Front Brake Problem

[Glenn]

Went riding yesterday. Had another first. The front caliper locked up. The lever was as tight as a tick and would not release. It had the front wheel locked up so tight it would not roll. I had a small open end wrench and was able to open the bleeder valve and as soon as I relieved the pressure the front caliper opened up freeing the wheel. After the pressure was off I could squeeze the lever and create a squirting flow of fluid until all the fluid was gone. At first I thought that the problem was in the master cylinder barrel assembly but after the initial pressure was released it functioned fine. Then my thought that the caliper was the problem, but it seems to me that the caliper would not have released so easily if it was the problem. I have a new barrel so I am thinking about replacing the old one and rebuilding the caliper. I rebuilt the barrel a couple of years ago honing the barrel out and replacing the inside components. I still think it is the barrel components not retracting back into the barrel holding the lever closed when I released it. That perhaps the spring broke, but then again it functioned fine when I was pumping the fluid ot. Of course that was an unloaded condition. However, I am still curious as to what created this problem since all I have are guesses and no concrete proof. As you can see I am all full of questions and possible solutions but the reality is I don't have a clue. Until I open up the barrel and take the caliper apart I will not know anything and even then I may not find anything wrong because eveything may look fine, but we all know that looks are deceiving. Anyone ever experience this? What are your thoughts?

 

[DaveM]

Well as you say pulling it apart now seems to be the only way to try and see what has caused this.

 

[otherwise]

I had exactly the same problem last year when getting a Ducati back onto the road after it sat for 13 years.
I just wrote a long story about it for you and some how deleted it
In short, I did the fluid twice, calipers, hoses and the master cylinder about 3 times before I found an additional almost invisible hole in the master cylinder blocked. I can't comment on your bike, from memory a T140? This Ducati has Brembo brakes, the blocked hole is aligned with the obvious hole that the piston passes but critical for fluid return. It's about 8mm closer to the banjo bolt than the big hole. It's so small that very fine suspended particles in the fluid can block it with dangerous results.

Edit,
I was all for persevering with the original master cylinder after I found the problem but my mate who owned the bike insisted after the problems that I had with it, and as it had been disassembled and assembled too many times (in his opinion) to purchase a new master cylinder. He had enough money to purchase peace of mind. It's been on the road with the new master cylinder for almost a year now and is working perfectly. Before that I was carrying a 13mm ring spanner to crack the bleeder nipple and free the front wheel, not a good look.:y11:

 

[avion]

That can be a nightmare, riding the bike with the thought that it might lock the front at any time.

I would tend to agree about a blockage, or some piece of debris floating around the system.

Definitly would do a total strip down and scrub everything good 'n proper. Use high pressure compressed air and brake cleaner, rebuild and fit.

 

[The Seeker]

In addition to all the above....

You've got an old bike with old hydraulic hoses. The hoses can break down over time and constrict inside while looking perfectly normal on the outside. They can begin to act like one way valves.

I'd probably overhaul the entire system since it is so critical.

 

[otherwise]

In addition to all the above....

You've got an old bike with old hydraulic hoses. The hoses can break down over time and constrict inside while looking perfectly normal on the outside. They can begin to act like one way valves.

I'd probably overhaul the entire system since it is so critical.

The blocked master cylinder I spoke about a few posts earlier was caused from the original hose deterioration. The hoses looked 100% on the outside but were sticky gum on the inside. That's why after I fitted new hoses I then changed the fluid twice but the damage was done with very fine suspended rubber particles blocking the very fine hole.

 

[The Seeker]

Yeppers...that too.

You can usually tell when the hoses are breaking down because they tend to turn the fluid dark.

 

[Glenn]

Otherwise, it is a '79 T140. The fluid has an almost new color. The hose had no more than a couple of hundred miles on it. However, new parts are sometimes defective. Had I thought of that I could have onserved this when it was in the locked up state, but being out in the middle of the road with cars zipping by did not allow my brain to even think of that. I guess I can feel (press) it along the entire length to see if there is a weak spot. My thought is to replace the hose and put a rebuid kit in the caliper as well as replace the barrell (I have a new SS one with the internal parts assembled). That is an interesting thought about the hose collapse. Thanks guys.

 

[The Seeker]

There are TWO flexible rubber hoses to replace.....the obvious one near the master cylinder and the one down on the forks so the forks can compress. Just follow the metal brake line out of the caliper and up the fork lower and you'll see the black rubber hose begin around the top of the fork lower.


PS: If you are rebuilding the caliper and master cylinder (for all intents and purposes you are) as well as replacing the flexible lines, you can switch to SILICONE brake fluid. Silicone fluid doesn't absorb moisture from the air and will last many years longer without changing than the petroleum based DOT 3.

 

[The Seeker]

By the way....I wouldn't trust simply feeling the flexible lines for weak spots.

Those are multi-layer hoses and the inner rubber can become swollen and deteriorated without you feeling anything on the outside. About the only way of knowing for sure would be to remove them and run something like a pipe-cleaner down inside them to see if they've become like jelly.

 

[Glenn]

I also have been thinking about the conditions what were present when I shut it down. At first I was going to rebuild the caliper, but I am now thinking that I will swap out the old barrel for the new SS one I have. Then go from there. Hopefully this will solve the problem. The odd thing is that the caliper was shut tight locking up the front wheel but the lever was wide open and I could not squeeze it any. It was locked out. Someone suggested that the fluid return hole may have been clogged up with a piece of trash not allowing the fluid to return to the reservoir. This makes me think that the problem is in the barrel and not the caliper. To my way of thinking if the problem was in a stuck caliper it would have no effect on the lever. Someone else suggested that (even though these are fairly new hoses-both of them) that the hose may have collapsed and was acting as a one way valve, but again to me if this was the case it would not affect being able to squeeze the lever. The funny thing is that full pressure was exerted in both directions which leads me to believe that the problem was created by a problem in the barrel and not a problem in either hose. Of course I guess the hose could totally collapse and create enough pressure in both directions to create the problems I encountered. What do you think?

 

[The Seeker]

I think I would rebuild the caliper and use the new master cylinder barrel you have to rebuild the master cylinder making sure you use brake cleaner and air to blow out all the tiny holes until they are clean. Then I'd replace the two flexible hoses, fill and bleed the system.

 

[otherwise]

It was locked out. Someone suggested that the fluid return hole may have been clogged up with a piece of trash not allowing the fluid to return to the reservoir. This makes me think that the problem is in the barrel and not the caliper.

This is EXACTLY the situation I had with the Ducati. It was caused by the old hoses falling apart internally and the muck prevented fluid returning through the small hole. The fluid looked clean, infact I changed it twice.
I'd say your calipers are fine. Your hoses and fluid require replacement. The master cylinder requires an ultrasonic clean or replacement.

 

[Glenn]

Fummy that you should mention that, because I talked to my Triumph Tech friend (actually he is my friend until I run into a problem only he can solve and I get his bill). He actually encourages me to fix all the problems I can on my own and gives me advice, so he is still my friend. When I called him 10 minutes ago and told him about my venture, the first thing he said was, that since my bike sat up in the Pennsylvania weather from Sept. until May and as he said, "I bet you did not change the fluid did you". Of course my answer was No. To which he said I'm betting something has stopped up the return hole for the fluid and this is why the caliper was frozen and the lever was stuck in its normal position but you were unable to move it. I also told him that I have a SS barrel and he said that replacing the original one with this one would be a smart move and would more than likely solve my problem. He also indicated that the original material used in the master cylinder assembly on my '79 bike was prone to rust up and have material flake off on the inside and cause some strange problems like the one I had. I asked him if it would be a good idea to rebuild the calipers and change out the 2 hoses and he said only unless something was wrong with them. That he would change out the barrel and go from there. He said that since the hoses are relatively new and since I use the correct DOT 3 fluid he would be very surprised if there was something wrong with the hoses. I'm telling the truth when I say I bet I have less than 200 miles on both those hoses. I found out that he does not like silicon fluid. He asked me if I was having any problems with the rear and I said that I already have a SS barrel on the rear, and he said "There you go". Thanks guys. I will keep you in touch on what happens in this situation. You guys are the best. That's why I like this forum.

 

[The Seeker]

I don't know what anyone would find wrong with silicone brake fluid. I've run nothing BUT silicone in everything I have and never had a problem. I replaced my old fluid with silicone in my '69 TR-6 (car) when it first became available in the 80s in the brake and clutch systems and both have never needed servicing since. Silicone doesn't eat into the rubber bits and doesn't absorb moisture.

 

[Glenn]

I have no idea but I will definately ask and report what he says.

 

[Glenn]

Update: I took the barrel off the bike and took it apart. There was crud and rust everywhere. It was a mess. No wonder the return hole was stopped up.

 

[DaveM]

So are you just going to clean it up or do a rebuild with new parts then

 

[Glenn]

I am going to clean the lines out and then but the new SS barrel (which came loaded) onto the cleaned up master cylinder and mount it. Hopefully when I take the lower hose off where it connects into the caliper and blow it out from the top of the upper hose I will get rid of any residual junk in the line. Anything else that I need to do to make sure everything in the system is clean and free of the residual junk.

 

[DaveM]

Would it not just be worth your time and effort to just replace the hose, I know you say they are still new but I was just thinking you may have tiny particles that may still be in the hose even after you clean them out. Rather a lot of effort to have to go through the process again to strip and clean if you do still have some dirt left in them and it blocks up again.