Master cylinder mod-opinions needed

[Guest]

I am rebuilding a front master cylinder from a 1980 750L model. I have to rebuild it due to the small pressure relief hole being blocked. Brakes are locking up. A new reservoir is needed as the old one is brittle and can't be removed without damage.

I have noticed that the relief hole in the mc body is covered by the bottom of the reservoir. Being able to see it without disassembly would be handy for inspection and cleaning.

Is there a problem with drilling the bottom of the reservoir to expose the pressure relief hole? Will this cause the fluid to jet up into the reservoir, or any other problems?

The wisdom of this forum solves all problems...

[Steve]

Personally, I would NOT drill anything in or near a master cylinder.

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[salty_monk]

I believe it's covered for a couple of reasons....

1. is that it will jet up as you put it when you're bleeding if you're rough with the lever

2. is that it's supposed to provide some protection to gunk I think.

I can't see any real reason why you couldn't drill the bottom of the reservoir to expose it as long as you are within the confines of the seal (which if I remember this MC you are).

[almarconi]

I am rebuilding a front master cylinder from a 1980 750L model. I have to rebuild it due to the small pressure relief hole being blocked. Brakes are locking up. A new reservoir is needed as the old one is brittle and can't be removed without damage.

I have noticed that the relief hole in the mc body is covered by the bottom of the reservoir. Being able to see it without disassembly would be handy for inspection and cleaning.

Is there a problem with drilling the bottom of the reservoir to expose the pressure relief hole? Will this cause the fluid to jet up into the reservoir, or any other problems?

Its good that you are asking the question, because you clearly do not know what you are doing. I don't mean that in a bad way so please don't take it personally. There is absolutely NO REASON to even contemplate what you are thinking about doing. You do not need to drill any holes in the master cylinder.

The reservoir on the 1980 750L is made of plastic and is held on with two screws. A new reservoir costs less than $15. Remove these screws and take the reservoir off. Under the reservoir you will find the pressure relief hole. Before attempting to clean the MC, remove the piston and cup assembly. Rinse the MC in clean brake fluid. Inspect the bore for pitting and/or rust. If you need to clean the bore, use a copper or aluminum bore brush and some solvent to clean it. In order to clean out the relief hole, take a single metal bristle from a brush and use it to clean out the hole. Use clean brake fluid and reassemble the components. Use a new O-ring on the reservoir.

Since your life depends on your brakes working correctly, make sure to either become knowledgeable on their operation or have someone inspect your brakes before putting the bike on the road. I'm not trying to be mean but modding a brake system and not knowing what you are doing could be deadly.

[MAC10]

Thank you for the information. I don't take it personally- I value the straight talk here!

I am asking because I know I don't know much, except within narrow limits. I haven't made any changes, and won't now. Safer to replace the reservoir and o ring than mess with something built that way for a reason.

The mc is in good shape. I have a new rebuild kit from suzuki, and a new reservoir, o ring, diaprham and plate on order. I wil take my time, and have a mechanic I can consult if I need to.