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Rebuiding brake master. Is it difficult?

Guest Anonymous

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........it's possible, easy with proper tools,

but not practicle given availablility of new part.

There is a reason it needs rebuilding - RUST, corrosion,

fluid contamination.

Buy New please.

I know this a CLUTCH cylinder - but it's the same sheit


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........it's possible, easy with proper tools,

but not practicle given availablility of new part. There is a reason it needs rebuilding - RUST, corrosion, fluid contamination.

You gave three reasons for rebuilding. There is a fourth: The rubber seals are worn or defective. Maybe this is not typical, but it can happen without rust, corrosion fluid contamination.

I had one that was new in the box that wouldn't retain pressure. Pulled it apart and one of the seals was obviously deformed. Put new seal on and everything has been fine.

The difficulty of rebuilding is the bore size, inspecting the bore and, if necessary prepping the bore. There are tools, although their cost may exceed the cost of a new part. On the other hand there is the convenience and comfort provided when you can fix things as needed.

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Rebuilding isn't hard--most kits come with pretty comprehensive instructions on what goes where. The main difficulty with a rebuild is to insure the cylinder bore is absolutely unpitted. Even a small rust pit will abrade the rubber cups/seals and cause internal leakage in short order (ask me how I learned this!)

To see if you have a rebuild candidate, pull the M/C, remove the innards (lay 'em out in order so you can see how they go back) and clean out the bore with denatured alcohol. Then run your fingernail up and down the bore--begin with the area that's at 6 o'clock when the cylinder is installed. That's where the moisture will collect and begin the rust pitting. You'll feel the pits with your fingernails. If your nails are too short, use a thin piece of copper or aluminum wire with a short crook formed into the end. Drag it up and down the bore and feel for it catching.

If the bore is nice and smooth, use a brake hone (buy at an auto parts store for $5-10 or so, hook it to an electric drill and smooth/deglaze the bore. This will work if you feel very slight pitting too. Once you've finished honing, to the fingernail/thin wire test again. If it's nice and smooth (no catching) you can clean the bore thoroughly with alcohol, lube the new parts with brake fluid and reassemble.

If you still have rough spots in the bore, buy a new M/C. However, I'd keep the old one for the day they're no longer available; then you can send it out to be sleeved in brass or stainless steel and rebored to standard size. This is a common procedure for antique cars with NLA M/Cs and wheel cylinders.



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I rebuilt my calipers and it was a pretty easy deal for the most part. If I were to do it over again, I would have just ordered rebuilt calipers. The experience was good to gain, but in the end, the amount of time it took me to clean up my calipers, and rebuild them, wasn't exactly worth it to me. Considering the cost of these items is pretty low, I should have just ordered rebuilt units.


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Calipers are a different beast than the masters and the clutch slave.

In the caliper, the piston is the part that the seal slides on, and it's

chromed. So it seldom rusts.

The bore is just a guide for the piston, so minor pitting won't affect sealing at


I carry rebuild kits for all the cylinders when I race, since they take up so

little room, and in an emergency, the kit will get me through a weekend.

However, whenever one starts leaking, I buy a new cylinder.


"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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