3.3TT Brake Pedal Travel - How far does YOURS go down?

[SteveCo]

I just had my car in at the dealer, having them look at the travel on the brake pedal. This is the GT Limited (Canada), which is the top trim with Brembo brakes.

When the car is off, the pedal is a good solid, high pedal - as one would expect. When the car is started, the pedal 'brake point' sinks somewhat, as one expects with power brakes - however, with moderate pressure on the pedal it continues to sink toward the floor until it contact the stops at the end of it's travel.

Brake performance so far has been fine, and I've had no issues with stopping in normal driving. The service department first tried bleeding it (and it seemed to get marginally worse, with a faster sink rate), then informed me that this pedal 'sink' was normal, and they looked at other cars on their lot and they did the same thing. I wouldn't have believed it, but I asked them to try another car when I picked mine up, and I'll be damned if it didn't do the same thing, sinking right down to the stops. If you tap it rapidly at that point, you can hear it clunk on the stops.

It's not the height of the pedal that bothers me, it's the fact that under moderate pressure it sinks all the way until it hits the end stops. I've got to think that could be a problem when the brakes were called upon to perform in a severe braking situation requiring steady pressure - obviously when the pedal is at the stops, it's not going to provide any additional braking force with increased pressure.

What does YOUR pedal do? You don't need to drive the car - just put pressure on the pedal while the car is running and in park. Does it continue down, and settle right to the bottom?

 

[Dochidalgo]

Definitely do not.....Not air in the brake system, then is a brake pump defective losing brake fluid pressure...

 

[SteveCo]

As I mentioned, they had no problem pulling in another Stinger off the lot that did exactly the same thing - and they claim to have tried a couple others as well. This is while applying what I would call 'moderate' brake pressure, so relatively firm but not pushing really hard.

 

[MerlintheMad]

I'm a light braker. So if I had not had a couple of emergency stops I'd have not been able to say that my brakes do not exhibit anything like what you describe. The pedal stays above the "stops", whatever those are. I can apply brake pressure at any time and not be anywhere "bottoming out". When I've had previous vehicles do this, it was always air getting into the line somehow. And brake fluid usually was at low volume.

 

[SteveCo]

The brakes (so far) work fine in an emergency stop - or a regular stop. There are no symptoms or problems one would associate with bad brakes other than this pedal behavior. There are no visible leaks, brake fluid is not depeleted/depleting, and they've tried bleeding the system.

The only time you would notice the pedal going down is when holding constant pressure on the pedal while stopped, with the engine running. Have you tried that?

 

[MerlintheMad]

Lately I don't even hold the brake with my foot. I use Auto Hold. Push the brake pedal until "Auto Hold" goes green, then hover over the gas pedal. If my brake pedal kept going down until it hit the stops/floor, I'd be on it right now. That should never happen. When you push hard in an emergency, you need to be able to push without a physical "stop" to the throw of the brake pedal. The ABS is supposed to take care of making sure that the brakes don't lock up. All my previous vehicles never used ABS, because I am in a lifelong habit of pumping the brakes. I have only slammed on them when an accident is iminent. I'd really hate the feeling of the brake pedal having given all it's got, and you can't increase pedal pressure because the stop/floor is there!

 

[SteveCo]

I agree, yet they pulled another car off the lot that does exactly the same thing. Give it a try next time you're in the car, and see if you can apply pressure and get the pedal to sink, while at a stop with the engine running.

 

[Ozstung]

My brakes are nothing but normal. A few months ago I was invited to a Kia track day. We had half of the track closed for our benefit where did laps, slalom through cones, repeated launch control starts AND lots of emergency braking from various speeds. We put the 6 cars through a torturous half day of driving. Before us in the morning another lot had done exactly the same. One thing we all concluded was how damn amazing the brembos had been, they really had lasted and there was no brake pedal sinking.

 

[SteveCo]

Thanks for the replies, and again I have to say I've experience (so far) no issues with brake performance - they respond quickly, and are perfectly capable of launching any unsecured objects through the windshield on demand. The pedal 'sink' under constant pressure is something I've only recently become aware of, although I've had the car for several months.

I've had many, many cars with power brakes, and never seen this behaviour before - yet the dealer claims this in normal, and produced another car that does exactly the same thing. They couldn't explain why they did this, and promised to have an answer from KIA for me this week - unless they have a satisfactory reason, I'll be following up with Kia myself.

Again, if you haven't I'd much appreciate positive confirmation that your car is NOT doing the same, which doesn't require any driving tests. You simply need to have the car running, and apply pressure to the brake pedal. As with all power brakes, the pedal will sink somewhat under vacuum boost - but with continued pressure, does it continue to sink, or does it reach a firm, hard pedal short of the stops?

Common sense says it shouldn't do that, but as I say they had no issues providing another Stinger off the lot that did EXACTLY the same thing. I've seen posts online about other brands of car with the same behaviour, and no clear answers.

Any feedback/confirmation on this would be much appreciated - just trying to gather some information on whether this is really the 'norm' for Brembo equipped Stingers in the real world ...

 

[MerlintheMad]

Okay. I am, this morning, inclined to believe that pedal "sink" under constant pressure, while standing is indeed normal operation. I haven't noticed it for the reasons I gave above. The reason why I am inclined to believe it is normal for the brake pedal to sink if you just push on it while standing still, is something I just read in the 27 August issue of Autoweek: about the latest 2019 Jaguar XE SV Project 8 (author and driver Robin Warner). In the second to last paragraph: "Every new car built today uses an electric throttle, meaning no physical connection between your foot and the fuel. It's software that decides, after going through several safety nets."

Should not the brakes be the same way? We probably don't have a brake pedal "cable" in the old school sense. So if the car "senses" that brakes are being pushed and no demand on them is required, i.e. the car is stationary, then the brake pedal descends to the needed pressure, thus alleviating the undue pressure applied by the driver; the car "knows" how much brake is needed in the current, stationary condition and adjusts accordingly.

Have just come inside from running up the car in the driveway: yes, the pedal sink is normal in N or D. I have to use a pretty heavy brake foot, but continual pressure eventually reaches the bottom and a further press taps the floor/stops. This must mean that the brakes, as the throttle, do not use a brake cable in the old school sense. Braking is done entirely through electronics. In "P" there is no use of the brake pedal at all; aside from pushing it to start or take it out of "P", at which point the brakes become operative.

 

[SteveCo]

Thanks for checking, @MerlintheMad. It's still surprising to me, and I don't understand why it works that way, but its good to have some independent confirmation. I hope to get an answer back on this from KIA this week.

The Stinger does not use a 'brake by wire' arrangement where a computer is responsible for the braking. Like virtually all production brake systems, the pedal physically pushes a rod into a master cylinder, which in turn forces hydraulic fluid out to the disk calipers and squeezes the pads against the rotors. The vacuum booster (which lends the power assist with the engine running) is merely a force multiplier to greatly reduce the pedal pressure required. It also provides a reserve of brake assist should the engine quit, as it retains enough vacuum for a few applications after the engine stops.

There is the added complication of ABS brake modulation, but that as well is an 'add on' to the basic physical brake hydraulic system.

Again, appreciate you verifying the operation on your car as well. Still looking forward to hearing from others ... ?

 

[SteveCo]

*BUMP* I'd appreciate it if others could take a couple of minutes to try this on their brake pedal when sitting in park with the engine running, before I follow up with KIA. So far the only person on here to actually try it (@MerlintheMad) found his did the same thing.

If anyone had asked me previously if my brake pedal did this, I'd have said NO as it isn't how you normally use your brakes. It came as a surprise, and especially when I found the exact same behaviour in the other car at the dealer.

 

[Manchuz]

Not sure what you're asking to check....you're saying when in park, you apply moderate pressure on the brake pedal, the brake pedal will sink to the bottom, leaving your foot in midair?

 

[SteveCo]

Not sure what you're asking to check....you're saying when in park, you apply moderate pressure on the brake pedal, the brake pedal will sink to the bottom, leaving your foot in midair?

No, presumably your foot would follow the pedal down ...

It sinks because of the constant pressure exerted by your foot on the pedal. I would expect it to stop at some point on the way down at a firm pedal, but everything I've found so far (including from KIA) says that is not the case.

I've never had brakes do this before, and frankly don't understand how or why that would be 'normal' operation.

 

[Dochidalgo]

@SteveCo Here you go....looooong

Stinger GT2 (sold in Mexico). Engine running in Park position, my foot with constant pressure on the brake pedal about 1 minute...the pedal was steady.....

 

[SteveCo]

Here you go....looooong
Stinger GT2 (sold in Mexico). Engine running in Park position, my foot with constant pressure on the brake pedal about 1 minute...the pedal was steady.....

Thanks for taking the time to do that!

Mine reaches a steady point as well, but unfortunately it's because it's on the stops - I can tap it a couple of times when it's all the way down, and actually hear it rap on the stops. This is the same as what I found in the other dealer car, and what @MerlintheMad described as well. Yours is not getting that far down? (difficult to tell from the video).

 

[Dochidalgo]

Thanks for taking the time to do that!

Mine reaches a steady point as well, but unfortunately it's because it's on the stops - I can tap it a couple of times when it's all the way down, and actually hear it rap on the stops. This is the same as what I found in the other dealer car, and what @MerlintheMad described as well. Yours is not getting that far down? (difficult to tell from the video).

Definitely, do not rap on the stops, even from park to drive or from start the engine and move the car, the brake pedal is steady...

 

[SteveCo]

Good to know it 'can' behave like I expect ... thanks again for checking!

 

[Dochidalgo]

Let me get you another video...

 

[BlaydeX15]

Mine does it. Foot on the brake, medium pressure (Think: Roughhousing with your kids/big dog, but not crushing them). It'll slowly sink about 3/4ths of the way down, and it'll sit there. If you stomp, it still has a bit of travel though. I'm wondering how hard you guys sit on your brake pedal. Lol.