Rear brake master cylinder rebuild time?

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henwil

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Hi Folks,

I am having issues with my rear brake, and here are the symptoms:

- When riding using the rear brake has no braking power. The pedal goes all the way down.

- When on the center stand and in neutral, I can spin the rear wheel by hand. I can push the pedal all the way down with my hand, and then I can't spin the wheel.

- There is no fluid leak anywhere.

- It takes about five seconds for the pedal to return to the upper posisiton on its own.

- I have not been riding my FJR much over the past few years, and the brake fluid flush is definitely overdue.

- Mileage is about 64k.

I friend thinks that it is the master cylinder that needs a rebuild, and that just flushing the fluid will not fix it. I tend to agree, but I am no expert.

Should I first do a brake fluid flush and see what happens? Does it sound like I need to rebuild the master cylinder? I just don't want to go through all the trouble and then find out that it was something else due to my wrong assumptions.

Thanks for any input!

 
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FJRay

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I would bet if you do a good job of lubing the brake pedal pivot and then bleed and flush the system including the front because they are linked you will solve the problem. Both items should be on your annual maintenance schedule.
smile.png


 

RossKean

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^^^ +100

The lower front right piston is activated with the rear brake pedal and is frequently the culprit when it comes to ineffective rear braking. Bleed the lower front right piston pair using the rear brake pedal, followed by the rear caliper.

As Ray said, that rear brake pivot is a key maintenance item (at least annually). Remove the lever from the pivot, clean thoroughly and use a generous coating of waterproof grease.

I think it is VERY unlikely that the master cylinder needs to be rebuilt or replaced!

 

Gen2Jockey

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I had a similar issue but with braking power. Turned out the brake lever pivot was sticking. FJRay has the right plan. Don't forget to bleed the linked right front caliper (Gen II ABS).

 

henwil

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Thanks Guys! Much appreciated.

I am going to lube that brake lever pivot first.

 

rbentnail

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After clean & lube of pedal and replacing brake fluid, cycle your ABS. It's in your service manual and there's a thread on this forum title "test and maintain your ABS system". There's even a switch setup for sale to do it with.

 
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Panman

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Gravel Roads work for cycling the ABS and for a few reasons.

They build confidence in the ABS system.

It cycles the fluid in the ABS pump.

You can feel the ABS pump working so you know it's there for you when you need it.

Do it be fore and after each fluid flush. (Should do the flush at least every other year if not every year).

Don't be afraid to grab the brakes hard, the ABS will just kick in and save your but.

I never have kicked in the ABS in and emergency and I can stop the big girl pretty quick.

 

harper

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I use the gravel road test Panman cites above. I run up to 20mph and stand on the rear only. Then I run up to 20mph and grab lots of front brake. Then I run up to 20mph again and hit both brakes hard. I do this at least twice a year and after flushing.

 

henwil

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Well it looks like you guys were spot on!

After I greased the brake lever pivot it released instantly again. It does not look like there has ever been any grease on that pivot.

My son helped me and first we bled the front brakes left and then right. Unfortunately we must have had a coordination issue that sucked some air, since the front brake is very soft now. We will bleed it again tomorrow to get the air out.

Then we bled the linked front brake. Some air came out and instantly the softness on the rear pedal went away. Great. Then finally we bled the rear brake caliper.

Tomorrow we will get the air out of the front brake line, and then I will go cycle the ABS.

 
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dcarver

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Gravel Roads work for cycling the ABS and for a few reasons.They build confidence in the ABS system.

It cycles the fluid in the ABS pump.

You can feel the ABS pump working so you know it's there for you when you need it.

Do it be fore and after each fluid flush. (Should do the flush at least every other year if not every year).

Don't be afraid to grab the brakes hard, the ABS will just kick in and save your but.

I never have kicked in the ABS in and emergency and I can stop the big girl pretty quick.
Take it a step farther and learn to turn w/ ABS engaged. Not natural response, takes time to develop reflex memory in panic situations..

 

henwil

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Fortunately it looks like I got rid of the air in the front brake line by tying the lever closed overnight as suggested in another thread.

I watched the YouTube video from twowheelobsession regarding brake fluid flush, and he mentions cycling the rear brake ABS and then doing a flush again on the rear brake.

So is the procedure?:

- Flush the lines front and back.

- Cycle the ABS front and back as described above. This releases the old fluid inside the ABS pump.

- Then flush all the lines again to get rid of this remaining old fluid that was released.

Thanks!

 

RossKean

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Unless the fluid was exceptionally crappy, I doubt that a second flush is necessary. But DOT4 is pretty cheap and the process isn't particularly onerous. Do whatever makes you feel good.

 

rbentnail

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Fortunately it looks like I got rid of the air in the front brake line by tying the lever closed overnight as suggested in another thread.I watched the YouTube video from twowheelobsession regarding brake fluid flush, and he mentions cycling the rear brake ABS and then doing a flush again on the rear brake.

So is the procedure?:

- Flush the lines front and back.

- Cycle the ABS front and back as described above. This releases the old fluid inside the ABS pump.

- Then flush all the lines again to get rid of this remaining old fluid that was released.

Thanks!
That's basically what I do. Mostly the 2nd time is just to use up all the new brake fluid in the qt I bought. When you practice it a couple times exactly 1 qt is what you'll use.

While you're at it, replace the clutch fluid. It takes the same stuff.

 

henwil

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I did replace the clutch fluid as well. Thanks for the reminder.

Since the fluid was older than I am willing to admit, and my wife bought me 32oz of new fluid, I will just flush everything again once I had a chance to cycle the ABS.

I assume that the ABS will give an error code if it is not working for some reason. I would hate to grab the front brake just to find out the ABS is not kicking in :p

 

rbentnail

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I would, if I were not sure if my ABS is functional, definitely NOT try it on a sandy (or any other type of) road. The ABS test connector is a simple way to ASSURE it works before you ever move the bike. I don't disagree with actuating it once in a while for training and/or practice but I believe in making sure it works first. Doing it with the test connector and an alligator clip once a yr or every other yr ain't gonna kill ya. Or you can one-time install a test harness -> https://www.fjrforum.com/forum//index.php/topic/175921-fjr1300-abs-test-harness/.

edit: I have pics in dropbox to show the test connection location and function if you want them.

 
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Gitbox

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I use a nice flat dirt road for ABS testing - just in case...
smile.png


You can look at the tire track to see the where the brakes are pulsing. Pretty neat.

 

RossKean

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If you are careful and travelling in a straight line on a dirt road or a sandy parking lot, there isn't much danger in testing the ABS. If it isn't working, there shouldn't be much trouble recovering from a minor skid if the brake locks up. The jumper is safer if you aren't comfortable with the parking lot or dirt road.

 

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