Hope Mini M4 Overhaul

This is a guide for a complete overhaul of a Hope Mini disc brake. Included in the guide are directions for removing and replacing the seals in both the caliper and the lever, ‘refreshing’ brake pads and bleeding the system. The instructions for bleeding the Mini (and M4) are copied directly from Hope’s manual, though my own notes are added in italics. Manuals and schematic diagrams for all Hope products can be downloaded from www.hopetech.com.

Through experience I’ve found that reusing rubber seals can sometimes be problematic, so, to be on the safe side, it’s worth having a set of new seals ready. Seal kits are available from suppliers of Hope brakes. This guide assumes that you will be using a full new seal kit.

Hydraulic fluid is an irritant. Always wear safety glass when working with hydraulic fluid. If you do get any in your eyes, rinse immediately with water and seek medical advice.

Hydraulic fluid will damage or remove paint. Isopropyl Alcohol is excellent for wiping away hydraulic fluid. I usually use clean tissues to wipe up spills then go over it again with a tissue and a few drops of alcohol.

I’ll start with the seal change. Although it’s not 100% necessary, at least for the lever, it’ll make your job much easier if you disconnect the lever and caliper from the brake hose. I drained the system when I did this procedure, but you should be able to retain the fluid from the hose if you wish. First of all, remove the wheel and brake pads. If you have a work stand; no problem, otherwise you’ll need to ‘jack the bike up. As you can see in the pictures, I just rest the chain stays on a small toolbox. The pads can be removed by unscrewing the pad retaining bolt that runs through the caliper. This may have a metal ‘R’ clip on the other end; just slide it off. Slide the pads and spring out of the caliper and put them somewhere where they won’t get contaminated.

It’s worth having a small container handy to drop all the components into as you remove them. I usually drip a little alcohol onto each part as I remove it with a view to cleaning/drying thoroughly before refitting.

Full schematic diagrams for all Hope calipers and levers can be found at www.hopetech.com.

These are the torque settings that Hope advises for the Mini caliper;

  • Hose Connector 8Nm
  • M6 Bolts 8Nm
  • M5 Bolts 4Nm

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To drain the system, first attach a length of pipe to the caliper bleed nipple (2). I send mine into a hole pierced in the top of a jam jar, but you can just drop the end into a pot/jar. At the lever, remove the top-cap and diaphragm from the reservoir (3/4).

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Using an 8mm spanner, loosen the bleed nipple a half turn (5) and allow the fluid to drain before removing the pipe.

Place a cloth/tissue to catch any spills and use an 8mm spanner/socket to remove the hose bolt assembly (6). Holding on to the hose to remove any tension will make it easier to remove this bolt, and also reduces the likelihood of damaging the threads. Wrap the hose end in tissue and tie it up. It is not necessary to remove the connector unless you’re shortening/replacing the brake hose. I’ve only done it here for the purposes of illustration. Picture (9) shows the assembly; two copper washers, hose connector and bolt and the brass olive. Leave the bleed nipple in place as you’ll need it for getting the pistons out. Remove the caliper from the frame, making sure you collect any washers/shims that are used for centring the caliper/rotor. Make a note of how many/which came from which bolt.

Remove the two bolts (5mm allen) that hold the caliper halves together (10). It is possible that these bolts will be very tight, so you may need to hold the caliper with a cloth, or even bolt it back onto the frame to allow you the necessary leverage.

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Split the caliper into its two halves (11) and remove the small rubber ‘o’ ring from its recess. NB. All the other seals in the Mini caliper are Hope only. The small ‘o’ ring, however, can be found in the plumbing section in most large hardware stores.

To remove the pistons from the caliper I use an old bleed nipple, a length of 5mm pipe and my tyre pump (12). A track pump works best for this. The pipe makes the job a little easier and also stops the pump from being contaminated with DOT fluid, as it will cause the rubber to perish. Note the plumber’s PTFE tape on the nipple.

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Screw the bleed nipple into the caliper half, attach the pipe/pump and back the nipple off a half turn. Place a cloth over the piston (important!!) and your thumb over the fluid hole (where the ‘o’ ring was) and compress the pump. You may have to pump it a few times, but the piston should eventually pop (literally!) out of the caliper body. The cloth should catch the piston and any fluid that is ejected from the caliper. Transfer the pipe assembly to the other caliper half and repeat the process.

You’ll now have two halves and two pistons (make a note of which piston came out of which half). Depending on how long the brake has been in use the pistons may have a rim of dirt (13). This should only be removed with a cloth/tissue. Resist the urge to use glass-paper as the piston is a precisely machined component. Use alcohol if the dirt is particularly stubborn.

The rubber seals in the caliper (14) can be carefully removed with a small point or jewellers screwdriver (15). Do take care not to scratch the caliper surface/piston bore.

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(16/17) Clean both halves of the caliper down using alcohol and prepare the new seals. Dip your finger or a cotton bud into some DOT fluid and run it around the recess’ for the seals. Also apply a thin layer onto the whole of each seal. Carefully push the each of the seals into their recess’, making sure they are properly seated. Apply a thin layer of DOT to each piston and push it slowly into its piston bore (18). Rub a thin layer of DOT to the ‘o’ ring and its recess’ and drop it in. Note that one half of the caliper has a deeper recess for the ‘o’ ring.

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Thouroughly clean the facing surfaces of each caliper with acohol (19), ensuring there is absolutely no dirt or grit which may prevent the two halves mating up cleanly.

Push both pistons fully into the bores and bolt the two halves back together. Don’t screw one bolt in then switch to the other; thread one in a little and then do the same with the other so that compression is similar on each. When the caliper halves are fully torqued together the pistons will need to be pushed fully into their bores in preparation for bleeding the brake. I use a block of pine wood that I filed to the correct thickness (20). The distance between the two halves of the Mini caliper is 11.5mm.

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Continue to part 2 to read how to overhaul the M4 Lever

SteveUK
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