[Mahler9th]

How do you know for sure that bias has shifted to the front?

I am pretty sure that all street cars have extra front bias by design. Lots of ways to move it back, even for street cars. A common method for some PAG models back in the day was to install a different brake proportioning valve from the various stock factory units. I still remember Kelly Moss Racing suggesting I switch from a stock 951S valve to a 965 valve, which cost about $40 at the time. Worked well for my application.

I have also experimented with different pad compounds front and rear. Lots of ways to monkey around with bias.

I have used a Mityvac for street car and race car bleeding for 30 or so years. My cars and friends cars. Many types of calipers. No issues.

I have never tried to figure out a way to stop air from being sucked in past the bleed screw threads.

I simply close the bleed screws while there is still strong vacuum. I have never drawn conclusions from "looking for bubbles in the tubing." Those bubbles can come from air sucking past threads in the various types of bleed screws.

I have two Mityvac units, one in my shop and one in my race car trailer.

I also use a Motiv bleeder at times. No particular reason- just a change of pace. The owners of Motiv are friends and they have a great family of products.

I have dealt with many brake system challenges in Porsches through the years-- the weirdest one was a leaky MC seal at the booster in a 951s. Fluid got in the booster and caused all kinds of problems. It presented in Friday afternoon traffic when I was on my way to Laguna Seca for a PCA driving weekend. I'd get about 20 minutes of driving in traffic done, and then the front brakes would lock on and I'd have to pull over. Finally ID'd the issue Saturday afternoon, and missed the track driving weekend. But I learned.