Very noticeable hissing under the dash, but only when in R or forward gears. Silent when in P or N.
Is this normal?
Check your Neutral Safety Switch vacuum connections. The NSS has a vacuum switch which provides vacuum to the parking brake automatic release. It is under the dash, on the steering column.
Master ASE Certified L1 Chrysler Technician- still a Ford fan at heart.
1964 Thunderbird Hardtop- Chantily Beige- 390 FE 4V V8-Uncle's Car
1966 Thunderbird Convertible- Red- 390 FE 4V V8- Uncle's other car- waiting for paint and body work!!!