Yamaha FZ-09 Forum banner
1 - 20 of 34 Posts

·
Registered
Joined
·
877 Posts
Discussion Starter · #1 ·
Have what I believe to be a defective front brake master cylinder.

This was originally on bike # 2.

Problem is that it acts like it's sucking air, or something.

The lever will randomly get soft in traffic and even start to drop to handlebar very close.

A quick pump brings it back to a somewhat normal feel.

Fault was confirmed by the following:

Bike # 1 I had put in a radial master cylinder and did dual braided lines at the same time.

When Bike # 2 was not acting right, I took the OEM master cylinder off the shelf ( from bike # 1 ) and put on bike # 2.

Problem solved for the moment showing the MC from bike # 2 to be the problem.

Last night, I put the suspect MC on bike # 1 and it now had the problem.

So now we have a double check that the problem was staying with the suspect MC.

OEM MC currently on bike # 2 works great. With dual braided lines, lever very firm with little travel.

A few weeks ago , another member from this forum was riding with us on Palomar and described brake fade symptoms.

Wonder if he may also have a bogus MC that acts like brakes are fading ?

Anybody else have a spongy front brake that bleeding doesn't help ?
 

·
Registered
Joined
·
2,330 Posts
sounds like a failed seal it n the mc piston.

take it to the dealer.
 

·
Registered
Joined
·
877 Posts
Discussion Starter · #3 ·
They want the whole bike for a warranty claim.

I ordered a seal kit for $ 18 and will take a look at the innards.

For now, I put on a 1980's master cylinder with a 16 mm piston ( FZ 09 is 15 mm ) .

Works excellent and even the brake switch from the FZ 09 mounted right on to the MC that I put on tonight.

Pictures in a bit.
 
  • Like
Reactions: v2Bob

·
Registered
Joined
·
1,081 Posts
Brake fade in the front is starting to become an issue for me too! I have to keep checking to make sure it is adjusted properly. Just tipped 2k miles on Tuesday.

I haven't bled it yet, I'm just starting to have issues.
 

·
Registered
Joined
·
877 Posts
Discussion Starter · #5 ·
The replacement MC from a 1983 Honda Interceptor, but probably used on a lot of other 1980's bikes.

The casting was solid where a mirror would thread in, so drilled and tapped it in the mill vise.

Had to make a right hand thread stud for the mirror.

Parts used: 10mm fine thread allen, head turned to 22 deg angle like the OEM one.

.................Top of bolt drilled and tapped for a 6 mm thread for stud .

Have to use very thin wall socket to get nut out and back in mirror base connector.

 

·
Registered
Joined
·
877 Posts
Discussion Starter · #6 ·
Put together, looks like :

 

·
Registered
Joined
·
877 Posts
Discussion Starter · #7 ·
Even the FZ 09 micro brake switch mounted right on with no mods.

Something to be said for luck. :cool:

 

·
Registered
Joined
·
877 Posts
Discussion Starter · #8 ·
Brake fade in the front is starting to become an issue for me too! I have to keep checking to make sure it is adjusted properly. Just tipped 2k miles on Tuesday.

I haven't bled it yet, I'm just starting to have issues.
You will definitely want to do the dual braided lines to make it more efficient and easier to bleed thoroughly.

Some HH pads would be cool, but given a choice , do the lines first.
 
  • Like
Reactions: FZjohn

·
Registered
Joined
·
1,081 Posts
I think that will be my next investment after tires. Hopefully it doesn't become a major issue before that.


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
730 Posts
I've been running the same configuration as the FZ on my 90 FJ (with R1 M/C and calipers) since 2001 and bleeding has NEVER been an issue..... And they work better. Less line length means less swell under pressure.


You will definitely want to do the dual braided lines to make it more efficient and easier to bleed thoroughly.

Some HH pads would be cool, but given a choice , do the lines first.
 

·
Registered
Joined
·
877 Posts
Discussion Starter · #11 · (Edited)
I've been running the same configuration as the FZ on my 90 FJ (with R1 M/C and calipers) since 2001 and bleeding has NEVER been an issue...

.. And they work better. Less line length means less swell under pressure.
Maybe in theory, but so much in the real world.

The line over fender is only 25 % shorter than a dual line to master cylinder setup, and a pain in the ass to thoroughly bleed.

2 ways to detect flexing:

A line will move a bit if it's flexing. __None noted.

Another test we did that is on You Tube, we put a digital caliper accurate to .0005 inch.

The test showed no change in diameter between no pressure and full squeeze of the lever with all 4 fingers.

This would tell me there is no usable difference in flex by a slightly shorter line.

On the other hand, the easier chore of bleeding a dual line setup makes the real world improvement of braking more likely.

 

·
Registered
Joined
·
644 Posts
Does the MC Reservoir have one of those small bleed holes downstream of the main fluid suction hole? Is it clear and functioning - spurt of fluid when the lever is squeezed?
Possible there is some bad machining (nicks or gouges or wrong diameters) in the piston bore also... as you have 2 MC's perhaps you can compare them to each other.

If you swap the seal pack and the bad MC stays bad, it isn't the seals
 
  • Like
Reactions: FZjohn

·
Registered
Joined
·
877 Posts
Discussion Starter · #13 ·
Does the MC Reservoir have one of those small bleed holes downstream of the main fluid suction hole? Is it clear and functioning - spurt of fluid when the lever is squeezed?
Possible there is some bad machining (nicks or gouges or wrong diameters) in the piston bore also... as you have 2 MC's perhaps you can compare them to each other.

If you swap the seal pack and the bad MC stays bad, it isn't the seals
I believe hole is clear.

I watch for it and bubbles coming up when I bleed with cap off.

Have seal kit ordered and will look for machine defects when doing install.
 

·
Registered
Joined
·
225 Posts
Interesting topic Dolan. I have always felt that my lever was a bit soft. I installed oem style lines with little to no change. I can lift the rear tire with the brake, it just is not solid feeling @ the lever. I will be interested to see if the seal kit helps.
 

·
Registered
Joined
·
3,079 Posts
Keep in mind the master is small. A smaller piston will take more stroke to build pressure but will produce more braking power. A bigger piston will give you a rock hard feel but will not give you as much stopping power. It's a trade off...

If there's air in the system the sponginess will accentuate as fluid temp rise. If the feel is the same... everything is fine.

If you need to "pump" the lever to get it hard again when you ride inspect your rotors. Warp rotors of too much free play in the bobine will push the pads away from the discs.

Racecars use knock off springs behind the piston to fix that. They comes in different rate from 2 to 7 ft/lb if I remember well.

Sent from my SAMSUNG-SGH-I337 using Tapatalk
 

·
Registered
Joined
·
877 Posts
Discussion Starter · #16 ·
Keep in mind the master is small. A smaller piston will take more stroke to build pressure but will produce more braking power.

A bigger piston will give you a rock hard feel but will not give you as much stopping power. It's a trade off...

If there's air in the system the sponginess will accentuate as fluid temp rise. If the feel is the same... everything is fine.

If you need to "pump" the lever to get it hard again when you ride inspect your rotors. Warp rotors of too much free play in the bobine will push the pads away from the discs.

Racecars use knock off springs behind the piston to fix that. They comes in different rate from 2 to 7 ft/lb if I remember well.

Sent from my SAMSUNG-SGH-I337 using Tapatalk
One of the 1st things I checked, though rotors are new / very low milage.

Warped rotors would have the mushy feeling more consistent , pretty much every full revolution.

The thing that was driving me bat$hit was in random nature of the failure.

Could be 50 feet or 5 blocks in between incidents.

Totally random and unpredictable.
 
  • Like
Reactions: marthy

·
Registered
Joined
·
225 Posts
One of the 1st things I checked, though rotors are new / very low milage.

Warped rotors would have the mushy feeling more consistent , pretty much every full revolution.

The thing that was driving me bat$hit was in random nature of the failure.

Could be 50 feet or 5 blocks in between incidents.

Totally random and unpredictable.
I had a '70 nova as a kid that did the same thing. It might work all day, or drop to the floor without warning, but would pump back up.
In that case I replaced the MC with one from the trash pile. when I took the old one apart the cylinder bore was pitted at one end.
 

·
Registered
Joined
·
877 Posts
Discussion Starter · #18 ·
I had a '70 nova as a kid that did the same thing. It might work all day, or drop to the floor without warning, but would pump back up.
In that case I replaced the MC with one from the trash pile. when I took the old one apart the cylinder bore was pitted at one end.
Which brings me back to defective seal or machine error on the OEM FZ 09 master cylinder.
 

·
Registered
Joined
·
225 Posts
Which brings me back to defective seal or machine error on the OEM FZ 09 master cylinder.
Agreed, it seems like the probable solution to me.
 

·
Registered
Joined
·
14 Posts
My wife and I each have FZ-09s. Ever since they were first delivered, my brake was way more spongy than my wife's. The first thing I did before ever even riding mine was a brake bleed. It did nothing. I have just been riding with a soft brake until last time we were out, we swapped bikes and damn it's nice to ride with brakes! So it seems there might be an issue with the MC on some FZ's?
 
1 - 20 of 34 Posts
Top