Generally one disconnects the vacuum line to the modulator when setting the pressure. The pressure is read by connecting the appropriate guage to the modulator pressure port on the transmission, and running the car at 31 MPH while reading and adjusting the modulator. Thats it.
1. Disconnect valuum line to engine & plug it.
2. Connect pressure guage to modulator tap on transmission.
3. Run car at 31 MPH.
4. Read pressure and adjutt the modulator till 48 PSI is achieved.
5. Put it all back together.
I got too many cars!! Insurance eats me alive. Dave
78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k