Rear master cylinder rebuild

[dan filipi]

I found out by surprise yesterday my rear master cylinder seals are bad when I went to hit it and there was nothing there!
Time for a rebuild but before I try a wrench on this chewed up fitting by a PO any tricks to getting it loose without completely destroying it with a vise grip?

I've done brake work on old crappy cars and those fittings have been my worst nightmare.

 

[scdmarx]

Hope I'm not too late.

With a good quality line wrench- not the one from the $1 discount table near the checkout at the hardware store.
Soak the nut with a good penetrate. Soak both the threads and the tube.
Put the line wrench over the nut, and try it in the tightening direction first. I don't know why, but sometimes that will crack it loose.
If you have the room and it feels right, smack the wrench with a hammer while applying pressure.
If the corners are rounding, put the line wrench over the nut, then use a hammer and flat tip punch to expand the nut into the wrench. These nuts are usually kinda soft.
I don't like this, but as a last resort before final destruction, use heat from a propane torch.
Patience!

May the force be with you.

 

[bk2valve]

I totally concur with my esteemed colleagues....
I use Kroil...as the penetrating oil....nothing I have found works better....

<https://www.kanolabs.com/>

Brian in NM

 

[dan filipi]

Not too late, been chatting with chas and procrastinating.

I don't got's a good line wrench but I'll let it soak anyways and procrastinate some more on it lol

 

[bk2valve]

Not the best solution but i have made them in a pinch out of the appropriate sized wrench....
Brian

 

[cmonSTART]

Line wrenches belong to that family of tools which you don't use often, but man are they great to have once in a while.

 

[scdmarx]

I don't got's a good line wrench but I'll let it soak anyways and procrastinate some more on it lol

Ayup. I'm bet'n neither did the po. Think about that. popcorn
One wrench size will probably fit all the brake line nuts on your bike. :salute:

 

[AApple]

If ya got a spare, deep, 6-point socket the size you need, and a Dremmel or cut-off tool, you can cut a slot down one side of the socket just wide enough, and deep enough for the line to fit into, and use that. Beats having to go to Sears, or Crap-On to get a wrench, if ya don't want to. Then again, the wrench might be easier. In an emergency, cutting a socket has worked before.
Just throwin that out there... :wave:

 

[bk2valve]

Aren't you thinking about a O2 sensor type socket Aapple? I have made them out of a box end wrench by cutting out the size of the line...
Brian

 

[mcgovern61]

I don't got's a good line wrench but I'll let it soak anyways and procrastinate some more on it lol

Ayup. I'm bet'n neither did the po. Think about that. popcorn
One wrench size will probably fit all the brake line nuts on your bike. :salute:

I am unfamiliar with a line wrench? Any descriptions or pics?

 

[dan filipi]

These are what I'm familiar with.

 

[mcgovern61]

Gotcha! Around here they are called "open box-wrenches"

 

[dan filipi]

Well I found my side cutters, That nut is soo chewed up I'm going to replace the line anyhow but thanks for the suggestions because the other end of this line is going to be a real treat to get off. Looks like I might drop the exhaust to get in there. Might have to pull the tire but I'm trying to avoid that.

A couple questions,
1. The rubber hose is real soft/deteriorated so it's getting replaced. Can I use the good quality (= expensive) fuel injector hose?
2. When rebuilding I know to clean with brake fluid but what about the barrel the piston travels in?
Should that be polished somehow?

 

[dan filipi]

Good idea chas, for once a fiberous material getting wound up in my drill bit will be on purpose lol.

 

[AApple]

A safer method would be to use a coat hanger. Cut the straight part to about 8"-9", then put a 180* bend on one end. Then stick the steel wool(emery cloth would work too...that's what I use) into the bent end, and flatten it a bit more, to hold the wool(or paper) tight. Then spin that down the hole of the cylinder, working it up/down all the time. That should clean it out fairly well.
They DO make hones for that, ya know? Don't know if you could find one that small, but I have a couple of dingleberry trees that are about 3/4" diameter, and they will go into a much smaller hole....
Just throwing that out there, too... :mrgreen:

I mention other methods because the thought of running a drill bit down a master cylinder bore would scare the heck out of me. With my luck the drill bit would gouge the hell out of the cylinder wall, and I'd be stuck buying another :crying: cylinder...

What size bore does this thing have, anyway? I gotta tear mine down sometime soon, and rebuild it... :builder:


and before ya even ax...this is a dingleberry tree... :smilie_happy:

 

[dan filipi]

and before ya even ax...this is a dingleberry tree... :smilie_happy:

THAT was going to be my next question

 

[scdmarx]

AApple's brake hone is the best thing to clean up the cylinder for anything brake cleaner and a shop rag on a wood dowel won't clean. Look for rust pitting where the piston seal rests. This is where the new seal will leak. Usually most of the pitting from corrosion will take place at the wheel cylinder/caliper because that's where all the extreeme hot and cold cycles are, but this part looks like it might have been there for awhile.
That hose from the reservoir has no pressure applied to it. But I don't know how fuel hose will react with alky based DOT4. You might ask at the parts store if they have a special hose for that and if so, buy a foot of it. It might be ok, I don't know. I don't remember having done that before. Me personally, I think I'd at least check with the bike shop and see what's available.

 

[scdmarx]

Another thing, I can't tell from the picture, but if it's aluminum you don't want to hone it. If for some reason it can't clean up then it's junk. If a magnet will stick to it then you're ok to hone it.

 

[dan filipi]

Okay, thanks guys.
I'll probably get it torn open tomorrow then I'll know.

 

[bk2valve]

Hi Dan...if it is aluminum and I believe it is....I think I would use some of the green scotchbrite on a dowel to clean it up inside. If it is pitted, I think it is shot....scotchbrite is safe on most things....
Brian