Rear Brakes

[Allegany]

Well I just got the car back from the dealer. It now has 46000 miles on it and I just had to pay for new rear brakes and rotors. Seems according to the dealer that the rear brake calipers were frozen up and not working properly, which also damaged the rotors. I have owned many Fords in my lifetime and usually the rear brakes last much longer than 46000 miles, usually the fronts are the first to go. Car is averaging about 43 miles per gallon but I didn't plan to spend my gas savings on early rear brake repairs.

[hybridbear]

What led you to bring it in? Did you get a second opinion? What's your lifetime brake score? With regen braking the brake pads and rotors are used very little and should not wear out for at least 100k miles. Some people have even gotten 200k miles on original pads and rotors in a hybrid.

 

FYI I'm moving the topic to the brakes-related section.

[jeff_h]

I have owned many Fords in my lifetime and usually the rear brakes last much longer than 46000 miles, usually the fronts are the first to go. Car is averaging about 43 miles per gallon but I didn't plan to spend my gas savings on early rear brake repairs.

 

To me, 43mpg + calipers freezing up (per dealer) doesn't seem to go together. And if there was an issue with a caliper doesn't it seem like one would be affected rather than both and thus only one pad is shot?

 

Like HB notes above, hybrids can go a long time on a set of brake pads, as I changed the pads in mine at 140k but then were only about half worn, I've posted pics in another thread here somewhere. But on the other hand, when my wife had a 2006 Escape Hybrid the car failed inspection around 50k miles when the shop said the rear brakes were shot, I thought sure they were just trying to rip me off by getting paid to replace brakes that were only half gone -- but I got home and pulled a wheel and sure enough the rear brakes were shot (fronts were fine)... why the rear brakes went out sooner I don't know (especially how she nosedives the brakes), I wonder if there is a proportioning-type valve/mechanism that is supposed to apply even pressure to front and rear but was not working properly? If that's the case and the fronts are being used a lot more it may be noticeable to the driver, but not so when the rear brakes are getting more than even use?

[Allegany]

I took it in because the rear brakes were rattling. I live on a dirt road and that seems to be part of the problem. I was there when they inspected the brakes and they were shot. I trust the dealer but when they pulled the wheel they showed me the problem. They got the pistons on the calipers freed up so they didn't need to replace the calipers, just the rotors. I was wondering if anyone else was having rear brake issues as most times rear brakes almost last the life of the vehicle. My brake score is around 96%.

[acdii]

On these cars it appears the rears are used more than the fronts. On the 2010 Sport I had to replace the rear pads at 30K, one caliper did hang and had to be replaced under warranty, but they wouldnt replace the pads. I think on the Hybrids, the rears are used to balance the regen for straighter stopping.

[lolder]

I question whether the rear brakes are used like that. The braking from regen should be equal on each front wheel. The stability controls would work to do that in heavy or slippery conditions but not normally when you are achieving high brake scores. If a lot of cars are seeing virtually no brake wear front or rear in over 100,000 miles, those that do have some problem. The parking brake warnings are so prominent that that is an unlikely culprit. The problem is apt to be rear pistons or calipers sticking from little use. Prii have little wear also. The mechanical brakes are always applied below about 5 mph but maybe not very much in the rear as you are milking the brake score up. I'm going to start pressing the brake hard after I stop to exercise them all. There is so little brake dust on the wheels compared to regular cars that sticking of the calipers floating action seems unlikely. There definitely appears to be a problem with some cars. It's not normal.

Edited September 16, 2014 by lolder

[acdii]

I can tell you one thing, if you need them, they work! I had a short light this morning, barely saw it as the sun was right in my face and a pickup in front blocked the view of the lights until he moved into the turn lane, and I had to slam on the brakes as a car turned left right in front of me. The car stopped FAST! From 50-0 in about 60 feet. It went from hard regen to antilock.

 

One thing I can say, when the pads are damp from a foggy morning, they grip extremely well, I did not slam on the brakes, but pushed it harder than I normally do, and it locked them up the moment the service brakes applied. Touchy is all I can say.

 

Still makes me wonder what the brake proportioning is on these, how they balance front to rear.

[Waldo]

With the EBD systems now, the proportioning can be varied based on load. In a conventional system it might be set for say 75% front, 25% rear all the time. But with EBD, you can have 50/50 or even 30/70 under light brake pressure, then ramp it up to 75/25 under maximum pressure. You can use this to improve the overall feel under braking, since it's easier to have anti-lift in the rear suspension than anti-dive in the front suspension (a geometry thing). For that reason, you want as much rear braking as possible, until you get close to the point of lockup, then you want more front braking.

[lolder]

With the hybrid I'm sure its all front and no rear until the max regen power is reached. After that I don't know. The only thing I have heard about max regen braking is a Ford engineer said ( somewhere ) if a heavy book falls off the front edge of the passengers seat, it's into mechanical braking. That was with the first Gen Escapes and Fusions with the NiMH HVBs. The LiIon have about 50% more power to give or absorb.

[hybridbear]

With the hybrid I'm sure its all front and no rear until the max regen power is reached. After that I don't know. The only thing I have heard about max regen braking is a Ford engineer said ( somewhere ) if a heavy book falls off the front edge of the passengers seat, it's into mechanical braking. That was with the first Gen Escapes and Fusions with the NiMH HVBs. The LiIon have about 50% more power to give or absorb.

The new hybrids can charge the HVB at a peak rate of 35 kW. Since there are some inefficiencies in the system the power at the wheels can be greater than -35 kW without engaging the brake pads.

[acdii]

With the EBD systems now, the proportioning can be varied based on load. In a conventional system it might be set for say 75% front, 25% rear all the time. But with EBD, you can have 50/50 or even 30/70 under light brake pressure, then ramp it up to 75/25 under maximum pressure. You can use this to improve the overall feel under braking, since it's easier to have anti-lift in the rear suspension than anti-dive in the front suspension (a geometry thing). For that reason, you want as much rear braking as possible, until you get close to the point of lockup, then you want more front braking.

This is what I experienced in the Sport. Under light braking there was more rear bias than front, I can feel it when stopping that the rear brakes were slowing the car rather then the front. It was most noticeable after putting EBC pads on. On the 13 HyTi though, when the pads are damp and really grabby, under light braking after regen, its all front brakes. The car will put its nose on the ground when they kick in.

 

Here is something else I noticed today, since most of the braking is done by regen, the service brakes tend to have reduced stopping power. A couple times I had to hit the brakes hard and one time I noticed some fade, another time they grabbed so hard that antilock kicked on. What I find is that when I have to stop quicker than regen allows, the service brakes act as if they are brand new and not bedded. Probably from so little actual use.

[lolder]

Do the 2013+ Fusions have a pre-collision function that applies the brakes more forcefully as some cars do? Might that be the cause of different braking feel? In my 2010 I've not seen any variation in mechanical braking. I think I've only braked hard twice at high speed; once driving the new car home 5 years ago and recently when somebody pulled into my lane with zero clearance. The brakes worked very well both times. The "grab" during slow speed transition to mechanical braking in wet weather is probably very difficult for designers to eliminate. Wet disc brakes clear themselves in one revolution but maybe the system is designed to overcompensate for even that one revolution. All-in-all, these are the smoothest brakes I've ever had and they're unlikely to ever pulse with age. If the electronic brake simulator ( the pedal ) ever goes bad, that will probably cost a bundle !

Here's a good description of Ford hybrid brakes: http://www.brakeandfrontend.com/tech-feature-ford-hybrid-braking/

This article says the early 2005-08 Escape/Mariner rear brakes are applied during regen and may cause them to wear 2-3 times faster. The 2009+ Ford hybrid regen braking does not use the rear brakes at all.

You can get under the dash with the car "on" and press on the pedal and see the servo mechanism move to put on the brakes and just keep slightly ahead of the positive mechanical engagement for emergency non-computer controlled braking.

Edited September 17, 2014 by lolder

[Hybrider]

...

Here's a good description of Ford hybrid brakes: http://www.brakeandfrontend.com/tech-feature-ford-hybrid-braking/

...

 

This article also has some really good descriptions some of the other hybrid components, with more details on some of them than I have ever seen before.

 

One such revelation for me was that the electric power-assist steering is not just for driving refinement or "techiness", but is a necessity for "full" hybrid engines since they completely turn off the ICE at times.

[Waldo]

 

This article also has some really good descriptions some of the other hybrid components, with more details on some of them than I have ever seen before.

 

One such revelation for me was that the electric power-assist steering is not just for driving refinement or "techiness", but is a necessity for "full" hybrid engines since they completely turn off the ICE at times.

 

You also can't have lane-keep assist or auto-park without electric steering. It also provides drift-pull compensation and vibration damping, never mind the fuel economy savings.