Wet brakes after carwash; I can’t stop my MME

[Joero715]

There is a thread on here about brakes getting wet and then the car sitting for a while. When owners then try to put their cars in drive, it will either ”clunk” into motion, or not go at all. This is felt to be caused by the pads oxidizing to the rotors.

My problem is completely different. It has caused me to almost get into several accidents at my local car wash and almost killed a couple of the towel-dry boys there. When exiting the car wash, there’s a slight downhill to the area where the boys dry the cars. Often there’s a line of cars already having been spit out of the car wash. My brakes absolutely will not grab and I continue rolling unless I literally STAND up on them and they kick in.

I know you’re all going to say “it’s the car wash spraying water onto the pads”, but it has also happened during some heavy rain storms. Moreover, it has NEVER happened with any other car I’ve ever owned. So clearly this is a MME-specific problem. I’ve thought about reporting this to NHTSA so they can take action, but I need to know if others have had similar problems.

Again, please spare me the “don’t use that car wash” comments. No other car has ever done this!

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[Nklem]

It happens every time I wash. I just brake very hard coming to the traffic light right after the wash. I do think it has to do with water
/chemicals on the rotors and pads. Just my opinion though. I am going slow enough so it’s not using regen brakes. After 1 brake application it’s fine. I am sure with open wheels soap and water saturates the rotors. It does not happen at home. Some washers use a drying spray to bead up water, it may be that product or applied spray wax as well.

 

[YFD_233]

Maybe pump the brakes several times. Might help.

 

[jlauro]

Only went through an automatic car wash twice with the MME, and no issue with brakes. Are you on whisper mode (which has the least aggressive breaking)?

 

[jbirdzee]

This happens when I go through the carwash as well. Now that I expect it I plan my exit strategy so I can use the mechanical brakes a few times before getting near an intersection/people. Freaked me out the first time it happened for sure.

 

[hybrid2bev]

I always use 1PD when driving around town. I’ve gone through the car wash many times without issue. The friction brakes don’t even engage until the car is almost stopped anyways. But no issues coming out of the car wash and immediately stopping for the towel dry.

I will purposely do a couple hard(ish) stops to engage the mechanical brakes sooner to dry off the rotors before getting home.

 

[Maquis]

I’ve never noticed anything like this post-wash. I’ll pay closer attention next time. The wash I use has a power spray to clean the undercarriage that absolutely soaks the brakes, so if this were an issue, I’d certainly expect it to happen to me.

 

[Motomax]

Unless you’re exaggerating the incident, it’s definitely not normal for wet brakes to not grab at low speeds.
I have noticed that if regen braking loses traction it just gives up completely for a moment and doesn’t bother applying the actual brakeS.

So my takeaway depending on the situation is take it easy on regen, don’t skip leg day, or take it in and get the brakes checked out.

 

[Ford Motor Company]

There is a thread on here about brakes getting wet and then the car sitting for a while. When owners then try to put their cars in drive, it will either ”clunk” into motion, or not go at all. This is felt to be caused by the pads oxidizing to the rotors.

My problem is completely different. It has caused me to almost get into several accidents at my local car wash and almost killed a couple of the towel-dry boys there. When exiting the car wash, there’s a slight downhill to the area where the boys dry the cars. Often there’s a line of cars already having been spit out of the car wash. My brakes absolutely will not grab and I continue rolling unless I literally STAND up on them and they kick in.

I know you’re all going to say “it’s the car wash spraying water onto the pads”, but it has also happened during some heavy rain storms. Moreover, it has NEVER happened with any other car I’ve ever owned. So clearly this is a MME-specific problem. I’ve thought about reporting this to NHTSA so they can take action, but I need to know if others have had similar problems.

Again, please spare me the “don’t use that car wash” comments. No other car has ever done this!

Hi there. Can you send us a DM with your VIN and dealership info? I can look into this on my end.

 

[Murse-In-Airy]

I’ve used car washes for years. Brakes have ALWAYS worked on the way out of the car wash. As you exhibit, not having brakes because they’re wet (and soapy) would be disastrous. Whether in my MME, or any other car, brakes still need to work when wet.
Will they rust if left to sit wet? yes.
May they act a little differently when yet? Yes.
Should they fail altogether? HELL NO.

 

[highland58]

Something to try: right when you exit the carwash, at the top of the hill, shift to neutral before going down the hill. In neutral there is no regen, only the brakes. If you are in neutral going through the carwash, you may be able to just stay in neutral if the car will roll out without shifting to drive to do that.

 

[bostondan77]

This has come up on the Taycan forum as well. Good to know, thanks for reporting.

 

[DevSecOps]

It may seem obvious, but you're not going into accessory only mode when entering the car wash are you? In other words is the car in full power mode as if you were gonna drive it?

 

[ARK]

Every car I’ve ever taken to a car wash or started up during a heavy rain storm hasn’t grabbed the brakes well for the first several feet after I start moving. This always resolves immediately after I step on the brakes a bit more than I otherwise would when slowing down.

I’m always extra careful, in any car, around the car wash attendants when leaving and pulling into traffic from the car wash for this reason. But the issue on any car, including the Mach-E, literally fully resolves before I’m even out of the car wash lot.

If this isn’t what OP is talking about, I haven’t experienced what he has said.

I am at week 51 of ownership and estimate I have been to the car wash about 45 times so far in my Mach-E (pretty much every weekend).

 

[breeves002]

My theory is because the brakes are electric.

I've noticed a similar phenomena in different scenarios. Just times where you have to press the brake pedal abnormally hard to stop at low speeds - it isn't because you're sliding - it's because of software.

I've found in my limited testing the EBB (electronic brake booster/abs pump/master cylinder) engages a limited range of pressure once the friction brakes are enabled - until you get nearly to the end of pedal travel. At the end of the pedal it maxes out the brake pedal pressure as fail safe. This is a 20x increase in brake line pressure at low speeds. What it appears the software doesn't do is compensate for conditions of the brakes at low speed.

In a car with normal hydraulic brakes and a normal booster you would just press the pedal a little bit harder because the rotors are wet. Nothing crazy and you probably wouldn't even notice you had to press them harder.

In the MME the software doesn't adapt so it only uses that limited pressure at low speeds - which normally would be all it needs to stop the car. It doesn't brake harder until you get the pedal way down there and it goes into its failsafe.

It's hard to make an electric brake software that's smooth and they're trying to make it smooth in transition from regen to friction brakes while getting maximum regen possible. They just need to tweak it to apply more brake at low speed in certain situations. Or allow you to apply more with a small movement of the pedal instead of that "flooring" of the brake pedal OP described.

tl;dr brakes are working as intended, its part of the software for the EBB that isn't quite perfect in this one scenario.

P.S. Some other EVs and all pre 2020 Ford Hybrids/plug ins have an electric vacuum pump and standard brake booster setup as opposed to the MME's electronic one. Ford is putting EBBs on a lot of new vehicles now - not just hybrids/EVs.

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