Re: 1951 Pontiac Chieftain
Posted: Thu Nov 19, 2020 1:41 am
Bought a couple of pieces to adapt the gauge to the gearbox. Got it all put in and checked to see what it was going to do.
Cranked over on the starter for a few seconds sees the pressure up to 60psi. Starting the engine shows that's definitely the regulated idle pressure. Engaging a gear makes the pressure dip as expected (shifting to Lo dumps main line pressure temporarily before engaging any gear, a clever bit of design to make it so Reverse always starts to engage from a zero engagement state). Dr to N dips briefly to 45psi before rising back up to 60.
Engaging R causes the high pressure valve to engage and sit, shuttling back and forth as it's meant to "somewhere above 120psi", in this case between 130 and 160psi.
Driving, the pressure modulates with throttle position from 60-100psi, this is an I8 variant behavior, causing the clutches and bands to clamp a little tighter the harder the throttle is pressed, to counter the additional torque the straight 8 has compared to the six.
It did misbehave one time tonight. The line pressure remained perfectly regulated as it should be, which means the pump, non-return, regulator and TV system are operating correctly. That means the problem is in the main valve block, the 1-2 valve is expanding and getting stuck. It's a cold day today and the gearbox being colder than usual it behaved beautifully for a few minutes. I need to pull the valve block apart again. Ideally it needs replacement but that's expensive so I'll try massage a few more miles out of this one.
Phil
Cranked over on the starter for a few seconds sees the pressure up to 60psi. Starting the engine shows that's definitely the regulated idle pressure. Engaging a gear makes the pressure dip as expected (shifting to Lo dumps main line pressure temporarily before engaging any gear, a clever bit of design to make it so Reverse always starts to engage from a zero engagement state). Dr to N dips briefly to 45psi before rising back up to 60.
Engaging R causes the high pressure valve to engage and sit, shuttling back and forth as it's meant to "somewhere above 120psi", in this case between 130 and 160psi.
Driving, the pressure modulates with throttle position from 60-100psi, this is an I8 variant behavior, causing the clutches and bands to clamp a little tighter the harder the throttle is pressed, to counter the additional torque the straight 8 has compared to the six.
It did misbehave one time tonight. The line pressure remained perfectly regulated as it should be, which means the pump, non-return, regulator and TV system are operating correctly. That means the problem is in the main valve block, the 1-2 valve is expanding and getting stuck. It's a cold day today and the gearbox being colder than usual it behaved beautifully for a few minutes. I need to pull the valve block apart again. Ideally it needs replacement but that's expensive so I'll try massage a few more miles out of this one.
Phil