Why the inside pads wear faster

[Constant Mesh]

I've noticed on my '04 that the front inside brake pads wear more rapidly. Why? I asked the service manager at my local dealer about this. He has an '05 FJR and has noticed the same thing. We discussed it a bit and concluded the following:

The inside pads bite first by design due to the hydraulic design of the caliper. The fluid leaves the banjo bolt on a straight shot to the inside pistons. So most of the fluid flow is first introduced to the inside pistons. Then the fluid flows down, crosses under and up to the outside pistons. Some flow must go directly from the banjo bolt to the outside pistons. Otherwise it would be difficult to bleed air bubbles from around the outside pistons, etc.

The SM called Yamaha Tech in California and they said "yes, it's normal for the inside pads to wear more". They didn't explain why but once one looks at the caliper design you can see how the inside pads might first experience the pressure buildup when the master cylinder is actuated. The outside pads likely experience a slight delay with a bit less pressure initially.

 

[SkooterG]

Interesting theory, and I ain't no expeeert on hydraulic theory, but I am having trouble buying into your 'inside pads might first experience the pressure buildup' hypothesis. Hydraulic pressure should be instantaneous and equal across whatever surface it is acting on.

 

[Ignacio]

Hydraulic pressure should be instantaneous and equal across whatever surface it is acting on.

I concur with my spinning-enhanced icon friend. Pressure is going to be the same throughout the system. I'm not buying the dealer logic there.

I think piston schmutz is a much more likely a candidate. Especially since we early FJR owners really haven't been replacing things like the manual suggests. Just a little muck in in that all-important seal area between the piston and the seal will make a big difference in wear. Start rotating pads if it bugs 'ya or get out your toothbrush and clean up those pistons with a bowl of Brake Kleen while watching America's Top Model like talked about here and many other places on the forum.

The other possibility are slider pins. They also should be clean and lubricated for proper action.

I've seen and experienced multiple Gen 1 bikes that wear evenly and unevenly. My experience is there's correlation between to the amount of crap on a caliper (or lack of caliper maintenance) and wear unevenness.

 

[Bustanut joker]

Thoughts...

The inside pads, like inside people, sit around all day watching springer and eating chips. When called to duty they are so outa shape they tire or wear out faster than us who play outside. Simple enough right?

 

[Constant Mesh]

Pressure drops occur in any fluid as it flows through pipes, lines, hoses, calipers, etc. When the master cylinder piston is in motion moving fluid pressure drops occur throughout the system. Once the master cylinder piston reaches its final equilibrium position and flow stops the pressure throughout the system will equalize and all eight pistons will experience the same fluid pressure. As long as fluid is moving pressure drops and differentials will occur.

 

[Redfish Hunter]

Pressure drops occur in any fluid as it flows through pipes, lines, hoses, calipers, etc. When the master cylinder piston is in motion moving fluid pressure drops occur throughout the system. Once the master cylinder piston reaches its final equilibrium position and flow stops the pressure throughout the system will equalize and all eight pistons will experience the same fluid pressure. As long as fluid is moving pressure drops and differentials will occur.

While that is all true, the amount of pressure drop and the time delay would be so slight in a system with that much pressure and such small volume that it would be virtually unnoticable. If the delay were great enough to cause that much difference in wear rate, you would probably be able to feel it as the outside pads came in progressively. That does not happen.

In fact the pressure to force the pistons out (clamping) during braking is much greater and faster than the vacuum (releasing) at the end of the braking cycle. Which is to say that when you grab the brake lever the force you apply is much faster and more powerful than the retracting force when you release the lever. Going by the logic of your theory, this would in fact cause greater wear on the outside pads because they would release much more slowly and therefore stay in contact with the rotor for a longer period.

I think that Ignacio is correct, dirt/crud inside or outside the system is preventing perfect clamping/releasing of the caliper.

 

[wfooshee]

The pressure difference from inside pad pressure to outside pad pressure, if it even exists, is momentary (picoseconds) and minimal (grams per sqaure mile.) The pads, even if they did touch the pads first, then stop moving until the ouside pads touch, because they cannot generate enough pressure to create friction as all the pressure buildup moves to the outside pad. Untill ALL the pistons are firmed up, there is not enough pressure to actually drag the pad on the rotor.

Which is good, or you'd bend your rotors.

OK, my units were kinda pulled out of a dark and unholy place, but you get the drift. Gunk buildup that keeps the pads from releasing evenly is the reason for uneven wear.

 

[Checkswrecks]

I'll go with Iggy's slider pin thought and add that the uneven wear phenomenon is not just in disc brakes used on motorcycles.

The applied force would be in proportion to hydraulic pressure for the inside pucks.

The outside would get the same hydraulic pressure, but the total mechanical system is more than hydraulic pressure at work. The force applied would be reduced ever so slightly by the crud and torsion on the pin that create friction. The difference in pounds would be very little if you measured what got applied to either side of the disc, but enough to wear the pads differently over a long period.

Plus Fooshee's gunk as far as releasing the mechanical system.

 

[Constant Mesh]

You guys are off on the wrong track. The Yamaha tech guy said the inside pads do wear more simply because the inside pads always bite first into the disc. It's a small difference but the effect accumulates over time with additional wear. A similar phenomenon occurs with more wear on the left side of tires. The additional wear results from the left side traveling more miles over the tire's lifetime. The distance traveled in a curve to the left is always more than the distance traveled in a curve to the right for those who drive on the right side of the road.

S = r theta, where S is the arc length, r is the radius, and theta is angle of the arc.

Since r is larger for a left hand curve S is also larger. The left side of the tire travels more miles so it wears faster. Maybe if you always ride on the center line so that r is equal for both left and right curves you can equalize the tire wear.

The Yamaha guy said the pad wear phenomenon is a quirk of the caliper's design. It wasn't intentional, just a fumble by the designers.

 

[Ignacio]

The Yamaha guy said the pad wear phenomenon is a quirk of the caliper's design. It wasn't intentional, just a fumble by the designers.

Well that's a completely different notion! And it can be true, but not necessarily because of alleged hydraulic pressure in one area of the brake being greater or earlier than another.

There could be a design shortcoming that is a friction issue--possibly through binding of the slider pins.

I've seen brakes that wear close to evenly, many that favor the one pad, but none that favor the other. This detail still points to gunk as a cause.

Maybe there could be two factors here. Design and gunk. I just don't think any of the factors in the design question are localized hydraulic pressure.

 

[Redfish Hunter]

First, I understand and appreciate about the tire wear but it has no relevance to the brake pad wear.

Second, I don't know your Yamaha tech and I am sure he is a smart guy so I will not insult him. I wonder about his qualifications and knowledge of hydraulics. I am more than certain based on my knowledge of hydraulics that my original explanation above is the correct one. If you notice every single person who responded said exactly the same thing, we just used different wording.

In the end, it does not matter. The pads wear at different rates, you know it, the tech knows it, we know it and Yamaha knows it. Replace them as needed. Whatever our individual theories are will make no difference to the outcome. If it makes you happy to think that your explanation is the correct one, then by all means continue with your theory.

 

[fjrob1300]

I can't believe I just read all this. Give back my 5 minutes!!!

 

[wheatonFJR]

I can't believe I just read all this. Give back my 5 minutes!!!

What? Did this interrupt your Three Stooges reruns ??

 

[Bustanut joker]

Get as logical as you must.. My example is the Only logical explanation...............

 

[Fred W]

You guys are all way off base here.

The reason that they designed the inside pads to wear faster is because they are much harder to see.

If the outer pads wore fastest it would be far too easy to know when it was time to rotate or replace the pads.

 

[fudgejerkin1188]

You guys are all way off base here.

The reason that they designed the inside pads to wear faster is because they are much harder to see.

If the outer pads wore fastest it would be far too easy to know when it was time to rotate or replace the pads.

Now there is an explanation I like and can understand

 

[Bustanut joker]

You guys are all way off base here.

The reason that they designed the inside pads to wear faster is because they are much harder to see.

If the outer pads wore fastest it would be far too easy to know when it was time to rotate or replace the pads.

Hey Yogi.. Hows the afterlife?

 

[Redfish Hunter]

Get as logical as you must.. My example is the Only logical explanation...............

You know after I re-read everything, you might just be right. It makes as much sense as anything else...

If it were actually a delay in the hydraulic flow, it would be exactly the same on every bike and every set of brake pads. All of them would wear exactly the same, and we know that they don't. The differences bike to bike have to come from an outside influence. Road gunk on the pins, whatever.

At the end of the day it does not matter. If I think that it is because at night pink unicorns come and piss on the rotors, that is my priviledge. I don't have to be right, I just have to think that I am.

 

[Bustanut joker]

Flying unicorns? You klown!! Everyone but scooter knows only pigs fly.. U r such a simpleton