Cadillac Repair: Transmission upshift of 83 Deville 4.1, engine vacuum, vacuum modulator

Question
1983 Deville with 4.1 DFI and I believe a T400.
Problem: The transmission upshifts very late - only when the engine hits high rpm's and the vehicle speed seems to be a factor as well...(inshort late upshift). no slippage or missing gears.  

Answer
A 1983 seville should have a 4T60-E in it.

Possible causes are:

1. Loss of vacuum to the VACUUM MODULATOR. I have seen many of the steel lines that provide the vacuum from the engine back to the modulator develop small pin holes in the steel line and this SLIGHT lose of vacuum can cause late upshifts.


also check the rubber hoses at the engine vacuum port and at the modulator.

Also could be a faulty modulator. or the small valve inside the trans could be STUCK in the valve body bore and needs to be freed up. You will see this valve once you remove the modulator.

BE CAREFUL so as NOT to re-installit BACKWARDS back into the valve body if you take it out.

Could also be a stretched throttle valve cable.



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