And that's a relatively good one! :ROFL:

Heavens only knows why they did it that way, there are so many better ways that are much more reliable than contacts sliding over a metal track in what is one of the most climatically exposed areas of a vehicle. :Confused:

I agree - having replaced my F125 switch on a gearbox which is only a few years old and has only 15K miles on it from new, it was extremely frustrating to find one of the little fingers inside had snapped off and was floating around inside the switch randomly selecting whatever gears it liked - for example stuck in first gear only or totally inhibiting start of the car at all!! :mad:

It's worse than that really Neil because, if I understand correctly, the F125 switch is sort of reporting a combination of what the gearbox is physically doing (or being told) and where the selector switch is, neither of which really needs to be done from such an exposed position.
So potentially it can not only confuse the ECU (limp mode etc.) but also mis-inform the gearbox potentially causing internal damage.

And using magnetic reed switches, or (probably better) Hall sensors would be so much more reliable. No doubt someone more knowledgeable can suggest an even better solution. :cool:
It only actually needs to read an angle (or finite number of ranges of angles) and translate that into a number of on/off signals via a table. :tuttut:

Exactly - but still causing occasional PRNDS light up on random occasions which in my case usually was when selecting reverse. I can see that temperature might affect the mechanism precisely because it is an electro-mechanical device with brass and alloy componments.

Having now seen the inside of the switch, I'm not surprised it's a common failure. It's also the type of thing I can imagine not working when cold/damp outside.

The job looks pleasant compared to the oil cooler, although I do have original exhaust hardware. Hopefully not too bad or I can get an impact driver in there, angle grinder on my back 2" from my face is not much fun!

Might give me something to do if I get bored over Christmas...

This was the inside of mine, nothing blatant but it kept throwing errors and the occasional Limp Mode, now all sorted:

Well, that was pretty hard work (on the floor) with an unexpected result...

I had to loosen and move the down pipe, but managed without removing the gearbox mount. My car has 12mm? spline bolts holding the gearbox mount to the subframe and I don't have a 12mm spline bit. However, with the mount unbolted from the gearbox it had enough movement in the rubber to hold it out of the way enough the extract the switch.

When I opened the switch it looks nothing like any of the examples I've seen.

Inside of my switch looks like this:-
https://i.imgur.com/yRJydQn.jpg

The plastic centre is a cam with various lobes that open and close contacts which look like points in an old school distributor.
I'll try to clean them a bit and apply some contact cleaner/lubricant I have and hopefully it'll stop playing up...

I've not seen that version before. Is that the one with the round connector? All the pics are of the later one with the rectangular connector.

That actually looks like a slightly better (and probably more reliable) design. Looks like a cam and micro-switches. Is that an earlier (inc. PF) design I wonder?



That's an interesting thought. It probably wouldn't be too much work to develop an improved replacement. I think personally I'd go for some sort of optical rotary encoder for ultimate reliability. A microcontroller and a number of relays would also be needed to translate the rotational angle information into the appropriate contact closures, but those could be mounted in an enclosure elsewhere.

Done.
Only time will tell if it's better, but it works ok at the moment.

This switch has the rectangular connector. My car is a 51 plate FL.

They aren't actually enclosed microswitches.

The black plastic parts at 11 & 1 O'clock in the picture each have 3 metal cam followers in them (you can see the top one in the 1 O'clock part - the shiney metal bit).
The middle plastic part that rotates has 3 layers of cam lobes which act on the followers.
There are 3 copper "tracks" around the outside which connect to the various wires at each end, and in the middle. The beige plastic parts with the blue paint on them hold the outer 2 sections of the tracks inboard against the centre section of the tracks.
As the cam rotates it pushes the various followers out which push the copper tracks up and break the circuit. You can just see the contact points at the top of the 11 O'clock black plastic piece.

The contact points are like old distributor points used to be, or the inside of old electric window switches etc. They have a tungsten (or whatever) bump on them.
I ran some fine wet&dry paper between the contact points and sprayed them with some RS contact cleaner/treatment oil I had laying around.

Unfortunately, what I intended to do but forgot, was to take a picture of the metal side of the switch with the part number on it.

I think this design is better than the "track sweeper" version, although still not ideal, although I guess it's lasted longer than the intended life of the vehicle.

I also run an '85 Ur quattro, and a 2000 A3 1.8Tq so my idea of vehicle life is quite different to Audi's. I find the trick is to not tolerate anything not working as it should, then I stay on top of it...