The PSM pump is unplugged, not removed. I assume that it does nothing when unplugged, which may not be correct.
I think all 997 master cylinders are the same, Carerra Turbo and GT. They all cross to the same TRW part.
The proportioning valve is on the line to the PSM pump, which is connected to the FRONT ABS input ("V" = Vorne = Front). The REAR ABS input ("H" = Hints = Rear) is direct to the master. So the prop valve is reducing front pressure.

Edited to add, I don't totally understand why the PSM pump is in the front brake circuit but it is. I would have thought it needed to be in the rear brake circuit. The way I piped the prop valve is the same way that it has been done by other people in the threads I found.
I don't know which wheels locked up although I know there are flat spots! When I remove the wheels to clean and inspect I will figure out which tires (tyres?) are flat spotted.

I also looked back through my notes and this car was occasionally throwing the code for the pressure sensor even before I made any changes to the brakes. I unplugged and replugged the sensor a few times and the codes stopped. I assumed that I had scraped off a little corrosion from the contacts. Perhaps the sensor is now failing for real. Too bad it's not available separately, I have not been able to find the sensor as a separate part. The sensor Bosch part# is 0 265 005 303.

 

A couple years back I did a PCCB refresh and the rear pads, 75k kms, were tapered from top (thickest) to bottom (thin) and the same on both sides. This was obviously due to unequal pressure being applied in some fashion, but I could never really figure it out.

 

Nevermind my train of thought above then in that case, I was remembering backwards. Been several years since I pulled it all out.

 

That is why the pistons are different sizes, which is supposed to reduce the tendency for the pads to wear tapered.

 

I know this doesn't help, but this is why I used 996 GT3 front brake calipers, stock 996 rear brake calipers, 350mm rotors all round and the stock 996 Turbo master cylinder...

 

Those calipers are the same as 997TT.

 

That makes sense, funny how in practice, it doesn't.

 

I'm running the stock 996TT rear calipers, not 997 ones. That lets me still use the 996TT master cylinder and not have any PSM errors

 

Is there really a big improvement going to the 997 rear caliper? Thought they were pretty much the same, at least in the 997.1.

 

The 997 TT rear calipers make the rear wheels do more braking. The 6TT rear calipers leave a lot of rear brake capability on the table. I doubt it matters even in agressive street driving though it helps on track.
A buddy runs 996 Carerra front calipers on the back of his 6GT3 to get even more rear brake capability.

 

Does the same apply to PCCBs? Sounds like the 997 rears have larger pistons.

To me, if I am getting a taper on the rear pads, I'm not applying enough pressure to get even distribution over the surface area of the pad, or there wasn't enough time spent on optimizing the rear pistons, and more force is being applied to the lower pistons, wearing the pads faster in that area.

 

The 997 rear calipers have about 50% more piston area than any 996 rear caliper, PCCB included.

 

That makes sense, probably dealt with the tapering issue.

Cheers,

 

After taking the wheels off for my usual post track day cleaning and inspection I found only the right front locked up. Makes sense as I was turning into a fast right hand corner (West Bend if you know Lime Rock) so the RF was unloaded.
From the amount of tire smoke I had expected more tires locked up.

 

I'm just pointing out the fact that 996 GT3 front calipers and 997TT front calipers are the same part number.