Réfection du freinage avant

( Tutorial réalisé par Marc )

caliper rebuild, master cylinder rebuild and pad replacement.

I went for a ride with a group of friends and after some fun, my front brake refused to work anymore.
Rotor and pads were smoking bad and disk turned blue. I stopped and waited for a while. It worked again but something was not fine with it.

I decided to inspect the caliper closely and found that dust seals were cooked. It was time for a rebuild.
Start by removing the bolt that secures the hose to the fender.
Remove both bolts securing the caliper to the fork.
See the image: hand is pressing support towards pistons, so that brake pads are released.
Pad is released.

It's quite difficult to figure out how this works.
Lots of photos for the newbies to make the pad replacement an easy work.

Ooops! Dust seal is out of its groove.

Bigger piston's dust seal is damaged too. (can't see it in the photo).

Advice: Clean piston surface before pressing them into the caliper when doing the pad replacement work, otherwise they will pull dust seals out of its place.

It's time to fix this.


You will need to pull both pistons out of the caliper to see seals and dust seals condition. 

They are difficult to remove: press the brake lever and you will note the pistons move out. If one of the pistons is not moving, hold the moving one into the caliper to force the stuck one it to move.

Press the lever till both pistons are not far to get out of the caliper. Pull one of them and a lof of brake oil will spill out of the caliper. Be carful: it is toxic and will ruin your skin and painted parts of the bike. You'd better wear rubber gloves.

Disassemble everything.

Seals and some rubber from the dust seals are still into the caliper in this figure.

See how to remove them.

Use a piece of wood to remove seals.

Use a piece of wood too to wipe out any dust/rubber in the grooves of the caliper. It's a difficult work, but *must* be done.

Do not use a metal screwdriver or you will damage caliper body and you'll need a replacement. (expensive)

All parts were washed with diesel and then with soapy water.

Then I waited some hours till they were completely dry and 
began the assembly work.

Reassembly is easy: seals and dust seals are *very* easy to
insert in the grooves.
Lubricate the pistons with fresh brake oil before inserting into the caliper body. They will slip in very easy.

Remove master cylinder from the bike.
Remove master cylinder lever and the rubber boot (dust seal) that keeps master cylinder clean. You will find a circlip that will need to be removed with a special tool .

See the photo.

Piston will come out of the master cylinder body. Inspect seals for damage. If less than *perfect* replace the whole piston+seals. (they are not sold separately).

My local Suzuki dealer told me that master cylinder is not a part prone to failure. They do not wear out easily, but seals might be damaged by wrong brake oil (mixture of different oils). 

Wash parts (I used soapy water and wait it for a complete dry)

Lube piston rubber rings before installing them into the master cylinder body. Use fresh brake oil to lube them.

WARNING: brake oil is toxic and will ruin your skin. Use rubber gloves to manipulate parts in contact with it.

Master Cylinder just assembled again. I did not replace any parts, just the rubber boot. I lubed everything.

It's a good idea to replace top cover gasket.

In this operation, I installed a steel braided hose and a brand new rotor (NISSIN).

OK, reinstall everything on the bike and it's time to bleed the circuit.

Get a rubber hose, plug it to the caliper and to a can with brake oil.

Drop oil into the reservoir.

Press the lever to push some oil into the hose.

It will take some time (and a lot of pushing on the lever) to fill the caliper. You will need to refill the reservoir a lot of times.

The trick for a good bleeding job is:
  • keep some oil in the rubber tube that's plugged to the caliper: this will prevent air from entering again to the caliper, only oil will get in.
  • keep some oil in the rubber tube that's plugged to the caliper: this will help to see air coming out of the caliper (bubbles: see photo).
  • you might want to screw the caliper cap when releasing the master cylinder lever, and opening again the cap when pressing the master cylinder lever: this will help to prevent the caliper from sucking oil/air remaining in the rubber tube: it will only suck fresh oil from the reservoir.
Install brake pads.

These in the photo are a couple of NISSIN syntherized pads.

Work done.

It might be necessary to continue bleeding after installing the caliper on the disk rotor. Front brake system in the Suzuki GS500 is quite difficult to bleed: take your time.

Be careful with next things when doing the job:

  • again: brake oil is toxic and will hurt your skin. use rubber gloves.
  • be careful when bleeding: keep brake oil from reaching disk surface and/or pads.
  • It is known that brake oil can damage painted parts, even rims. Use a ruber tube to drive it to a can.
  • Replace oil every 2 years of whenever it gets dark. 
  • brake oil will eat mist from air and degrade: do not leave oil brake can cap open. Work quickly when having the master cylinder top cover open. Degraded oil will be darker.
  • Do not mix differend brand oils. NEVER mix different grade oils. Use DOT#4 oil.