What does the button on the gear knob of an automatic car do?

NeilF · 25 Apr 2021 at 10:15

So the button on the front of our SMax automatic gearknob broke off. A new replacement was £300!

I replaced it with a £10 Ebay version, and then managed to source a second hand one.

I'm trying to work out if all is working well, as the button on the front of it seems to do nothing? ie: I can basically move to any gear while driving without needing to press the button.

Should I need to press it when driving to change from [D]rive to [R]everse for example?

NeilF · 25 Apr 2021 at 11:24

paradigm said:
On most mechanically operated automatic gearboxes, the button should lift the locking pin via a cam or actuator. In more modern automatic shifter mechanisms this will be electronic.

Either way you shouldn't be able to shift from Park to anything else without the button being pushed. The same is likely true for Drive to Reverse, but usually you can shift from Drive to Sport or Drive to Neutral without needing the button.

To come out of park I have to press the brake pedal.

But the trigger in the gear knob seems to do nothing (& never needs pressing), which seems wrong!?

NeilF · 25 Apr 2021 at 13:17

Hotwired said:
Maybe you actually should pay someone £300 to look at it

The £300 was just for the replacement knob. Nothing else. The 2" of plastic...

NeilF · 25 Apr 2021 at 15:55

Yeh, looking at the top of the plastic 'gear pole' which the gear knob fits onto, the top 1cm or so has broken off, so there's no hole for the gear knob trigger mechanism to catch into and alter the behaviour. So I'll get a garage to change that selector unit. By chance, when I ordered the replacement knob (off ebay), it came with the entire selector unit, so fingers cross a straight swap over for them

NeilF · 25 Apr 2021 at 17:10

Luke said:
If you can shift into reverse without pressing anything then you need that sorted before you lunch the autobox and cause an accident when it gets knocked when you're at speed.

Yeh... As I said above, luckily I have a replacement shifter unit, as it came with the gear knob I bought off ebay.

If the gear knob is £300 new, god knows what the shifter unit is :eek: