Front Master Cylinder Problem

[pamcopete]

Thanks for the info and pic. I hope you didn't get down on your back!

Is the 1/4" the nominal inside diameter when the clamp is all the way closed?

Yes....there is some "squeeze" factor there because it is rubber, but the 1/4" grips the line nicely.

 

[Travis]

Are those lines covered in a clear plastic like most braided brake lines you see for motorcycles?

 

[Pandorasglocks]

Travis: Yes they are covered in plastic.

Ok so I got all my new parts all set up and I am now in the process of bleeding the lines. I'm about 3 hours in and I have a question. When I unscrew the bleeder, should the system be sucking back air/fluid? Does that indicate a faulty MC or can I just keep pumping the lever and eventually get a good pull?

 

[gentlemanjim]

Pump the lever with the bleeder screw closed. Attach a hose to the bleeder screw and insert in a bottle with the end covered with brake fluid. Sqeeze the lever to the handle bar while opening the bleeder screw. Close bleeder screw and pump lever repeat the process until no air bubbles appear and clear fluid is coming out of the hose. Be sure to keep an eye on the MC resevoir and not let it get low enough to draw air.

 

[Pandorasglocks]

Holy God I finally got my brakes rock solid today . Thanks for all the help guys!

 

[emzdogz]

hehh, I see this is an old-ish thread, but I am really REALLY needing this info. Bled in my rear brake 1st and that was easy as pie, especially with Mity Vac. I mean it was like instantaneously sucking fluid through.
But the front one is being really difficult.
I am using a brand new from MC from Mike's. Seems I can get nothing whatsoever to flow out of the MC by pulling the lever. And the Mity Vac pressure is way up, like 50 steady lbs with bleeder screw open (i think it's a speed bleeder screw) and there's just nothing doing.

I almost feel like this round clear plastic piece on the bottom surface of the res. is supposed to be removed? It's hard to see it well, even with my glasses. I get a little air bubble in there when the res is filled and I pump.

Anyway, this is being difficult too, because the bike is up on a riser and so the MC is like up over my head and I have to stand on a milk crate. Thinking I should get the bike down before doing this.

Question: can I take the whole deal, MC, brake line and caliper (with a piece of wood stuck between pads) OFF the bike to bleed it in?

thx!

 

[gentlemanjim]

Every time you pull thelever and release it fluid is drawn back to the MC. Remove the brake line at the MC. Put your thumb over the discharge port. and squeezed the lever until you feel pressure on your finger. Reinstall the brake line and open the bleed valve and squeeze close the bleed valve and pump up some pressure continue until the air is all removed. I struugled even with a vacuum pump until I learned the thumb over the hole trick.

 

[XSLeo]

Yes, sometimes bleeding the M/C is required as a separate step. Putting a finger tip over the hole works well, as the pressure builds it pushes your finger tip out of the way just enough to let the air out. Then as you release the lever your finger tip seals the hole so fluid has to be drawn out of the reservoir. Do this til fluid sprays out around your finger tip.
Now hook up the line. It should bleed out better now.

 

[emzdogz]

Got it! not sure what did the trick, but eventually I think enough dribbled south and filled the space in the caliper. Even with Mity Vac. I cracked both banjos a couple of times, tried the finger over the hole thing - not sure if it helped. Maybe. If it did, the result wasn't instantaneous. Oddly, the very last thing I did before I finally got some fluid flowing, was to unscrew Speed Bleeder like almost all the way out, and then put it back in. After that I began to see a hint of fluid coming out and then after a couple dozen more pumps of the lever, voila, here comes vaguely brownish but clear stuff out. After that I just pumped a bunch more through til it was clean and no bubbles. Fairly firm lever. I need to get my bike down off the table it sits on, to see how the brakes actually work.
thanks!
(this thread should help lots of people, I would think.)

 

[XSLeo]

I've never used the speed bleeders. From what I know of them they have a spring loaded ball that the pressure pushes open to let air and fluid out, then immediately closes to prevent air returning.
I have found that setting still the lever feels much different than when used in motion.
Leo

 

[emzdogz]

It makes me wonder if the Speed Bleeder's mechanism (spring loaded ball) wasn't all gummed up.

 

[gggGary]

It makes me wonder if the Speed Bleeder's mechanism (spring loaded ball) wasn't all gummed up.

wus thinkin' the zack same thing great minds and all....

 

[jservant]

Does anyone know of any good diagrams for rebuilding the brake master cylinder, how to put it together, piston and seals?

 

[petew41133]

This is a common issue. I just did an 80 with the same issues. there are two ports in the master cylinder the bid one in the middle and a VERY small one at the hose end it is under the tab from the plastic reservoir extension. I just used a utility knife and trimmed the tab out of the way so I could get a fine wire (sharpened on a wet stone) into the port to open it. Here is a little trick, you can see the little air bubble in the port. you can use a wire to coax it out, Repeat till you have enough fluid to start the master pumping. There is just as much crap inside the the master cylinder as everywhere else. I got mine clean as I could and got new fluid pumping, kept flushing and the brakes are solid hard now. To get the last bit of air out. with the bike on the side stand and the MC cover bolted back in place turn the bars full left and wait an hour or two, hit the lever once or twice and the last air will bubble back up into the reservoir.

Have to say this;
AFAIK
Once you have used brake parts cleaner the master cylinder HAS to be disassembled and all rubber parts replaced Brake parts cleaner is NOT compatible with the rubber seals they will swell and become useless. That said I tend to spray a little through the hoses to flush them out then flush them with air and fresh fluid before installing. The rebuild kits are kinda pricey, a new master is pretty tempting.

Thanks to gggGary, got pointed in the right direction-- than figured out more. Learned some valuable tricks in salvaging a really badly clogged master cylinder, and front brake lines on my 1981 XS w/ 5K miles that sat for 25 years. After picking out the "gel o" out of the master cylinder, I found out a great way to fix the issue where you think you've break parts cleaned everything an still won't prime/build pressure. I disconnected the hose from the cylinder, (after removing the snap ring and the piston and spraying all down w/ brake cleaner). Put the master back cylinder together except the hose side and cover. Then I used a siphon pump like the red one they sell at discount auto/autozone or pep boys,and pumped the air OUT into the hose side of the cylinder (a bike pump might work too). This unclogged the little port/hole gggGary mentions. I used a piece of wire to unclog the bigger hold in the bottom of the reservoir. Cleaned everything really well. Then... assume the two brake lines are both clogged too (they were for me). Unclog each connecting directly to the master cylinder (first add Dot3, check with your finger and squeeze the level a few times to make sure cylinder works). Connect each hose firmly and pump until it unclogs-- should get pressure real quick then wala-- if it won't, reverse the direction. That will take care of both hoses. Assembled, bled and now works like new.

 

[XSLeo]

If your lines are that plugged up you should replace them. The rubber rots from the inside out.
Most of the XS650 brake lines have a plastic collar on them. This collar has the build date of the line on it. If more than six years old replace them. The braided stainless lines work best.
Leo