Front brake Frustration

[usin13]

I've been having a locking/dragging problem with my front brake. The bike is a 1977 GS750. I have scoured the other posts to see what is the best and twice now I thought that I've had the problem beat and it still keeps happening.
The front brake drags on the disc. I bleed it and it releases. It will then work fine for a couple of days, then it will do it again. I don't have to bleed a lot, just a little for it to release and then it works.
I have cleaned out the master cylinder completely. It was brown and gravy like but now it's fine. I have taken apart the front caliper, cleaned everything and put it back together. Piston moves back and forth by hand in the caliper (takes a little muscle, but not bad). I cleaned the inside with fine steel wool, removed the rubber ring and scraped in their with a dental pick. I feel confident about the caliper. It also had the brown gravy type brake fluid, but now when I bleed, it comes out nice and clear.
I believe that this leads me to the piston in the grip itself, or the line. I did not take apart the piston, simply because when I had the brake lever off the bike, the piston seemed to go in and out with no problem. However, if you all tell me to take it apart, I will, I just don't want to do it for no reason.

Help me get the brake tool and brake fluid out of my saddlebags please.

 

[Guest]

They still make new brake pistons for that bike. I took mine out and the inside looked like mud. Maybe the return port is clogged. I had to borrow some modified snap ring pliers to remove mine but the job is a snap.

 

[usin13]

Thanks for the quick reply

Thanks for the quick reply

Tonight when I get home, I will take that apart. I will let you know what I find.
Very grateful for the answer and for this forum.

 

[ptm]

Yes, it's worth replacing the piston and cup set in the master cylinder. The set also comes with a replacement for the little boot thet covers the end where the lever hits it and helps keep it clean inside.

It is a real b!tch to get the circlip out. I went through 3 circlip pliers with major modifications before I finally go it out. Then I heard about these http://www.mikesxs.com/mikesxs-chassis.php?category_id=1.2 (scroll about 1/4 of the way down) The right tool for the job...

Another thing to check is the little holes in the bottom of the master cylinder reservoir. One of them is the one that lets the fluid back into the reservoir after you release the brake. If it's plugged, the pad will drag, sometimes enough so the the wheel won't turn - it acts like the brake is on full, since there is still a lot of pressure in the line pushing them against the rotor.

 

[usin13]

cleaned

cleaned

I have taken apart the handle and piston. It was pretty nasty in there. No problems putting it back together. Re-bled the system, so I guess it is just a matter of waiting to see if it grabs again.

I have a question on the front caliper. There are two pads, the stationary pad and the moving pad. The moving pad sits in the caliper holder. When the piston comes out, it pushes this pad. What is stopping this pad from popping out of the caliper holder? Seems to me like it could pop it out, or is the movement actually so little that it doesn't push it much? I'm just trying to understand how the brakes work in general.

One more brake question, when you pull the brake lever, it puts fluid behind the piston which pushes it out. What makes the piston go back in? I assumed that when you let go of the lever, that the fluid kind of sucks it back in, but if this were the case, then pumping the lever with the caliper off the bike, wouldn't pop out the piston, and it does.

Thanks for bearing with me on some (i'm sure basic) questions. I figure it's time I start understanding the theory of what i'm trying to get it to do.

 

[usin13]

It did it again

It did it again

I drove around fine Sunday and yesterday. Today when I went to lunch, it was dragging again. Bleed a little fluid out and it's fine. The return whole is not dirty as I completely cleaned the system.

Observation: I noticed that it is usually happening after the bike has been sitting in the sun.

Question: Is it possible I'm putting too much fluid in the reservoir, then when it heats up from the outside temp, it is preventing the fluid from coming back into the reservoir?

At this point, I'm completely stumped, short of changing the brake lines.

Thanks again for the help.

 

[BadBillyB]

Carry a wrench and some rags with you when you ride. The next time it starts dragging, turn the handle bars all the way to the left (so as not to spill brake fluid on your tank, it will eat the paint) and break loose the banjo bolt right on the brake master. If that releases the drag, than the problem is in the master cylinder...Might want to ride home with a rag tied around this area until you can properly clean off the brake fluid. It will eat through your paint in a matter of seconds.....Not likely that the brake hoses are at fault, but this is how you narrow it down......BadBillyB

 

[Guest]

Thanks Billy. I learned something today.

 

[usin13]

Thanks for the quick response

Thanks for the quick response

So, while you were replying to my post, I was in the garage trying different things. Not being as clever as you, I tried different things first. I cleaned the piece where the two brake lines meet, under the front blinker mount. It was pretty dirty, but no luck. Eventually just took the hand brake off the bars, took the caliper off the rotor, used one of the pieces of brake line to connect the two. I would squeeze the hand brake and watch the caliper. As it was filling with fluid, it would go out and in a little bit. Once it filled with fluid, it would only go out, not back in. I pushed on the piston in the caliper as hard as I could, and it wouldn't go in. Finally, I "cracked the banjo bolt by the master cylinder" and I could push the piston right in. Of course, if I had waited a little while and read your post, I could have saved myself some time. So, it looks like a cleaning wasn't good enough and I'm off to buy a rebuild kit.

Any recommendations on where to look? I usually check out bike bandits. Would a local dealer have this?

Thanks for all the help so far.

 

[BadBillyB]

Now try doing the same test, but instead of opening the banjo bolt, remove the lever and see if it frees up......BadBillyB

 

[frosty5011]

I know you say you cleaned the master cylinder assembly, but did you really make sure that the tiny little return hole in the m/c (On your model, I think it's hidden under the plastic of the reservoir) was clear? If there was corrosion or hardened dirt, it may not have come out during a regular "cleaning". If it was clear/open, you should have seen bubbles pouring out from it's location during the bleeding process.

 

[usin13]

Master cylinder return hole

Master cylinder return hole

I know you say you cleaned the master cylinder assembly, but did you really make sure that the tiny little return hole in the m/c (On your model, I think it's hidden under the plastic of the reservoir) was clear? If there was corrosion or hardened dirt, it may not have come out during a regular "cleaning". If it was clear/open, you should have seen bubbles pouring out from it's location during the bleeding process.

Sure did. I paid special attention to that hole. If I have the plastic reservoir off and squeeze the handle, I can see the piston moving back and forth in the hole. To be honest, that's why I didn't think it was the master cylinder because I could actually see the parts moving through that hole. I did double check it though last night and no problems with the hole. In fact, when I have the piston out, i can see the light coming through it into area where the piston sits.
When I look at the handle, the piston isn't getting stuck in it either, it is releasing completely until the circlip stops it.

The piston, is made of a spring with a rubber cup on the end, then the piston, which has a rubber cup built on it, then the washer, circlip, rubber gasket, plastic ring and wire. (So far so good?) How is the fluid supposed to travel back into the master cylinder throught that assembly? Is it possible that the rubber cup I have on the spring I have reversed? This is one place where the suzuki manual, clymers manual and Bike Bandit microfiche were not helpful as I cannot see which direction that little cup is facing. I put it in so that the open end was towards the spring and the closed end was hitting the piston.

I will re-clean the piston assembly again tonight and try what Billy asked about removing the handle and seeing if that frees it up.

Thanks for continued help and for reading my long winded replies.

 

[frosty5011]

Sure did. I paid special attention to that hole. If I have the plastic reservoir off and squeeze the handle, I can see the piston moving back and forth in the hole. To be honest, that's why I didn't think it was the master cylinder because I could actually see the parts moving through that hole. I did double check it though last night and no problems with the hole. In fact, when I have the piston out, i can see the light coming through it into area where the piston sits.
When I look at the handle, the piston isn't getting stuck in it either, it is releasing completely until the circlip stops it.

The piston, is made of a spring with a rubber cup on the end, then the piston, which has a rubber cup built on it, then the washer, circlip, rubber gasket, plastic ring and wire. (So far so good?) How is the fluid supposed to travel back into the master cylinder throught that assembly? Is it possible that the rubber cup I have on the spring I have reversed? This is one place where the suzuki manual, clymers manual and Bike Bandit microfiche were not helpful as I cannot see which direction that little cup is facing. I put it in so that the open end was towards the spring and the closed end was hitting the piston.

I will re-clean the piston assembly again tonight and try what Billy asked about removing the handle and seeing if that frees it up.

Thanks for continued help and for reading my long winded replies.

Then you have much better eyesight than I do....the hole I'm talking about is tiny...too small for me to see anything moving through it. Going from memory, it's something like only a fraction of a millimeter in diameter.

 

[Road_Clam]

I drove around fine Sunday and yesterday. Today when I went to lunch, it was dragging again. Bleed a little fluid out and it's fine. The return whole is not dirty as I completely cleaned the system.

Observation: I noticed that it is usually happening after the bike has been sitting in the sun.

Question: Is it possible I'm putting too much fluid in the reservoir, then when it heats up from the outside temp, it is preventing the fluid from coming back into the reservoir?

At this point, I'm completely stumped, short of changing the brake lines.

Thanks again for the help.

In your wheel calipers there is only a TINY amount of piston to wall clearence. When you apply the brakes the piston pushes, then when you release the lever, the piston is supposed to retract a small amount. 99% of the time brakes sticking is a result from corrosion in the piston bore causing the piston to jam and not retract. Use some gentile compressed air to "blow out" the piston from the bore (use a thick rag between the piston and the caliper bracket). The piston will abruptly pop out. Inspect the piston bore VERY closely for corrosion, if you see some use some #220 emery and oil to gently sand out the corrosion. Water that's been sitting in your brake system for 20+ years is the BIG culprit of corrosion.

 

[usin13]

Hmmm

Hmmm

Then you have much better eyesight than I do....the hole I'm talking about is tiny...too small for me to see anything moving through it. Going from memory, it's something like only a fraction of a millimeter in diameter.

I guess I will have to look again. Maybe I'm confusing it. When I look at that area, with the reservoir removed, it is a circle with the two screw holes on each side. Towards the front is a hole that goes through into the piston area. There is a divot for a whole of the same diameter next to that, but it is just metal filled, it doesn't go anywhere. I must be missing the return hole. Where would it be besides the ones I pointed out?

 

[usin13]

In your wheel calipers there is only a TINY amount of piston to wall clearence. When you apply the brakes the piston pushes, then when you release the lever, the piston is supposed to retract a small amount. 99% of the time brakes sticking is a result from corrosion in the piston bore causing the piston to jam and not retract. Use some gentile compressed air to "blow out" the piston from the bore (use a thick rag between the piston and the caliper bracket). The piston will abruptly pop out. Inspect the piston bore VERY closely for corrosion, if you see some use some #220 emery and oil to gently sand out the corrosion. Water that's been sitting in your brake system for 20+ years is the BIG culprit of corrosion.

The piston in the caliper sparkles as does the bore. It was really nasty in there as well as under the o ring. However, I can move the piston in and out by hand which is why I don't feel it is the caliper. Had I not already cleaned it (even using a fine steel wool), and if I couldn't move by hand, I'd be in agreement. Howver, if working the master cylinder doesn't end up being the problem, I will got back to the caliper.

Thanks for the response.

 

[frosty5011]

I guess I will have to look again. Maybe I'm confusing it. When I look at that area, with the reservoir removed, it is a circle with the two screw holes on each side. Towards the front is a hole that goes through into the piston area. There is a divot for a whole of the same diameter next to that, but it is just metal filled, it doesn't go anywhere. I must be missing the return hole. Where would it be besides the ones I pointed out?

Look carefully inside the small depression.

 

[usin13]

Sure will

Sure will

Look carefully inside the small depression.

Thanks for the quick reply.
I will look once I get home tonight. I bet (hope) that is the problem. What is a good test, short of re-assembling the whole thing again, to see if it is clean?

I'm gonna be real red in the face if that's the issue

 

[Road_Clam]

Does your calipers slide freely back and fourth on the bracket pins?

 

[usin13]

Bracket Pin

Bracket Pin

Does your calipers slide freely back and fourth on the bracket pins?

I'm not sure how to test to tell you yes or no. When the caliper is off the bike, there is a metal bracket the pins go through, and that slides back and forth with no problem. Should I put it on the bike and try the same thing? If so, do I leave the pads in, or out?