Unsettling behavior under hard braking

[BTFPTM]

Hi everyone,

My GTI has a very unsettling behaviour under what I call sporty braking. First some details:

- Bought the car used last winter, 2014 Performance edition, 25k miles
- car has the electronic suspension options and the LSD that comes with the performance package. 6-spd manual gearbox. Stock.
- According to VW service docs, the car is accident free (not a guarantee, I know, but a good start)
- All related components are in good condition.
- Front rotors are new and EBC pads on all four corners are new.
- The new brake parts helped, but did not eliminate the problem completely.
- Brake fluid has been flushed and bled by VW.
- Wheel alignment has been set by VW after having taken the car to them twice, it was always 'in spec' but they added some caster and toe by shifting the subframe around in hope of making the car more stable.


Ok, so the problem is, under hard braking at speeds of over about 90mph, in a straight line, the nose of the car sways back and forth, often starting first to the left and then back to the right. Some details:
- steering wheel does not move with the swaying, it stays pointed forward.
- it does not feel like one corner dips more than the other, the suspension seems to be compressing equally
- neither the ABS nor ESC activates, it's not a panic-brake situation, simply a hard sporty brake situation
- under gradual braking, call it 'not sporty', problem does not occur


It's a very unnerving feeling, especially at 100+ mph (gotta love the German Autobahn), and does not inspire confidence in taking the car to the track which I would very much like to do. VW has now had the car twice, and made adjustments, and the problem is improved but not gone, they say the behaviour is 'in spec'. I disagree, I think a car that's built for 150mph needs to brake down from that speed without the nose drifting side to side, especially when the car is just going straight.

My brother races an oldschool Rabbit, he's suggested that I might be out-braking the suspension bushings, which may be plausible.

Another unlikely but possible scenario I've thought of could be the LSD reacting to the brakes, maybe if one wheel slips a little under hard braking then both the braking control and LSD are fighting to control it.

In any case, I don't like it, and as mentioned it does not inspire confidence in a car that's built for performance. My last car, a Skoda station wagon, did not have this problem, and it was a 150hp diesel beater that I used for work. If that car can be built to brake stably from speed, so should a GTI be.

I'm open to suggestions, any feedback is welcome. Thanks, guys!

 

[ucfquattroguy]

What tires are you on? If still on factory All-Seasons, hard braking is very sketch as they don't have much longitudinal grip. The side-to-side you feel is most definitely the electronic "nannies" keeping the car where it should be. ;-)

 

[AdamSheikh]

Just curious - what tires do you have on, and what pressure are they set to? If everything is within spec and there are no obviously worn suspension components, it could just be down to bad or inferior tires.

 

[volks6]

Sounds like the dynamic steering is compensating and actually stepping in even though you aren't feeling it in the steering wheel even a small compensation under severe braking will cause the large swaying feeling you are getting.

The other thing could be a failing tie rod end or ends.

 

[BTFPTM]

I should have mentioned the tires, my apologies. The tires are new, bought this summer, they're 225-40 Conti Sport5's. Not race tires, but not junk, either. I have them set to 2.7bar (39psi) at present. I did first discover the problem when the car still had its winter tires on, and it was significantly more pronounced which is probably to be expected. Winter tires aren't built for that sort of driving.

I asked VW repeatedly about tie rods and and ball joints, I basically made it very clear to them that I understand how a car is built and where the problem areas could be under hard driving conditions, and they assured me that everything is in good working order. Granted a ball joint can be very difficult to troubleshoot, it could be just fine with the car on a lift but have play when it's under stress, but the shop didn't think so. I certainly want to trust them.

Another point is, if a tie rod were going out, I feel like I would notice the symptoms more erratically, and also under acceleration considering it's a FWD car. It's only under braking, and only under hard braking.

If the problem is in fact the 'nannies' in the electronics, I feel like VW should have noted that and pointed it out. Having a control system that actively wanders the front of a car right and left under heavy braking seems like a pretty important point for an owner to be aware of. 'By the way, this car may make you crap yourself under heavy braking'.

Another note, does anyone know if the electronic LSD works both in the power-on and power-off direction?

thanks guys, keep it coming!

 

[Sandman GTI]

What is spec pressure for car?
Here it is 37psi.
Maybe try 37.
Lower psi can increase foot print and might add grip to help tires handle braking.
Think of it this way, if you inflated to 50psi, the round small foot print would cause tire to slide more. With more contact it might have more control. Try 37, then 35 to see if it helps.
At higher speed small items become larger problems. Stop from 60mph and this is not an issue.

 

[volks6]

Another point is, if a tie rod were going out, I feel like I would notice the symptoms more erratically, and also under acceleration considering it's a FWD car. It's only under braking, and only under hard braking.

Nope I've seen bad tie rod ends only show themselves under hard braking. All other times they never acted up. Even under the shake tests. A minuscule amount of play under hard braking will show up bigger at the tires.

I'd get them to check it out again.

 

[Visceral]

OK, so I don't have the experience to advise to the cause but I can tell you that you should not let this go. Have you taken it to an independent shop? I can only assume VW is not looking that hard... Also, is the car under warranty? I don't know what it would cost to have a 3rd party take a hard look under the car but it seems it could be a good investment in resolving your issue.

 

[fretburnr]

It's possibly an effect of some of the built-in electronic nannies. For track or high-performance use, most folks (myself included) recommend disabling/reducing the "hydraulic brake assistant" that amplifies your hard braking inputs. This can cause some wiggle under hard braking, similar to this: https://www.golfmk7.com/forums/showthread.php?p=221808&highlight=brake+assist#post221808

You can change this coding using VCDS or OBDeleven under 03 Brakes / Adaptations / Hydraulic brake assistant.

There may be another setting change to help with that sort of behavior.

 

[BTFPTM]

At higher speed small items become larger problems. Stop from 60mph and this is not an issue.

Figure that out all by yerself, didja? Just kidding, sorry, I couldn't resist. You're quite right, this symptom is non-existent under about 80mph, and the more speed is piled on, the scarier the back-and-forth swaying feels as the car is hauling down. As far as the 2psi affecting this problem, I had the same problem with different-width tires on different-diameter wheels before, and although I understand that tire pressure has an effect on handling, a tire pressure that's within factory spec for the car and factory spec for the tires should not cause this kind of issue.

I completely agree that I can't let this problem go, but I'm not going back to VW, they've pretty much signed off on this problem and I therefore wouldn't expect them to look at anything any deeper with any real motivation. I'll find a good tuner shop that can help. I didn't get the car from VW anyway, it was a smaller dealer, and unfortunately the year warranty runs out this month, I didn't notice the problem until spring cuz I couldn't drive it that fast until the weather and roads were warmer. Anyway, if the problem is in fact a tie rod of ball joint, those parts aren't warranty parts, those are wear-and-tear parts.

I'll look into a set of tie rods, parts like that I can replace myself in my underground parking space. I'll definitely look into the computer settings as well, thanks for that. I didn't know such things could be tuned, I figured the traction control and braking systems were blackbox items.

The nannies thing does make some sense, one thing I haven't tried yet is turning traction control off and testing the system. Tomorrow should still be warm enough for that to be a safe test.

And also as mentioned, if this symptom is in fact the nannies, and it's a known issue but isn't a safety thing, rather just a weird effect while the car still handles and brakes as it should, then I could learn to get used to it. But my gut tells me that a car built for sport driving shouldn't do what it's doing in this case.

 

[seanmcd1]

I would definitely lower your tire pressure. Try 2.5 bar - you shouldn't be over inflating the tires. Not saying this will be the fix, but over inflating the tires is not helping anything. Otherwise, get thee to a mechanic asap.

 

[Sandman GTI]

Figure that out all by yerself, didja? Just kidding, sorry, I couldn't resist. You're quite right, this symptom is non-existent under about 80mph, and the more speed is piled on, the scarier the back-and-forth swaying feels as the car is hauling down. As far as the 2psi affecting this problem, I had the same problem with different-width tires on different-diameter wheels before, and although I understand that tire pressure has an effect on handling, a tire pressure that's within factory spec for the car and factory spec for the tires should not cause this kind of issue.

I completely agree that I can't let this problem go, but I'm not going back to VW, they've pretty much signed off on this problem and I therefore wouldn't expect them to look at anything any deeper with any real motivation. I'll find a good tuner shop that can help. I didn't get the car from VW anyway, it was a smaller dealer, and unfortunately the year warranty runs out this month, I didn't notice the problem until spring cuz I couldn't drive it that fast until the weather and roads were warmer. Anyway, if the problem is in fact a tie rod of ball joint, those parts aren't warranty parts, those are wear-and-tear parts.

I'll look into a set of tie rods, parts like that I can replace myself in my underground parking space. I'll definitely look into the computer settings as well, thanks for that. I didn't know such things could be tuned, I figured the traction control and braking systems were blackbox items.

The nannies thing does make some sense, one thing I haven't tried yet is turning traction control off and testing the system. Tomorrow should still be warm enough for that to be a safe test.

And also as mentioned, if this symptom is in fact the nannies, and it's a known issue but isn't a safety thing, rather just a weird effect while the car still handles and brakes as it should, then I could learn to get used to it. But my gut tells me that a car built for sport driving shouldn't do what it's doing in this case.

I do stay at the Holiday Inn Express once in a while.
Might not be a joke you understand as it might be only a USA commercial.

Not claiming to be an expert just suggesting items to investigate. As you eliminate them then maybe it narrow down on the issue. I have hear that high air pressure in rear tires can make the rear end quite to come around and in a straight line brake mike cause rear to feel like it is floating.

Not sure if discussed but any way to measure or verify brake line pressure and pad pressure as each corner to see if even. Could a line blockage or bound brake cylinder cause this? Brake pad or disc condition?

To test tires you could swap them around and try.

Just ruling out items.

Keep us updated.

 

[gboticus]

I have this issue braking from 200kph+ to 30KPH on the straights at the track. It's super unsettling but controllable with very careful steering. At first I thought it was brake related, then suspension related and everything checks out.

It only manifests after the tires are well heated and had attributed it to my tires being overheated and "slipping" on the rubber slightly due to the heat.

I drop my pressures to 31/32 PSI cold on my PSS at the track, and was going to upgrade to tires more suited to regular track driving. However, I had not known about the hydraulic assist coding and will try that next season.

 

[sandmangti]

I do stay at the Holiday Inn Express once in a while.
Might not be a joke you understand as it might be only a USA commercial.

Not claiming to be an expert just suggesting items to investigate. As you eliminate them then maybe it narrow down on the issue. I have hear that high air pressure in rear tires can make the rear end quite to come around and in a straight line brake mike cause rear to feel like it is floating.

Not sure if discussed but any way to measure or verify brake line pressure and pad pressure as each corner to see if even. Could a line blockage or bound brake cylinder cause this? Brake pad or disc condition?

To test tires you could swap them around and try.

Just ruling out items.

Keep us updated.

Holiday in Express reference.


https://youtu.be/8dOHEw8izno

https://youtu.be/Ff9soPDP7Pc


Sent from my iPhone using Tapatalk Pro

 

[fretburnr]

The other thing I was thinking of is here:
https://drivetribe.com/p/performance-vcds-tweaks-Dky7b-PTQpqIwVFrasMoeA?iid=CjMS5X6_Q7igNwstTVI_VQ

help the car feel more natural on a road course is to set the ABS long coding byte 29 to “08” (which removes ESC when you hold the button by the shifter for 5sec) and disabling the “straight ahead brake stabilization”. The stabilization setting is most noticeable at higher speeds, if you have ever felt your car tug back and fourth this is the system doing some weird stuff behind the scenes and it can make for a sketchy scenario with it on when you are deep in the triple digits.

The "Straight ahead brake stabilization" setting is known to cause this unsettling behavior. I coded it out before getting this car on track, and I have no issues with normal brake use coming down from ~110mph repeatedly at track days.