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How long did your Rear Brake & Rotors last?


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59 replies to this topic

#1 OFFLINE   cmax-nynj

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Posted 16 September 2015 - 10:19 AM

How long did your Rear Brake & Rotors last? Does Regen brake accelerate rear brake wear?  I am asking because in order to get a great braking score you generally have to drag the brakes longer; and the rear does not have regen-braking









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#2 OFFLINE   stevedebi

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Posted 16 September 2015 - 11:46 AM

How long did your Rear Brake & Rotors last? Does Regen brake accelerate rear brake wear?  I am asking because in order to get a great braking score you generally have to drag the brakes longer; and the rear does not have regen-braking

The physical brake pads are not used unless you brake really hard, or for just the final stop. The regenerative braking is used otherwise.

 

On my FEH, I never replaced the brake pads. I had it for 80K miles.



#3 OFFLINE   cmax-nynj

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Posted 16 September 2015 - 12:46 PM

yes but i thought the rear does not have regen braking.  Is it true when you brake gently or harshly the rear physical brake pads press against the rotors just like a regular car?



#4 OFFLINE   raadsel

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Posted 16 September 2015 - 12:54 PM

yes but i thought the rear does not have regen braking.  Is it true when you brake gently or harshly the rear physical brake pads press against the rotors just like a regular car?

 

My understanding, and I fully admit I don't know for certain, is that rear brake pads are not used during regenerative braking; they are only used in conjunction with the front physical brakes.



#5 OFFLINE   cmax-nynj

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Posted 16 September 2015 - 12:59 PM

the reason I'm asking is after 40K my rear rotors look like crap; but still with plenty of pads remaining.  Dealer wanted $500.  I think I can tackle this job myself turning a few bolts.  BTW, my front brakes still look like new, both rotors and pads



#6 OFFLINE   Adrian_L

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Posted 16 September 2015 - 01:15 PM

It's within the scope of DIY fix, provided you know what you're doing :) 

 

Not sure if Haynes puts out a service manual for the C-max.



#7 OFFLINE   cmax-nynj

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Posted 16 September 2015 - 01:34 PM

since the Stock rotors are so crappy I wonder what's a better version of it out there.  Stock rotors are about $60 each at MSRP; $45 each online.



#8 OFFLINE   stevedebi

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Posted 16 September 2015 - 01:42 PM

the reason I'm asking is after 40K my rear rotors look like crap; but still with plenty of pads remaining.  Dealer wanted $500.  I think I can tackle this job myself turning a few bolts.  BTW, my front brakes still look like new, both rotors and pads

Interesting. It is possible that you need to do a bit more hard braking periodically. It sounds like the rear rotor is not getting used much, resulting in rust damage. Just a thought.

 

If it were the regen, the brake pads would also be worn.



#9 OFFLINE   obob

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Posted 16 September 2015 - 01:46 PM

the reason I'm asking is after 40K my rear rotors look like crap; but still with plenty of pads remaining.  Dealer wanted $500.  I think I can tackle this job myself turning a few bolts.  BTW, my front brakes still look like new, both rotors and pads

 

My understanding is that the rear brakes work during regenerative braking only for the last few miles/hour, like 5 to 0, to make it a smooth stop.  I reached this conclusion by listening with the windows open.  I am thinking perhaps this very light use of the brakes may contribute to the rotors being so ridged-out.

 

I would think about not changing the rotors if they look like crap and the pads have plenty of pad left.  The pads shape themselves to the ridges.  They could still be braking safely.

 

My rear rotors looked pretty bad way earlier than 40k.  Maybe 5k.

 

ADDED LATER: the left side is way worst than the right.


Edited by obob, 16 September 2015 - 05:32 PM.


#10 OFFLINE   cmax-nynj

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Posted 16 September 2015 - 01:47 PM

No I do not do much hard braking, in fact my brake score is usually 95% or higher.  I do drag the brake a bit (regen braking) compared to driving regular cars.  My rear rotors look like they have grooves on the disc surface.  That's why I wanted to know if the rear brake functions or not during regenerative braking.



#11 OFFLINE   ptjones

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Posted 16 September 2015 - 04:54 PM

Checked mine at 106K and my rears are a little grovey, but should make 200K easially. Fronts look better.  I'm wondering if their is something out of adjustment. :)

 

Paul


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#12 OFFLINE   SnowStorm

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Posted 16 September 2015 - 09:47 PM

Agree with obob that you should be sure they really need repair (but that's for you to decide).  Mine look "awful" compared to the front (76k miles) and pretty much always have.  Right now the outer 30 to 50% looks rather mottled while the inner part is smoother but lots of grooves.  My guess is its just from the light use they get being on the back, combined with hybrid driving that avoids friction braking as much as possible.


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#13 OFFLINE   hybridbear

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Posted 17 September 2015 - 08:08 AM

From the Workshop Manual:

 

Electronic Brake Force Distribution (EBD)

On initial application of the brake pedal, full pressure is applied to the rear brakes. The ABS module then uses wheel speed sensor inputs to evaluate rear wheel slip. Once the rear wheel slip exceeds a predetermined threshold, the ABS module commands the HCU to close the appropriate isolation valves to hold the rear brake pressure constant while allowing the front brake pressure to build. This creates a balanced braking condition between the front and rear wheels. If the rear wheel slip continues and exceeds a second predetermined threshold, the ABS module commands the HCU to open the dump valves to decrease the rear brake pressure and allow the rear wheels to recover. A slight bump sensation may be felt in the brake pedal when EBD is active.

If the ABS is disabled due to a DTC being present in the ABS module, EBD continues to function unless the DTC is for wheel speed sensors or the HCU . When EBD is disabled, the ABS warning indicator, the red brake warning indicator and stability/traction control indicator (sliding car icon) illuminate.

 

Brake Modes

Because much of the brake torque required to stop the vehicle can be achieved through regenerative braking, it is not always necessary for the conventional friction brakes to be applied. The brake pedal uses a pedal feel simulator that acts against a curved bracket to give the driver a simulated pedal resistance as the brake pedal is applied. The ABS module uses the driver input on the brake pedal, wheel speed sensor input and the lateral deceleration messages from the RCM to determine the amount of deceleration the driver is requesting and which brake mode is necessary.


Regenerative Braking Mode

The ABS module determines the amount of braking torque necessary and sends that info to the PCM along with the current threshold for ABS intervention. The PCM determines how much braking torque the electric motor can provide based on the High Voltage Traction Battery (HVTB) state-of-charge and sends this information back to the ABS module. At the same time, the electric motor is switched to a generator which supplies the determined amount of braking torque. Based on the amount of braking torque the PCM can deliver, the ABS module determines whether it is necessary to apply the friction brakes or if the brake torque from the electric motor is sufficient to safely stop the vehicle.


Friction Braking Mode

Under some circumstances, the brake torque generated by the electric motor is insufficient to bring the vehicle to a safe, controlled stop and requires the assistance of the conventional friction brakes. Additionally, the state-of-charge in the High Voltage Traction Battery (HVTB) may not allow for regenerative braking to take place or the vehicle may be experiencing an ABS or stability control event.

In these instances, the ABS module activates a mechanical relay which supplies power to the brake vacuum pump. At the same time, the ABS module sends a PWM voltage to a solenoid mounted on the brake booster. The solenoid allows vacuum from the vacuum pump to enter the brake booster which moves the booster push rod and applies the conventional friction brakes.

During certain braking events, the friction brakes can be applied directly by the driver. The brake booster push rod is equipped with an adjustable stop, once the brake pedal travels far enough to engage the stop, the brake booster push rod is forced into the master cylinder and the conventional friction brakes are applied.

 

Summary: friction brakes are only used when needed. Rear brake pads are used first since regen happens only on front axle. When braking & turning the regen brake force is reduced & the pads are engaged. This is because regen braking can only brake at the axle. When turning you need to brake the inside wheels differently than the outside wheels. Thus, regen braking is drastically reduced when braking & turning. The transition when braking & turning from regen to friction brake pads should be imperceptible.


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#14 OFFLINE   fbov

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Posted 17 September 2015 - 09:29 AM

From the Workshop Manual:

 

Summary: friction brakes are only used when needed. Rear brake pads are used first since regen happens only on front axle. ...The transition when braking & turning from regen to friction brake pads should be imperceptible.

Nice description. Thanks for quoting. This explains my Sister-in-law's comments about the rear brakes sounding rough... (It was her Father's car.)

 

The transition is quite evident if it occurs while I'm turning, similar to clutching a manual tranny entering a turn.

 

Frank



#15 OFFLINE   hybridbear

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Posted 17 September 2015 - 10:09 AM

The transition is quite evident if it occurs while I'm turning, similar to clutching a manual tranny entering a turn.

Has this been true since the day you got the C-Max? Have you had the RCM recall (14S21) & PCM recall (15E03) done? Our car now has a lurch/surge when the transition happens, but it isn't supposed to. Ford is trying to figure out what they broke. Our Focus Electric has no noticeable transition from regen to friction brakes when turning. My parents' C-Max Energi has no noticeable transition as well.

 

I've described the behavior of our car since those recalls were performed in this thread along with graphs of what is happening.



#16 OFFLINE   scottwood2

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Posted 17 September 2015 - 10:58 AM

I have also never seen or heard of rotors that need to be replaced before the pads are worn.  The pads and rotors are burnished together (basically a break-in).  This gives you the most surface contact and best braking.  Replace the rotors and I would think you should replace the pads too. 

 

You can also check the thickness of the rotor.  There should be a minimum spec.  Grooves are normal on rotors. 


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#17 OFFLINE   stevedebi

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Posted 17 September 2015 - 12:10 PM

From the Workshop Manual:

 

... Rear brake pads are used first since regen happens only on front axle. ...

 

Do you have a source for that statement?

 

I don't believe this is the case. I should think that none of the brake pads are used during regen, unless additional braking force is needed, and I think in that instance all brake pads would engage. Why whould the rear brakes be used when the eCVT is doing a good job of slowing using regen?

 

Traction control is not used in braking, and antilock brakes are only used when the actual brakes are engaged. So I don't think those systems are impacting anything.

 

It would be nice to hear from the forum members who have access to the advanced documentation on the car.



#18 OFFLINE   hybridbear

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Posted 17 September 2015 - 12:46 PM

Do you have a source for that statement?

Yes, my post says: "From the Workshop Manual". That is the source.

 

I don't believe this is the case. I should think that none of the brake pads are used during regen, unless additional braking force is needed, and I think in that instance all brake pads would engage. Why whould the rear brakes be used when the eCVT is doing a good job of slowing using regen?

Please re-read my post. When you are turning you need a different amount of braking force on the inside wheels versus the outside wheels. Regen braking cannot provide this. Regen can only brake both wheels with the same amount of force because it's braking at the front axle. Thus you must use the brake pads to apply differing amounts of brake force. Since regen is braking the front axle, brake pads engage first on the rear axle.


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#19 OFFLINE   stevedebi

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Posted 17 September 2015 - 02:34 PM

Yes, my post says: "From the Workshop Manual". That is the source.

 

Please re-read my post. When you are turning you need a different amount of braking force on the inside wheels versus the outside wheels. Regen braking cannot provide this. Regen can only brake both wheels with the same amount of force because it's braking at the front axle. Thus you must use the brake pads to apply differing amounts of brake force. Since regen is braking the front axle, brake pads engage first on the rear axle.

HB,

First, sorry I missed the main quote; when someone provides a quote in a thread I'm following, I don't usually read it, because I would have already read it. I see now that you were using the gray quotes to indicate you were quoting an outside source. I'm not used to that, since that gray area generally indicates one has hit the "reply" button to a post.

 

Second, the statment from the manual does not tie in the rear brakes with the regenerative braking. In the first paragraph. I believe they are describing the EBD process, which would apply after the regenerative braking has been used - in fact, later paragrahs say that sometimes the physical brakes may not be engaged.

 

It is that second sentence in your summary that doesn't seem to jive: "Rear brake pads are used first since regen happens only on front axle."

 

EDIT: However, the EBD does explain why the rear brakes will have more wear, very important for the OP.


Edited by stevedebi, 17 September 2015 - 02:36 PM.


#20 OFFLINE   hybridbear

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Posted 17 September 2015 - 02:36 PM

It is that second sentence in your summary that doesn't seem to jive: "Rear brake pads are used first since regen happens only on front axle."

Rear brake pads are used first in comparison to front brake pads, but after regen braking.


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