Building too much pressure after front master cylinder change... Long...

[Guest]

I just changed out my front master due to cosmetic reason's. The brakes were ok,,just a little spongy. But I new I wanted a different master, and stainless lines, so I didn't mess with it.

Fast forward to Sunday. I finally got my bike back on the road after being backed into by a van. I swapped the fork's, tripple's, and other various part's. I put 150 miles on it Sunday. Which actually I don't believe that mileage is no where near correct, (reads too much) but that's another issue. I had no major issue's at all, except I thought the brake lever might have been getting firmer, and the brake lever seems like it is missing a return spring. I am missing the rubber dust cover. Should there be a return spring, or does the dust cover act as one. I have too much slop in the lever.

So Monday I go for a ride. The brake lever feels like it's getting firmer and firmer. I'm out on the highway and the front brakes get super hot and slow the bike down to a stop. I can't hardly go. I'm also getting a hell of a noise. Before this happened I had some speedo cable noise so I thought that was it. Which by the way as it turns out it was it, but I think from getting hot. So I let it cool off for awhile and then head home. When I get home I jack it up and the wheel is stuck. I let thing's cool again, and I get a little movement. I crack one bleeder loose and get some more movement, crack the other bleeder loose and the wheel turns free. Now I'm thinking there's no way I can get 2 stuck calipers, from being a bad caliper that is. It has to be the master.

Before installing the new to me master, I took it apart and cleaned it. It was cruddy, but everything looked ok. I used this pictorial for re-assembly. LINK REMOVED BECAUSE OF WRONG INFORMATION!!

Now that I've had this happen, I've tried to tare apart my original master to make sure I put the new one back together right. Problem is it is rusted enough I can't get the plunger out. But I was able to see the secondary seal is a rubber part. On the one I am using, it is hard as a rock. But it's not leaking externally.

This has me thinking. When I initially bled the system I was getting some air bubble's out of the smaller hole in the reservoir. But now I'm getting them out of the big hole. I've heard of a master leaking internally. Could this be what is happening. I would think I would have a leak around the snap ring. But I don't.

So anyway. I'm going to go ahead and order a master cylinder piston/cup set, along with caliper rebuilds.

Do you guy's have any insight as to what is happening. Or, any other advise would be greatly appreciated. Thanks.

[Steve]

It is probably as simple as a blocked return hole in the bottom of the reservoir.

Either the seal is covering it, or there is some crud in the hole.

I was going to send you to BassCliff's site so you could see the return hole, but I can not find it, so I am not going to send you on a hunt.
If you look in the bottom of the reservoir, you might see a hole that is about 2mm across, it might be near the center of the reservoir. There is another, smaller, hole that is downstream. On some reservoirs, there might be a plastic tab covering the small hole, you will have to remove the reservoir to access the hole. Drain and remove the master cylinder from the bike. Poke a strand of wire through the hole to clear it out, follow that with a quick spray of brake cleaner and compressed air. Re-assemble, fill and bleed the system, it should work better.

While you are at it, why not do the rear system too? Same thing can happen.


.

[TooManyToys]

Blocked compensating port in MC.

[Quick Cal]

Thanks for the replies.

I know for a fact all the port's were cleaned a free when I re-assembled it. But, it sounds like something has broke loose from a rubber piece or something. Or maybe it's because of the rock hard seal.

I'm ordering a new piston set. Thanks for the help.

[Steve]

It is also possible that the piston is ever so slightly compressed, blocking the compensation port. That port is too small to stick a needle through it, even strands of wire are usually too big, unless you find some really fine strands. Find one and use it to verify that the port is open. While the wire is in the hole, move the brake lever carefully to verify that the piston is behind the port. It will snag on the wire, so move gently so you don't tear it up.

.

[Quick Cal]

It is also possible that the piston is ever so slightly compressed, blocking the compensation port.

.

I think this is what is going on.

Even though I used all the original part's putting it back together, I had a hell of a time getting the piston in far enough to get the snap ring in. That would also explain too much free play in the lever. It has too much movement before actually contacting the end of the piston. I'm assuming there is no return spring, and the lever ride's on the end of the piston as is.

I think I need to pull it back apart, make sure the port's are clear, and re-assemble before ordering a new kit.

[Big T]

The best way to confirm the relief port is open is to fill the MC partly and pump the piston, you should see a spurt of some fine bubbles coming from the relief port when you release the piston

[Quick Cal]

The best way to confirm the relief port is open is to fill the MC partly and pump the piston, you should see a spurt of some fine bubbles coming from the relief port when you release the piston

Which is the relief port. The big hole,or the little one.

When I first bled the system, I had little bubble's coming out of the little hole. Noe I have them coming out of the big hole.

Pic's on the way.

[Quick Cal]

The first pic is with no pressure on the lever. Both hole's are open.




The second pic is with the lever pulled. The smaller hole is blocked off.





As you can see by the light shining through the hole's,,, both are clear.

[TooManyToys]

http://www.thegsresources.com/_forum/showpost.php?p=1624231&postcount=36

Explains the ports. IMO your piston assembly is not returning all the way, not something in the port. You also have the remote possibility that there a a hose issue blocking the return of fluid if there is a single line out of the M/C even though the line is new. If it is the M/C, cracking the fitting at the hose-M/C connection will release the brakes. If not then it's the hose.

[Big T]

The small port is the relief port - if bubbles are coming out of the big port, the relief port is clogged

[Quick Cal]

The small port is the relief port - if bubbles are coming out of the big port, the relief port is clogged

As you can see in the pic's, the relieve port is not clogged.

I took it apart last night. I had a very hard time getting the plunger out even after the snap ring and washer was out. It's like something is keeping it from coming all the way to the full rest position. That would also explain the sloppy lever.

I have another piston kit on the way. I'll see what happens.

[Quick Cal]

It's doing it again.

I put the new rebuild kit in. Everything went well. I bled the brakes with my Mighty-Vac, and everything was Golden. I rode around town all evening, putting about 20 mile's with lots of braking. All was good.

I have a little slop in the lever that I was concerned about and made a thread about it. Chuck told me about the bungee cord on the lever over night thing. I did that. The lever was just a touch firmer. I went for a ride and with in a mile the front brakes locked up again.

I broke the line loose at the master and everything is good again. I was able to make it home. The brakes don't even feel like they need bled. I just put about 5 mile's on it, and everything seems normal.

What the heck am I doing wrong. Why is this thing building up
pressure. The ports are clear. It has a new factory rebuild kit. I bled it with a Might-Vac.

Please advise. I'm about to loose my mind.

[tc862011]

mine was doing this and i got a shorter brake line from the brake line connector under the steering stem to the master cylinder, i only got one that was about an inch shorter cause i had gotten different handle bars and i have had a single issue with it now

[Quick Cal]

OMG!! I FIGURED IT OUT.

The damn guide I followed, and linked to in my first post, was wrong. He has it assembled wrong. That being said, I can't blame him. I'm the idiot that forgot how it went together. I should have took pic's. So if that's a fellow member here, I'm sorry,,,but you did it wrong. The link will be removed and I will try to let the guy know who wrote it.

I had a few thing's that kept nagging at me.

1. Where the guide had me put the seal, it left the dust seal end of the plunger with out any type of rubber seal. I thought how can this not leak. But it didn't, and still isn't even after tying down the brake lever over night.

2. On my original master that I was unable to disassemble, the rubber seal was on the end of the plunger that I could see. I was able to dig it out. But the way the guide had me assemble, that seal was on the other end of the plunger.

3. I kept wondering if I had this thing put together right. It was driving me nuts that I couldn't get my original master that I was replacing took apart because of rust. So I just took a sawzall,,God I love sawzall's,,,to it and cut it open.

The cut away master in the top of the picture has it correct. The plunger in the bottom has it WRONG!!

Well now I have to go a rebuild this thing again. Hmmm. I bet that extra slop in my lever goes away too. Now I'll just crap a brick if I rebuild this again and it's worse. I'll be eating some Crow.

What's sad is I had searched and found where a couple of members had just gone through this. I even bookmarked the page's. I just didn't follow those thread's. I had me an online blog I was a followin. Lesson learned,,, USE TRUSTED SOURCES OF INFORMATION!!