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Rear Brake Failure after service


adamv

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Hi,

 

I'm looking for some suggestions.

 

I recently had my VFR serviced. During the service, they replaced the rear brake pads.

 

After the service, I took my bike for a ride, and felt that the rear brake was a little spongier than normal. I figured that it may just be me or maybe that's the effects of having new pads on.

 

About 40 miles later, going through some mountains I went to apply the rear brake, and then pedal just went down - right down well past where it normally does with no resistance at all - and there was no braking at all. (I was only applying rear brakes - I didn't notice or feel any braking from the linked/front wheel at all).

 

After pulling over, I could use a single finger and push the brake down a significant way without any back pressure. If I pump the brakes, the pressure slowly builds up and the brakes come back online.

 

I reported this to the shop who said that they only replaced the pads. They hadn't replaced the brake fluid, and that there's nothing that they have done that should have caused this to occur.

 

They had another look, and ended up replacing the rotor telling me that the rotor was on it's way out (wearing thin) and that's most likely the problem.

 

It didn't make much sense to me, as if the rotor was thin I'd expect it to be consistent with issues, but I'm no mechanic, so left it in their hands.

 

I took the bike riding again, and found the brake still a bit spongy, but it was working again. I did notice a vibration through the rear brake on occasion if I applied the brake lightly. My mates said this may just be due to the new disk, and to hit the rear brakes hard to wear them in, which I did. I only noticed the BRRRRRR vibrations a few times.  (This is a NON-ABS model).

 

I then went and toured around 2,500 miles without having an incident with the rear brake until this weekend, where it did the same thing as straight after the service (just goes straight down again with no pressure).

 

I'm not sure what to do. I'm no mechanic and have very limited understanding on the workings of bikes. The shop swears that they haven't touched anything in the brake lines and that they only replaced the rotor and the pads, and they have been unable to find anything wrong.

 

Has anyone experienced this before, and/or do you have any recommendations on what I can do or where I should look?

 

Cheers

 

Adam

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My initial reaction would be to think that they messed up when they replaced the pads. They could have pulled

the pads, hit the lever, and pushed the piston/s out, then screwed up a seal when they replaced them. But not

screwed up the seal enough to completely fail but enough to cause issues. Not necessarily a cut but perhaps a fold

or crease, but whatever it is the seal isn't working as it should.

 

My other thought is they pulled the slave cylinder, and pushed the slave cylinder out. Why they would do this

I have no idea. This led to the need to bleed the brake, and then a poor bleeding job resulting in mushy brakes.

Also they may have folded/creased the seal and cause it to fail partially, but reset itself, but is prone to do the

same thing all over again.

 

Any way you look at it they screwed the pooch and are not admitting it. If you're not a mechanic, then you need to

have someone look at it that knows how things are supposed to work. Something is not right, and it's downright

dangerous to keep riding it as is.

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Hi Adamv.

Sorry to hear of your issues.

Further to what FJ12Ryder has mentioned. I personally believe the need to replace your rear brake rotor to be utter bullsh@t. With new pads, there is no way even a badly worn rotor would cause next to no braking and a pedal you can fully depress with your finger! Even if that was the case, it wouldn't happen just after a pad change which in fact would lessen the effect.

 

If your reservoir is properly full and you are not losing fluid from somewhere, and provided the seals are not damaged then most likely air has entered the system. If you had NO brake issues prior them changing your pads then there is an extremely high probability they've stuffed up. Your statement of "pumping the brakes brings back brake pressure" points to air in the system.

 

I would fully flush/bleed the rear brake system with Dot-4 fluid and re-assess your situation. 

 

Unless they can show you that the rotor was worn below limits (5.0mm minimum thickness) then I would be chasing a refund, as you have proven the rotor is not the cause of your issues.

 

Couldn't agree more in what FJ12Ryder stated. You have a very dangerous situation on your hands and it needs to be positively sorted out ASAP.

 

Good Luck.

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Hi Guys,

 

Thanks for the reply.

 

When you're mentioning the seal (being folded, etc) - is this something that if I took to another mechanic they would be able to easily identify if it has been crushed / folded, or is it something that you can't really tell when you remove it (because you have to damage it to remove it, etc), and it just has to be replaced and see what happens?

 

Also would this be a costly thing to get another mechanic to do? (To replace the seal, and/or reset the pistons).

 

Primarily I would very much like to have a positive identification on what the cause is, in part to go back to the original shop and inform them, but moreso to know that the issue is resolved and I can have peace of mind.

 

Thanks

 

Adam

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Well, since I think the issue is with the slave cylinder, I think it's possible any damage would be visible if

you remove the piston, especially since it has happened again. And you can take the slave cylinder apart

without any damage to have a good look see. And to make sure no foreign material has been introduced.

 

I hadn't considered the possibility that they introduced some junk into the system when they did the job,

but it could have happened. I think a thorough look-see and flush is in order.

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It's a misconception that the pistons can be accidentally popped out with the pads removed. If you have ever tried to extend the pistons to clean them, you will see how many times you have to push the lever to get even a small movement. If a single lever throw would move the pistons full travel the brakes would uncontrollable and would lock solid at the lightest touch. Not to mention that the pistons are longer than the available space inside the caliper. Again, if you have ever tried to rebuild the calipers you would know that it's required to split them to remove the pistons.

Take it to a trusted mechanic and have the system fully bled. Even a fellow VFR rider who is experienced in their own maintenance as the linked brakes can be a bit tricky if you are used to unlinked.

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What you're saying is true, but if only one piston is free to move, the other one is blocked, and the brake

pedal gets pushed full down a couple times, I'm not so sure the piston won't come most of the way out.

 

Just an opinion of course. But if these guys screwed up and won't admit it, it makes a person wonder how

badly they screwed up.

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I'm with Buzzner on this, one accidental push won't cause a piston to pop out. And if the seals were buggered, I think you'd have fluid leakage there.

 

The disk replacement sounds to me like the shop seeing an opportunity to sell a part and install it while just bleeding the brake to fix your problem.

 

That the problem occurred in the first place is a bit mysterious, but they would have had to push the pistons back to fit the new pads and maybe that has pushed some crud back to the master where it is causing some intermittent pressure loss. I agree with Grum that a flush out is probably the first step. 

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Sounds like some sound advise has already been given but I think I'll odd a comment on the vibration issue. If it only happens when using the rear pedal only and not with or in conjunction with the front lever, I have experienced a vibration too. I appears that it comes from the front left caliper, it seems that when the center piston is the only piston applying pressure to the pad (as what happens with the rear pedal being pressed) it can sometimes vibrate in the caliper. When I feel this happening, I just do a light squeeze on the front brake lever and the vibration stops. I can also make it go away if I press harder on the rear pedal but I prefer the light squeeze of the front lever. I believe that the two out pistons creates a more equal pressure on the pad and helps quell the vibration.

 

That being said, I would pull the seat off and look at the PCV bleeder as well as the rear and front SMC bleed points and see if there is fluid leakage, as it sounds like the system has air in it. Where that air was introduced at is the big question. Worse possible scenario is that there is a hole or slit in the line. Also, what does the rear reservoir level look like?

 

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13 hours ago, Marooncobra said:

Where abouts are you in Oz? Anywhere near Maroubra, Sydney as I am happy to come round and assist you in fixing the issue.

Thanks very much for your generous offer, but unfortunately I'm in regional Victoria. (so not even in the same state) :-)

 

To answer the other questions - Reservoir levels look fine.  I'm going to see if I can find someone who's mechanically minded  (unfortunately we only have this one shop in town), to look at bleeding the brakes, and maybe at the same time check to see if we're able to inspect the seals.

 

The seals are the suggestion that intrigues me the most at this stage along with bleeding the brakes. If the seals were creased or damaged, but not broken, under certain conditions (temperate, atmosphere, etc) - maybe they let some leak out on the very odd occasion which causes this. Anything else such as a brake in the line and I'd be expecting the problem to be getting consistently worse. But as said, I'm no mechanic.

 

Are the seals exposed when changing the brake pads? As mentioned, the shop swears they didn't touch the fluid in the line, and whilst I've lost confidence in them I still doubt (and hope) that they would outright lie about something like that.

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Its possible you boiled your brake fluid because it was contaminated with moisture and your new pads generated excessive heat...

 

Understanding Brake fluid

DOT 3 DOT 4 and DOT 5.1 are Glycol based brake fluids whereas DOT 5
are Silicone based... Glycol based fluids are designed to signal
moisture contamination by changing color... the fluid will start to
turn golden, then light brown, then dark brown indicating that it has
absorbed progressively more moisture. Eventually, if left unchanged
beyond the recommended service interval, the fluid will become dark
and yukky, indicating high amounts of water absorption and thus badly
contaminated fluid... user friendly Glycol based fluids also reduce
the effect of both corrosion and compressibility because it is not
only designed to accept significant amounts of moisture, but even to
neutralize it by dispersing this moisture evenly throughout the
system, thus preventing its concentration in any one area...


Boiling point of Glycol based brake fluids
DOT 3 205 °C (401 °F)
DOT 4 230 °C (446 °F)
DOT 5.1 270 °C (518 °F)

DOT 5 Silicone based fluid will not turn color to signal moisture
content...

Boiling point of Silicone based brake fluids
DOT 5 260 °C (500 °F)

If you wish to use the latest in Glycol base fluids then its DOT 5.1

Note: DOT 5 silicone was created at the request of the military for
use in vehicles that are required to be parked for years at a time and
be ready for deployment. Harley-Davidson used DOT 5 until a decade ago
because it would not negatively affect paint but currently specifies
DOT 4 or 5.1

WARNING: Dot 5.1 glycol (yellow) and Dot 5 silicone (purple) will not mix.

 

Moisture Contaminated
attachment.php?attachmentid=515996&stc=1

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Thanks all for your replies.

 

I've found someone who's going to be able to help me out. Going to get the brake lines flushed, the seals checked, and I'll get new pads and rotors on the front while I'm at it I think just to make sure all is well and good.

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Please come back when you get it all lined out and tell us what the results were.

It helps to know so you can tell the next guy what he might check next.

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I actually had the same problem once only on a 8th gen, hasn’t happened again since. It was around 9,000km since it’s previous service. I was riding down a very twisty downhill road but I am no Marquez so would be surprised if it was a overheating of the brake fluid problem in my case. It is due for it’s next service in 1000km and brake fluid will be changed then.

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3 hours ago, Philois1984 said:

I actually had the same problem once only on a 8th gen, hasn’t happened again since. It was around 9,000km since it’s previous service. I was riding down a very twisty downhill road but I am no Marquez so would be surprised if it was a overheating of the brake fluid problem in my case. It is due for it’s next service in 1000km and brake fluid will be changed then.

Hi Philois.

The rear brake on the 8gen is very easy to flush, so is the front for that matter. Your bike is out of warranty - not interested in doing the job yourself?

Hate other people touching my pride and joy, unless it's out of my ability.

Can assure you if using the rear brake down a lot of mountain twisties the brake will get very hot, surprisingly far hotter than the fronts. Just try it the next time you do a run using some of the rear brake, as per your twisty downhill road, pull over at the end and have a touch of the front and rear rotors!

Cheers.

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  • 2 months later...

Make sure the slider pins for the caliper are well-lubricated. Also, make sure the pad bracket is lubricated at the contact points withe brake pads. And, finally, make sure the brake pad pins (the screw that goes through one end of each brake pad to hold them in the caliper) are smooth and allow the pads to slide without binding.

 

I suspect the rear pads are binding. When you apply the rear brake they stay applied even as the caliper seal pulls the piston back. When you engage the rear brake again, the lever sinks to the handle because the caliper piston is now pushing out without any resistance.

 

An update would be great!

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