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Transmission shift indicator/adjustment

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#1 nallman


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Posted 19 April 2017 - 05:19 AM

I'm pretty new to this, so forgive me if I'm overlooking the obvious.


I have a 1979 Esprit with a transplanted Pontiac 400, stock TH350 and posi 3.08 rear. Right now the transmission is almost always in a higher gear than I would like, it doesn't downshift when I'd like, and it shifts way to early under part throttle and WOT. It also seems to often take off in 2nd gear, which confuses me.


With this car it is hard for me to tell if it is in 1st or 2nd at certain speeds. I'm wondering how most people go about testing their transmission adjustments. 


Is there an option for an aftermarket shift indicator light? Should I be able to determine which gear I'm in simply by RPMs?


I have the resources to take the transmission to a reputable shop, but I really want to try and learn how to make these adjustments myself.


Here are the current articles I'm referencing:






Thanks in advance!

Edited by nallman, 19 April 2017 - 05:22 AM.

#2 JoePeek


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Posted 19 April 2017 - 02:32 PM

The 350 turbo shift points are controlled by the governor and the vacuum modulator. Reminds me a lot of an old school distributor where the weights and springs react to RPM and the vacuum advance react to engine load. The same thing is true for the shift points where the vacuum modulator has input on shift points as a function of engine load, while the weights and springs in the governor effect shift points as a function of the output shaft of the transmission. First make sure you don't have a vacuum leak that will make the transmission think the engine is under more load than it really is, but since it seems it upshifts sooner than you like, a vacuum leak is probably not a problem since the trans would not want to upshift if the modulator was getting a weak or no vacuum signal. It could be the trans is calibrated to work with a different engine or gearing. In any event, as long as the trans is in sound condition, you can get different weights and springs for the governor to mess with shift points, and to a lesser effect there are replacement/adjustabe vacuum modulators as well.

#3 JOE68


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Posted 19 April 2017 - 03:25 PM

most of the 70's GM's I worked on had a cable to the carb that reaked havoc when out of adjustment

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