Transmission shift point

[Mr.Buick]

I just noticed that my transmission is shifting at different points depending on boost level and wondered if any one knows why this would happen? At 10 lbs boost the transmission shifts around 5000 RPM and at 19 lbs boost it shifts at 4200 RPM. I had the transmission checked at a local transmission shop and he said that everything looks good and the kickdown cable was adjusted correctly.

 

[chris718]

that is a difficult question.ive heard of it shifting later with more boost by driving thru the converter but not that.the symtoms are common with a modulated tv upshift oil pressure loss at the shift valve caused by tv limit ,tv valve ,tv plunger or tv upshift valve circuitry loss that gets worst with heat.if youd like to nail it down you need to do both tests at the same temp.ie car fully warm one back to back aright after the other.a wideopen throttle 1/2 shift at 10 psi,stop crank up the boost and then a wide open 1/2 at 19 psi.if the situation is what you say it is still install a pressure gage and redo tests.im very interested in the results.

 

[Mr.Buick]

I will get a line pressure test and let you know the results, I believe 280 with the kick down cable pulled?

 

[Mr.Buick]

Chris, Here is the whole story, I had a Monte Carlo 200R4 in the car for about a year and could never find the right speedometer gear combination to get the rught speedometer reading. It shifted at about 3700-4000 with a 2800 lockup converter. I decided to get the original transmission rebuilt and put in a Pat's 3000 lockup converter. I just installed the transmission 2 days ago and it was shifting at 4200 with 19 lbs boost. I stopped by the transmission shop that rebuilt the transmission last night and had them double check my installation. He went for a ride and said that this 1984 Buick transmission has all the right parts, valvebody, governor to shift at 5000 and wasn't sure why it would shift at a lower point. I have a 1984 Buick GN, but all electrical componets are changed to 1987. He called another transmission guy and they want to do a line pressure check to make sure it's up to spec. If it is, he wants to change out the valve body. My understanding is that the Buick turbo valve body is different and switching it may not be in my best interest. On the way home I changed my Caspers 8 step chip from the position 5 to 2, which is the stock chip setting for 1987 Buick GN. This lowers the boost to 10-12 lbs and changes the timing back to stock. The transmission then shifts at almost 5000. The timing of the Caspers chip also increases as it raises the boost. Thanks for your help

 

[OneLethal87GN]

Whatever you do don't put a non-performance valve body in. It won't have the same shift characteristics and the shifts themselves will be alot weaker. I had one installed when the guy who rebuilt mine couldn't get my BQ valve body to work correctly and installed a regular 200-4r valve body. If you can't get a replacement GN body at least use the valve body out of your MC SS tranny.