Does this go back to the 727 torqufight? The 727 was introduced before Park was put in as a safety feature. The first 727 had 3 buttons. R-N-D. Park was added to the existing Trans design and the pump does not run in park.
Well, the pump does run in park in a 727.....just not at as high a line pressure since by design it allows some to leak by (see below)
I have actually flushed the fluid by taking the line to the cooler off and letting it pump it out as I fill it from the funnel.
The torque converter hub has slots that engage the tabs on the inner rotor of the oil pump to create oil pressure and oil flow from the pump while the engine is running. So, if the engine is running, the pump is pumping....but the circuits it is pressurizing & how are different in gear vs in park.
Reason:
The hydraulic difference between neutral and park is mainly that the “Park” location of the manual valve (inside the valve body) allows fluid to leak from the valve, creating a line pressure drop. This low pressure in park keeps the converter from completely filling and loading the engine unnecessarily.
Once in neutral, the converter fills and there is no more pressure drop from fluid being allowed to leak by. This is the reason Torqueflites should always have the level checked only in neutral. If you check the level in park, the level checks higher than it really is.
It is also the reason that Dodge/Chrysler owners complain of slipping or delayed motion of the vehicle after dropping it in gear from park. This is due to the converter not being fully charged in park. The best remedy for this is to start the vehicle in park and then immediately shift to neutral. This will fill the converter which gives a quicker vehicle response.
