removing caliper piston, GS650?

[snowbeard]

I want to rebuild, or at least look at, the internals of the front calipers for my '81 650, parts 1, 2, and 3 on the schem

so how does one remove the piston gently so as not to scuff the seals? can it be done? does it just pull right out? should I bother if they retract and didn't leak?





my older ones are gunked badly enough that I can't get a new set of pads in there...

due to Andrew's unfortunate destruction of his bike I now have an extra set to get in shape before I install them.

[Cyg]

the preferred method is too use an air compressor, but be warned it does shot it out at a high velocity. Use a lare c vise grip too start it too depress. The using your air, too shoot it back out. Eventually this works the piston free. I use a towel too shoot it into. Now remember this, nine times out of ten, you will destroy your dust boot. So make sure you have a new one too put on. Brakes are a messy business.

[Nessism]

Yup, air.

Corrosion is very common on these parts it's fairly likely the piston and seal will be junk but ortunately, they are not too expensive to replace. Good luck.

[retrex]

Piston removal

Snowbeard, the easiest and least damaging way to remove a piston is to pump it out of the bore. Just remove the filler cap on the resevoir and refill as you pump the piston to the end of its bore. Once the piston makes it past the primary seal it is an easy finger only removal. Keep a rag or small plastic container handy to catch the fluid as is pores out of the caliper when you remove the loose piston. Using this method does no damage to the piston or the seals. I have used this method on single and dual piston brakes and never damaged anything. If your rubber is in good condition you can reuse it after a cleaning in denatured alcohol, if you are using DOT 3 fluid that is. I would recomend that you diassemble the caliper at this time and give is a good washing inside and out with the DA. If there is a lot of dried brake fluid on the caliper you can use Xylene to remove it, test your caliper paint first for fastness. Upon reassembly lightly lube the rubber and piston with brake fluid and you should be good to go. Good luck and post your results.

[koolaid_kid]

If you encounter any rust, you can lightly sand it away using 400 wetrdry sandpaper with the brake fluid as your lubricant.

[Nessism]

If you encounter any rust, you can lightly sand it away using 400 wetrdry sandpaper with the brake fluid as your lubricant.

You should not attempt to sand down the piston to remove corossion or you will create surface discontunities which will lead to leaks.

[snowbeard]

cool, I'll try that soon as I get the rest of the system in line! at least I know I have a few to work with for now, and having to get the new seals won't take me off the road at least...

Thanks, I'll report how it goes!

[koolaid_kid]

You should not attempt to sand down the piston to remove corossion or you will create surface discontunities which will lead to leaks.

I am afraid that I cannot agree with this observation. The piston itself does not provide any seal. It is there to push against the back of the brake pad and push it into the rotor. The piston seal (#2) provides the sealing action for the piston.

[Nessism]

I am afraid that I cannot agree with this observation. The piston itself does not provide any seal. It is there to push against the back of the brake pad and push it into the rotor. The piston seal (#2) provides the sealing action for the piston.

The rubber caliper seal is held in a groove in the caliper bore and the piston pushes through the center of said seal. So basically, the outside surface of the piston IS the critical surface in the entire system. Pitts/scratches in the piston will provide a fluid leak path as soon as the pitt is positioned over the seal. Some times these leaks do not show up right away because the piston is pushed onto a different postion away from the seal. As soon as the pads wear though, the pitt in the piston will move over the seal and the caliper will start to leak.

Frankly, I learned this the hard way myself. Took apart the caliper on my 450 and replaced only the seal dispite pitts in the piston. In my case the caliper started to leak right away, which was fortunate actually. Ordered the right rebuild kit, including piston, and the caliper worked like new - which it basically is since the piston was new.

[koolaid_kid]

I agree that pits in the piston will cause problems. Pits in the caliper will also cause problems. However, what I am suggesting is removing the build up on the piston. The goal should be to polish the piston and inside of the caliper, not scratch it. That is why I suggest "lightly" sanding, removing the buildup, not the metal.
I have been using this procedure on both drum and disc brakes for many, many years, despite the protests of the parts suppliers, who always want to sell me replacement calipers and cylinders.
In the end, the rider must feel comfortable that the repair he (or she) implemented will hold up to the task.