Difference Between Shift Times and Base Pressure

[ssvolvo]

Having a hard time understanding the differences between base pressure and shift times. Say D1108 and D0701.

Like I know they are far different but don't they do the same thing? Trying to have firm but smooth shifts.

Really looking for an explanation.

Thanks guys, John

[ssvolvo]

Like in "seat of the pants" feel when changin g tables in either.



Anyone??? Joecar?.... Pwease?

John

[joecar]

The shift pressure tables control the line pressure during the shift (the PCS solnoid produces Torque Signal pressure which assists the pressure regulator spring to push harder on the pressure regulator valve thereby increasing Line Pressure.

The shift time tables control the duration of a shift... my guess is that the shift solenoid is ramped up/down (using PWM...? I don't really know... I want to look at this with my oscilloscope one day)... and/or the PCS solenoid is additionally manipulated beyond the what the shift pressure tables do...

Those 2 tables are not the same thing, because you can reduce/increase the shift pressure table and still have the shift time table control the shift time.

The Hydra-Matic literature alludes to the shift feel being controlled solely by the PCS solenoid... (but then what is the 3-2 shift control solenoid in the 4L60E for then...?)

In short, I don't really know, but an oscilloscope on the shift solenoids and the PCS solenoid will reveal what is going on.

[joecar]

If you want firm but smooth shifts do this:
- increase shift pressure tables (to avoid high torque slip),
- decrease shift time tables to 0.2s (to make the shift quick and definite),
- increase shift torque reduction tables (to avoid being hard/harsh and to protect against parts breakage)...

i.e. by pulling spark you can have a firm/positive shift without being hard/harsh.

This works fine on my F-body on which I noticed that adaptive shifting seems to be disabled (the adaptive shift cells are always all zeros).

[ssvolvo]

Been manipulating all 3 tables. I seem to have the best luck leaving the times stock and bumping up pressure, and increasing the torque reduction at the top of the tables (WOT).

My alternator belt squeals during WOT shifts. Will try a "clutched" alternator pulley from a VW/Audi to try and eliminate the squeal. No matter how I try to eliminate the squealing of the serpentine beltmit persists.

Thanks Joecar...I knew you'd come through.

What kind of scope? Pico?

John

[joecar]

Yes a Pico 3423 (quad channel) I got from Autonerdz... it's helped me diagnose a few things on my wife's car, and I like viewing various waveforms (like ignition secondary using the capacitve coupled clip).