Packard Forum Index » V-8 (1955-56)

56 400 problem with transmission wont shift till its warm then shifts perfect fluid needs to be changed ??? along with screen???

G'day pasquale,
to PackardInfo and I invite you to include your '56 400 in the Packard Owner's Registry.

I'll also ask BigKev, our Webmaster, to move your post to the V8 Forum where more will see your request and can respond.

BigKev for moving these posts to the V8 Forum.

If it is old fluid it won't hurt to change it. Sounds like there may be a valve sticking which is causing the problem until the fluid warms up and becomes a bit thinner.

The closest to the original type A fluid which was used with the original cork clutch plates available now is type F. Others have used B&M Trick Shift for a fluid which has different friction modifiers and seems to alleviate the groaning of the hard and glazed direct drive clutch plate as it goes into direct drive. With the cork you want something like type F or Trick Shift that will grab fairly quickly so the plates do not slide against one another and heat. If the transmission has been rebuilt at some point with plates lined with modern materials then GM Dexron fluids will work well and provide a smoother shift.

The filter is a fine mesh metal screen and just washes. It is not replaced unless it has been damaged and there are holes in the mesh.

can the valve body be services with out removing transmission?

Yes. If you don't have a printed manual download section 7 on the Twin Ultramtic from the 55-6 service manual. It details the disassembly procedure. If you are thinking of doing that best to get a pan gasket ahead of time as it is possible the old one will not be reusable. If you are thinking of cleaning for a possible sticking valve, before going to that extreme I would try a fluid change or perhaps a bottle of one of the snake oil products which claims to free sticky valves. Neither will take much effort or cost terribly and might do the job.

If you do remove and clean the valve body be extremely careful to do a bit at a time following the illustrations in the 56 supplement section. The valves and springs can look alike or be reinstalled backward and then you have a real problem if something is mixed up. There are some 56 differences from the 55 valve body that is shown in the main section.

Basically it is drain the fluid and remove the pan to access the valve body. The entire assy is held by several bolts and a bit of linkage. Once those are removed the assy will drop down. Once removed, there are valve body sections on the bottom and another on the top of a separator plate. There are some jumper tubes to other components so it is possible in order for the valve body to drop one of the piston or brake assys will also need to loosen. Be very careful if that is needed that the band struts do not dislodge and fall out of position so the piston can no longer operate them.

Pay particular attention to bolt sizes and lengths. Also be careful when replacing the valve body that the bolts are properly torqued. A haphazard tightening can cause problems by distorting the body and causing a valve to bind. With the 56 aluminum case, the threads can strip if not treated carefully.

If you go in also check the tightness of the manual valve lever to the shaft. The pot metal lever threads can wear and strip so the nut and setscrew will loosen and allow slop in the movement. Once tightened properly, a roll pin thru the lever and shaft will prevent any further or future problems with that part of the trans.

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If it were me, I'd take the car to a facility where they do power flushes on automatic transmissions. Have it thoroughly flushed and fresh fluid installed-and make sure it is thorough since these guys are accustomed to doing little modern Honda automatics and don't fret over how big a transmission like yours is. The flusher guys just wanna get you in and out-fast. This will take more time than their usual operation, so don't let them rush it. Then without driving a distance drop the pan and do a final cleaning.

Also, make absolutely sure to check the cooling circuit for your Ultramatic.
? First make sure there IS a cooler of some kind still piped onto the Ultramatic. If not, stop right there and figure this is part of (if not all of) your problem. Get a working cooler on there.

? If somebody has customized it with an air-cooled type, be sure it isn't plugged up or leaking. And make certain that the air-type cooler has enough cooling area (fins) to actually handle the job of cooling a V8 Ultramatic.

? If it still has the original transmission cooler, check it for flow and internal leaks. Nobody ever does this or pays attention to the cooler, but when things gum up inside the Ultramatic, this has often been the culprit. ANY coolant (especially water or treated water) that gets into the transmission is an eventual recipe for disaster.

Check all these points first, otherwise anything you do may be a wasted effort.