TC Slip Desired - 'blip' when shifting into 5th OD?? (pics)

[usapadyra]

Originally put this over on 'Transmission & Transfer Cases' but there isn't much footfall on that part of the forum

I'm just going to copy and paste from the other post, but my main interests here are:

- Does anyone else observe the same behaviour with a 5r55e when monitoring TC_SLIPDSD at the moment of the 5th (OD) gear upshift?
- Am I right in thinking the PID 'TC_SLIPDSD' is commanding and not 'measuring' or 'reactive' in any way? For example, when I first checked out the PID 'TC_SLIPACT' I saw the upswing during the overdrive shift and panicked, thinking the shift into 5th was causing the TCC to slip. But then I saw the same 'lump' in the 'Desired' PID so it must be something instructing the action, no?



"Since I got my truck 50k miles ago, it has always had a slight RPM flare when shifting into 5th (OD) gear.

It has always been a small flare. Maybe 100 or 200rpm. And it hasn't gotten any better or worse over the time I've had the truck.

Under certain heavier throttle / higher speed shifts it won't flare at all. It's almost 'worse' when accelerating very gently.

Today I recorded a few PIDs on ForScan, and was very surprised to see that there is a 'blip' on TC_SLIPDSD when the shift into overdrive happens.

The pics show first a regular shift into overdrive from joining a 55 zone, and the second two are me disabling overdrive and re-enabling it while cruising.

You can see the small RPM increase I'm talking about.

Is this normal?? If the blip is appearing on the desired PID that must mean it is actually being commanded by the PCM or some other module? Right?

I guess I'm wondering if this is causing extra wear on the TCC or overdrive band?"

Screen recording if it's useful:

 

[C420sailor]

SLIPDSD is the PCM’s way of commanding the TCC solenoid duty cycle, if I remember correctly. If the PCM detects undesired slip, it will drive SLIPDSD toward 0, actuating the TC to lock up more, and vice versa.

As to why the SLIPDSD blip is there…I’d imagine it’s a form of programming to make the shift smooth by easing off the TC a bit. If it was at 0, you’d have a pretty firm engagement, methinks. I’m just speculating, though.

Edit: as to why it’s causing an rpm increase…perhaps the “size” of that blip is fixed in the programming, and a slightly worn torque converter or lower system pressure or 1,000 other things is resulting in excessive slip from that?

Think of it like a clutch. Driving on the highway in 5th and you apply a quick couple pounds of force to the clutch pedal…on a new clutch, it may just barely slip. On an old worn clutch, it may slip to the moon…all with the same input.

The only thing I can think…at higher RPM/throttle position, system pressure is likely higher, applying more force to the TC.

 

[usapadyra]

SLIPDSD is the PCM’s way of commanding the TCC solenoid duty cycle, if I remember correctly. If the PCM detects undesired slip, it will drive SLIPDSD toward 0, actuating the TC to lock up more, and vice versa.

As to why the SLIPDSD blip is there…I’d imagine it’s a form of programming to make the shift smooth by easing off the TC a bit. If it was at 0, you’d have a pretty firm engagement, methinks. I’m just speculating, though.

Oops I forgot to update this copy of the thread.

I posted on another forum and got a reply from a guy who worked as a Ford trans engineer for many years.

He said it's normal, and as you said, it is to give a smoother shift.

Obviously it only happens in overdrive since it's the only gear shift where (under normal accel) the TC will be locked.

It also explains why it doesn't happen under heavy throttle, I believe. Since it will either be commanding a faster shift if TC is locked, or at high speed high throttle I think it will actually hit 5th gear before the TC locks.

 

[C420sailor]

Makes sense!

I’m no transmission guru so take this all with some salt…I just find them fascinating. I love reading the manuals and studying them. Nerd alert lol.

 

[usapadyra]

Makes sense!

I’m no transmission guru so take this all with some salt…I just find them fascinating. I love reading the manuals and studying them. Nerd alert lol.

Same - the more I learn about these electronically controlled transmissions from so long ago, the more amazed I am. I thought peak technology in 1998 was a calculator wristwatch...