humanpotatohybrid wrote: He has a 54th series car, so he would have one of the 54th series valve bodies which is somewhat different than the chart shown and what they were doing in 49. BTW, even though he replaced it, these are by far the most common type, being introduced in the 23rd series (1950). The valve (3.577) has an inner spool valve (4), follower (6), and dowel pin (5).
The throttle pressure land is .388 sq .in. and the inner valve land is .141 sq. in. The dowel pin is .062 sq. in. The governor pressure land when the DD clutch is engaged is hence .326 sq. in.
Let's consider accelerating at 15-20MPH at half throttle, with DD already engaged. Throttle pressure at half throttle is about 42 PSI. The modulating valve regulates its pressure to be 52% higher than the throttle pressure: 64 PSI in this example.
At closed throttle acceleration (e.g. coasting downhill), the DD clutch should engage at about 15 MPH which is the speed that the governor pressure jumps from being vented, to 30 PSI. (Remember that the lands of both the governor and throttle sides of the valve are the same area when the DD is disengaged.)
The inner valve pushes on the dowel pin and hence gives hysteresis to that effect. We can see that in this case, the governor exerts 9.8 lbs to the left. The modulated pressure exerts 9 lbs. to the left. The throttle exerts 16.3 lbs to the right. So, we would not expect a disengagement. In fact, we can easily calculate that the "effective area" of the throttle pressure side of the valve, during the proportional range of modulated pressure, is .174 sq in. So, we would expect a throttle pressure of 1.87x the governor pressure to be required to disengage the DD clutch. For a governor pressure of 30 PSI (15 MPH), this would be 56 PSI throttle, which is full throttle.
Of course, at and beyond full throttle, the modulated pressure starts to match the pump pressure, and at kickdown position it then matches throttle pressure, for an effective throttle land area of .247. Considering this 85 PSI throttle pressure, we would expect it would overcome a governor pressure of up to 64 PSI. Considering that this is the governor pressure at 56 MPH, this result matches the prescribed "end of kickdown" speed of approx. 50 MPH.
So we can see that once the DD clutch is engaged, it will not disengage until the accelerator is pressed to the kickdown position, so this is normal operation. But then this begs the question of why this behavior was not previously observed.
As 53 noted, you can raise the throttle pressure to lessen this effect. However, I believe it is set properly as it is, and raising it significantly may result in the engagement happening at annoyingly high speeds. But, you are certainly free to adjust it to your liking even if it deviates from Packard's intention.
P.S. While I don't believe the essence of my previous comment was wrong, the pin which I referred to is very difficult to remove, so unless it happened to fall out for some reason, it's unlikely to have went astray. Instead, I believe OP is misinterpreting the designed behavior of the transmission.
P.P.S. Actually, re-reading his post, I am concerned by this phrase: "but that is even more jerky and painful during the second or two it takes for the transmission to react." As soon as you floor the gas, the DD clutch should disengage and you will immediately hear the engine flare from normal torque converter operation. If there is a delay for the direct drive clutch itself to disengage, then there must be some problem.
Roland: you said the pressure tests were within specifications, but: if the direct drive clutch pressure falls at the same time the clutch disengages, then the direct drive valve is sticking. Perhaps the valve body was overtorqued? If the pressure falls but the clutch disengages later, then the clutch itself must be sticking somehow.
Hello and big thanks for the very comprehensive description of the valve actions under various conditions. I had similar discourses with my transmission specialist and he eventually concluded that the problem I have now is normal operation, i.e. a DD-clutch release requires Kick-Down. I am not so sure. As you wrote, i also begs the question why this problem was not there before the overhaul, when the clutch would open at part throttle and completely natural depending on car speed and load. Also spoke to a '54 Pacific owner (same non-gear-start type) in the national Packard Club. He does not need Kick-Down to open the clutch on lower speeds. The logic of hydraulic pressures and valve operations would suggest my cars problem to be "normal operation". A feature, not a bug. Still, gunning the engine for downshift every time will not hold for long. Likely, also the Packard folks back in the days would have agreed. More thoughts very welcome!
I would increase your throttle pressure adjustment slightly and see if it helps.
By the way, who is this Ultramatic mechanic in Sweden you are talking to?
What else changed during the rebuild? If the small parts of the direct shift valve are jammed with grime, but the valve as a whole slides back and forth, the hysteresis functionality will be lost.
