Loss of stopping power/pulsation when braking HARD!!

[gmdiluca]

ok guys so recently I've been having an issue with my brakes. When I brake hard from high speeds my brakes do not function like they used to. Its as if my braking force has cut in half and my pedal pulsates. I used to be able to stop on a dime from speeds and now I struggle to slow down. I went to my local mechanic and he suggested it could be the Yaw sensor activating my brakes to prevent my car from losing control. I just recently went stage 3 and he thinks now that I'm going much faster the car is thrown off balance when braking hard (car noes dives hard) which is sensed by the yaw sensor thus tripping some safety mechanism that modulates braking. Does that sound possible? any suggestions?

Any one experience this before? its some what terrifying to drive at high speeds right now.
Brake setup:
-18z bbk in front
-hawk hps front
-stock rear brakes (300mm bbk sitting on shelf lol)
-ebc red rear

[MarlinFoundNemo]

Yaw sensor? Wtf haha in my 2 years of having a B5 I've never once heard about that. Really bad pulsing/shaking is often warped rotors.

[S4tech2]

It sounds like your abs is acrivating when it shouldn't, check faults in the abs module.

[gmdiluca]

Yaw sensor? Wtf haha in my 2 years of having a B5 I've never once heard about that. Really bad pulsing/shaking is often warped rotors.

ESP cars have yaw sensors for the stability control

[gmdiluca]

It sounds like your abs is acrivating when it shouldn't, check faults in the abs module.

I believe this as well. He said he checked the abs tone rings and they weren't damaged. I'll have to scan for abs codes. Are they in a separate module from engine in vag-com

[ADCS]

Module 3, Brake Electronics.
You should check through the measuring blocks to see which one shows the ABS status and log it.

http://wiki.ross-tech.com/wiki/index...A4/S4/RS4_(8D)

You should probably flush and bleed your brakes as well.

[gmdiluca]

No abs codes


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[funkin]

Sounds exactly like my rotors when they were warped.

[getslideways]

you could pull the ABS fuse to see if the pulsing goes away or remains. Keep in mind this is not a fix, just a means of diagnosing if the cause is mechanical (warped rotors for example) or electronically induced (ABS/ESP activating erroneously)

Did your local mechanic check out the rotors? You should be able to spin the wheel and check for inconsistent contact with the pads, but you could also pop the rotor off and have it spun up on a brake lathe and that would give you an answer really quick as to if it is warped or not.

[james 408]

step 1: is your abs going off? ABS feel is unique vs a warped rotor or anything else that's once/twice per revolution, totally different feel. can pull fuse like slideways said to check mechanical only. You should also be able to detect which corner it's coming from if it's not even on both sides.
step 2: bed in pads again (thinking pad deposits, those HPS' are pretty easy to melt -- this may not solve the issue without wire brush/brake cleaner first)
step 3: check for runout (assuming not floating)

And no stage 3 has nothing to do with it except maybe giving off more heat due to additional speed.

Usually with severe pad deposits or bad warping of rotors it will begin to show up in steering wheel shimmy as well. but sometimes not if it's still early days, or it's the rear (far less likely).

i'd strongly advise ditching those HPS' if you're doing a lot of hard braking. track pads are far better.

also be aware after you heat up your pads, don't come to a stop and sit on the brakes. this is the #1 cause of pad deposits. Pad deposits can form a sort of concrete when it fuses with the rotor material, super hard to get rid of. This is often the reason it's misdiagnosed as warped rotors. very rarely is a rotor actually warped outside of tracking the vehicle (or similar activities).

please also note: pad deposits and warped rotors can trigger your abs prematurely at near threshhold braking. you can diagnose it independently at partial brake applications below the abs threshold (or again pull the fuse).

[S4James]

Don't go back to that mechanic. What a stupid thing to suggest.

[jaychen]

ok guys so recently I've been having an issue with my brakes. When I brake hard from high speeds my brakes do not function like they used to. Its as if my braking force has cut in half and my pedal pulsates. I used to be able to stop on a dime from speeds and now I struggle to slow down. I went to my local mechanic and he suggested it could be the Yaw sensor activating my brakes to prevent my car from losing control. I just recently went stage 3 and he thinks now that I'm going much faster the car is thrown off balance when braking hard (car noes dives hard) which is sensed by the yaw sensor thus tripping some safety mechanism that modulates braking. Does that sound possible? any suggestions?

Any one experience this before? its some what terrifying to drive at high speeds right now.
Brake setup:
-18z bbk in front
-hawk hps front
-stock rear brakes (300mm bbk sitting on shelf lol)
-ebc red rear

did you recode your abs module to accommodate for larger brakes? i know not a lot of guys on az have done it, over on audisrs they swear by it. some even said after a while they would notice the car becoming more nose heavy until they recoded the abs module again (brake bias i believe ?).

just a thought, although the vibrating is usually from warped rotors.

[gmdiluca]

did you recode your abs module to accommodate for larger brakes? i know not a lot of guys on az have done it, over on audisrs they swear by it. some even said after a while they would notice the car becoming more nose heavy until they recoded the abs module again (brake bias i believe ?).

just a thought, although the vibrating is usually from warped rotors.

I have read that. The thing is the car has never done in in the 2 years I've had this bbk. It has only been an issue in the last couple months. How would I go about changing the brake bias code?

[jaychen]

hmm id say its unlikely to be the problem then.

if you have enough meat, i'd be skimming the rotors first to see if it fixes it. cheapest option first and most logical.

[01audia4]

did you recode your abs module to accommodate for larger brakes? i know not a lot of guys on az have done it, over on audisrs they swear by it. some even said after a while they would notice the car becoming more nose heavy until they recoded the abs module again (brake bias i believe ?).

just a thought, although the vibrating is usually from warped rotors.

Link to this? I upgraded to 17z and don't believe I have read this?

[jaychen]

Link to this? I upgraded to 17z and don't believe I have read this?

i dont have any links saved, unfortunately. have a squiz on audisrs!

quick search:

http://audisrs.com/archive/abs-codin...t__t_6058.html

[01audia4]

i dont have any links saved, unfortunately. have a squiz on audisrs!

quick search:

http://audisrs.com/archive/abs-codin...t__t_6058.html

That is all I've found however I don't know what Elsa is and have no idea how to find the coding for 17z - nor do I see it anywhere, so for me, if it ain't broke I'm not going to try to fix it.

If you connect vagcom to the ABS unit it will display the current coding. Mine was 04395 (HP2 brakes). After checking in Elsa, I went for the RS brake coding of 04295 (FN3 brakes).

You will have to login with 09595, then change the coding accordingly. 10 minute job max, and the coding can be changed back to original.

[S4James]

i have a hard time believing that recoding the ABS module will do a damn thing.

[NOTORIOUS VR]

pulsation from ABS and pulsation from rotor/pad issues are two totally different feelings, so kinda have to know what pulsation you're talking about here.

loss of stopping power and pulsations tends to make me think you over cooked the brakes and embedded pad deposits on your rotors... effectively making them pulse and have reduced stopping power as the pad deposits don't have the bite that the iron rotor material does. Basically glazing them.

IF that's what happened, you're only option is new rotors... and at the same time new and uprated pads since you're obviously out driving them with all your powah

[S4James]

Just tune him for 10psi... That should solve that problem. ;)

[james 408]

That's interesting stuff about the brake module, I hadn't heard some of that, and the chart in the post for aftermarket bbks is useful (if you're on it and weren't already aware of it). Certain brake kits aim to neutralize brake bias using piston sizing. I know brake pads have an impact on brake bias. maybe i'll try that FN3 setting and see how she blows. Sorry to further the offtopic, but does anybody know which one generates the most rear bias? I'm assuming it's the FN3 coding. Obviously I think I'm still planning manual prop valve system in the future, but would be curious if there's a setting around that might do enough.

This has between little and nothing to do with your issue though OP.

I'll test the fn3 code in the common method: 1) stopping distance 2) stopping while cornering (want a neutral slide). Unfortunately a lot of the chatter i'm reading is rather unscientific (and some flat wrong).

Please keep in mind that increased grip = greater desired brake bias disparity (eg full slicks in the dry you want more front bias). That said, i got 4pot 355 monoblock Alcons so it's more front bias than I want, especially in the corners or in slippery conditions. As a result I actually lift the brakes to allow the car to rotate and sometime reapply as a late braking tactic.

It should also be said that increasing negative camber reduces the contact patch under braking. Given on a track setup you're usually running much more camber in front than rear, this would increase the desire for a less front biased brake setup.

[Silentmdrummer]

Does your lack of braking power happen at all speeds or just high speeds? Could be a brake booster issue. Have you checked the vacuum line going to the brake booster?

[gmdiluca]

Does your lack of braking power happen at all speeds or just high speeds? Could be a brake booster issue. Have you checked the vacuum line going to the brake booster?

High speeds. I just replaced the brake booster line recently as it it snapped. Could be an issue there. Any way to test it??

[getslideways]

Flyboy did some testing with the brake bias coding not to long ago:

http://www.myaudis4.com/2016/09/08/b...istance-check/

http://www.myaudis4.com/2016/09/09/more-brake-checking/

http://www.myaudis4.com/2016/09/12/brake-check-results/

I think testing was done before and after installation of a Stoptech kit

[james 408]

thanks slideways. That's not particularly surprising -- especially since the stoptech kit is designed not to alter brake bias much at all. Also the rs4 has larger front and rear brakes so i'm not entirely convinced the files are all that different. but even so 6 feet on average (ballparking) is nothing to sneeze at granted the sample size is kinda small.
Edit: it looks like the rs4 brake bias is even more rear biased than the s4. This is probably why you see performance gains on the stoptech 332mm front kit because it's actually weaker braking force than the s4 stockers (and the percentage decrease in f/r bias is almost identical). The 4pot alcon kit appears to be almost identical to the stock s4 bias... although i've got the slightly upgraded rears so maybe that rs4 file would serve some use. further digging to continue, deserves a new thread for sure

Even more than the stopping distance, i'm looking for corner entry composure. the braking while cornering check i'll weight more than anything else. I actually really like the feel on entry of low speed corners with the fuse pulled, saves having to grab e-brake. Not so much for high speed stuff.



Gmdiluca, got a video or anything that shows what the deal is? can just narrate what you're feeling as it happens if it's not clear from a vid.
brake booster just unplug it, it should hold vacuum even with the car off. if no air rushes, it's bad.
rather than throwing darts at the problem, with a clear description of the symptoms many of us can probably point you to the problem pretty easily. Honestly based on your initial description, the only thing that confuses me is the nature of the pulse, a video with good audio would tell me whether it's abs triggering or warped/pad deposits. just brake from 100 at max brake, then brake from 100 at 70% brake -- should be pretty clear. Can usually do it from much lower speeds like 40 mph.

there's other things like rusting/debris on hub surface, bad wheel bearings, offcenter wheel spacers, out of balance tires and many others that can cause vibrations that only really show up under braking. but step 1 is figuring out what the nature of your problem is, and that's a test drive. can use the ebrake to isolate the rear brakes. or if you have a dial indicator, runout should be less than 5 thousandths. Any vibration will set off abs prematurely, slap your pads/piston around, and drastically increase braking distances (especially if it's rotor runout).