Topic: Brake master rebuild

[beemerbum]

After exhausting my extensive vocabulary of dirty words, I finally got the F'n little snap ring out of the '71 master cylinder. When the piston, spring, etc. were removed, there was what I expected, crystallized brake fluid residue. What is a good liquid to soak the cylinder to clean it out before the new parts go in?

[70CB750]

Brake Kleener or Xylol will do.

[mystic_1]

Get down in there with a brush or something too, crap likes to hide in the corners.

mystic_1

[madmtnmotors]

Get down in there with a brush or something too, crap likes to hide in the corners.

mystic_1

+1

I like to use an appropriately sized brass bottle brush for the bore, and then a dental pick for the snap ring groove.

[Flyin900]

Make sure you clean the very tiny return hole in the master cylinder body. Very easy to miss if you aren't familiar with the two fluid holes in the master cylinder. If that remains plugged the brakes will either seize on the caliper or drag.

If you have the plastic fluid reservoir it should be removed and the O ring cleaned up. I have found soaking the whole master in very hot water for 15 minutes and then using a rubber strap oil filter device used for removing car oil filters works really well.
The strap is adjustable down to a small size if the strap tool itself is one of the smaller ones. It won't damage the plastic reservoir and will allow you the start to get some purchase on twisting it loose.

I usually hold the master in a vise in a cloth to enable me to get a good twist on the part.

[beemerbum]

I'm glad you mentioned the two tiny holes. One of them is now clear and a probe inserted into the hole shows up in the bore, The other little hole next to it appears plugged. When I push on the obstruction from the reservoir, it seems like there is a tiny ball in it that springs back as if it has a spring under it, sort of like a pressure relief device. Am I imagining things? Maybe better whiskey is in order.

[mystic_1]

They're both just plain holes, no check valves, but one of them is tiny in comparison to the other.

Try going in there with a single strand of copper wire pulled from a piece of scrap wire.

mystic_1

[robvangulik]

I'm glad you mentioned the two tiny holes. One of them is now clear and a probe inserted into the hole shows up in the bore, The other little hole next to it appears plugged. When I push on the obstruction from the reservoir, it seems like there is a tiny ball in it that springs back as if it has a spring under it, sort of like a pressure relief device. Am I imagining things? Maybe better whiskey is in order.

I recommend Bushmills Black Bush, smooth but still cleans the sinusses.
And no tiny balls in the master cylinder, I use sewing needles to push those holes open, they are thin enough, available in many, also very small, sizes, and more sturdy than copper wire.

[madmtnmotors]

one of them is tiny in comparison to the other.

Very, very tiny...

[krusty]

Steel #1 or top E guitar string is perfect for the job of clearing that little hole. Copper wire is too soft.

[BobbyR]

OK, all of the above as far as cleaning out the holes at the bottom of the MC is great. The dried brake fluid simply quickly dissolves in denatured alcohol. Soaking is not required.