Groaning when auto hold disengages

maurice28

Does anyone else get a groaning type of noise when setting off with auto hold engaged? My petrol manual Hyundai Tucson has started doing it recently after 5,500 miles.

When I lift the clutch to set off, there's a short groan. This is only when auto hold is on, it doesn't do it if I'm holding the brake with my foot or its on the EPB, so doesn't seem to be the brake or clutch itself.

Auto hold seems to disengage normally, it's just the noise. It did it last weekend, then stopped in the week and has just started again.

Anyone else get this, regardless of make and model? 

Goudy

My Clio has an electronic parking brake and it sometimes does this a little when the auto hold is selected.
Not really a groan, but a "D" noise/feel, it's hard to explain in writing, but as soon as I touch the accelerator there's a small noise and a feeling of the brake releasing.
I've heard/felt in on every car I have driven with an electronic brake set to auto hold.

Modern braking systems are pretty complicated.
There's your normal hydraulic functons, press the pedal and the brake fluid pushes the pistons in the calipers out.

Some of this can be controlled by the ABS, like hill hold system that holds a car on a hill for a few seconds.
The car senses it's at an angle and the ABS pump will apply pressure to the rear brakes for you, enough time to swap your foot from the brake to the accelerator.

They you have the electronic handbrake system.
As with a normal handbrake, this doesn't utilise the hydraulics or ABS system, it's a separate system. Motors built into the rear calipers operate the handbrake.

This is why there is a difference when setting off in different modes.
Turn the auto hold off, keep your foot on the brake you are holding the car on the normal hydraulic system. Take your foot off and the hydraulic pressure reduces that instant and you're free.

Turn the auto hold on and it uses the motors within the calipers to hold the car.
It takes a fraction of a second for the system to detect you want to move the car (pressing the accelerator) and it releasing the brake, hence the small groan as it's trying to move with the brake still slighly on.
You can get the same effect with a manual handbrake, pull away just before you release the handbrake fully and that will groan too.

If the groan is really bad and perhaps you can hear it groan with the brake off when reversing, you might want the rear calipers cleaning and regreasing. Brake dust tends to clog up the free movement and calipers out of the factory tend to have minimal brake grease applied.

daveyjp

Does the autohold actually engage the handbrake?  It doesn't on my car, it just holds it on the footbrake system, evidenced by brake lights being on, no handbrake actuator sounds and no handbrake on light on the switch or dash.

maurice28

Thanks both.

I did at first think it was the auto hold holding the brakes a fraction too long. But on my car, if you are stopped with auto hold engaged and put it in reverse, the auto disengages before you go anywhere. The noise occurs as soon as I put it in reverse, before moving anywhere, so doesn't seem to be a result of straining against the brakes in that scenario.

On the Tucson, auto hold doesn't engage the handbrake, it holds the brakes as you would with your foot (the brake lights appear on as well). 

I don't get the noise when pulling away with the EPB on or when holding the brakes down with my foot so it doesn't seem to be an issue with the brakes per se. All a bit of a mystery really! Don't think I'll bother a dealer with it just yet anyway, unless it gets starts to affect the operation of the brakes/auto hold themselves.