I've got a 59 chevy impala, just swapped out the 283 for a fairly beefy 327. The car still has the original cast iron powerglide in it. I know nothing about automatics and this is the first car I've done with one. I was wondering if there was any way to change the shift speed. Right now the car shifts at around 20 mph and downshifts at about 10 mph. It would really be nice to get some more rpms out of first gear to get up to speed.
Some of the modulators are adjustable, remove the vac hose there will be a screw driver slot inside the vac port, I dont remember the direction you need to turn it. There is not a lot of adjustment to it, maybe will help.
There are a couple of adjustments that could be made, but they won't make a big difference however. It's best to go to your local library, and hope they have some older editions of MOTOR'S MANUALS; the adjustments are detailed in them, and the directions are too involved to go into here. I am Butch/56sedandelivery.
Do you have the throttle valve (kickdown) linkage installed? If you don't have the TV linkage installed then it is going to shift as if you are just babying the throttle all the time, and it will not downshift using the throttle. If the TV linkage is installed and adjusted correctly, then the upshift and downshift points will change based on the throttle position; as you increase the throttle the RPM where the upshift occurs increases, the more throttle you give it, the higher the RPM where it shifts. If you have the TV cable installed and adjusted correctly, and you still want to change the shift point, there is one more adjustment you can make on the TV valve, but as 56sedandelivery said, you should get the manual and read and understand it first. The manual is available online if you search. Note, the vacuum modulator on the Powerglide is not adjustable and that is not where you make adjustments for the shift point. The VM controls how firm the shift is, not when it occurs.
What Blues4u said--the linkage on the early iron glides has a lot to do with shift points. There is a bellcrank affair on the dr side bellhousing with linkage to the trans and the carburetor that must be there and set properly as I recall.
I do have the linkage on the carb and I'm ***uming that it is adjusted correct. I opened the carb full throttle and adjusted the linkage so that it easily went into the hole on the carb. I have a 59 shop manual but there isn't much info on the powerglide in it. Have to do a little digging and see if I can find a better manual for that ******.
I have a 1959 edition of the MOTOR'S Manual, and it has everything in either the Powerglide transmission section or the actual car section. There's a huge difference in the cast iron VS aluminum Powerglide transmissions. The only things the same are, they are both 2 speeds, and from 58 on, have the same shifter detent display patterns. As long as you have the complete bellcrank/linkage setup, carb to bellcrank, bellcrank to throttle valve lever linkage, you should be able to make some adjustment, but not a huge amount. You could swap to an aluminum Powerglide, do some shifter linkage/throttle-kickdown linkage adjustments, and be better off with a stronger transmission, lighter transmission, easier to find parts for transmission. Or, like someone else already said, swap to a TH350, aftermarket shift displays are available, and use a cable the TH350's came with. You have to buy a carb/intake manifold bracket also available from the aftermarket or from a newer year car/truck. I am Butch/56sedandelivery.
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