Regular twang revisited...

[GTI_PAPA]

Hey guys,

I have had a regular twang (sounds like flicking a ruler) under my car since new. Have been back to VW several times, and they can find anything. Have been reading other forums etc, and have stumbled across one that might make sense. The twang/vibration can be felt through the brake pedal, which leaves the question, "Might it be a sticky hand brake cable that suddenly, fully releases causing this?"

Any suggestions would be appreciated,
Con...

[Ben_GTI]

Is it when you first start moving? I think this is an ABS test....

Otherwise, if you car sits for a while, it is the handbrake stuck to the disc... it does it once then goes away...

If you heard a knock when you brake in reverse, its just calipers sliding around and there isn't much you can do about it.

[noone]

Does this only happen when braking?

[danish]

When you say you can feel it in the pedal, does the pedal lose a bit of its resistence as well?

I encounter a similar problem of shuddering brakes accompanied by a scraping sound occasionally when I brake. However I can only make it happen when on very loose surfaces (like gravel) or going down my driveway, which is quite steep.

Seems like an ABS issue to me, although I really don't like the sound of the scraping!

[ACTGTI]

danish - That's just the ABS working isn't it?

Everyone should familiarise themselves with what happens when ABS (and ESP) is working. It's quite dramatic on the brake pedal and it doesn't take much for it to kick in on a gravel road.

Take out all your loose items in the car (important - if you don't, everything in the back will end up in the front), drive out to a country road and at 80km/h hit the brakes as hard as you can (make sure no-one is behind you). You should feel your brake pedal shuddering under your foot. This is normal. You will be surprised how well the Polo pulls up as well.

You'll also feel it if you take a corner too quickly as ESP tries to apply brakes to various wheels to straighten the car up and avoid a spin.

[break]

I have a similar issue with the ESP system.

I find it cuts in far too early on some surfaces, where it comes in at exactly the right time on others.

Do you notice any consistency on which surfaces and what speed this occurs at?

[ACTGTI]

A little inconsistency I guess but I don't think it's the ESP getting it wrong. It's all to do with the angle you approach the corner, the speed, and whether or not there's anything on the road that's making it slippery or not.

If there's anything at all that is making the road slippery, it will come in earlier than if the road is grippy. An example of this is on a drying road after rain where maybe the left of your lane is damp but the right is dry. ESP will try and help you out here when it really doesn't need to.

I don't think ESP has ever really saved me but I don't find it overly intrusive if I can predict it's going to kick in. It's all about reading the road in front and knowing how your car behaves on its tyres. I don't know what speed but I'm talking as quick as I can on tighter bends with recommended speeds of 25-45 km/h. Never really noticed on faster bends as that would be breaking the speed limit and all ;-)

[break]

The particular road I have a problem with ESP on is a long right hand bend coming off the motorway nearby, where the inside wheels on the bend have to run through undulations on the road while the outside wheels are on a flatter/smoother area of the road.

The ESP kicks in and makes the car very unstable on the surface, where as turning off ESP vastly improves the ride through the section.

[noone]

I have a similar issue with the ESP system.

I find it cuts in far too early on some surfaces, where it comes in at exactly the right time on others.

This is with stock suspension?
I found with my new coilovers the traction is improved. It was better with the H&Rs and standard shocks for a little while, but when the shocks started to give out, it got worse again.

For the first few weeks with the new kit, the whiteline front swaybar was set to hard. Whilst the handling was a bit twitchy and uncomfortable, the abililty to take corners at speed and accelerate without wheelspin was pretty impressive.

I'd be looking at your suspension, Think the stock setup is pretty basic.

[ACTGTI]

I'd say it's a case of the weight on inside wheels is lighter as they hit the undulation. ESP is probably reading this as just about to lose traction and thus applies a little brake to the inside wheels. When it does this, you would find that when the weight becomes normal again as the wheels leave the undulation it would feel unstable probably because of a split second where the brakes are still slightly being applied when they shouldn't be.

When I say brakes being applied, it's very subtle and lightly applied but less weight on the wheels means this would be less subtle as there is less resistance from the road.

It's hard to explain but I think I know what you mean. Are you sure that when ESP is off it's actually off? I thought that in the Polo, ESP still operates over a certain speed regardless if it's off or on (it does for me and I remember reading it somewhere). Only the Traction Control remains off when ESP is off.

So maybe it's the traction control causing your issue rather than ESP in which case all of the above applies except that instead of the brakes being applied the engine is slightly retarded inder TC?

[break]

<snip>I'm fairly certain it's the ESP being a pain in the backside as it's definitely braking only the two inside wheels, throwing the balance of the car mid-corner.

ESP/TC off at the same speed through the same corner with ~1/4 throttle (it's a long smooth corner, only keeping enough throttle to maintain momentum.... it's definitely not the TC cutting in) gives a much quicker and smoother experience, and removes the balance issues.

I've noticed similar issues previously on other undulating road surfaces.

And yes, stock suspension.

[seangti]

with regards to ESP and ABS, if your inputs are smooth you can load the car up significantly before they intervene. Even in track conditions, it's rare that ESP or ABS has interferred. Undulations are obviously going to invoke it more due to the unloaded weight distribution - which is exactly what happens when the car slides.

Most enthusiasts may be happy for the car to slide a bit (i.e. wanting less interference), but put your loved one in it, I'm sure the level of inference is fine if it gets them home safely. Or saves your bacon when you have a brain explosion.

[break]

with regards to ESP and ABS, if your inputs are smooth you can load the car up significantly before they intervene. Even in track conditions, it's rare that ESP or ABS has interferred. Undulations are obviously going to invoke it more due to the unloaded weight distribution - which is exactly what happens when the car slides.

Most enthusiasts may be happy for the car to slide a bit (i.e. wanting less interference), but put your loved one in it, I'm sure the level of inference is fine if it gets them home safely. Or saves your bacon when you have a brain explosion.I don't mind interference when it helps, not hinders, the driving experience.

A good example of interference done right is any of the modern EVO's (VIII, IX and X). It's truly idiot proof performance thanks to the active center diff being intelligent about the power, and instead of running to the hills when traction loss is detected, the system automatically adjusts the power to go to the wheels that still have traction.

On the flip side, I'd rather not have traction control, stability control, abs and whatever else they decide to put on in the future if it means it's going to deter from my experience behind the wheel. For the Polo, most of the time the ESP/TC system falls into this category... and as such I turn it off.

[noone]

On the flip side, I'd rather not have traction control, stability control, abs and whatever else they decide to put on in the future if it means it's going to deter from my experience behind the wheel. For the Polo, most of the time the ESP/TC system falls into this category... and as such I turn it off.

I started a thread on this most of a year ago, got slammed by a few people...

The only time I think its required is when its wet. With the extra power (or even stock power really) it does not take much to loose front end traction in a corner and end up going straight. Scared myself once or twice, I don't turn off TC in the wet any more.

That you have found a particular circumstance where it seems to inhibit performance is not overly surprising, the technology in our cars only has so many different things it can monitor and limited ability to shift power like the Evo you mentioned.

Personally, I'd be looking at better suspension rather than turning off or wanting to change the ESP / TC. Even a rear swaybar may correct your body roll and weight distribution enough to bring back your confidence.

[ACTGTI]

Yeah the Polo is designed for girls (I'm ducking :rolleyes:). The Evos and WRXs are for a different market entirely. They have been built for handling. The Polo wasn't so much built for handling, but it is more compliant and easier to drive with the light steering (for girls haha) and soft suspension. It is an easy car to live with.

Overall the ESP/TC system works well but in perfect conditions I like to turn it off. :cool:

[GTI_PAPA]

Hey guys,

I think my original post has gone off on a tangent somewhat.

Let me explain what happens. On a cold start, I reverse out of my driveway (slight downhill+twist), and as i hit the twist, I apply the brakes slightly and a loud TWANG+vibration accompanying it. If i don't apply the brake, it rarely happens, but upon moving forward, I get a very light TWANG, every time (but only once after every cold start).

I asked the VW service guy about an ABS self test, to which he replied "Never heard of it."

Anyhow, thought I'd clear things up with regards to my issue.

Cheers.

[Jmac]

Sound like ABS for sure its doing its job when it shouldnt be, self test???? that happens behind the scenes mate and wont cause a twang. Only time ive seen this is a maladjusted sensor on an A4, but you can set the position of its sensors, the Polo sensors are bolted on mate so that doesnt apply. A bit more than just a basic scan reqd i think, problem is you got to know what you are reading, thats where it all goes pear shaped.
cheers
Jmac