Ainars that was my thinking, but equally, just because the capability is there it doesn't means it's being used. ;)

If, as MJ says, the gearbox is measuring input vs output speeds (and it definitely does because we've seen many references to the errors that occur when there's a mismatch) those circuits could well be unused.

On the other hand, let's have a look at my old F125 switch for evidence of movement in that area. There are photos somewhere..... :rolleyes:
Yes indeed, definite evidence of movement through the full arc, and my car this was removed from is a (very) late FL2 with S mode....
The mystery deepens, my shifter is incapable of doing that! :Confused:

Ainars, yes, you're correct. I was wrong earlier about the shifter cable not moving for 432. I suspect I have confused the shifter cable for the shifter lever inside the valve body, or possibly the shifter cable not moving in tiptronic. It was a couple of years ago, and I've slept since then :o

The selector lever on the gearbox definitely has positions for PRND432, even in the S version, however the diagrams for the valve body only show PRND and I'm sure when I had the valve body out of one that behaviour was visible too. So, the TCU is seeing PRND432 or PRNDS from the F125 (where 4 and S are the same) depending on the year, but the actual valve body doesn't care about anything after D as by then its all software control by the TCU.

Looking at the shifter, PRND432 and PRNDS are all definitely on the F125 with only the tiptronic controls on the shifter body itself (as far as gear selection). The shifter cable does not move in tip, so that operation is purely electronic. I think this is what I was thinking of in my previous post.

Yes, the S shifter basically has a big block at the back of it to stop the lever moving in to 3 or 2, plus of course the alloy top which doesn't have a slot for them. That behaviour is all software, but you're both correct that the F125 is still capable of moving the full range of PRND432 even on an S car. There are FL2s with the PRND432 shifter as well.

So the gearbox is presumably doing that as it selects different gears, though the TCU may well not be very interested in the information? Or does it use the F125 position as well as the input/output speeds? We may never know.... :D

All of which diversion leads back to the earlier conundrum. Your reversing lights were working normally but the TCU didn't recognise you had selected reverse, which suggested to me a problem with the 5-contact arc......

The gearbox doesn't move the selector. D engages the gubbins in the valve body to allow the TCU to control the various clutch packs to allow it to select forward gears. Anything after D is synthetic as far as the gearbox is concerned. That just lets the TCU do different things depending on the position of the F125. Think of S or 432 as 'driver request' to the TCU to do something different to D. Mechanically the gearbox doesn't care.

The 5-arc set in my switch looks flawless. The contacts are slightly grubby but nothing stands out. I'll get a pic later.

I realise that if you mean the "gear stick" inside the car, I was really wondering why the internals of my old F125 switch clearly show that the arm has been moved regularly beyond the PRNDS section?
As we know, that can't be done from the gear selector (S version) so how? I'm judging it by the deep score marks on the cover plate behind the contact arm. The marks on the tracks are less deep/obvious and could easily have been done when installing/removing the switch. Unless that's a replacement itself from a PRND432 vehicle.

This is the other side of the F125. It does make sense that these contacts are the range selection for the TCU, and the others are just switches for extra stuff. The base contacts look fine, but the moving contacts do look pretty dirty. I cleaned all this up with scotchbrite, greased it up and bolted it back together.

http://forum.a8parts.co.uk/attachmen...1&d=1599423616

http://forum.a8parts.co.uk/attachmen...1&d=1599423616

I learned a new way of refilling 5HP gearboxes the other day - pump it in through the oil cooler return :) I got 6 litres in to it this way, compared to the usual 3 from underneath. This should mean it is very close to normal level on first start and just needs a little bit topping up once its up to temperature, or possibly a little letting out.

http://forum.a8parts.co.uk/attachmen...1&d=1599423616

http://forum.a8parts.co.uk/attachmen...1&d=1599423616

Taking the gearbox off the engine stand and putting it back on the engine and gearbox machine:

http://forum.a8parts.co.uk/attachmen...1&d=1599423616

http://forum.a8parts.co.uk/attachmen...1&d=1599423616

The refurbished torque converter should be back from JP Automatics tomorrow so I can put the engine and gearbox back together, and a replacement exhaust manifold will hopefully be here on Tuesday.

In case you've never seen where the main scuttle drains are, here's a pic:

http://forum.a8parts.co.uk/attachmen...1&d=1599423616

[img]

Looking at that there's a definite "dodgy" section on the #2 ring (innermost being #1) roughly where I'd expect R to be (give or take a bit) AND the corresponding contacts look pretty ropey too....
(Number 4 looks a bit marginal too in the same area)
I reckon that #2 is probably supposed to go open circuit when in R but was actually shorting across to the "bypass" section of the track, thus confusing the TCU.

While you had it apart, I don't suppose you had time to test it with a multimeter and confirm which track connects to which pin?
I started trying to work it out logically and did reckon the inner one was pin 1 then pin 2 but the next going out might be 5.....
(Maybe I'll just open up my cleaned up old one and check?)

OK, I've done that one mine, I'll put the details in the other F125 thread, but the relevant bits are:
The 5 sectors from the inside outwards are pins 1, 2, 5, 3 and 4. And the 5 corresponding wires are not in that order....
So the segments with discolorations are pins 2 and 3 which are largely to do with identifying PRN.

The refurbished converter from JPAT arrived:

http://forum.a8parts.co.uk/attachmen...1&d=1599503552

Filled with oil and installed in the gearbox:

http://forum.a8parts.co.uk/attachmen...1&d=1599503552

And back on the engine courtesy of the machine:

http://forum.a8parts.co.uk/attachmen...1&d=1599503552

I've made a lot of tools in my time, either to solve problems or to make life easier. The engine and gearbox machine makes life so much easier when doing this one very specific job that it has to be the best of the bunch. When the two are lined up well, they can be joined with a push from one finger :love: