99 Chevy Venture Slams when shifting
If the van shifts ok when cold but hard when hot then the pressure control valve in the trans is bad. When the fluid temp climbs past a certain point the PCS sensor shorts out and stops controlling fluid pressure. This usually causes a whine from the trans (pump) and hard shifting. This is because the PCS can no longer control the pump pressure so the pump now runs at full pressure and shifts as if you were using full thottle all the time - the opposite of what your doing, which is to feather the throttle trying to ease the shift. So now the trans calls for a full pressure shift when your using part throttle and it slams. The (PCS) part is cheap enough but the trans has to be removed to replace it and that's not cheap.
Give this a shot, it often works and it's cheap enough to try.
First, have a good mech carefully check the rediator trans cooler section to be sure there's no leakage of coolant from the enging to the trans coller section of the radiato. This is important!, if antifreeze is leaking into the trans fluid via the cooler it'll cause problems that are otherwise impossible to diagnose and eventually complete trans/torque converter failure.
If there's no radiator problem then power flush the trans and change the filter, then install an aftermarket trans cooler in series with the built in cooler (the instructions with the cooler detail this). It's about $60 for the cooler and maybe one hour to install it.
This whole process will drop the trans fluid temperature 40-50 degrees and often that's enough to get back into a temperature range that will allow the PCS to work reliably again.
If it doesn't work your not out much, if it does work you'll probably get another couple of years out of it.
Jun 24, 2009 |
1999 Chevrolet Venture