Parking brake fail? Wet, not icy surface

[Effonefiddy Lightning]

No, in fact, I've had cars that lock only 1 rear wheel by design. One was manual trans to boot so I could have easily left it in neutral.

Electronic parking brakes use a motor inside the caliper to drive the pads on, no pesky cables to break or seize

Salt and sand are your friends in the winter. If you have an inclined driveway then you should be prepared for winter. The truck is great! Operator error is not the trucks fault.

Just take responsibility for your actions, shit happens. It's not ford's fault that they built an electric f150 that has most of the same systems as every other f150.
Also, the stock all season tires aren't that good for winter weather. One of the big advantages of winter rated tires is that the rubber compound has better adhesion when the temperature drops.

I don't have Ice, I was concerned about the parking brake failure.

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[RickKeen]

The Lightning parking brakes are only on the rear axle. The front axle has no parking brake action. The weight distribution of the Lightning is apx 50-50 between the two axles. So if the coefficient of friction of the rear tires goes to less than 50% of the grade of the hill, then the truck is going to slide down the hill.

Ice is damned slippery. The coeff of friction of tires on ice is down around 10%. With only one axle braking, 50% of 10% means the truck held by just the rear axle parking brakes will slide down a 5% grade on ice.

Note on e-brakes:
The e-brake on the lightning is on the two rear brake calipers. It is an electric worm-driven threaded-drive actuator that pushes on the back of the hydraulic cylinder to engage the brake caliper with fairly high force. There is an actuator on both brake calipers on the rear axle. Unlikely the e-brake clamping force is insufficient unless the e-brakes are completely failed and not actuating.

Anecdotal stories of holding on the slippery slope with the AWD or the driving brakes but sliding with just the parking brake are likely explained not by the parking brakes having failed, but by the fact that the driving brakes on the front axle doubles the available friction.

Note on Parking Pawl:
Perhaps even worse if just the parking pawl is engaged. It locks the axle before the differential. Not clear if the diff lock gets engaged as well. If the rear diff is not locked, then the differential would still be active and if one wheel slips on ice the other wheel on the rear axle is just going to turn due to the diff. In that situation, if the coefficient of friction is less than 25% of the grade, the truck is at risk of sliding. On ice, that could be as low as only a 2.5% grade.

 

[MaintGrl]

The Lightning parking brakes are only on the rear axle. The front axle has no parking brake action. The weight distribution of the Lightning is apx 50-50 between the two axles. So if the coefficient of friction of the rear tires goes to less than 50% of the grade of the hill, then the truck is going to slide down the hill.

Ice is damned slippery. The coeff of friction of tires on ice is down around 10%. With only one axle braking, 50% of 10% means the truck held by just the rear axle parking brakes will slide down a 5% grade on ice.

Note on e-brakes:
The e-brake on the lightning is on the two rear brake calipers. It is an electric worm-driven threaded-drive actuator that pushes on the back of the hydraulic cylinder to engage the brake caliper with fairly high force. There is an actuator on both brake calipers on the rear axle. Unlikely the e-brake clamping force is insufficient unless the e-brakes are completely failed and not actuating.

Anecdotal stories of holding on the slippery slope with the AWD or the driving brakes but sliding with just the parking brake are likely explained not by the parking brakes having failed, but by the fact that the driving brakes on the front axle doubles the available friction.

Note on Parking Pawl:
Perhaps even worse if just the parking pawl is engaged. It locks the axle before the differential. Not clear if the diff lock gets engaged as well. If the rear diff is not locked, then the differential would still be active and if one wheel slips on ice the other wheel on the rear axle is just going to turn due to the diff. In that situation, if the coefficient of friction is less than 25% of the grade, the truck is at risk of sliding. On ice, that could be as low as only a 2.5% grade.

Yes, I understand, and thank you for the explanation . . appreciate it...

 

[nofreecell]

Are you sure.....

But it was upper 30s and a light rain. Not a solid sheet of ice. And my son has been parking in the same spot all winter

 

[nofreecell]

It is possible the parking pawl is broken and you weren't putting the brake on.




Are you parking on an icy hill still?

It will take all of less than 5 minutes to test your truck parking systems.

Dealership came and got the truck first thing Monday morning . Had not looked at it as of yesterday. We ordered the

Happened in his garage as well ?‍

I’m assuming that floor was fairly level and dry

No did not happen in the garage: my son is post op from major surgery so not supposed to be outside and the truck won’t fit in his garage anyway

 

[nofreecell]

?‍You are correct sir. I had to reread the original post. I could’ve swore i read him say something about being pinned against the wall in the garage. Now that has me wondering if he was reversing into the parking spot like the video of the other guy sliding down the hill?? may be having your “anchor” tires on the downhill side would be better. Due to lack of reply from the OP we may never know.

Wasn’t reversing

 

[nofreecell]

Are you sure.....

I have lived in snow country for decades (Syracuse, Buffalo, Central Oregon). One question I had was when that person jumped back into his truck and hit the brakes, why did he stop? We have all hit black ice (I did a 180 in a toyota vehicle off I 90 near Utica NY once and drove away from it). Would be nice if the service department told us they couldn’t find anything and we buy new tires, parking bumpers and replacement charger cord and go on our way all the wiser. Now will have a rental car over the weekend which if the truck is fine is an added unnecessary expense.

 

[nofreecell]

Looking forward to reports from the shop about this situation.

Us too. Dealer says when they picked it up all 4 tires had low pressure. No lights were on when I was coming home from the store. Driver side rear had been at 28 the night of my son’s surgery so I inflated it (at 10 pm) and the lights never came back on . . . may just be cursed

 

[TaxmanHog]

Us too. Dealer says when they picked it up all 4 tires had low pressure. No lights were on when I was coming home from the store. Driver side rear had been at 28 the night of my son’s surgery so I inflated it (at 10 pm) and the lights never came back on . . . may just be cursed

That's pretty low, depending on wheel/tire fitted to the truck, (see door jam tire placard) the pressure should be 36 to 42 psi

 

[nofreecell]

The display was very clear showing all 4 tires and their pressures. He said it had happened once a few days earlier. Maybe colder (but I think it was just as cold during the last few weeks). Why all 4 tires were low the next morning is just crazy. I guess they can see when these sensors come on, but seriously, since there have been other reports I would think Ford could alert all their owners by email or a blast text that this is an issue

 

[TaxmanHog]

The display was very clear showing all 4 tires and their pressures. He said it had happened once a few days earlier. Maybe colder (but I think it was just as cold during the last few weeks). Why all 4 tires were low the next morning is just crazy. I guess they can see when these sensors come on, but seriously, since there have been other reports I would think Ford could alert all their owners by email or a blast text that this is an issue

The tire pressure can drop several PSI with the cold season, all four dropping is a sign of environmental change.

Yes, they and the owner can see it from the vehicle online profile.

https://www.ford.com/support/vehicle-dashboard/

 

[nofreecell]

The tire pressure can drop several PSI with the cold season, all four dropping is a sign of environmental change.

Yes, they and the owner can see it from the vehicle online profile.

https://www.ford.com/support/vehicle-dashboard/

Yes, we had snow early Sunday to midday when the temps were upper 30s (38, 39) and rain turned to light rain at the time of the incident. No tire lights were on for the short trip I made Sunday afternoon. Probably never really know what happened and just replacing everything that could have contributed.

 

[NW Ontario Ford Lightning]

Low tire pressure would Increase the contact area of rubber to surface. Could make sliding LESS likely.
The weight of the truck doesn't change, lower tire pressure increases contact area, reduces contact pressure. The area x the contact pressure = the weight of the truck.
Higher contact pressure could cause the ice to phase change to water - like under an ice-skate - and reduce friction.

 

[DenverDan]

Vehicles slide all the time on ice when they are parked. The truck is fine. suggest sanding and salting the driveway.

 

[nofreecell]

Yesterday I returned from the grocery store and parked my son’s truck in the usual spot and plugged it in. By the time I got back in front of the vehicle to get groceries out of the passenger side the truck began rolling back into the street. The charger pulled out of the port (connector is damaged and needs to be replaced). My son who is recovering from major surgery and limited on activity came into the garage and guided me to park again (we have had snow so wanted to make sure I was completely on a clear spot). I again put the truck in park, turned on the parking brake, vehicle was powered off. I walked around and got two bags of groceries with no problem, but when I went back to get the rest, as I was 1/2 way in the door bending to pick up stuff from the floor board, the truck again began to roll trapping me between the door and the vehicle. I was able to grab the overhead handle and step up on the running board as it rolled back into the street.
I had the dealership come and get the car. My son uses a different service department since the one at his dealership is inefficient, but that is further away. They may get to look at the truck by tomorrow. They don’t see any sensors off, but because I was honest, the sales manager said maybe it is my inexperience driving the vehicle or that it had a low tire pressure light last week, or the severe weather, all that sort of BS when a car guy talks to a woman. I grew up driving a split axle cattle truck so know how to drive and especially park.
Had I slipped (it was raining but hadn’t started to ice over yet) I would have been at least run over by the front wheel.
I am going to try and alert everyone because the service manager said he hadn’t seen any thing on any forum but I saw here that there have been recalls and some issue with wiring on the rear axle or something.
A vehicle in park with a parking brake activated should stay parked.
Regardless of the repair I am ordering an airline bumper or something like that and now refer to the vehicle as Christine (for you Steven King fans).

So final answer:
(unfortunately someone retitled my topic which took people off on tangents)
Nothing wrong with the truck, tires are under inflated (by son didn’t know that he should go by the door sticker vs what the truck was telling him so they were 32 psi) . His tires have 10,000 miles left of them but he is replacing them.
So, we will never know except this may have been a perfect storm situation. I parked exactly where he has parked all winter. It has snowed and frozen many days this winter. Nothing was particularly unusual on Sunday except for light rain.
He is parked in the same place today. It is sunny and the snow and ice are melting all around him. The parking brake comes on as expected when he parked the car.
THere is no snow melt /salt any where as has been the case for several weeks so fingers crossed and thanks for all who contributed thoughtful input.

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