My powerglide tranny shifts just fine when the car is warmed up but it is very slow to shift when I first stated it in the morning. This is my first powerglide so I don't know much about them. What triggers them to shift and is this normal or do I have a problem?

 

Not normal, whether you are shifting into gear manually or automatically with partial throttle. The vacuum modulator, the device having a vacuum tube connected to it from the intake fitting behind the carb, also a place to check for broken hoses, controls when the upshift occurs. Less throttle, sooner mph upshift; heavier throttle, later upshift,
Check oil level when both cold and hot. If cold has more oil level, say a couple of pints, could be the oil pump has too much clearance within itself and the torque convertor has drained through the pump back into the pan. During start up, the pump pumps oil into the torque convertor. Once the conv gets full, then the pump supplies oil for the rest of the trans functions.

The kickdown linkage has nothing to do with partial throttle upshift, only WOT upshift.

 

Thanks for the reply Everett. The vacuum fitting in the back of the intake manifold has a tee in it. One of the lines goes to the tranny and the other line goes down under the brake booster to something I can't see. Here is a picture.


The tranny does not appear to be over filled. Its right on the full mark when running and about a half inch above the fill line when shut off.

I don't understand why it shifts fine when warmed up but up shifts late when cold.

 

Does the trans seem to slip when cold too, or is it only the sluggish shifting? The issue could be worn internal seals or gaskets causing fluid to get past, then swelling up and sealing better once they get hot. How many miles are on the trans?

 

It doesn't seem to be slipping at all. When it finally does shift it is nice and crisp. I have no clue how many miles are on it. For the first three weeks that I owned it, it shifted just fine. It just started doing it this last week. Would an additive like Lucas help it any?

 

Then I'm thinking it may be with your valve body. Either a valve (piston) getting hung up, or its not holding pressure like it should till things warm up and expand. A modulator vacuum, or lack of vacuum issue would be there cold or hot. Try the Lucas, it won't hurt the trans. Has the fluid been changed? Dab some from the dipstick on a paper towel. How does the color look?

 

I didn't change the fluid because the color looked fine and it didn't smell like it had burned. Its full now so I guess I'll have to get some fluid out in order to add some Lucas. Are there any tricks to get a small amount of fluid out without dropping the pan?

 

I have one of these, you'll need to add a longer section of hose to reach further down the fill tube and into the fluid: Oil Suction Gun | eBay

 

I've got one of those. I just hope I can find it. Thanks! I'll let you know if the Lucas additive works.

 

Don't expect miracles, but you may get lucky. The Lucas additive reduces internal slip (not your issue), and it also is supposed to help eliminate seal leaks. Maybe it might help clean out any crud in the valve body, if that's what's causing your problem.