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.
These are the torque settings that Hope advises for the Mini caliper;
Hose Connector 8Nm
M6 Bolts 8Nm
M5 Bolts 4Nm
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).
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.
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.
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.
(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.
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.
The Mini/Mono/M4 Lever
Most of the fluid will have drained away long ago, but it's worth stuffing a little tissue into the lever reservoir. Use a 10mm spanner to loosen the hose bolt (21) then remove the two bar clamp bolts from the lever. When the lever is free from the handlebar, unscrew it all the way from hose (24). Wrap a lttle tissue around the joint to catch the dribbles (22). Note the copper washer (23).
Use an 8mm spanner/socket and a 3mm allen key to remove the lever pivot bolt/nut (25), and a 2mm allen to remove the lever piston pin (26). NB Turn CLOCKWISE to remove the pin from the brass barrel (27).
The piston seal is held in place with a retaining clip. This can be carefully prised out with a small jewellers screwdriver (28) or use the circlip pliers.
The piston assembly is sprung, and held in place with a brass washer and a circlip (29). You will need a set of circlip pliers to remove/replace this circlip (30).
With the circlip removed the pin and washer can be pulled out (31)(remember it's under a small spring load).
Use a soft/round tipped tool to poke the piston assembly through and out of the lever body. Do not use a screwdriver. A 3mm ball-end allen key is ideal (32)
Picture (33) shows the full lever assembly. Take note when you remove the piston which way the two piston seals sit. I they are fitted the wrong way around they will not function.
Clean all parts with alcohol. Prior to refitting the piston, pour a little DOT fluid into the piston barrel and run a thin layer around both piston seals. Insert the piston/spring into the barrel and carefully push it all the way in (34).
Insert the piston pin and brass washer. Whilst compressing the piston, use the circlip pliers to refit the circlip over the brass washer (35). This is a bit fiddly, and may take a few attampts to get it all straight, so take your time.
The piston seal and clip can now be replaced and the lever refitted.
Refitting the lever to the hose is the opposite of removal. Remember to fit the copper washer.
Once the hose is reconnected and tightened up, the lever can be refitted to the handlebars.
You're now ready to refill the system with DOT fluid…
Bleeding the Mini and M4 disc brake
Wear safety glasses
1. Remove the wheel and brake pads to prevent contamination
2. Push the caliper pistons back into their bores and insert a spacer between the pistons to prevent them coming out during the bleed operation. (spacer is 11.5mm, pic.20)
3. If necessary reposition the brake lever so that the lever and master cylinder is horizontal to the ground.
4. Remove the master cylinder cap using a 2mm allen key (2.5mm on the newer, flat-top bolts). Then remove the rubber diaphragm.
5. Place the closed end of an 8mm spanner over the bleed nipple on the brake caliper. Fit a length of clear plastic hose (approximately 30cm) onto the bleed nipple and place the free end into an empty container. The hose should be a snug fit and not fall off, the free end does not need to be submerged under brake fluid.
6. Fill the master cylinder reservoir with brake fluid.
7. Open the bleed nipple a ¼ turn. Slowly pull the brake lever to the handle bars and hold. Close the bleed nipple. Release the lever. Caution, squeezing the lever too fast will cause brake fluid to squirt out of the master cylinder.
8. Repeat step 8 until no air is seen coming out of the bleed nipple. You will need to keep filling the reservoir during this operation. Caution, if bleeding a rear brake be careful not to spill brake fluid onto the front caliper and disc.
9. Ensure the pistons are fully retracted in the caliper, the pistons may require manually pressing back.
10. Place a rag around the master cylinder to catch any spillage and fill the master cylinder to just below the top surface (36).
11. Place the diaphragm into the master cylinder and allow the fluid to overflow (37). Close the bleed nipple and remove the bleed hose. Caution, do not over tighten the bleed nipple. Wipe away any spilt fluid from the caliper and lever.
12. Fit the master cylinder cap and gently tighten with a 2mm allen key (2.5mm on the newer, flat-top bolts). Caution, do not over tighten cap as you are only sealing the rubber diaphragm (38) (At this point you may want to refresh your pads. Trace a figure 8 on a piece of 100ish sandpaper until the pad surface is evenly cleaned/deglazed (39)
13. Replace the pads (40) and insert the wheel. Pull the lever several times to allow the pads to reset themselves to the disc.
14. Check the brake for correct function and that there are no system leaks.
Here's what Hope have to say about bedding your pads in;
" To achieve the maximum braking effort the new brake pads need bedding in. Bed in the
pads by riding a short distance with the brake applied, it also helps to pour clean water over the
caliper and pads whilst bedding in. This procedure will achieve good braking performance but will reach its full potential after a few rides."
Head outside with a bottle or pint glass of fresh, clean tap water. Get up a head of steam and brake hard. Pour water liberally over the caliper. Pedal off again, this time with the brake applied lightly. As you pedal you're going to feel the pads bedding in to the rotor. Keep going, pulling the brake gradually harder as you have to pedal harder. Do this for 20-30m and then pour water of the caliper again. Repeat a mix of hard stops, water; brake/pedal, water until your brakes are hpow you like them. I can get two Hope Minis bedded in in under 10mins using this method. They'll improve further after a little trail time, but at least you'll have decent braking to begin with.
Rotor can be 'roughed up' in a similar way, though you should use a less abrasive paper, something like P320. Work across the rotor's braking surface, not around it, and make sure you clean it with alcohol when you're done.
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Thread: Hope Mini Disc Brake Overhaul