Brake pad thickness/specs?
 

Mechanic is telling me front breaks are at 7 mm and rear brakes are at 6 mm.

How do I know when it's time to replace them?

Anyone know the new pad thickness and what does Audi recommend for replacement? Is there an official document that lists these kinds of things?

Thanks

https://cimg8.ibsrv.net/gimg/www.aud...a242521469.jpg

Do you know how that was measured - was it an Audi dealer or independent? Brake pad limits are typically in the 2-3mm range. But I've seen a lot of Audi specs/service manuals that give measurements including the backing plate, and the minimum is typically about 7mm, which equates to about 2mm in actual pad.

New pads are typically 10-12mm, so 15-17mm including the backing plate

If he told you 6mm and 7mm and didn't tell you it was time to replace them, I'd assume these were measurements of just the pads. So you're a bit more than 1/2 way through the thickness (though pads sometimes wear faster as they get thinner).

I haven't found the actual manual/specs for our car - this is just my Audi experience.

Yes, new pads are typically around 10mm, and it's recommended to replace them once they are worn down to 3mm. Depends on your driving, but once they are down to 3mm they don't deal with heat all that well anymore. You also have a brake wear sensor in the front, so the simplest answer to your question is replace them once the car tells you, but the dealership will start telling you to replace them at about 3mm. Typically the front pads wear faster than the rear pads, but in your case it's the opposite. Are you the first owner and is this the original set of pads? You definitely wanna keep an eye on the rear pads. Some Audis have sensors in the rear as well. My B8 RS5 does for example, but I'm not sure about the B9 A4.

Thanks PghRich.

It was at the dealership.

I had just asked to let me know what they find, and that's what he emailed me, I haven't talked to him so I don't know if he's going to recommend replacement, but I wanted to have some information before I talked to him...

Sounds like I need to find out exactly what was measured...

Any ideas what the diagram showing the the 3 4s and 3 for the back right could be indicating?

Thanks superswiss.

I am not the first owner, and I am not sure if these are the original pads...but in the maintenance records I have for the car I don't see anywhere that they were ever changed. But I'll go back and double check in case I missed it.

So if new pads are typically 10mm I am still OK (unless like PghRich points out they measured 6mm and 7mm including the backing plate).

I was flushing the brake fluid last weekend and noticed that B9 A4 also has a rear pad sensor. It's only one sensor on the Passenger side rear though.

Thanks minmet. How do those sensors work? Can the car show you a history of when the sensors went off or once they're cleared or reset, that's it you can't see them again.

Any ideas what the technician's diagram above the 6mm and 7mm could be indicating?

Sorry! Don't know much else. For me, I would change them before the sensors tell me. As mentioned above, 3 mm would be the general guideline. If you are going to have dealer or other mechanics work on your cars, just bring it to them when the sensor gives the signal. I saw you need change your tires right away as the sheet indicated they are down to 4/32" and one already at 3/32". That's legal limit in our state.

Thanks minmet.

Yes, definitely getting the tires done.

How can you tell about the 4/32" and 3/32"? (I'm thinking that's the diagram I was asking about? where it says 4 4 4 3, right? I didn't realize that was about the tires.).

Yes. That's the info. Unless the tech was talking about something else. The diagram definitely looks like for Tires.

The sensors are simply a wire embedded in the pad about 3 mm from the backing plate. When the pad is worn to 3 mm the wire wears through also and opens the circuit setting off the warning. It cannot be reset until you change the pads.

Thanks for the explanation! Do you know if the sensors need be changed along with the pads or can be reused? Although I have been changing brake pads and rotors for years, this is my first car with a wear sensor. All my previous cars had only the traditional spring indicator which just makes scraping noise when pad is too thin.

Thanks for the explanation, SchwarzS6.

The sensors are not reusable as they are built into the pads. When you throw out the pads the sensors go with it, You get new sensors with new pads.

OE pads comes with the sensor wire, Pretty straight forward.

https://cimg4.ibsrv.net/gimg/www.aud...a4a4bb0820.jpg
https://cimg8.ibsrv.net/gimg/www.aud...7d36d95c1d.jpg


This is the front brake wear sensor for B9 A4 on ECS Tuning. Trying to understand how it is attached to the pads. No sensor/wires come with the pad set though.

There is space on one of your front pads to slip the sensor into. Plenty of YouTube videos that show you how. Only on the drivers side front.

Thank you! Will look into it.

I am pretty sure these are built into the OEM pads. From what I can see the OEM catalog does not list a separate sensor wire. Are these for aftermarket pads?

It is OEM. You can find it in Audi parts site here: https://parts.audiusa.com/p/Audi_201...W0615121E.html
It appears there are two versions of pad set for B9 A4. There is also some confusion as to if the sensor is included or not with different version of the pad set.

When you buy the OE pads, it includes the above wear sensor already clipped into place. If for some reason it gets damaged you can buy it separately and just clip it right in.

The design looks exactly like that for a BMW - I used to buy them separately when using non-OEM pads and rotors. I'm pretty sure that what actually happens is that as the pad wears the sensor gets closer and closer to the rotor. When the pad is at the wear limit the sensor contacts the rotor and completes the electrical circuit, setting off the warning light.

https://parts.audiusa.com/p/Audi_201...0698151AF.html



https://cimg0.ibsrv.net/gimg/www.aud...a7b0cc2397.png

That's for the 314x25 mm rotor version. There is another version of pad set for 338x30 mm rotor with Parts# 8W0698151AD which does not include the sensor. The sensor itself cost $80.
https://parts.audiusa.com/a/Audi_201...M/1321380.html

Hard to see which version of rotor is on which car. Even after I gave my VIN to a dealer site to look up parts. They still listed both version of front brake pad sets as applicable to my car which surely not.

Weird - both sizes are listed as applicable for my '17 PP Quattro. As you said, it can't be both. $74 for a wear sensor is crazy. For my old M5, for which prices were always very high, they're $28 OEM)

(if you want to see how they fit, at least for the 314mm rotor, start at 6:38 of

(Hmmm - unlike every other forum I use based on this software, I can't uncheck "Automatically embed media". It also doesn't seem to respect "start at xxx time" in the URL)

)

Thanks for the video! Guess I will have to measure my rotor for the proper pads when the time comes to change them.

The video was great, unfortunately it is for the earlier series cars. The US spec B9 have the 4 piston front calipers so the procedure is probably different.

These are definitely different from the last 4 C-series (S6/A6) cars I owned. On those the wear sensor was molded into the pad and there was one on both the driver and passenger sides. I typically do my own brakes and the older C-series had calipers very similar to the ones in the video. On the A6 you did not have to remove the caliper carriers to remove the disk. That was in the instructions but I found that you could sneak the old one out and the new one on with the caliper carrier in place. Another hint - you don’t need to bang on the braking surface to break the rotor free. The best way is to take a 16 oz hammer and give the disk a couple of hard wacks on the center hat. While this seems counter intuitive because you are pounding the rotor on rather than off the hammer blows break the rust bond and the rotor will come right off. This way you do not damage the rotor in the event you want to have them turned,

There don’t seem to be any You Tube How-To’s on our cars brakes yet. Who wants to make one? Maybe one of the guys who tracks their car and changes pads a lot could do the rest of us a favor and create one. There is no rush, I have at least another year on my pads. ;)

Can you run without the wear sensor?

Yes, they can be bypassed by simply connecting the two wires leading up to the sensor. I think somebody posted it above. The sensor is merely a piece of wire embedded in the pad, that at certain thickness starts to get worn through and eventually interrupts the circuit. Once the circuit is open the warning light on the dash comes on. I have aftermarket pads on my RS5 and the rear pads don't have a sensor, which is very common for aftermarket pads, so I have the rear sensor bypassed at the moment.

Thanks @superswiss !

2018 Audi A4 Quattro Premium Plus
 

New to the whole Audi thing. Can anyone tell me how many brake pad sensors come on my Audi and which wheel(s) they would located? I haven't messed around too much with my whole brake system yet, but I've been hearing this little squeak starting to sound every time I brake, regardless of climate/weather. It may be time for a change.

Thank you!

type 8K (B8 A4, US MY09-MY16) was inner pad at front left (8K0 615 121).
type 8W (B9 A4, US MY17+) is inner pad at front left (8W0 615 121 H) and inner pad at rear right (8W0 615 121 E).