928DK

Maybe because both the workshop manual's and information sheet (mods, data, settings 87) say its a switch, and Porsche write "Ignition timing retarded in cars with automatic transmission for full load shifts 1 to 2 and 2 to 3" (Ignition system EZ-k page 5)

And page 6: "Transmission protection switch on brake band bearing B1: Ignition is retarded by 16” approx. 0.5 seconds for the shifts 1 to 2 and 2 to 3."

Alan

Maybe you should trace the actual circuit and see what you find...

What you have described are the kick down solenoid connections, it does indeed control ~full throttle shifts - but I don't see any transmission switch in this circuit only the one on the throttle pedal and the one inside the kick down relay... where?

Maybe I'm nuts - but alternatively parhaps the rest of you are...

Alan

WallyP

Apples and oranges.
The system that Alan is talking about ensures upshifts at max RPM by breaking the power to the kickdown solenoid.
The system that is being discussed here is a later system to very briefly reduce the torque during shifts.

Totally different systems for different purposes...

928DK

Found the mixup.

Ezk pin 25 goes to v12 (and then u13) and then to the switch.

GregBBRD

You are talking about the kickdown switch. we are talking about the transmission protection switch.

My reference to pin 26, instead of pin 25, really confused things.

I'll go back and fix that.

Sorry.

TheoJ

yes, it is the protection switch which retards the ezk at upshifts of 2nd and 3rd gear. The manual states a bit about this but is not very precise (as usual). I will run a test in my car to confirm actual behavior and report back. Maybe I was wrong and must adjust the manuals/website.

Speedtoys

So..the interesting question now is..how much Tq is too much for various years/thicknesses of driveshafts?

TheoJ

IMHO the driveshaft is good for 500Nm and probably 20% more and Germans always take sound safety margins. Often the driveshaft snaps with pulsating erratic engine behavior, making it twist back and forth based on mass of the driveline. That breaks it.

Speedtoys

SO..a <490Hp SC kit, shouldnt be abusing an S4 driveline with shift-retard in the ECU _too_ much then?

TheoJ

ok, checked the protection switch again. And I must say that what I said before is absolutely correct.

The switch is open in 1st gear, closes when you go to second, opens again when you go to 3rd. The change in signal triggers the ecu to protect the transmission and reduce torque for half a second.
I think activation of one of the clutch actuators triggers the switch. When the hydraulic pump in the transmission is not running, the switch does not work.

Geojerry

The kick down switch. Here is a photo of a switch on my door side padding with
2 small dials next to it. If this is that switch, what purpose do the 2 small dials serve ?

TheoJ

no idea what that is. A kickdown switch would be a push button or flip/tumble switch. This looks like it is adjusting something. Audio maybe?

Alan

Yes the trans protection switch is on CE U13, to Pin 25 on the EZK (not LH).

My point was that the initially referenced circuit on U22 is in fact the kick down solenoid (Magnetventil) - obviously not what was actually intended here.

Alan