Rebuilding Master Cylinders & Calipers

[sail4free]

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I was leaning towards flushing my system clean and switching to DOT 5 but after reading "The Great DOT Brake Fluid Controversy" in the BRAKES section? Not so much!
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"Both DOT 3-4 and DOT 5 fluids are compatible with most brake system materials except in the case some silicone rubber external components such as caliper piston boots, which are attacked by silicon fluids and greases."
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"Silicone fluids also exhibit a 3 times greater propensity to dissolve air and other gasses which can lead to a "spongy pedal" and reduced braking at high altitudes."
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"The only major user of silicone is the US Army. It has recently asked the SAE about a procedure for converting from silicon back to DOT 3-4. If they ever decide to switch, silicone brake fluid will go the way of leaded gas."
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I see where mineral spirits cause all manner of havoc in brake systems . . . what is the recommended solvent (if any) for cleaning and rebuilding our master cylinders/calipers? My '79 XS1100 Special has been parked since '02 -- think the calipers will need to be rebuilt? Or can I just rebuild both MCs, install the new SS lines and give that a go?
JIM P. ~ BOISE, ID
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[IanDMacDonald]

You could use a simple degreaser, or use brake cleaner.

My take on it is this: $100+ for brake caliper/MC rebuild kits, and it's insurance of braking power for many years to come on your bike. Rebuilding them is super-simple, and you really cannot brake anything doing it. However, make sure you remove the front brake switch properly . . .

[DiverRay]

I rebuilt all the components in my '79 10 years ago, and filled it with DOT5. After parking it for 7 years, it still pushed, and stopped as it should. My MNS has the fronts sticking a little after just 4 years and DOT4. I LIKE the silicone fluid because it is NOT Hydroscopic(sp?). The DOT 5 keeps the internal oxidation down to almost nothing, and that is the biggest problem with the brakes on our bikes. JMHO
But yes, DO rebuild everything, and use brakeclean and brake fluid ONLY for cleaning out the internals of the system.

[phatts27]

I've read that because the dot5 doesn't absorb water, water will collect near the lowest point in the system. The lowest point is usually the calipers. Under heavy braking, the water will boil and your brakes will go bye-bye. That scares me more than a stuck or dragging brake from ol' dirty fluid.

[DiverRay]

I put about 40K miles WITHOUT a problem on the DOT5. I DID do some VERY HEAVY BRAKING without a problem. What people don't seem to understand is IF YOU CLEAN THE SYSTEM WELL and then put in DOT 5, there are no down sides that I've found. IF you have water in the system from NOT flushing and cleaning it properly, ANY brake fluid will have problems.

[sail4free]

You could use a simple degreaser, or use brake cleaner.

My take on it is this: $100+ for brake caliper/MC rebuild kits, and it's insurance of braking power for many years to come on your bike. Rebuilding them is super-simple, and you really cannot brake anything doing it. However, make sure you remove the front brake switch properly . . .

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Is there a step-by-step on the brake switch detail somewhere? I'm assuming this is a switch built into the front MC? I can no longer see the fluid level through the used-to-be clear (kinda') portion of the front MC. Okay to paint these and re-use as-is or should they be replaced? I don't mind popping the cover once in a while to check the fluid level, but then that lets in moisture -- dang it!
JIM P. ~ BOISE, ID
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[sail4free]

I rebuilt all the components in my '79 10 years ago, and filled it with DOT5. After parking it for 7 years, it still pushed, and stopped as it should. My MNS has the fronts sticking a little after just 4 years and DOT4. I LIKE the silicone fluid because it is NOT Hydroscopic(sp?). The DOT 5 keeps the internal oxidation down to almost nothing, and that is the biggest problem with the brakes on our bikes. JMHO
But yes, DO rebuild everything, and use brakeclean and brake fluid ONLY for cleaning out the internals of the system.

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Sounds real good -- guess I'm still undecided. It does sound like if one decides to go with DOT5, there is no going back to DOT4 without compounding problems. I had the rear MC stick in the braking position last time I got the ol' girl running -- don't want to have to deal with that again -- plus it's a good time to replace those 36 year old flex lines.
JIM P. ~ BOISE, ID
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[sail4free]

I've read that because the dot5 doesn't absorb water, water will collect near the lowest point in the system. The lowest point is usually the calipers. Under heavy braking, the water will boil and your brakes will go bye-bye. That scares me more than a stuck or dragging brake from ol' dirty fluid.

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I read that, too, but the resultant steam (if any) should just push fluid back into the MC -- like when you release the brakes. Is there a vent of some sort which equalizes air pressure inside the MC vs. outside? If not, what would keep the brakes from applying on a super-hot day with the black MC cap heating the air under it? If there is a vent, I don't see a problem. If there *isn't* a vent, it seems the worse that could happen is the brake pads dragging (wearing prematurely) or even braking the wheel. Would loosening the bleed fitting and bleeding out a bit of fluid bring any water with it?
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I know that even a single drop of water expands in volume 1,600 times(!) when it changes to steam but -- man -- it seems like that would require some extreme braking over quite a period of time for the liquid contents of a caliper to get that hot, no?
JIM P. ~ BOISE, ID
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[DiverRay]

The "splooge" hole in the MC is the return for the fluid. It allows some to go back in, and would be the place the "steam" would escape. I don't think you can get these calipers that hot without REALLY trying.

[crazy steve]

... I don't think you can get these calipers that hot without REALLY trying.

I've got a rear caliper in the scrap pile that's partially melted, so you can get them pretty hot....

[oakback]

Kinda on topic I guess:

I just rebuilt my front calipers tonight. The rebuild kits each came with a split metal ring. Am I supposed to use this for anything?

[MPittma100]

Split Metal Ring.

These rings go on the outside diameter of the rubber boots to secure them.