.
4 Pull the brake pads and their spring clip out of the caliper. Retain the spring clip, and discard the brake pads.
5 Reinstall the brake calipers, following the reverse method of removal.

I hope this will help you. thanks

Put the bike up on the main stand. Remove the rear brake caliper assy. Loosen the rear axle and pull it out. Now pull out on the wheel, pull it away from the rear gear housing, the wheel will disengage a gear inside and then it is ready to pull out the back.

No, there are no special tools required beyond everyday hand tools.

Raise the vehicle.
Remove the rear wheel and tire assembly from the vehicle If the vehicle is equipped with rear drum brakes, remove any retainer clips from the wheel mounting studs, then pull the brake drum off the hub and bearing.
If the vehicle is equipped with rear disc brakes perform the following:
Remove the two guide pin bolts securing the front disc brake caliper to the steering knuckle.
Remove the disc brake caliper from the knuckle and brake rotor.
Hang the caliper out of the way using a wire hanger or cord. Do not support the caliper by letting it hang by the hydraulic hose.
Remove any retainer clips from the wheel mounting studs, then pull the brake rotor off the hub and bearing.
Remove the dust cap from the hub and bearing assembly
Remove the retaining nut, then the hub and bearing from the knuckle's spindle

To remove front tire. Raise the bike off the ground so that the front tire is just barely on the ground. Remove the large nut on the axle and loosen the two bolts on the axle clamp on the other side of the wheel. Drive the axle out. Now, roll the front tire out from under the front fender being watchful of any spacers and speedo drives that are with the front wheel. Remember which side any spacer go and mark them. Reassembly is virtually the reverse except that you may have to use a screwdriver to spread the front brake pads. Make sure you get the speedometer drive tang in the hole on the front disc if you have a mechanical speedo drive.

To change the rear brake pads, remove the two bolts that hold the rear caliper onto the caliper support bracket. Carefully lift the caliper off the bracket. Notice how the rear pads and the anti-rattle clips are positoned on the caliper support bracket. Replace old parts with new parts.

You'll need to depress the brake piston back into the caliper in order to get the caliper back on over the new pads. Use a large C-clamp or pair of slip joint pliers to depress piston back into the caliper. Use a rag or something to prevent damaging the paint on your caliper. Reinstall the caliper down over the new pads being careful not to disturb them. Replace the two bolts and torque them to 25 foot pounds. Pump the brakes back up to a full pedal by pumping the rear brake pedal up and down slowly. Check for proper operation of the brakes. Failure to properly service the brakes can cause serious injury or death.

Remove the two bolts that hold the rear brake caliper into the rear brake caliper support bracket. Lift off caliper. Notice how the pads and anti-vibration clips are positioned in the rear brake caliper support bracket. Install new pads and anti-rattle clips or springs.

Now, using a large C-clamp or a large pair of slip joint pliers, depress piston all the way back into the caliper. Carefully reposition the caliper back on the rear brake caliper support bracket without disturbing the pads or clips. Install the two bolts and torque to 25 foot pounds of torque. Slowly depress and release the rear brake pedal until a good firm pedal is obtained. Check the brakes for proper operation prior to riding the bike. Failure to properly service the brakes can cause sever injury or death.

Pull the rear axle, and spacer on the brake side of wheel. Un hook brake rod and brake strut. Position yourself on the brake side of the bike and pull the rear wheel straight out of the final drive housing. Put a little grease on thhe final drive splines upon reinstalling the wheel to aid removal next time.

If the clip has a slot in it then it fits in the caliper where the ends of the pads fit.
If not & it has a sprung tab then it fits in the caliper where the top of the pads fit

Hope this helps.
(If it does then please mark this as 'useful')
Ride Safe
Bike-Doc

I don't know what a "Thumpstar 120 Pro" is but you're right on about what the little silver wierd shaped clip things are. They're anti-rattle clips and the do hold the brake pads in the caliper bracket while you replace the caliper. You are putting the brake pads in the caliper bracket instead of trying to put them in the caliper, aren't you? Put the pads in the bracket and then carefully slide the caliper down over the pads without disturbing them. Make sure your pads are installed correctly.

Always test the brakes before attempting to ride the bike. Improper installation of the pads could cause brake failure that could cause serious injury or death. Make sure they're right before you ride.