Rear brake caliper strip-down

The SELOC wiki's "How to Rebuild a Brembo Caliper" is the standard procedure for a rear VX220, Speedster or Lotus Elise S2 caliper. This guide adds what one owner found when he stripped, powder-coated and rebuilt a pair: what to do about the grub screw, how to pop the piston off its rod, and how to get the circlip out. His own pictures are the best part of it. They're in his photo album (see Sources), which is worth opening alongside this page.

How the mechanism works

The rear caliper has a handbrake mechanism inside the piston. Pulling the lever turns a plate with four ball bearings, which grips a threaded rod and pushes the piston out. Releasing the lever lets the plate let go, and the external spring winds it back. An internal spring pulls the rod back in, held by a circlip. A threaded ring inside the piston turns a little each time the piston pulls in, which adjusts the piston's resting position along the rod.

The grub screw stops the threaded rod rotating with the plate, so the rod only slides. It sits in a notch in the rod.

Before you start: the grub screw

• Soak it for at least 24 hours. Fill the boss it sits in with rust-penetrating fluid and leave it. Stripping this screw is the thing to avoid.
• Look at the thread in the boss. If it's damaged, gently run a tap over it first so the screw can come out through it.
• It needs a 4.5 mm hex key. Most people only have 4 mm and 5 mm keys. Don't use a ball-head key: it will round off the screw.
• Don't use heat. The ball bearings are held in the clutch plate by a thin plastic part in that area, and heat will damage it.

If it won't move, the options are:

• Cut the boss down and drill the screw out, or use your preferred screw-extraction method.
• Carry on with some of the strip-down with the screw still in, and free it from inside the caliper later.
• Have a replacement made from a standard M10 × 1.0 flat-point grub screw. The dimensions are in the SELOC instructions.

If it does move, don't take it out completely yet.

Strip-down

1. Strip the outside. Remove everything from the outside of the caliper (the bleed nipples, sliders and rubber sleeves) and bag the parts you might reuse. Keep the handbrake lever and the external spring. Leave the grub screw in.
2. Wind the piston out. Pump the handbrake lever, or use a piston winder, until the piston stands about 2–3 cm proud of the inside face of the caliper. Peel back the boot to expose the shoulder at the top of the piston.
3. Pop the piston off the rod. The piston is held on the threaded rod by a C-clip. Hold the caliper in a vice from the back. Stand the 17 mm and 18 mm sockets on either side of the piston, and use two large flat screwdrivers as levers over the sockets. The sockets should be about as tall as the length of piston you wound out, so the screwdrivers don't slip. Lay a rag over the piston to catch it. Push down gently: you'll feel a springy resistance from the internal spring, then you'll clearly hear and feel the piston pop off the rod. Take care of your hands, and don't scratch the piston.
4. Remove the dust boot, and the grub screw if it's free by now. Bag the screw so it doesn't get lost.
5. Release the threaded rod circlip. The internal spring is kept compressed by a circlip in a groove deep inside the bore. The circlip has tiny tabs. Move the washers on the rod out of the way to see them. Slide a medium flat screwdriver between the bore wall and the tabs, starting near the two ends of the "C", and rotate it gently. Work round the other tabs. Pushing the end of the threaded rod over to the side like a joystick, away from the open end of the circlip, helps it pop out of its groove. Once it's out, the whole rod assembly pulls out easily. Don't try to remove the tiny screw at the end of the rod, even though the SELOC instructions suggest it. The author advises against it.
6. If the grub screw is still stuck, apply more penetrating fluid from the inside. Cold didn't work for the author.
7. Remove the clutch plate. With the grub screw out, the handbrake clutch plate pushes inwards with very little force. It comes out in up to three parts: the plate with the ball bearings, a ring of needle bearings, and a flat washer, which is sometimes stuck inside. Also remove the piston seal and the tiny O-ring that seals the clutch plate.
8. Clean everything with brake cleaner, and have the caliper reworked if you want it refinished. The author had his powder-coated.

Tips from the thread

• Matching the ramps on reassembly. The ramps on the end of the threaded rod and on the handbrake plate don't match each other. Turn the handbrake arm shaft the way you would to apply the handbrake: the two ramped parts should push apart. For that to happen the ramps sit opposite each other.
• Pushing the piston back in. One owner found a cheap brake-pad wind-back tool works better than a G-clamp or a press. The pins on the caliper are only about 20 mm apart, so many tools are too wide. He ground down the edges of the pins on his, and another owner bought a tool with several fittings.
• Mixed-up sides. If you have mixed them up, the ramp test above helps you work out which parts pair up. Better to avoid it by working on one caliper at a time.