Over the last few months I’ve bought, refurbished and sold a few sets of Tokico 6 pot callipers. So I’ve decided to offer a refurbishment service for them and see how things go. I’ve detailed the process I use as a guide if anyone wants do it for themselves or I’m happy to do the work for £65 inc return postage (normally charged at an extra £6.50 for the P&P)
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What you’ll need to do the job.
Time
5 to 6hrs minimum depending on the condition of the callipers.
Tools
Precision screwdriver,
Torque wrench,
Allen key socket set (that fit the torque wrench)
Spanner set
Socket set & wrench
Bit of clear fuel pipe to bleed brakes back up
A large syringe is helpful but not a necessity
Container to catch brake fluid
Pliers / sliders
Toothbrush
Air compressor (an in car one will do just as well)
Latex workshop gloves (It’s a messy job)
Wire brush
Consumables
500ml Dot 4 Brake fluid
Rubber grease (IT MUST BE RUBBER GREASE)
Copper grease
Brake cleaner spray
Plenty of rags
Pack of cotton buds (Steal them from the missus if needs be)
A new set of dust seals depending on the level of refurb? The inner piston seals are usually good enough to put back in.
The first thing to do (with the callipers still mounted to the forks) is remove the dust shields from the callipers and remove the brake pads and pin. Then pump the brake to force the pistons out against the brake disc. It’s the fastest way to force out seized pistons. Keep an eye on the fluid level as the pistons are forced out it will need topped up.
Now using the correct Allen key socket, slacken the 4 calliper bolts, (It’s much easier to do while attached to the forks than on a work bench) Not all the way out, just enough to brake the seal that will have formed on them with the oxidisation. Repeat process for both sides.
Next, slacken the banjo bolts and let the brake lines drain into a container. Make sure not to loose the banjo bolt washers. Don’t throw the old brake fluid away yet. Remove the callipers from the forks.
Once removed, the refurb begins.
Remove the 4 Allen bolts on each calliper and split them. Take care not to loose the 4 small seals when splitting them (2 seals in each calliper). Depending on how badly seized the pistons are, will depend on how much work is needed to remove them. Sometimes they will come out in your hand, sometimes I’ve had to use pliers / sliders. If you need to do this, use electrical tape to tape around the teeth a few times so as not to damage the pistons. I also use a rag between the piston and tool. Hold the calliper half and use the pliers / sliders to grip the piston and rotate it in the calliper whilst pulling at the same time. It can take a while, but the piston will eventually rotate and you’ll be able to draw it out of the calliper. Repeat the process for the other pistons.
My tip for removing the pistons if you have to use pliers / sliders is try and grip as little of the piston as possible, that way if your unlucky enough to mark a piston, the mark should be in front of the main seal in the calliper. When they are rebuilt it should not cause any leaks. I use a set of sliders that I have ground off the teeth to help minimise the chance of marking a piston, but it can still happen.
**Note, on some 6 pots, there are 2 different sizes of pistons, 2 large & one small in each side**
Once all the pistons are removed, use the precision screwdriver to pick out the dust seals and piston seas, taking care not to damage them. The dust seals are usually the cause of the problem. Moisture eventually gets in behind them and causes they alloy to oxidise behind the seal and jam the piston.
Once the seals are out, you’ll see the oxidisation in the seal grooves. That needs to be cleaned. Use the precision screwdriver to scrape it out. It takes a bit of digging to get them clean.
At this stage I’ll decide weather the outer dust seals need replacing or not? Unless they are stretched or badly perished, I tend to clean them and put them back in and accept I’ll need to strip the callipers again in 12 / 18 months time. (I removed the dust seals altogether from my track bike) I clean the seals with the old brake fluid and a rag.
After all the grooves are cleaned, use some brake cleaner spray and a toothbrush to give them a final clean. Use an air compressor (an in-car one will do the job) to blow out all the oxidised residue from the calliper halves. If you don’t have one, then a big deep breath and blow them clean. Eye protection is recommended. Then whatever is left, clean with plenty of cotton buds.
Once the grooves are clean, pack the grooves with rubber grease.
This will help prevent the oxidisation from reforming. It won’t cure it, but should give you the longest life from them before you need to strip and refurb again. Now put the piston seals in first, then the dust seals. Make sure the dust seals are seated in the groove correctly. I carefully run the screwdriver blade around the seal to make sure. Wipe the excess grease that is forced out of the grooves with a rag.
Now clean all the pistons with a rag and brake cleaner.
Once they are all cleaned, dip a finger into the old brake fluid and coat the piston chamber and seals in the calliper halves, then dip the piston into the fluid and coat them before refitting to the piston chambers. This will help them slip past the seals with ease.
I clean the threads of the Allen bolts with a wire brush, and also remove the bleed nipples and clean the threads on them as well. Dip the thread in the old brake fluid before refitting to the calliper. It helps prevent splitting the bleed nipple thread on the calliper when bleeding the brakes if the nipples move freely.
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Now refit the small calliper half seals, again coating the seals in the old brake fluid. Make sure the seals are seated correctly before joining the calliper halves. Screw the halves together, but don’t over tighten. The torque spec is 21Nm or 16Ftlb (according to Haynes manual) for the 4 bolts in each side. Again, I run the bolts in untill they are tight, and do the final torque tighten when they are refitted to the forks.
Use the brake cleaner spray and tooth brush to clean the callipers before refitting.
Refit the callipers to the forks, and tighten the bolts to the specified torque. Make sure the calliper half bolts are tightened correctly to the specified torque.
Connect the brake lines, making sure the 2 banjo bolt washers are fitted correctly to each banjo bolt (One on either side of the brake line). Tighten to specified torque, Fill the brake reservoir with dot 4 fluid. Refit the brake pads and pins.
There are various ways to bleed the brakes. The standard way is to attach the fuel pipe to the bleed nipple. Use an old small water bottle, cut a hole in the lid and feed the pipe through. Pour enough of the old brake fluid into the water bottle to submerge the pipe end in the fluid. Open the bleed nipple, pull brake lever, Don’t let go of the lever, close the bleed nipple, let go of brake lever, open nipple, pull lever, repeat process on both sides until the fluid runs clear and no air is left in the system and you have brake pressure at the lever. Keep an eye on the fluid level in the reservoir, as you bleed the brakes, the level will drop. If it drops bellow the hole, your back to square one.
Brake bleeding tips.
I bleed the brakes with the lever span setting set at it’s closest to the bar. This is where a large syringe comes in handy instead of the water bottle. Attach the syringe to the pipe on the bleed nipple. Open the nipple and draw the syringe, Once the syringe is drawn out to it’s maximum, Close the nipple, detach the syringe, push plunger back in, re-attach the siring to the pipe, open bleed nipple and repeat process until fluid runs clear with no air bubbles.
Refit the dust shields.
Job done.
.I want another cycle before I start spending big money on the bike, but the R1 monoblocks are on the wishlist at some stage (Brembo's being out of the equation on cost)
