Here's one that might stump you

[ChiefJP_imp]

I have an issue with the front brake on my DLX and it seems very weird. So of course I'm thinking why not bring to the best and the brightest. Here it goes.

Let me start off by saying i've already had the dealer rebuild the front break master cylinder and the front brake lines have been bled and refilled 3 times by a dealer. And the problem still exists.

The problem: At what are seemingly completely random intervals when I get on my bike and pull the front brake lever there is little to no resistance. Then if I pump the handle 2 or 3 times the brake seems to get almost too tight.

I've tried all the things mentioned above and it still happens periodically and seemingly very random.

A perfect example might be that I bring the bike out and the brake feels fine. Then I ride 30 minutes to get something to eat. And when I come out there is absolutely no resistance to the front brake. I'm basically grabbing air. Then with a few pumps the brake gets almost too tight.

Now before everyone says air bubble, I want to repeat that the dealer has bled and refilled the brake line 3 times already. Also, one interesting point, sometimes this happens a few times a week, sometimes once a week, and sometime once every few months.

Stock Nissin brake but I'm seriously considering just replacing them with Brembos to provide some confidence in my breaking again. I'm always riding with the feeling they will fail at any minute. Not a great feeling.

Thoughts??

[mattmcuomo@yahoo.com]

I've had a similar situation, I used to park my bike in the parking lot at work, outside in the heat. At the end of the day I would get on the bike and I would have to pump the front brake to get pressure back. I attributed it to the heat and maybe crappy brake fluid. Now that I park it inside it doesn't happen anymore....

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[Gone in 60]

I’ve had the opposite problem as MMC with my car, which shares the same fluid for clutch and brake. If the car is parked outside on a very hot day, mid-nineties at least, the clutch pedal is very stiff and the brakes a bit more grabby than normal.

I agree with a master cylinder issue. I had the same problem on an old Nighthawk. Rebuilt the master myself and replaced the old rubber brake hose with steel and the problem went away.

[Cormanus]

After all the help I got from members of this forum, I pulled my clutch master and slave cylinders apart to help me try to fix a problem with shifting into neutral when the engine is hot. When I put it back together, the clutch worked fine until suddenly it didn't. It would work and then there would be no pressure until I pumped it. I then discovered that by working the lever gently at the point where the clutch started to engage (or disengage; I'm not sure) I could remove all pressure from the system. I bought a new pistin kit for the master cylinder, replaced it and all was well. Sounds a bit the same as your issue, Chief, except with the clutch.

[dave]

My thought is this: There's a very small hole inside the master cylinder that is clogged, or partially clogged. You need to completely drain the reservoir to see it. (There might be two holes, I don't remember). Once drained, use a small wire to poke into the hole and dislodge any contaminate, and high pressure air to blow everything out. I would either do the work yourself, or find another mechanic to perform the work. Whatever you do, don't continue to ride your brake with a front brake that you can't rely on. Good luck.

[pdedse]

CB1100 forum is worth its weight in gold this morning.

[peterbaron]

That “ small hole” is called a compensating port and allows fluid to enter a brake line from reservoir.
Any restriction could mainly cause brake dragging ….. less likely spongy lever/pedal or more…

[dave]

That “ small hole” is called a compensating port and allows fluid to enter a brake line from reservoir.
Any restriction could mainly cause brake dragging ….. less likely spongy lever/pedal or more…

So, you're saying that if the compensating port was clogged and did not allow the proper amount of fluid to enter the brake line then this would cause dragging?

[peterbaron]

That “ small hole” is called a compensating port and allows fluid to enter a brake line from reservoir.
Any restriction could mainly cause brake dragging ….. less likely spongy lever/pedal or more…

So, you're saying that if the compensating port was clogged and did not allow the proper amount of fluid to enter the brake line then this would cause dragging?

So, you're saying that if the compensating port was clogged and did not allow the proper amount of fluid to enter the brake line then this would cause dragging?
m in sc, just aswered your question : if its clogged it will just build pressure behind it and it drags.
.....due to the fluid expanding when the brakes are hot and instead of returning to the reservoir, it will push the brake piston out towards the pads and rotor, causing the brake binding.

[dave]

[quote='m in sc' pid='350956' dateline='1724696004']
yes & actually i said that. its is the absolute bane of existence on vintage bikes with disc brakes. it will displace fluid back into the res when the lever is pulled. (it fills behind the main seal when the lever is released). if its clogged it will just build pressure behind it and it drags. I've seen it bad enough where it caused a crash, a 75 S3 right into a guardrail on the cherahola skyway about a decade ago. Luckily Bill was ok and .. well, frankly, he is/was used to crashing so he did ok.

Interesting observation. When the compensation hole on my bike became clogged it caused a mushy feeling at the lever, exactly like air in the line would cause. I rebuilt the master cylinder, and bled the brakes twice, but this did not correct the mushy feeling at the lever. Cleaning this hole cured my brake issue completely.