Odd brake pedal behavior under heavy braking - AudiWorld Forums

Go Back  AudiWorld Forums > Audi Models > Audi Q3 /Q5 / Q7 > Audi Q7 > Q7 Discussion
Reload this Page > Odd brake pedal behavior under heavy braking
Notices
Q7 Discussion Discussion forum for the Audi Q7 SUV built from 2005 to 2015

Odd brake pedal behavior under heavy braking

Reply

 
 
Old 02-09-2018, 02:59 PM
  #1
JKJ
AudiWorld Member
Thread Starter
 
Join Date: Nov 2007
Posts: 103
Default Odd brake pedal behavior under heavy braking

I had occasion to make a max effort stop from 70-0 (well, maybe 70-5, as I didn't come to a complete stop) today, and encountered what I thought was odd brake behavior. The brakes were maybe slightly warm from regular driving, but not to the point that fade would be an issue at all. Circumstances required me to start braking "hard" (maybe 80%), with resulting good pedal feel and effort as normal. Around 40 mph I increased pedal force ("stop NOW"), and with enough force that the ABS was just starting to cycle), the pedal effort suddenly became very light and the pedal traveled more or less to the floor. Braking performance remained good throughout (ABS was cycling, and I stopped safely). Is this normal behavior? It's almost as though I pushed hard enough to go through a detent, and on the other side of the detent there was no pedal force at all. After the event, I drove off and the brakes were back to normal when being used in "normal" traffic conditions.

Later on in a deserted location, I tried stomping the brakes from ~40mph, and didn't encounter the odd pedal feel. I did it again from 60, and the "firm/nothing" detent effect occurred again, again with no reduction in braking performance.

Not what I'm used to in my other vehicles at all. Is something wrong, or am I just not used to brake behavior at the limit in the Q7? Discs and pads were replaced earlier this month, but they're pretty well bedded in and have not behaved oddly until now.
JKJ is offline  
Reply With Quote
Old 02-10-2018, 03:48 AM
  #2
AudiWorld Member
 
Stevereddy's Avatar
 
Join Date: Jun 2017
Location: Portland, Maine
Posts: 309
Default Thanks for heads up

Since May when I bought my A8 I haven't had to brake hard like that, I suppose I should go out and do a few max performance stops like that, it is good to know that a car stops in a predictable fashion
Stevereddy is offline  
Reply With Quote
Old 02-10-2018, 01:26 PM
  #3
AudiWorld Member
 
Join Date: Jun 2013
Location: Suburbs of Toronto, Canada
Posts: 243
Default

Assuming something was in front of you on the first stop then maybe the pedal feel changed when Audi Grake Guard kicked in and the car helped to slow down automatically by applying full force on its own when you got nearer to a collision? If it was something like this then it would explain why you couldnít replicate it on subsequent test stops as Iím assuming you did your test stops in an open area with nothing in front of you as you slowed down.

Description - Audi braking guard - Adaptive cruise control (ACC) - Controls - Audi A4 Owner's Manual - Audi A4 - Audihelp.com

Safety based on radar technology ? Audi braking guard

This assumes that you have Adaptive Cruise Control which includes Audi Brake Guard.

If not, then it may have been Brake Assist where the system can sense the difference between the brakes being applied aggressively vs the brakes being applied in a panic. If it senses that itís an emergency/panic situation then it kicks in to boost the system to full pressure in order to help you reduce the stopping difference. This would explain the difference in pedal feel in the initial scenario. Then in your subsequent test runs Brake Assist never kicked in because the system didnít detect a panic stop - your tests may have been aggressive but not enough to have been picked up as being a full on panic stop, so it didnít activate Brake Assist in your tests.


Originally Posted by JKJ View Post
I had occasion to make a max effort stop from 70-0 (well, maybe 70-5, as I didn't come to a complete stop) today, and encountered what I thought was odd brake behavior. The brakes were maybe slightly warm from regular driving, but not to the point that fade would be an issue at all. Circumstances required me to start braking "hard" (maybe 80%), with resulting good pedal feel and effort as normal. Around 40 mph I increased pedal force ("stop NOW"), and with enough force that the ABS was just starting to cycle), the pedal effort suddenly became very light and the pedal traveled more or less to the floor. Braking performance remained good throughout (ABS was cycling, and I stopped safely). Is this normal behavior? It's almost as though I pushed hard enough to go through a detent, and on the other side of the detent there was no pedal force at all. After the event, I drove off and the brakes were back to normal when being used in "normal" traffic conditions.

Later on in a deserted location, I tried stomping the brakes from ~40mph, and didn't encounter the odd pedal feel. I did it again from 60, and the "firm/nothing" detent effect occurred again, again with no reduction in braking performance.

Not what I'm used to in my other vehicles at all. Is something wrong, or am I just not used to brake behavior at the limit in the Q7? Discs and pads were replaced earlier this month, but they're pretty well bedded in and have not behaved oddly until now.
Canadian Lurker is offline  
Reply With Quote
Old 02-10-2018, 03:47 PM
  #4
AudiWorld Super User
 
J. Patterson's Avatar
 
Join Date: Apr 2004
Posts: 3,161
Default

I can’t find documentation of it but I have experienced that once too. ONCE in over 100,000 miles. It was a long time ago and details are vague in my memory. I do remember that I wondered if the vehicle helped with a panic stop. I wondered if it was due to suddenness of brake application and or pedal pressure applied. Perhaps it is related to this.
https://www.euroncap.com/en/ratings-...-brake-assist/

Last edited by J. Patterson; 02-10-2018 at 03:52 PM.
J. Patterson is offline  
Reply With Quote
Old 02-10-2018, 03:51 PM
  #5
AudiWorld Super User
 
J. Patterson's Avatar
 
Join Date: Apr 2004
Posts: 3,161
Default

Originally Posted by Canadian Lurker View Post

If not, then it may have been Brake Assist where the system can sense the difference between the brakes being applied aggressively vs the brakes being applied in a panic. If it senses that itís an emergency/panic situation then it kicks in to boost the system to full pressure in order to help you reduce the stopping difference. This would explain the difference in pedal feel in the initial scenario. Then in your subsequent test runs Brake Assist never kicked in because the system didnít detect a panic stop - your tests may have been aggressive but not enough to have been picked up as being a full on panic stop, so it didnít activate Brake Assist in your tests.


That is my theory too.
J. Patterson is offline  
Reply With Quote
Old 02-10-2018, 07:06 PM
  #6
JKJ
AudiWorld Member
Thread Starter
 
Join Date: Nov 2007
Posts: 103
Default

Since mine is a 2015, I don't have ACC (not available on any trim level that year, even my Prestige). The incident didn't involve another vehicle, so I doubt ACC would have done anything. Could have been brake assist, but the application was in 2 clear stages. A second or so of heavy, but not max, and then full push. Interesting if it kicked in with that situation. If it were all in one big push, I'd easily agree it could be Assist. Still not sure why the pedal went so soft, though. Does Assist make it easier to get full travel? If so, that was probably it.
JKJ is offline  
Reply With Quote
Old 02-10-2018, 08:04 PM
  #7
AudiWorld Senior Member
 
dreadlocks's Avatar
 
Join Date: Mar 2017
Location: Denver, CO
Posts: 697
Default

I hadn't noticed that, weird I have ACC on my 2014 but it was not offered in 2015.. I love it and dont know if I can now live without it.

If the brake assist is taking over hydraulics in a panic stop I could totally see the pedal going limp, since it clearly stopped fine when this happened I would just wrap this incident up to the car outperforming the driver.. when safety systems take over things get wonkey, ABS, ASR, and ESP all have their own unique reactions when engaged and you can feel em all through the break pedal too.

I enabled European panic brake lights on my Golf, basically it turned flashers on if you panic brake.. I thought I didnt have it enabled because I tried several times to mimmic a panic brake and trigger it and never saw it engage.. but then I did have to just mash on em once for an emergency stop on the interstate and I could see the flashers activate.. guess I never got it fast enough in my testing.

Last edited by dreadlocks; 02-10-2018 at 10:40 PM.
dreadlocks is offline  
Reply With Quote
Old 02-11-2018, 07:09 PM
  #8
AudiWorld Senior Member
 
Greystoke's Avatar
 
Join Date: Sep 2013
Location: California
Posts: 951
Default

ACC was definitely offered on the 2015 Prestige models. Look in the brochures which were recently posted.

Grey
Greystoke is offline  
Reply With Quote
Old 02-12-2018, 08:54 AM
  #9
AudiWorld Member
 
Join Date: Mar 2008
Location: PNW
Posts: 209
Default

Definitely Brake Assist kicking in. Happens on my '07 when I'm bedding in the brakes.
chingwodapigu is offline  
Reply With Quote
Old 02-12-2018, 08:59 AM
  #10
AudiWorld Member
 
Join Date: Jun 2013
Location: Suburbs of Toronto, Canada
Posts: 243
Default

Originally Posted by JKJ View Post
Since mine is a 2015, I don't have ACC (not available on any trim level that year, even my Prestige). The incident didn't involve another vehicle, so I doubt ACC would have done anything. Could have been brake assist, but the application was in 2 clear stages. A second or so of heavy, but not max, and then full push. Interesting if it kicked in with that situation. If it were all in one big push, I'd easily agree it could be Assist. Still not sure why the pedal went so soft, though. Does Assist make it easier to get full travel? If so, that was probably it.
From your description it really sounds like Brake Assist kicked in.

After your initial application of the brakes the system (a) primes to be ready to apply all available brake pressure and (b) monitors to confirm that itís a panic stop situation. After a predetermined time, if youíre still braking hard, then the Brake Assist system will take over - hence your experience with the pedal pressure changing. Had you eased up before it kicked in then it would have remained primed but stayed on standby.

It senses some some combination of how quickly you hit the brakes and how hard youíre braking to know when to kick in. This is why you didnít replicate the feeling in your test runs.
Canadian Lurker is offline  
Reply With Quote
 
 
 

Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
jamiepstewart
TT (Mk1) Discussion
8
03-09-2011 09:40 AM
90QuattroKid
Audi 90 / 80 / Coupe quattro / Cabriolet
13
03-16-2009 09:38 PM
Shagin'Wagon
A4 (B6 Platform) Discussion
2
03-16-2004 09:42 PM

Thread Tools
Search this Thread
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -8. The time now is 07:25 PM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: