Parking Brake Issue? - just how does if function

[Lil Red Broncette]

I was recently away for 6 months. My Bronco was sitting. My driveways is also very steep or otherwise I wouldn't bother with the parking brake. When I drove it after getting back there was a very severe shake when applying the brakes. I mean very severe. My bronco is 2 years old with barely 7K miles. I "resolved" the issue by getting some speed and hitting the brakes hard. Did this a couple times forward and also reverse though slower when reverse. Now there is no evidence.

I would normally expect, and have experienced, after leaving other vehicles sitting for extended periods some rust would develop on the rotors that causes some minor to moderate noise and vibration/shake that goes away with some driving. This was so much worse than anything I experienced.

That got me wondering. Other than older vehicles with drum brakes where the parking brake cable actually activated the main drum brake shows, the disk brake cars I had the parking brake cable apply a rather small drum brake in the center of the rear rotors. It was completely separate from the main brakes. Given how in the bronco I can feel the brake pedal move when applying the parking brake, I am wondering if they are having a servo actually compress the main brake pads against the rotor? Can anyone confirm this? That seems like a recipe for causing brake imbalance. Like maybe rust got on the rotor except for under where the pads were compressed. That would cause a different brake force as it went over that area without rust compared to with some surface rust.

I am just glad it went away the way it did.

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[Brian_B]

Good question - watching

 

[Ducati1098]

Rust is going to be everywhere on the rotor except where the pads were at whether the parking brake was applied or not.
Look at any car that sits for an extended time (even with the parking brake off) and you’ll clearly see an outline of the brake pad that usually isn’t rusted unlike the rest of the rotor. So it makes no difference in this case. Any vehicle sitting for 6 months is going to have some pretty severe brake vibration until the rust is removed.

But to answer your question, yes the rear calipers have an electric motor on them which apply the regular brake pads for the parking brake.

 

[Brian_B]

But to answer your question, yes the rear calipers have an electric motor on them which apply the regular brake pads for the parking brake.

Oh I was hoping for more detail. I know it’s electric actuated. Seems like it’s a ratcheting mechanism or something - once it’s applied you can pull the battery and they stay applied. Something electric reverses the process (unratchets it? I don’t know). It must go via the caliper since you can feel it in the brake pedal (at least on the 2.3 with vacuum boost)

 

[Ducati1098]

Oh I was hoping for more detail. I know it’s electric actuated. Seems like it’s a ratcheting mechanism or something - once it’s applied you can pull the battery and they stay applied. Something electric reverses the process (unratchets it? I don’t know). It must go via the caliper since you can feel it in the brake pedal (at least on the 2.3 with vacuum boost)

It’s just a single speed reversible electronic motor directly connected to the brake piston via splines.
The motor spins one way pushing the piston in, and reverses the opposite way retracting it.

 

[Brian_B]

It’s just a single speed reversible electronic motor directly connected to the brake piston via splines.
The motor spins one way pushing the piston in, and reverses the opposite way retracting it.

Thanks - that is useful!

 

[AZ_Liberty]

Thus the reason I will never use the parking brake when actually parked. If you battery dies, you can't even push your car.

 

[Lil Red Broncette]

Rust is going to be everywhere on the rotor except where the pads were at whether the parking brake was applied or not.
Look at any car that sits for an extended time (even with the parking brake off) and you’ll clearly see an outline of the brake pad that usually isn’t rusted unlike the rest of the rotor. So it makes no difference in this case. Any vehicle sitting for 6 months is going to have some pretty severe brake vibration until the rust is removed.

But to answer your question, yes the rear calipers have an electric motor on them which apply the regular brake pads for the parking brake.

Thank you for confirming it is the actual brake pads compressing. You say any car would do this, I disagree as leaving a car sitting for 6 months is not unusual for me. My experiences were minor, this was uniquely severe.

 

[Lil Red Broncette]

Thus the reason I will never use the parking brake when actually parked. If you battery dies, you can't even push your car.

very good point. I normally won't but unfortunately with as steep as my driveway is, I don't trust the trans in park to be reliable.

 

[Ducati1098]

You say any car would do this, I disagree as leaving a car sitting for 6 months is not unusual for me. My experiences were minor, this was uniquely severe.

I work on many different vehicles that sit for months sometimes waiting on backordered parts, they’re all the same

 

[RHeinz]

Any chance you have a swimming pool and store chlorine or muratic acid anywhere near your vehicle. Muratic acid (even in a capped bottle) will exacerbate rusting/corrosion.

 

[Lil Red Broncette]

Any chance you have a swimming pool and store chlorine or muratic acid anywhere near your vehicle. Muratic acid (even in a capped bottle) will exacerbate rusting/corrosion.

No I don't. Although there is salt in the winter.

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