Transmission shift

[Jimb1231]

Recently my transmission shift from 3rd to 4th is occurring around 3900 RPM.  Up until now, it was very smooth and shifting at approx 2500 RPM.   Trans fluid level is OK and color is OK.  What might be the cause?  Shift points for lower gears is also very smooth and not at high RPM (shifts are approx 2000 RPM.  I find it aggravating when in traffic because it downshifts from 4th to 3rd at speeds less than 40 MPH causing high RPMs even though trying to maintain speed under 25 MPH.

[Coops]

I think I have the solution which has been discovered on my car and tested on one other with positive results. I tried everything for a period of 20 years, filter, valve body, modulation presssure etc. My problem turned out to be an oil passage pin in the drive to the centrifugal step pressure converter at the rear end of the gear box. This pin had slipped slightly 4mm but enough to block one of the passage-ways to give exactly your symptoms. Let me know how practical you are or if you intend to give it to a transmission shop ?
Can be checked with transmission in car but entails taking rea end off. I have photos and intend to create a section in the tech manual but my computer skills are not great.

If you are interested I can send instructions via direct mail

[JIMV]

I can say with near 100% confidence that Coops has the right answer for this problem Jimb. I contacted him after reading his previous threads last fall describing delayed 3-4 shifts which were identical to my shift issues. He was kind enough to send me an extensive array of photographs and diagrams of the issue.  His photographs and explanations were spot on and helped guide a very experienced transmission shop near Seattle with the repair. The guys at Sun Vally Transmission in California also were helpful and have a good understanding of this problem as well. Good luck.

Coops.... You could easily post the photos and diagrams that you sent to me in the technical manual. Many will benefit.  Thank you and Well done !!