Car Pulling right under braking

[waveblaster200]

Most pronounced under medium to heavy braking. The car seems to pivot around the right front (also pulls), seems like the right front is almost on the verge locking up during heavy braking, tire is starting to cherp (Right front).

Brake setup is zimmerman 345mm B6/7 S4 front rotors, B8 S4 calipers, Parts store premium pads, rubber B8 S4 lines from car hard lines.

Tires are rather new sub 500 miles on 225/40/18 Conti DWS 06

Things I have done to diagnose this.

-Another set of B8 S4 calipers both sides.
-Another set of new rubber lines to calipers.
-Swapped pads from side to side.
-Replaced left rear caliper
-All new control arms upper and lower and tie rods and sway bar links.
-Fresh alignment today 9/2/20
-Used motive bleeder and regular bleed technique, not seeing any air bubbles.

I'm out of ideas and also worried if I have to get on the brakes hard at speed. Id rather not swap back to the stock HP2 to test.

[MetalMan]

Do you VCDS?
Does your S4 have ESP?

[waveblaster200]

Yes I have VCDS and yes it’s a ESP car.

[MetalMan]

Yes I have VCDS and yes it’s a ESP car.

Reason why I'm asking is because you mentioned: seems like the right front is almost on the verge locking up during heavy braking, tire is starting to cherp. This kinda sounds like the car's electronics are intervening. Some things that come to mind...

• steering wheel angle sensor: you can check that it shows zero degrees when the steering wheel is centered
• Have you watched individual wheel speeds in VCDS to see if they all match each other when the car is moving in a straight line?
• any ABS fault codes?

Also wonder if you considered replacing the right-rear brake caliper (since you replaced the left-rear already).

Did you get a copy of your alignment sheet? I think mis-matched front caster can contribute to pulling when braking. Naturally caster isn't really adjustable other than shifting the subframe to equalize it between right/left.

[waveblaster200]

-I will check the steering wheel angle sensor next time I get out to the car.
-I have not checked the wheel speeds but I will check that as well.
-No ABS faults codes

I ordered a right rear caliper should have that on next week or next weekend. I have a copy I can upload.
I cycled the ABS pump while bleeding today, no air bubbles. I experienced no changes while braking.

[waveblaster200]

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[waveblaster200]

Not seeing any faults on the abs controller. Wheels speed is all the same and reading correctly.

I did see the rotational rate dancing around when I was stopped and not moving. Dancing from 0.00/s to 0.27/s-0.54/s to zero.

I did find the controller did stop responding a few times. I attempted to calibrate the system but I need better instructions. I’m out of time for today.


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[MetalMan]

Some good diagnostics here.
I think the ABS module may disconnect from diagnostics when wheel speed reaches a certain threshold (or something like that, for safety reasons).

2.5 degrees off-center doesn't seem like it'd be enough to cause pulling when braking, but it can't hurt to attempt calibration.

So far I'm not seeing any smoking guns

You haven't noticed any extra drag on right-front wheel compared to left-front with the front end up?

[dozer103]

Was there any modification or event coincident to the start of this behavior? By front camber readings looks like car is lowered. If I'm seeing alignment sheet right at -1.9 left front camber that's a big difference from right front and would result in pull to right. Consider alignment with subframe shift to even out camber side to side or adjustable upper control arms?

[waveblaster200]

Yes the car is lowered on KW v2’s. Not slammed at all. I have a old set of adj 034 upper control arms I pulled off the car last year. They either need to be rebuild with a kit or I should maybe change to the other style that do not use the himes joint. What brand you style would you suggested.


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[dozer103]

Great question. I'm on Eibach Pro-Kit springs with camber even on both sides but wore through the inside edges of a set of Michelins in 20K miles. Camber is at the negative limit of specs and the car tracks on the road noticeably, pretty twitchey. Not my preference. Looking for a set of adjustable arms and latest info I've seen is Amazon arms are the same as SPC and cheeeep.

[waveblaster200]

So swapped out the right rear brake caliper with a new rebuild and cranked up the KW V2s in the front to max firm. Car still pulls right under med to heavy braking. It starts to pull to the right I can get into ABS with more brake and the ABS will keep the car straight. Checked the temps of rotors, were with in 15 deg of each other. I think I see more brake dust on the pax side.

I'm not sure if I should try and find another abs unit to try next?

[waveblaster200]

I ordered a used ABS unit should have it late next week, Ill swap that out and then report back. Any one have any ideas what to try next?

[MetalMan]

Man, this is starting to feel like my brake issue thread: https://www.audizine.com/forum/showt...dead-zone-quot

Different issue than you, but not a too-terribly-different parts shotgun approach. A few weeks ago I replaced the whole ABS unit but that made no difference... hopefully that won't also be your result.

Have you inspected for pinched hardlines? Perhaps for example the hardline going to driver-front has restricted flow, meaning the passenger-front has greater braking (as evidenced by more brake dust). For that line it might just be a function of pulling the driver-front fender liner to check it.

[waveblaster200]

I swapped to a different ABS unit today. I bleed all 4 calipers, no air and fluid look perfect. No changes! I checked all the lines, hard lines look good. At least my 50 dollar ABS unit works great.

I will be swapping back to the stock HP2s and rotors tomorrow. Ill let you know what I find... I'm a bit perplexed...

[waveblaster200]

Stock HP2s are back on the car, The car still has the same symptoms. It still pulls right/pivots under harder braking. I'm really running out of ideas.
I will say the B8 S4 calipers with the b6/7 rotors really have a lot better feel than HP2s with crappy pads.

[CELison]

You try pulling the abs fuse and seeing if that makes a change?

[Silverex]

By looking at the alinement print out I’d say you have too much camber on left side which would make the car pull to right....so I’d get the subframe adjusted so both front camber are similar

[waveblaster200]

Would you get the sub frame shifted or try adjustable control arms?


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[CELison]

That alignment isn’t bad, I would look towards it being related to the braking system.

[waveblaster200]

I haven’t replaced the hard lines yet or master cyl. So much has been replaced.


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[CELison]

I would pop the abs fuse out to completely disable it and see what happens.

[waveblaster200]

I’ll try that this afternoon and let you know. Thx


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[waveblaster200]

Pulled the abs fuse and the car tracks nice and straight under braking!! Finally figured it! Thanks for all the suggestions.

I swapped out a abs speed sensor at the beginning of the summer because the pad sensor wiring was messed up and those 2 are Mated together in the same loom, this was left front.

I looked in VCDS at wheel speeds everything look good, but it would kick me out at 20mph. I believe it’s a issue with the speed sensor.

I’m going to swap back to the old sensor now and see what happens. That would explain why I felt some slight modulation in the brake pedal under medium braking.


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[MetalMan]

Wow, really? Considering everything you've gone through and for it to be something so simple is... mind boggling. In my mind what's worse is that up to 20mph or whatever the wheel speeds were consistent. Too bad the ABS module doesn't have some mode which allows viewing wheel speeds @ >20mph.

Also, have you looked at the tone ring? On an old B5 of mine a tone ring was cracked (among other ABS issues). It may stay in place at low speed but then come loose at high speed.

[CELison]

I got you

[waveblaster200]

Slapped the B8 calipers back in, put some miles on this weekend. Car brakes nice and straight still so that’s a plus.

Under medium braking I do feel 2 blips in the brake pedal, almost like abs modulation but not the same. But it’s not organic feedback.

Any ideas?

Considering replacing both abs front sensors with new and not the cheap ones.


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