Rear Brake "Joint" Failure

[SouthSoundRider]

I thought I better mention this as I don't hear about rear brakes failing on Street Motorcycles often.

When riding earlier this week I couldn't figure out why there was suddenly so much play in the rear brake pedal. Yamaha OEM Part # 5SL-27222-00-00 failed, i.e. broke. It's called the "Joint" and listed as Reference #14 under the Rear Master Cylinder category of any Yamaha OEM Parts website vendor.

I don't stomp on the rear brake and use both front and rear brakes and I would describe my use of brakes as conservative. My guess is that there is a manufacturing defect in the part, likely old fashioned inferior aluminum/alloy. It failed, as you can guess, at it's weakest point, where the Pin (ref # 22 in the diagram) inserts into the round hole to connect the rear brake lever to the master cylinder.

It was about $40 to replace all the parts I left on a street somewhere in Oregon! That's cheap compared to your life though........

 

[HotRodZilla]

Hmmmmm, probably first reported failure ever, which makes me think, not a defective part issue. My bet would be on improper reassembly after someone took it apart for a service.

 

[SouthSoundRider]

No one touched it except for the mechanic that took it out of the crate and serviced it when I bought it. Let's hope this is the first and last reported failure ever.......

 

[wfooshee]

That may be the most unstressed moving part on the entire motorcycle.....

Are you saying one side of the fork broke in two at the hole? I wonder if someone got a bit enthusiastic with a wrench on that nut and twisted it somewhere.

That part simply can't fail unless it was damaged before or during assembly, and by damaged, I mean already broken or cracked. All it does is push on the master cylinder's piston. It doesn't turn, twist, or pull anything. It's never under tension. It has no "weak points."

I'm not saying that I don't believe yours broke, I'm saying that you're not onto any recall-level defect discovery. Whatever made it break happened before the bike was put together, if that joint has never been removed, cleaned, or otherwise serviced. That's not even one of the dealer-installed pieces, it comes assembled in the crate.

 

[majicmaker]

That may be the most unstressed moving part on the entire motorcycle.....Are you saying one side of the fork broke in two at the hole? I wonder if someone got a bit enthusiastic with a wrench on that nut and twisted it somewhere.

That part simply can't fail unless it was damaged before or during assembly, and by damaged, I mean already broken or cracked. All it does is push on the master cylinder's piston. It doesn't turn, twist, or pull anything. It's never under tension. It has no "weak points."

I'm not saying that I don't believe yours broke, I'm saying that you're not onto any recall-level defect discovery. Whatever made it break happened before the bike was put together, if that joint has never been removed, cleaned, or otherwise serviced. That's not even one of the dealer-installed pieces, it comes assembled in the crate.

I agree!! There's no way that level is going snap in two all by itself.

 

[SouthSoundRider]

Guys...I'm not a mechanical engineer but when something has a hole in it and part of it doesn't , that defines a weakest point by anyone's definition. The stress, pressure or whatever terminology you'd like to use is real. That is how your foot energy converts into your rear brake pads clamping on your rotor..through the mechanics and hydraulics of the braking system.

Anyway, I am just reporting what happened and what I can hold in my hand. It's okay if you believe or think otherwise. I would feel pretty bad if I didn't mention it and someone was injured because I didn't speak up. I have found these Forums very helpful.

 

[stealth1]

I believe you.

I also believe a company can make 100,000 copies of a part and there's a chance 1 of them will be defective.

I don't suppose you still have what's left of the broken part and could post a picture.

I would be interested in seeing it.

 

[infrared]

Guys...I'm not a mechanical engineer but when something has a hole in it and part of it doesn't , that defines a weakest point by anyone's definition. The stress, pressure or whatever terminology you'd like to use is real. That is how your foot energy converts into your rear brake pads clamping on your rotor..through the mechanics and hydraulics of the braking system.Anyway, I am just reporting what happened and what I can hold in my hand. It's okay if you believe or think otherwise. I would feel pretty bad if I didn't mention it and someone was injured because I didn't speak up. I have found these Forums very helpful.

SouthSoundRider,

There are many reasons why any part can fail. Glad to hear about this failure, and I would not doubt there is more to the story. As just one scenario, hardening a metal part can make it stronger, but that process can also make the part become brittle. A "softer" part might bend or "give" a little, where a brittle part may just shatter. A part that somehow goes through the hardening process twice could make for a "one of a kind" failure. In this case, pictures may help with the detective work, if you can do that.

Cheers,

Infrared

 

[HotRodZilla]

Don't get us wrong, we're not doubting you, we're just wondering what happened. That's a pretty weird part to break, and like Walt, I was thinking someone twisted it or did something to it that shouldn't have been done. Maybe it was just a bad part. It could happen, it's just VERY uncommon.

FWIW, I'd like to see a picture also.

 

[Fly Bye]

Hmmmmm, probably first reported failure ever, which makes me think, not a defective part issue. My bet would be on improper reassembly after someone took it apart for a service.

How timley, I have the same problem on my '08.

It happened just before taking off for SW-FOG.

A J, I hope you are correct in your assessment and SouthSound Rider thank you for the post.

The FJR in going to be looked at this coming Tuesday.

I'll post up what they find.

 

[Constant Mesh]

If it's like mine there's a bit of slop in that pinned connection.

When you first press the pedal the master cylinder rod doesn't move.

So, there's a bit more acceleration and force on the pinned connection due to the looseness of the joint.

 

[Fly Bye]

If it's like mine there's a bit of slop in that pinned connection.
When you first press the pedal the master cylinder rod doesn't move.

So, there's a bit more acceleration and force on the pinned connection due to the looseness of the joint.

It just feels like mush with very little break at the bottom.

 

[Constant Mesh]

Adding an o-ring on the pedal shaft between the back vertical plate and the footrest bracket bushing might be beneficial. This would help keep the lube contained between the bushing and the pedal shaft. On mine the lube migrates out over time and covers the vertical plate. An o-ring would help keep the lube in and dirt and moisture out. You could also add a second o-ring on the shaft between the pedal and the bracket bushing.

 

[Geezer]

I've seen parts fail due to poor manufacturing or a bubble in the casting. Every once in a while something like that slips past quality control and gets into production.

For example, I remember TWN had a chunk break off of his triple tree when he was taking the fork tubes out for service.

I'd like to see a picture of the failed part showing as much of the actual failure as possible.

 

[Mihalis fjr]

Adding an o-ring on the pedal shaft between the back vertical plate and the footrest bracket bushing might be beneficial. This would help keep the lube contained between the bushing and the pedal shaft. On mine the lube migrates out over time and covers the vertical plate. An o-ring would help keep the lube in and dirt and moisture out. You could also add a second o-ring on the shaft between the pedal and the bracket bushing.

Sounds very good..!

 

[wfooshee]

That part could last 100,000 years with no grease. As a matter of fact, there is no provision whatsoever for greasing it. It doesn't need any grease because there's no motion of its parts relative to each other. The pedal pushes upward on the cross-pin, which pushes upward on the joint piece, which pushes op the cylinder piston. The pieces bear weight, but they have no rotation or any other motion against each other. Grease serves no purpose whatsoever in that joint.

A casting defect with a big bubble inside right where it's supposed to carry that weight, that would do it. A tweak on the assembly line somehow, twisting the part and maybe cracking it, that would do it.

But without those, that part should last as long as the planet.

 

[bluesdog]

That part could last 100,000 years with no grease. As a matter of fact, there is not provision whatsoever for greasing it. It doesn't need any grease because there's no motion of its parts relative to each other. The pedal pushes upward on the cross-pin, which pushes upward on the joint piece, which pushes op the cylinder piston. The pieces bear weight, but they has no rotation or any other motion against each other. Grease serves no purpose whatsoever in that joint.
A casting defect with a big bubble inside right where it's supposed to carry that weight, that would do it. A tweak on the assembly line somehow, twisting the part and maybe cracking it, that would do it.

But without those, that part should last as long as the planet.

Nah. It needs a zerk, man!

 

[Fly Bye]

Reporting back, as promised.

I took the '08 to the local dealership to have front and rear tires replaced, I mentioned to the service manager to please flush and replace the brake and clutch fluid.

I did not mention that the rear brake was mushy.

I figured if the tech found something they would let me know.

After picking the FJR up I immediately tested the rear brake and it was back to perfect working order.

I will be changing these fluids on a regular bases from now on. Lesson learned.