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Cold Shifting


larry n

I have a 59 powerglide. I am just now installing it in my rebuild baby. It was rebuilt about 5 years ago. It will shift great when its cold. From first to second and then downshift. When the engine temp gets to about 150 it will not shift out of first. I have tried a new modulator valve and it helped, but now it will not upshift after the temp gets to be about 180. I have talked to several transmission people. Some say its the transmission some say its not due to it shifting when cold. I don't think I am getting a lot of vacuum but I am think I am getting enought to make it shift.
Any suggestions???????

Larry N.


Well-known member
Jun 17, 2002
North Hollywood, Ca.
Miss my '62 & '80 4- Sp. Vettes
If this has a 'Governor Valve," it might be sticking. Look for a stuck closed valve. this will keep the transmission in first gear. If the vavle was stuck open, it would start in other than first gear. Since the oil travels faster when warm or hot, this could cause oil pressure loss. Make sure there is no excessive bleed off which would cause pressure loss due to worn out tolerances.

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