904 slipping in all gears.

[twodko]

After reading the earlier thread about slipage here's the deal with my 69. The tranny is freshly rebuilt however if the car is started in "Park" then shifted to a drive gear its slips and needs more throttle before the car moves. I call the guy who rebuilt the tranny and he tells me that when the car is started in "park" the tranny fluid is not circulating. He said start the car in neutral because the fluid begins circulating right away. Sure enough the car moves as it should when started in neutral. He also said make sure the fluid is full while the car is running, that's obvious. The rest of it makes no sense to me, the fluid should be circulating throughout the tranny in "park" or neutral. What's the story here guys? Thanks.

Tom

[FLG]

Tranny does not pump fluid in park, general consensus is start it in neutral and let her warm up a bit before driving off. But that does not mean it should slip if started in park. There have been numerous times were I just want to pull the car out of the garage to wash it and don't feel like sitting there, started in park put it into drive and have had no problems pulling out (there's even a slight uphill before she gets to roll down the driveway) mind you this is with a unrebuilt tranny. Something sounds odd but I'm sure rd or john will chime in.

[twodko]

I still don't get it FLG. What were they saying in the showrooms back in the day? "Well the car won't move very well from "park" to whatever, you have to shift to neutral for a moment or two then it'll drive just fine". It just doesn't sound right to me..........I dunno.

Tom

[John_Kunkel]

The transmission pump is driven by the engine through the converter, any time the engine is turning the pump is pumping but where the pumped fluid goes is the problem.

When the aluminum TorqueFlight was introduced it was operated by pushbuttons, there was a separate Park lever and the transmission had to be in Neutral when the engine was started. In Neutral, the manual valve in the valve body keeps the fluid pressure contained but when console shifters were introduced in '64 there had to be an additional position in the valve body for Park so the end of the casting was bored out to allow the manual valve to move one more position.

Boring out the end of the casting makes a wide open leak when the manual valve is in the Park position and the fluid just dumps out the opening back to the pan. This prevents the pump from quickly refilling the torque converter that has drained down from extended sitting. Placing the shifter in Neutral before the start closes off the end of the casting and allows the converter to rapidly refill.
The factory has known about this problem from day one and chose to do nothing about it other than printing a couple of bulletins advising owners to start in Neutral instead of Park.

Aftermarket suppliers like TransGo and Sonnax offer modified manual valves that allow converter filling in Park.

In the pic below of some typical manual valves, the top and third down have added segments to slow down the pressure loss in Park but the TransGo valve on the bottom positions the segment to completely close off the leak.

[twodko]

This is just one of the many reasons they call you Commander Kunkel! Thank you for that, now I know the real story. You're the best John.

Tom

[FLG]

Thanks john,

Any particular reason I don't have this issue? Even sitting for extended periods of time I've never noticed slipping when I just go from park to drive to get her out of the garage 

[John_Kunkel]

The amount of converter drainback depends on the clearances in the pump, tighter clearances mean less drainback.

I bought my '98 truck brand new and didn't experience any "morning sickness" until it had about 20K miles on it.

Also, if the trans has been overhauled in the last 15 years or so it might have the modified valve, many rebuilders put one in as part of the overhaul.