Rear master cylinder rebuild

[Guest]

One of the things that I can do on my project during the winter is rebuilding my rear brake master cylinder. It is all there, but the seals seem to be shot. I have not even taken it off the bike yet. I did a bit of searching and looked at Basscliff's site, but found nothing on rebuilding the rear master cylinder. Any help out there?

Thanks,

[allojohn]

One of the things that I can do on my project during the winter is rebuilding my rear brake master cylinder. It is all there, but the seals seem to be shot. I have not even taken it off the bike yet. I did a bit of searching and looked at Basscliff's site, but found nothing on rebuilding the rear master cylinder. Any help out there?

Thanks,

It's pretty simple. Take it off the bike and tear it down. Clean everything and replace the rubbers with OEM, if you can get them. Push a strand of wire through the tiny breather hole in the main body - it almost certainly has crud in it. It's easily missed and the unit will not work properly if it's not clean.
Have confidence, you can do this easily.

Take digital photos as you go, makes it easy to remember how it goes back together!

[cowboyup3371]

Do a search on here and you'll find tons of threads about it. But basically Allojohn has it right.

Make sure you bleed everything properly.

[Nessism]

Inspect the aluminum master bore for pitting. If corrosion has set in, the master can not be rebuilt.

[7981GS]

If you don't have a two stone wheel cylinder hone, you can roll various grits of sandpaper up and hone it with that.

Daniel

[snyderman]

Thanks for the info, I will have to see how bad it is when I tear into it!

[Nessism]

I wouldn't bother to hone an aluminum GS master. Honing is good to clean up cast iron automotive master cylinders, but not aluminum masters. The GS master cylinder bore is highly polished from new and any abrasives you put inside only degrade the surface finish and reduce seal life.

[7981GS]

Pessimism and "I have never done that" or "had any success with that myself", strikes again!


It works and I have been doing it for over 35 years.


Daniel

[Nessism]

Pessimism and "I have never done that" or "had any success with that myself", strikes again!


It works and I have been doing it for over 35 years.


Daniel

The stock finish is something like Ra<8. This is a very smooth finish - equal to polishing with something like 600 grit sandpaper.

Putting a grinding hone inside an aluminum master cylinder bore will degrade this finish significantly and should be avoided. A rough finish will wear the rubber plunger pieces.

The only reason to hone a master cylinder is if there is contamination on the surface of the metal. When a aluminum GS master cylinder corrodes the damage goes down into the metal forming a pit. Sanding over the top of the pit does no good.

I don't care if someone has been doing something wrong for 35 years without consequence. Doing something wrong is doing something wrong.

[7981GS]

Sorry to hear that some people just can't repair much of anything.
Just buy new OEM parts and be happy.
After all, nothing works on these bikes but OEM, right? LMAO!!!

Daniel

[hampshirehog]

There are 1000s of good rear MCs out there and they're cheaper than buying the bloody sandpaper!

[Nessism]

Thanks for reminding me Daniel...

Original Suzuki brake system seals (master cylinder kits/seals, caliper seals/pistons) are WAY better quality than commonly available K&L parts. In many cases the OE parts are cheaper as well. Two times I wasted considerable time farting around with brake system problems only to eventually trace the issue to crappy K&L parts. Consider this an official warning.

[rustybronco]

To the OP, lets see what the factory has to say about the matter...

using a piece of wood or soft metal, push the internals out of the cylinder bore, taking care not to nick or scratch the bore wall

and the service limits as stated in the GS1000 service manual...

bore standard 14.0mm (.551 in) service limit 14.05mm (.553 in)

you can take that for what its worth.

to 7981GS, yes I have sanded 'many' a master cylinder/ wheel cylinder bore over the years. did I have 100% success at it? no. would I try sanding the bore on my own bike? sure, and I have. would I recommend else to polish out anything more than a 'light' pitting on there own equipment? no.

[hampshirehog]

Original Suzuki brake system seals (master cylinder kits/seals, caliper seals/pistons) are WAY better quality than commonly available K&L parts. In many cases the OE parts are cheaper as well.

99% accurate. You can get better, stainless steel pistons (well we can anyway ). Non OEM rubber isn't - it's jelly. It's junk.

[1_v8_merc]

I've Used K&L on all my bikes...Never had any of these "problems".....
You guys make it sound like the brakes will fail at 1,000 miles!

My advice to the OP...install what you can afford.
You want Good brakes...switch to stainless steel lines...THAT'S well worth the money!


I have the same bike as you, the Rear Master Cylinder is the EASY one, lol.
I think I have photos of the Tear-down for this bike.