Front Master Cylinder Problem

[Pandorasglocks]

Bike: 79 XS650, single front disk brake. All stock.

So today I finally decided to stop putting it off and flush my front brakes (owned the bike for 3 years now). No surprise the fluid looks like red deck stain. Once I got most of the old fluid out of the bleed screw I added some fresh DOT3 with the intention of flushing it all out as well. BUT the new fluid would not pass through the master cylinder. So I proceeded to pull and clean all of the banjo bolts and hoses with brake parts cleaner. More red liquid but everything was moving through fine. I then had the master cylinder with no lines attached to it, pumped the brakes a bunch of times and nothing. So I removed the assembly from the handle bars and dumped out the reservoir, a bunch of sand and dirt came out I then sprayed the shit out of it with brake parts cleaner, even stuck the tube into the bottom of the reservoir and nothing would come out the other side, regardless of the lever being pulled or not. Filled the res again and still nothing.

I've rebuilt the rear caliper and flushed it's lines before but I've never touched either master cylinder. Is it worth trying to rebuild something like this or should I just replace the whole assembly?

Thanks!

 

[gentlemanjim]

I found them hard to get primed - used a vacuum pump to help draw the fluid. Either a rebuild kit or new MC is for sure a better option, but the kit is much cheaper.

 

[gggGary]

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.

 

[Pandorasglocks]

Ok thanks for the suggestions, I also blew some brake parts cleaner through the last line and through the caliper out the bleed screw, followed by some compressed air. Does that line contact the rubber caliper piston seal ??

 

[XSLeo]

Yes, anything that goes in where the line hooks will contact the piston seal.
The cleaner wont hurt things, Just flush the system well to be sure the cleaner is gone.
I have often had trouble bleeding M/C's. I start with a full reservoir. hold a finger tip over the banjo bolt hole. Now as I slowly pump the lever, the air will push past my finger tip on the pull stroke. My finger tip now seals the hole for the return stroke. Keep pumping until fluid comes out without air.
I then quickly hook the line on. I then move down to the next line joint and do the same at each joint along the line untill I get to the caliper. Then I bleed the caliper.

 

[gggGary]

Also the next day; bleed the caliper a little bit more there will usually be a bubble or two there also. While doing all the vigorous bleeding and pumping some air gets dissolved in the fluid. it will raise out over a few hours and the last little bit of bleeding gets you a hard lever.
My latest iteration of brake bleeding (two systems the last week) is a couple wraps of teflon tape on the bleeder screw threads and just a long piece (18") of clear tubing over the bleeder nipple I place the tubing straight up and just do the old lever pump bleeder open close bleed. when the tube gets full I drain it off, keep going till it's clear fluid then do those final burps a couple of hours later. HTH

 

[gggGary]

Hey I just realized that you have not taken the caliper apart. You really need to to do that. It isn't hard, often no parts are needed, and the brakes will never be right till you do. Loosen the 12mm head bolt that holds the caliper to the bracket. remove the 14mm head bolts that hold the bracket to the fork leg. Remove the brake pads, the stainless anti chatter bracket, gently pry the dust seal metal retaining ring and dust seal off. Pump the master cylinder to push the piston out. Add fluid as necessary. This is the easiest way to get the piston out. If I am too late with this advice use air pressure but stuff a rag to stop the piston from flying when it comes loose. Alternate air and squeeze back in a little with a c-clamp if it is stubborn Use a pick and remove the piston seal, clean the huge amount of gunk out from behind the seal, trust me on this one. Inspect the piston and caliper bore It is common to find a some rust on the piston. You should replace it but if the pits are minor and you round the edges with fine paper they are often fine. Clean everything metal with brake parts cleaner, clean the rubber parts with a rag dipped in a little brake fluid, wipe dry. Push out the caliper to bracket slider, you might have to tap it out, gently stretch the rubbers out of the grooves in the slider so it can come all the way out. leave the rubbers in the bracket if you aren't replacing them. clean the old grease out, buff corrosion if necessary, reassemble the slider with a LITTLE synthetic brake grease. you should be able to slide it in and out with finger pressure. reassemble the caliper with a little clean brake fluid as lubricant. Now bleed the brakes and ride.
I am working one right now that even a grease gun won't budge, LH caliper of course

 

[Pandorasglocks]

XSLeo: Thanks a ton for that finger tip trick! Took my over 200 pumps but I finally got dot3 to spray 10 feet across my garage I then moved to the next banjo bolt and liquid started coming out quick so I just bolted it back on and moved to the caliper. 100 pulls later and both of my wrists are throbbing, gotta take a break, but I can see the light at the end of the tunnel

gggGary: Thanks for the reminder, I was meaning to take the caliper apart but this whole ordeal made me forget about it. Now that I know my MC is fine I can check out the caliper.

The rear brake was so damn simple to flush! I thought something was seriously wrong when the front one was not as easy, thanks again for the help guys!

 

[Pandorasglocks]

Got around to cleaning the caliper out, damn that thing was dirty! Only minor rust that I gently sanded off. The piston has a little pitting:




I shouldn't need to replace the piston ya?

 

[gggGary]

Yeah that's pretty bad, not all that deep but a lot of it. I pulled apart 7 calipers last week every one had at least some piston pitting (midwest). A few were reusable by my standards but many are not. Three needed the grease gun removal technique.

 

[pamcopete]

Bleeding the front brakes on a XS650 is a pain. Everybody has their own tricks to do it. Here's mine:

1. Do all of the conventional bleeding first.
2. Remove the cover off of the M/C.
3. Remove the caliper from the bike.
4. Hold the caliper with the piston facing the floor.
5. Squeeze the caliper piston in and watch for air bubbles in the M/C reservoir.
6. Squeeze the brake lever to extend the caliper piston out again.
7. Repeat from step 5 until your arms fall off.

The end result is a rock solid brake lever. I have used this technique on all my bikes with great success.

Some people think that if you squeeze the brake lever with the caliper removed that the piston will blast out of the cylinder, but that's not so. You can actually pump the lever several times and the piston just comes out a fraction.

 

[Pandorasglocks]

Kk I'll get a new piston then, would hate to have air leakin in after I wrecked my wrists gettin all the air out .

Thanks for the tip pamco pete, do you do the "piston pushing" when refitting your brakes or only when bleeding them?

 

[pamcopete]

pando....,

I guess I don't understand what you mean by refitting the brakes. I use the piston pumping method whenever I bleed the brakes, so I assume I would have to bleed them if I refitted them.

I'm also a great believer in replacing the hoses and M/C with new at least once in the 30 year life of the bike. So, if you didn't replace the hoses and the M/C, then they have probably never been changed. The caliper is a different story because it is a very simple part and you can see and clean everything.

The hoses accumulate junk that can break loose and migrate to the M/C. The hoses also flex as they get older and this makes for spongy brakes that no amount of bleeding can correct.

So, I installed a new M/C on all three of my bikes along with new hoses. All three have a rock solid brake lever. I installed Mikes Stainless Steel one piece hose (41") which is cheaper by half than buying the two rubber hoses separately.

 

[TwoJugs]

The easiest method I found for getting the MC prime started to do a good bleed job is to fill up the MC, open the caliper bleeder, put a hose on it into a small glass jar and go to bed. If all is well in the morning the MC will be empty and the jar will have the fluid. Seems once this is done the bleeding goes as normal. Gravity will force the major air out of the system with time and hold enough fluid to help the bleed process work.

 

[Travis]

Did I just miss it or has no one mentioned vacuum pumps like the mityvac? They don't cost much and you can bleed an empty brake system in a few min. I don't know what I would do without it. Teflon tape on the bleeder screw are a must with vacuum pumps. And, as pamcopete already mentioned, new braided lines are almost a necessity when dealing with 30 year old brake systems. Also, if there is any junk in the system, I would always completely take apart the master cylinder and caliper... and with a new line, you'll have brakes you won't have to worry about.

 

[Pandorasglocks]

PamcoPete: Took your advice and ordered the 41" steel line from mikes, thanks!.

Travis: My neighbor saw me bleeding the brakes and tried to find his vacuum bleeder but after 20 mins of digging gave up. If I had more than one bike I would look into one but after this I probably won't be bleeding brakes from a long time (that's the hope anyway!)

 

[Travis]

I suppose.. I've used mine on ATV's, scooter, cars, trucks, and many motorcycles.... and have lent it to friends. Definitely got my moneys worth considering I bought it used on ebay.

 

[xjwmx]

The 41" line, I was thinking about getting that. Do you have a good way of securing the middle of the line to something? Is it not necessary?

 

[pamcopete]

xjwmx,

I used a rubber lined "Adel" 1/4" clamp available from a well stocked auto supply store or aircraft supply store or:

http://www.allensfasteners.com/sear...&txtsearchParamType=ALL&txtsearchParamVen=ALL

Here is a view from underneath the Yamaha plate on the lower triple tree:

Boy, that's a terrible picture. It's from the bottom looking up. When you remove the fitting that connects the stock two hose lines together, there is a threaded boss there to bolt the clamp to.

Make sure that you fully extend the forks before you tighten the clamp!!

 

[xjwmx]

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?