Uneven Brake Pad Wear

[Blue Dave]

Brakes??? I didn't know that these 4 strokes had brakes. LOL

LOL! How true! I rarely use my brake now that I have mastered using the engine braking for cornering. It really throws off my two stroke buddies when they are trying to follow me through the twisties fast at night and they do not get any brake light warning from me on all but the sharpest corners.

Seriously, I am beginning to suspect that the uneven pad wear is not being caused so much from when the brakes are applied but rather by the constant slightly uneven drag between the pads and the rotor caused by the pistons trying to self center themselves over my rotor which is about 1 mm off center with respect to the caliper. What do the rest of you guys think about this theory?

 

[Soldier'spapa]

All four pistons move easily. To install the new pads I pushed all four pistons all of the way back in using just my thumbs.

B.D.

In all my years of auto repair, uneven wear indicates that parts intended to move freely are not... this is assuming, however, that the rotor surface is consistent on each side and pad linings are of the same composition.

With the caliper mounted in a fixed position this leaves only (in this case) the pistons within the caliper or an unbalance of hydraulic pressure between the two sides of the caliper... but the problem is within the caliper. I doubt there is a pressure balance problem. There is likely a simple open passage between the two sides and unless there is a large chunk of debris inside blocking off the fluid transfer I would rule that out.

You stated that they compressed back into the caliper freely... Did you try extending them out? I believe this is where the problem is. If you were to pop the pistons out I suspect you would find some sort of pitting/corrosion that slightly inhibits movement of the two pistons as they travel out towards the rotor. I think it will be the pistons related to the thicker old pad (forgot if you said it was inside or out).

It might need new pistons and a rebuild.

 

[thor452]

I have never seen a apex that didnt wear the pads exactly as dave discribed in fact i too have a single brand new pad hanging in my garage as well from my 07 apex only wearing out the one pad i dont think there is any thing wrong with the sled i think it is a design flaw. please let us know if you are able to center the brake disk as i remember the shims are all on the out side and you may have to machine down the spacer with the torx set screw to move the rotor the direction you need to center it.

 

[Blue Dave]

Since so many other guys have apparently experienced the same uneven wear I am inclined to rule out pitting / corrosion induced piston sticking or any other malfunction. Especially if everyone is reporting that the same (outboard) pad wears much faster than the inboard pad.

Instead I would tend to agree that it is more likely a design flaw. For me it is too much of a coincidence that my outboard pad (which had more wear) has to push the pistons back more than the inboard pad does because the rotor needs to move 1 mm towards the chain case to be perfectly centered.

I think that the inboard and outboard pistons inherently want to self center themselves when the brakes are NOT being applied and consequently if the rotor is not centered then one pad will have slightly more constant (non braking) friction against the rotor which over time makes it wear faster.

 

[Soldier'spapa]

I read earlier in this thread that many guys have reported the same wear. Although typical it seems for Apex's... it doesn't make it right.

The pads are not actually pushed back. They ride against the rotor when not in use and are pressed tighter when the lever is pulled. If one side is closer when the caliper and pads are first installed you're right the pistons self adjust and in theory should apply equal pressure right from the start resulting in even pad wear.

I wonder if any of these sleds with this same wear have ever had the brake fluid flushed regularly as maintenance? Contaminants build and are suspended in the fluid. In time this will interfere with moving parts. I flushed the fluid a couple times on my 07 Attak over the years I owned it. While the sled is sold so I'm unable to see the pad condition today, I don't recall uneven wear the last time I flushed the brake fluid. I'm also a stickler for maintenance.

I'm not saying shimming the caliper will not change the condition... just don't think it will.

In the end, as long as there are no fluid leaks and the caliper provides sufficient braking, this is not a safety issue and can be left alone. I simply am intrigued by the condition and am interested in finding the solution.

 

[Blue Dave]

SP,

First of all thank your son or daughter for their service! I also am intrigued by this condition which seems to be prevalent in older Apex's. I am not sure if that is because the newer models have not had enough miles on them yet or if there was a design change made.

The more I think about it now I am second guessing my own theory. If the outboard pad were to wear more initially because of the non centered rotor it will eventually wear to the point where both sets of pistons are extended equally. At this point from the piston's perspective they will have become centered over the rotor.

If my theory was correct then this small amount of initial additional wear to the outboard pad would stop at this point and then both pads would wear evenly from that point on. However on my sled the outboard pad had so much additional wear that in the end the outboard pistons were extended much more than the inside pistons.

Now my head hurts! I agree that it is not a safety or performance issue so I should just let it go however my OCD will probably not let me. LOL!

 

[Soldier'spapa]

Thanks for the sentiment regarding my son's military service! It means a lot. I go out of my way to thank our military when I encounter them.

Just took a look at Yamaha Parts... same caliper part number for both an 07 and 12 apex. No design change.

 

[Soldier'spapa]

I'm sticking with my contaminated fluid idea. Contaminants form by the movement the metal pieces in the system (Master cyl. and caliper pistons.

Gravity works.

Since the hose is connected to the same side of the caliper that has less pad wear, contaminants generated by the master cylinder movement (tiny metal filings) migrate down the hose and settle in the side of the caliper the hose is connected. In general the contaminants are not distributed to the other side... gravity causes them to fall out into the hose side. Over time these filings coat the back side of the piston and eventually cause a greater pressure requirement to move them outward. This is what creates an imbalance of pressure within the caliper and uneven pad wear.

The problem is intensified by the long off season when the brakes are inactive.

This is only a theory so please none of this !!!

 

[Trucker]

If the Caliper is fixed. Thats why there is uneven wear. Unless you float the Caliper the problem will never go away.

 

[Blue Dave]

Isn't this fun! It looks like we all have way too much time on our hands waiting for it to snow. LOL!

Just FYI I was at my local Yamaha dealer earlier today and I asked about this in the service department. They told me that they see it all of the time. If they notice it early enough they simply swap the pads to extend the time until replacement is required. If they catch it late (like mine) they simply replace the pads. They had no theory or explanation for the cause, they just said that it was "normal". I said you mean "common" not "normal".

 

[Soldier'spapa]

BD,

Throw a theory a bone... Did you flush the brake fluid at all over the years?

 

[TBay Sledhead]

I'm sticking with my contaminated fluid idea. Contaminants form by the movement the metal pieces in the system (Master cyl. and caliper pistons.

Gravity works.

Since the hose is connected to the same side of the caliper that has less pad wear, contaminants generated by the master cylinder movement (tiny metal filings) migrate down the hose and settle in the side of the caliper the hose is connected. In general the contaminants are not distributed to the other side... gravity causes them to fall out into the hose side. Over time these filings coat the back side of the piston and eventually cause a greater pressure requirement to move them outward. This is what creates an imbalance of pressure within the caliper and uneven pad wear.

The problem is intensified by the long off season when the brakes are inactive.

This is only a theory so please none of this !!!

So what are you trying to say, that the side with the contaminants is getting more or less wear. If what you are saying is that the inside is getting the contaminants, it means that to move it would would require slightly more pressure therefore the outside would move first and wear the most. So if it requires more effort to advance the piston would it not mean that the piston would not retract as easily causing more wear. A dilemma. What came first the chicken or the egg?

 

[Soldier'spapa]

In my mind definitely the chicken but that could start a theological debate we ought not to engage in.

That is a dilemma! Hum.

It would be interesting to disassemble a caliper and inspect all the components.

Volunteers??

 

[woolyviper]

i think blue dave hit on something when he mentioned slight braking pressure - i suspect that has more to do with the uneven wear than anything you rarely apply the breaks and hold tight - mostly just squeeze and off.

 

[Blue Dave]

In my mind definitely the chicken but that could start a theological debate we ought not to engage in.

That is a dilemma! Hum.

It would be interesting to disassemble a caliper and inspect all the components.

Volunteers??

Mmm..... sounds like a project for me if we do not get any snow soon! My only worry is opening a can of worms and going against the "if it ain't broke don't fix it" mantra!