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Master cylinder bypass port

1

1948man

Forum Sage
Past Site Supporter
I've been reading old threads because something is amiss with my brakes. They are dragging. The fluid is not the prettiest. Exactly where do you find the master cylinder bypass hole. Is it in the bottom of the brake fluid resorvior? How would you clear it?
Also, I have my 1100GL buckhorn bars rotated so the hand grips are more parallel to the ground rather than angled down. This tilts the resorvior at angle. Could this be any problem? I just damn sure can't spell resorvior. Thnx Jim M
 
I just cleaned out mine, which just consisted of running as much brake fluid thru the entire system continuously bleeding them until the fluid came out clean. Simple and cheap, but i don't know how effective if there's a real problem. But looking into the resevoir, the bypass is the smaller of the two holes and is relatively easy to clog. I didn't have to clean mine, but starting wiht clean fluid might be a start.

Or else drain and clean the whole resevoir, which is probably better, but i'm easy and learned that if it aint broke don't go fixing it, because something probably will be broke by the time I'm finished.

Just as a guess, I would poke a copper wire thru the hole. I think they are straight to the cylinder, so as long as you don't lose an end of the wire (or whatever) in the cylinder you'll be fine.

But I'm sure someone will pipe up to correct me if i'm wrong, moreso than to give you this simple information.
 
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Thanks Rob. I'm going to try to drain and refill tomorrow but I think maybe the cylinder is hung up.
 
There are two ports at the bottom of the reservoir. One about ?2.5 mm, the other maybe ?1 mm. Mine needed a sustained assault with a chunk of wire and some brake cleaner before I could get the wire though the port.

This is worth verifying with a wire, because if it blocks the return path entirely, overheating brakes can cause water in the old fluid to expand, causing the front brakes to lock until they cool again. A total rebuild wouldn't be a bad idea at all.

The angle of the reservoir is probably OK as long as the level of the fluid can never fall below the intake port. I think you have the square reservoir, so I'm not sure what angle might be safe, since I've never been into one of those.
 
Thanks Dog. Both the holes are covered with fluid. It is nice to hear that probing with wire won't hurt anything. I'd be lost without all the help here.
 
Everyone else that has replied are right. You need to unblock the smaller of the two holes. But my guess is you can't see the holes because of the dirty fluid. Am I correct. You may have to empty the reservoir of fluid to do the job right. When I did mine I used a steel wire from a wire brush. Just pull it out of the brush with a pair of pliers.
 
Sounds like it's time disassemble & clean/rebuild your MC & front calipers...

You don't want to fool around with your brakes, they come in pretty handy when you need 'em.

I've had very good luck with just taking all the bits apart & giving them a good cleaning, then reassemble with new DOT 4 fluid. Of course, replacing the lines with SS ones is best.

Good luck
 
Get a can of spray brake cleaner, remove the master cyl, empty it, Clean the resivoir. As said you might need a small piece of wire to clean the return port. Blead it at the master first then at the calapers
 
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