Thread: Powerglide shifts early

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The powerglide in my 63 Nova shifts too soon. It's been suggested to me that there's a pin that sits inside the vacum modulator valve that can get stuck, or lost when previous work was done on the tranny, that would cause this problem. What do you think?

There is a pin, but I don't think that's the problem here. I just changed the modulator on my powerglide(1965). Mine too is shifting too soon. When I changed the modulator, I left out this pin. This made the trans slip REAL bad. This shifting too soon is most likely caused by the TV linkage adjustment. I'm fooling with mine too, trying to find the right shift point.

If your Nova is a inline six check the vacuum advance...You can watch it's action with the engine running and reving it up a bit..The external arm should move a little.. The vacuum line from the carb sometimes has a tee fitting operating both the vacuum advance and the vacuum modulator..If the vacuum advance has a ruptured diaphragm then the modulator doesn't get the correct vacuum..Man !!! how many times have I said Vacuum....Of course a good inspection of the line going to the tranny is needed..The hose on the modulator end rots and gets pin holes...I replace ALL the vacuum flex lines if they need it or not..Pin holes can cause all kinds of problems...A good replacement modulator has an adjustment for the rod it operates..Read the instructions...Do yourself a favor and stay away from SHUCKS and K-MART !!!!....Ever pulled the pan and changed the filter ????....If it has a cooler in the radiator it needs flushing once in a while....WARNING!!!..If the tranny fluid smells like it is burnt be careful about flushing with new oil..The new oils of today can wipe out the bands or clutches...It's time for an overhaul...And last but not least the throttle valve linkage (TV) has to be in place and correctly adjusted...Powerglides have got me around for many years........Al..

Been fooling around with the TV linkage on my 65 Nova and found
that making the arm longer makes the shift point higher. Here's what I did and like the shift points much better.
Disconnect the TV linkage and hold it as far in (or down) as it will go. Then hold the throttle wide open and adjust the TV linkage to go right into the hole while holding the TV and throttle as mentioned above. Now turn the TV nut out 10 full turns and try it at this point. This is where mine is and I like the shift points.

The problem I have is when it down shifts to first. It down shifts at about 10-12 MPH but it bangs real hard...almost like the rear end is sloppy. If I manually down shift at a little higher speed (like 15-20), it seems perfect. Any suggestions?

Try turning the TV cable nut only five turns... The cable is not really designed to change the shift points ..Read what GM wants and adjust exactly what is recommended.. You got the correct pin behind the modulator??...Is the modulator new ???...A vacuum leak between it and the carb will cause harsh down shifts...The vacuum advance?????...Check it...

I figured out my harsh down shifts problem. Had nothing to do with vaccuum or really even the TV linkage. It was the idle speed!This motor is supposed to idle at around 425 and mine was idling at over 600. I knew the idle was slow and I thought I had it real low, but obviously I didn't. I dropped the idle to 425 and it shifts fine now.
Again, for the gentleman who's car seems to shift too soon. Lengthen the TV rod.

Another question. There was mention of new oils of today. What fluid should I be putting in this powerglide? I've been using Dextron III from Advance Auto Parts store.