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-   -   Brake pedal hard on second press? (http://www.jeepgarage.org/f107/brake-pedal-hard-on-second-press-73116.html)

StaticFX 03-22-2014 03:42 PM

Brake pedal hard on second press?
 
Just noticed this today.. I pressed the pedal, stopped (on an uphill).. let my foot off and pressed again (not sure why i did) but it became like a rock to press??

once I moved abit forward.. it was fine.. but I can reproduce this.

pensfan414 03-23-2014 11:34 AM

Mine does the same, very reproducible. Perhaps someone with more automotive knowledge can chime in on this and tell us if this is normal.

Peter_K 03-23-2014 05:52 PM

Normal. The first press preloaded the brakes. On the second press they barely need to travel to make contact, hence the harder feel.

pensfan414 03-23-2014 06:03 PM

Thanks!

Peter_K 03-23-2014 06:50 PM

I also just noticed the "uphill" reference as well. That could also be hill start assist -- it will also pressurize and preload the brakes to hold you on an incline before you accelerate. Either way it's normal behavior.

mswlogo 03-23-2014 08:30 PM

Re: Brake pedal hard on second press?
 
Quote:

Originally Posted by Peter_K (Post 996470)
Normal. The first press preloaded the brakes. On the second press they barely need to travel to make contact, hence the harder feel.

So why doesn't it do it downhill?
And if you just touch the gas why are the breaks suddenly no longer preloaded.

The breaks actually preload when you take your foot off the gas.

I believe it's some sort of anti rollback feature.

My wifes VW has an "Auto Hold" feature on her manual transmission. But the Automatic Transmission version also has the same "Auto Hold" feature (dual clutch transmission). I think it's some variation of that. It would allow engine to run at lower RPM at idle with less friction in the torque converter. Cars generally are not supposed to roll back with automatics (with in reason) even with foot off the brake.

It disengages as soon you touch the gas.

Yet another reason why alarms go off if you drive two footed.

Peter_K 03-23-2014 09:15 PM

Quote:

Originally Posted by mswlogo (Post 996554)
So why doesn't it do it downhill? And if you just touch the gas why are the breaks suddenly no longer preloaded. The breaks actually preload when you take your foot off the gas. I believe it's some sort of anti rollback feature. My wifes VW has an "Auto Hold" feature on her manual transmission. But the Automatic Transmission version also has the same "Auto Hold" feature (dual clutch transmission). I think it's some variation of that. It would allow engine to run at lower RPM at idle with less friction in the torque converter. Cars generally are not supposed to roll back with automatics (with in reason) even with foot off the brake. It disengages as soon you touch the gas. Yet another reason why alarms go off if you drive two footed.

Read my second post

Willx 03-23-2014 09:20 PM

Re: Brake pedal hard on second press?
 
Quote:

Originally Posted by Peter_K (Post 996495)
I also just noticed the "uphill" reference as well. That could also be hill start assist -- it will also pressurize and preload the brakes to hold you on an incline before you accelerate. Either way it's normal behavior.

Correct, you are stacking pressure ahead of the ABS module, already charged for the hill keep assist.

mswlogo 03-24-2014 08:45 AM

Re: Brake pedal hard on second press?
 
Quote:

Originally Posted by Willx (Post 996592)
Correct, you are stacking pressure ahead of the ABS module, already charged for the hill keep assist.

Actually you are probably pushing against a closed valve. And not applying any pressure to the actual brakes. Hence the "rock hard feel".

StaticFX 03-24-2014 09:22 AM

Re: Brake pedal hard on second press?
 
lol ok.. i thought maybe it was something to do with the hill assist.. It was odd I had never noticed this before! Panicked a little (Bad memory of my old 68 camaro Master cylider lock up! lol)


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