# Super turbine 300



## CPL (Feb 11, 2016)

Hello 
Dose anyone know if there is a shift kit for the st300?
And is there an adjustment or mod to get the st300 to shift in to drive sooner then 55to 60 miles per hour?
Thanks:


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## RT-1 (Mar 21, 2012)

Sounds like you have a problem with your vacuum modulator. Mine never shifts that late. 


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## CPL (Feb 11, 2016)

I replaced the vacuum modulator as well as the govonor. What speed dose yours shift at?


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## RT-1 (Mar 21, 2012)

It depends how deep I'm into the throttle. Normal driving it shifts around 20 mph. If I'm full throttle, probably 45. There are only two gears as you know. What color modulator did you go with?


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## CPL (Feb 11, 2016)

Stainless steel looking
Got it from opgi


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## Pinion head (Jan 3, 2015)

what was wrong with original vac modulator?


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## CPL (Feb 11, 2016)

Nothing I changed it cause I was hopeing for a sooner shift.no different


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## CPL (Feb 11, 2016)

Any ideas pinyin


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## RT-1 (Mar 21, 2012)

There are several variants and one adjustable catchall. You might try that especially if you have a low vacuum producing engine. I would suggest checking the vacuum line from one end to the other. Is the fitting on the carb side stock? The rubber hose on the other side ok? The correct stock modulator for the V8 is the red stripe.


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## CPL (Feb 11, 2016)

Vacuum is very strong I put a vacuum gauge down at the trans.there isn't any strip on the modulator.


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## RT-1 (Mar 21, 2012)

What are you calling a strong vacuum? What does it do during acceleration? Does your modulator have an adjustment screw?


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## RT-1 (Mar 21, 2012)

Also, can you manually shift the transmission using the lever? You could have an issue with the governor weights being stuck in the outer position. 


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## 1968gto421 (Mar 28, 2014)

RT-1 said:


> Also, can you manually shift the transmission using the lever? You could have an issue with the governor weights being stuck in the outer position.
> 
> 
> Sent from my iPad using Tapatalk


That's not uncommon with GM transmissions (including the TH350 and TH400) where the previous owner(s) did not change the trans oil and filter regularly. The governor can easily get "gummed" up. Had a TH350 that did all shifts below 20 mph because the governor was gummed up. It's an easy job, though, to pull it out and clean it.


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## RT-1 (Mar 21, 2012)

I'm linking the transmission section from the service manual. The two tests I would do is to see if it will shift manually (likely the governor) or if it will shift at WOT (possibly a stuck detent valve).

https://www.dropbox.com/s/502t1twingmy9km/ST300.pdf?dl=0


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## CPL (Feb 11, 2016)

I found I have the wrong modulator I contacted opgi the one I bought from them is for the th350/400.they don't have the one for the st300 so I'm getting it from rockauto it is adjustable


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## CPL (Feb 11, 2016)

How dose the adjust screw work will it come with directions


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## RT-1 (Mar 21, 2012)

From the Summit Adjustable Vacuum Modulator instructions....

"To adjust the shift points of the transmission, disconnect the vacuum hose. With a flat blade screw driver turn the screw on the inside of the modulator end clockwise to raise the shift points and firm up the shifts. To lower the shift points turn the screw counter clockwise, this will also soften the shifts. Only turn the screw two full turns at a time, reconnect the vacuum line to the modulator, and then test drive the vehicle. Re-adjust if necessary."


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## CPL (Feb 11, 2016)

Thanks for all your help I should get it by Saturday hope it takes care of it
OK now dose firming it up get it to shift sooner or is it the other way softer


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## 1968gto421 (Mar 28, 2014)

The "soften" shift setting will lower the shift points (shift sooner), the firmer setting will raise the shift points (shift later).


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## CPL (Feb 11, 2016)

Cool thanks


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