Can't lock up the rear. Normal?

[WildHorse]

Try unplugging the nanny plug under the hood next to the air box. It will disable the ABS and you will be able to lock the rear brakes up like conventional brakes and pass the test. Once you’re done, reconnect the nanny plug.

It will then fail the safety. Kobayashi maru.

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[NGOT8R]

Maybe the rear ABS sensors and rings are gunked up like mine were with just 8300 miles and the sensors are unable to take a proper reading. Jack the rear of the car up to check and see if they are dirty. If they are, clean them with brake and parts cleaner and a rag and then retest. Here’s what mine looked like before and after cleaning them.

 

[ShadesOfBloo]

Maybe the rear ABS sensors and rings are gunked up like mine were with just 8300 miles and the sensors are unable to take a proper reading. Jack the rear of the car up to check and see if they are dirty. If they are, clean them with brake and parts cleaner and a rag and then retest. Here’s what mine looked like before and after cleaning them.

Ooh... My car has twice that mileage. Maybe I want to check for this.

 

[NGOT8R]

Ooh... My car has twice that mileage. Maybe I want to check for this.

I definitely recommend it. I will add this as a regular maintenance item on my car moving forward.

 

[Keeffa]

So every year, we have to pass a safety inspection here in Spain, and one of the tests is a braking test on each axle individually.
The car gets put on some mechanical rollers, and you have to slowly apply the brakes until, they lock up and they take a measurement.
My fronts lock up no problem. The rears however don't. I stomp on the brakes as hard as i can, but it's not enough to lock up the rears. Is this normal? It's enough to pass the braking test, but it definitely doesn't feel like it's doing much braking. Doesn't feel right.
I'm running OEM ford pads with Steeda 2 piece rotors, and goodridge braided hoses.
Tires are Continental Sport Contact 7 in 305/30 R20 all round.
I've bled the whole system multiple times, and there is definitely no air in the system.

Is it really that the rear pads are that weak that they aren't able to lock up the rears?

I feel like that's wasted braking performance if the rear isn't able to lock the rear tyres. I know you ideally don't want to lock up the rear, but it honestly feels week.

Any thoughts or opinions on this? Anyone know who makes pads with a more aggressive friction coefficient that are still streetable?

When you apply your brakes weight transfer takes place, meaning the weight of the car is put on the front wheels and so the front brakes do most of the braking. This makes locking the rears very easy. In older cars locking up the rear wheels was a problem coursing the car to go sideways.

 

[Garfy]

Maybe the rear ABS sensors and rings are gunked up like mine were with just 8300 miles and the sensors are unable to take a proper reading. Jack the rear of the car up to check and see if they are dirty. If they are, clean them with brake and parts cleaner and a rag and then retest. Here’s what mine looked like before and after cleaning them.

I would imagine that if the rear wheel speed sensors weren't reading correctly, it should've set a code in the ABS system as it monitors all 4 wheel speed sensor. If it sees a conflict (say the fronts reading 55 mph and the rears 30 mph or erratic readings) it should set a code and many systems will also deactivate the ABS system altogether since it wouldn't be able to determine whether it's applying the correct amount of braking force to prevent wheel lockup.

 

[NGOT8R]

I would imagine that if the rear wheel speed sensors weren't reading correctly, it should've set a code in the ABS system as it monitors all 4 wheel speed sensor. If it sees a conflict (say the fronts reading 55 mph and the rears 30 mph or erratic readings) it should set a code and many systems will also deactivate the ABS system altogether since it wouldn't be able to determine whether it's applying the correct amount of braking force to prevent wheel lockup.

I don’t know for certain what systems are tied together. All I can say from my personal experience is, I had received the following DTCs and or warning messages off and on until recently, when I made my own Magneride delete sensors for the rear shocks, (P2BFB and U0416, Suspension Fault - Speed Limited to 80 MPH, as well as Adv. Trac and ABS fault lights which stayed on). Cleaning my ABS sensors before testing the MR delete sensors seemed to make sense, given how dirty they were. I can’t imagine them not having some sort of negative effect on the ABS system.

Granted, some of my issues may have been self induced by trying to circumvent the rear portion of my MR, but recent testing has come up void of any codes and I hope it stays that way too.

 

[NightmareMoon]

Weight transfer is a factor too. Under notmal circumstances, when you’re braking the rear is much lighter and will lock up much mich easier and thats the situation the rear brakes are designed for.

That said, I’d think you should be able to lock up your rears on a roller with equal weight on all the tires, if ABS isnt doing it’s thing.

 

[swoop1156]

Put it this way, the quickest way to stop the car is to have all 4 brakes reach the point where they are just about to lock up the wheels, but not actually lock them up. If your rear brakes aren't even close to that, then you're not braking the car as quickly and efficiently as possible. No?

I think you're speaking about "threshold braking". This is pressing the brake pedal, for example, to 99% of the limit of the tire's ability to not lose traction with the road surface, which at 100%, will lock up/skid/slide, which increases stopping distance and decreases control of the vehicle.

This test, I get it, but it's just kinda dumb that they need the brakes to lock, thus imitating a skid/slide, which is the opposite of what ABS does.

In a panic situation where you need to stop ASAP, 99.99999% of people are simply going to mash the brake pedal as hard as they can and hang on. That, in a non-ABS equipped vehicle, will lock-up the brakes and you'll be in a skid/slide, as well as have less control. Hence the reason ABS was created. It's in the freakin' name, Anti-Lock Braking System.

This is a wild thread.

 

[DB83]

The test doesn't require you to lock up the brakes. It measures the breaking force applied to the rollers and determines wether its enough to pass the test.

It was more my curiosity as to how a braking system in a performance car isn't capable of applying enough force to lock up.

 

[thornclaw]

i think u should be able to lock the rears. sometimes if the parking brake isnt adjusted right, it takes a deep pedal push to get the rear pads to touch the brake disc. to test this, engage the parking brake. if it only engages near the end of the pull, your parking brake may need adjustment. it should engage at the beginning of the pull.

 

[Buldawg76]

An experienced driver that knows his car and its braking limits to the point that he can apply the brakes to the very limit of tire lockup will be able to stop in less distance than someone that just slams on the brakes and allows the ABS to control the braking forces.

ABS is designed to allow an average driver to maintain control of the vehicle in a panic stop situation, but it will absolutely not allow the vehicle to stop in less distance than a driver that can bring the braking force to the very limit of tire lockup and maintain that level of force to a complete stop.

BD

 

[Ritchie]

In normal use you should never be able to lock the rears, why do you think brakes are smaller on the rear? Rears do very little braking in normal use. The brake rollers you are describing are purely to test brake balance and efficiency. There is nothing wrong with your car, the brakes are working exactly as per design. One more thing to keep in mind is that there are likely 2x contact patches on the rollers creating more grip on the tyre than there would be on the road. Regardless, there is nothing wrong, you're overthinking it.

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