Rear Brake Master Cylinder

[Elielrosario]

So, I found that the M/C needs to be primed a certain way in order for fluid to pump thru. It seems that I needed to put it together, fill the reservoir with fluid, and then from the top [opposite of the pushrod] pour some fluid, then push down the piece atop the spring to allow fluid to enter the chamber. I did that until it seemed to be completely full. Then the fluid flowed freely.

All parts (all oem caliper piston set, seals and rubbers, m/c rebuild set) came in the mail and were installed this week. I'll be test riding today if it doesn't rain much.

Also, this model m/c doesn't have that tiny return hole everyone talks about.

[Elielrosario]

...worst luck ever: brake still locked up right after the first hard braking. Tomorrow I'm going to feed something thru the brake line to make sure nothing is clogged in there; and replacing the brake fluid with another "type" (I bought this DOT3 high temp stuff but idk if its really any good, I seem to be having more problems since I started using it).

I honestly don't know what else to do here, any suggestions would b awesome.

[hjfisk]

Sounds like you may need to replace the brake line, if it is a 30 year old rubber line, it wouldn't be the first one to start to deteriorate from the inside and cause a blockage.

[Elielrosario]

It's a stainless braided line, that was the first thing I replaced about a year and a half ago

[cowboyup3371]

Did you clean out the return port of the master cylinder when you rebuilt it? If not, that's going to cause your lockup. It's a hole so small you can barely see it but must be cleared out so the fluid returns to the reservoir. You'll want to use a wire strand, about 16 or 18 gauge wire will do you, and push through the hole. If it doesn't, soak the master cylinder in some brake cleaner for a bit and try again. If not, look real close as I had one MC that I needed to have that hole redrilled - it just wasn't there like it should have been. For that, I found a machine shop in town as that hole is smaller than a drill bit you'll find at any store.

I just went back and read another one of your posts where you said it didn't have one. Trust me, it does have one and/or needs it - otherwise, those brakes will continue to lock up on you. Post up a picture of the MC itself please so we can look at it.

[btbarb]

Breather hole pic example

.... Also, this model m/c doesn't have that tiny return hole everyone talks about.

See if this thread with pics will help you find the breather hole: http://www.thegsresources.com/_forum...d.php?t=204796

[Nessism]

Don't forget to remove the pistons from the caliper and clean that out too. You can't do a complete job until you break down both caliper and master, AND replace the brake line.

[Elielrosario]

I found the stupid hole, used a wire strand and cleaned it!

Just test rode around downtown (Orlando) and over to a coffee shop and they seem to be working well.

[Elielrosario]

Don't forget to remove the pistons from the caliper and clean that out too. You can't do a complete job until you break down both caliper and master, AND replace the brake line.

Yeah, I replaced all caliper parts (pistons, seals and everything except the pads), brake line, and all m/c parts too.

Thanks guys, hopefully this continues to work.

[Elielrosario]

No luck, brake still locked up after a longer ride.

[Nessism]

Did you use OEM Suzuki brake system parts? Aftermarket brake system parts are hit or miss sometimes. Other thing that comes to mind is to inspect the master cylinder for pitting in the piston bore. Maybe the piston is hanging up somehow.

[Elielrosario]

Yes, all oem parts.

I did see some light spots of pitting, but seemed to be "within" the walls, not extending out of the cylinder walls.
Do you think this would still cause it to "hang up"?

[Nessism]

Not sure about slight pitting causing the piston to hang up. Something isn't right (obviously). Somehow the return port is blocked.

[Elielrosario]

A couple months ago I bought a m/c off a gsxr-750 (hoping to upgrade from the stock m/c and caliper), but the stock mounting bolts don't fit the newer m/c. From research I've done I've found that from 1978 (or '79) through present the mounting bolts are a bit thinner.
Does anyone have an idea if the m/c's structure would be compromised if these mounting holes would be drilled to fit the stock bolts?