onlybnz

Hello,
First time MB SUV owner and poster (accidentally posted in W166 first). We purchased our car CPO 2021 GLE450 (~26k miles) last November and have been hearing this loud brake squeal every time we come to a normal slow traffic stop. Once we do, the car's parking sensors start going off if there are any other cars at the intersection or parking garage. Needless to say, this is a bit annoying.
We have taken the car back to the dealer a couple times. In November, they told us that this was normal and nothing can be done about this. The CPO papers also stated that the brakes and pads were completely green or OK.
Fast forward to May and we have not driven the car much (~27k) but due to a recall we sent the car back to the dealership. When they had it, I asked them about the same two issues. This time, the service advisor said that the rear brake pad and rotor needs to be changed because there is excessive rust. When I pushed them on this, they said that this is part of the MB service manual and will solve the issue. Unfortunately this isnt covered by warranty or maintenance packages and will be out of pocket. The car is garage kept and we do not get much rain (sunny california)
Here are my questions:
- Is it normal for this car to go from OK brakes and rotors to excessively rust within such a short period and mileage?
- The issues existed at purchase, the squeals have remained consistent as well as the parking sensor sensitivity. How is the brake rotor an issue now if it was not before? Should this be covered under warranty?
- The dealer is also refusing to share the old service records. Is this allowed? I have always been able to request and receive service records for all my cars at other manufacturers and dealers.

stktyz33

For the loud squeaking brakes in dry climate, you may need to replace the rotors and brake pads, there is usually no magic here. When you do it, it's usually better to do all four at the same time. As for the "why"s, you have no idea how the car was driven before, so it's unlikely you get any answers.
For the parking sensors and intersections, looking at 2021 manual, I'd suggest making sure that "Warn Early All Around" option is not set (see the screenshots attached). Unless there is something defective in your particular system, your driving behavior may be triggering it - you're getting too close too fast, the system panics and starts warning you.
For the parking sensors and tight garages, it's tricky, the speed and your angle of approach matters, I have just a few inches of clearance of the sides and I'd say the parking sensors go nuts 3 times of 10 when I enter the garage.

wildta

I think you have a history of showing this brake issue existed since purchasing the CPO and I would make a strong case showing that this should have been resolved from the CPO checklist.

mikapen

Regarding replacing the brakes because of the rust:
Normally, rust on brakes doesn't cause squealing, but rather a course-sounding scraping. Maybe like sandpaper. Once every revolution.
Unless the rust has caused runout, or worn below minimums, I doubt that replacing them would reduce squealing. It's a different sound, by my definition.

Causes of rotor rust:
If you wash the car or go to a car wash, and park the car before the pads have dried, they will rust to the disc. You will notice that because it'll take extra throttle when you first move the next day, to break the pads, loose. It jerks. That's because parking brake is applied automatically when you shut the car off.
It seems to take more than 5 miles to completely dry brakes, so I have a little ritual that I do to keep the parking brakes from automatically engaging.

Potential causes of brake squeal:
If you drive gently, and stop gently all the time, the pads can develop a glaze that makes a squealing sound at low speeds.
A possible solution is to do a series of a half a dozen really aggressive "slowdowns," from 60 or 70 mph to 10 mph, but not stopping. Repeat five or six times - you'll need a lot of room behind because you wouldn't want to be following you doing this.

Try that and see if it fixes your squealing, before you have the work done.

Regarding pad and disc wear, they are "wear items" or "consumables." They aren't covered by warranty, unless something was amiss in the braking system, causing that wear.

Revealing prior service records is considered a privacy issue. See if you can get them to provide those records with customer information obscured.

If they didn't provide a Carfax, get one of those too. It'll have much of the service records.

onlybnz

Thank you for the detailed response.

the sound I experience is more of a squeal and less of a sandpaper sound. I’ve had rust on my prior cars but never experienced this sound. In your example, does the sound only manifest when pressing the brake or is it always there?

Great point on the rust causes, we have not had a detail done in many weeks but I’ll be mindful of this.

Re: Brake glaze, I had tried it at a slower speed (30-40–> 10) a couple times based upon another thread on this forum. I want to say it made a difference but the sound came back so I assumed we were doing something wrong. Is this something that needs to be repeated at regular intervals? Since we bought this car as a baby mobile, we usually stop gently. Unless it’s just dumb dad in the car trying to make this whale dance 😀


thank you for the context on the service records and carfax. Will ask them for those as well.

onlybnz

Thank you for this. If memory serves, I had already done this as part of my early troubleshooting. The system still went bonkers when we came to a traffic stop. It’s so annoying that we just switch off the feature using the “P” button on the touchscreen after every ignition.

onlybnz

Exactly. This was the point I was trying to make. If the CPO did not allege this but we’ve been bringing the car back for the same issue, it seemed unlikely that we had caused rust/brake glaze within less than a month.
any pointers on what we should do?

stktyz33

How fast are you approaching the car in front of you and how close to it do you stop? The reason I keep getting back to it is that it's not typical for these cars to behave this way under normal conditions. I don't have a MY2021 but MY2024 only shows the 360 cameras screen and opens its rear camera when you get too close to somebody else's car at speeds or angles it deems worrisome. For me, it happens on extremely rare occasions but when it does happen, I clearly understand why. I heard a similar story from a person owning a Toyota that it slams the breaks as it passes through intersections in certain situations or approaching other cars at stop signs, which sounded like their driving behavior could be triggering it.

Try applying the brakes earlier and in a more gentle way (where it's possible and safe), keep an extra foot or two between your car and the car on the intersection and see if it resolves it.

wildta

Have you spoken with a manager yet?

hutch300

How do you prevent the parking brake? I'd like to after a wash.

cupecoy

My break squeal a lot too, I am at 24,000 miles as of this morning on a 2020 GLE450 (original brakes)

onlybnz

this dealership has been extremely unhelpful. They were 6 months late giving me a title, refuses to acknowledge any difference between a CPO and a used car (it’s missing cargo cover) and keeps changing management. So the managers have been of zero help

onlybnz

we are pretty gentle drivers since this is the baby car. Ironically, we were told by the first service advisor to brake harder since constant gentle braking seems to contribute to the squeal too according to them. However, as you said the 360 and rear cameras pop open almost every time we come to a stop. This also sets off the incessant beeping that leads us to switch it off.
I have an 2024 GLC rental that they gave me and it’s working as intended. Only turns on in the garage when I’m parking and never turns on in traffic. So I can tell that there is an actual sensitivity issue.

mikapen

Here's my "after car wash Dance."
Normally, when you come to a stop and put it in Park, the parking brake will apply automatically. A red "PARK" (meaning brake, not transmission) displays in the instrument cluster. Then you open the door and exit.

The Dance sequence - engage Park, open the door, turn the engine off, PARK will display.
Before turning engine off, release the P Brake with the switch (red PARK goes off). (The engine must be running in order for the P Brake switch to work.)
Then turn off engine. Exit.
Done.

hutch300

Thanks @mikapen!