Hello all, I am at 20k miles and my dealership (whom I trust) has recommended me to do a brake replacement. They let me see the brakes and told me at 4mm usually it isn't too urgent but on the GSF there is a sensor that sits right below 4mm which may get affected if they are not replaced soon. They also said due to the nature of the rotors they also were suggested to be replaced. Since they are slotted rotors they can't be resurfaced and the "lip" at the edge of the rotor is a sign they should be replaced. I didn't look it up, but they mentioned the standard brake replacement interval is 25k miles for the GSF. Total cost for brake + rotor job would be $1300. I don't remember if they mentioned the rears as well for this quote, but we only looked at the front.

While I am okay with a brake replacement, I am wondering what everyone's thoughts are on the rotor. Also, what is the sensor for? I feel like it's bad design if such an important sensor doesn't give notice as to when it is about to be destroyed by the brakes, a regular wear item. They mentioned the sensors were $200 each to replace.

Also, anyone recommend pad/rotor replacements that aren't too dusty? It's my wife's car now so it won't be driven like a maniac, but I still would like to keep the wheels clean.

Here is a picture of the sensor, it is the little black thing the wire which splits into two is connected to, right in the middle of the pad:

Caliper at 20k miles

 

The sensor burns through at 2mm pad thickness. The factory service manual says to change the pads at 1mm thickness. At 4mm thickness, you're throwing away 3mm of pad that starts at 9.75mm. So you have 8.75mm of useful pad according to the factory, and at 4mm thickness, you're just a little over 65% used. There is no sensible reason to change your brake pads.

The only person who benefits from turning a rotor is your service manager. There is no good reason to turn a rotor UNLESS is has a deep groove, and then you have to weigh the simple economics - does it make sense to make the rotor thinner (when there is a minimum thickness stamped into it) only to remove a groove and throw the rotor away sooner, or is it better to just put on a new one? I haven't turned a rotor in 35 years, and never will again. It's just dumb if you are paying the bill.

I am sorry, but as much as you trust your SA, he's not doing what's in your best economic interest. Don't change the pads before the light comes on, and even then, you've got 3k - 5k miles before you really need to act. FWIW, the factory's 1mm is still conservative. I have run pads down to fractions of a millimeter and believe it or not, the brakes worked perfectly - not on the street, but on the track where they're getting stupid hot and dealing with more stress than you can ever create on the street.


Full race pads used until they were truly done. They were successfully slowing me from 105 mph to 35 mph between turn 10 and turn 11 at CMP and gave no indication there was anything amiss. I figured it out when I tapped the brakes in the pits before I was going to get another tank of gas for my last session. Sadly, after hearing the CLANK I decided to put my street pads back in and drive home 4 hours to Atlanta.

 

Thanks for the info. So is the sensor there to let you know when the pad needs to be replaced? Is the sensor supposed to be worn down and replaced with the brakes? I'm confused as to the purpose of this sensor.

I do trust my service manager but I am very wary of dealerships and take everything with a grain of salt. I'm sure if I read through the manual a bit I'd be more educated than her. They just play it very safe because yes, it makes them money.

I think I'll just have them measure it each time I do a tire swap and just replace the brakes at 1mm.

 

Your warning light cannot be dimissed. It will come on at 2mm, guaranteed, AMHIK. Suggesting you should do anything at 4mm is an egregious violation of trust. I sell to household brands for my company, and if I suggested anything as foolish as an early brake pad replacement, I would lose my customer's trust and open opportunity for my competitors. Despite what you believe, your SA i gouging you in the most common of ways.

Do what you think best, but I would never follow your SA's advice. She is lining her pockets, not serving you.

 

Thanks for your input. I think I agree with your assessment but I'm still unsure what the sensor does. Is it supposed to wear down so it can warn you to replace the brakes?

What I believe the SA was trying to say is "why wait for it to hit the sensor which is $200 to replace, just replace it now and save yourself the money." Of course the rotor bit I didn't believe for a second but I just wanted to confirm what the sensor does. I didn't bother asking them at the time.

 

The sensor is a piece of wire that burns through and opens the circuit to turn on the light. They come with new brake pads as part of the kit, so this "spend $200 for sensors" makes no sense at all unless you are going aftermarket with the sensors. I have spliced together a new sensor just by replacing the wire in the worn out sensor. Takes about 15 minutes if you work slowly, but I've been doing electronic repair for 40 years, so it's pretty simple to me. It definitely is messy though. Brake dust isn't the easiest thing to wash off your hands.

 

I appreciate that. It wasn't made known to me that it comes with the brakes as part of the kit.

I should probably get a digital copy of the service manual / maintenance schedule so I can be better prepared next time. Correction to the original post- my car is at 25k miles now, not 20k. But the brakes are at 4mm so still no need to replace yet.

 

Back of the napkin arithmetic says you should get at least 35k miles from your pads based on current mileage of 25k and 4mm pad left.

 

Who pays $200 for these sensors? I'm not tracking my car so maybe there's a need for OEM in that case to prevent what lobuxracer showed above.

I've used these and they are just fine.
Rock Auto - GSF brake wear sensors

 

I got sensors with the pads I bought from Rock Auto. I didn't like the quality of the seal, so I just took the wire and restrung my old sensors with the new wire and the old connector (much better quality seal on that one). It's working perfectly.