Shift points for TH400
Registered User
Joined: May 2011
Posts: 26
From: Fitchburg, WI
I can't find any normal shift speeds for the 400. I've looked in my repair manuals and cannot find what you need. The good thing about the 400 is you can adjust the modulator on the passenger side of the trans to shift at just about any point you want. This is an easy adjustment. When I first installed my trans, it was shifting through the gears pretty quick, even on WOT. I adjusted the modulator to shift later, which also produces a firmer shift.
GT73
Joined: Nov 2014
Posts: 6
From: Toronto
How to do it right!
The following applies to the TH-400
3 speed automatic transmissions…
For normal driving, (light acceleration),
most TH-400’s shift at around 1,600 - 1,800
RPM. From 1st to 2nd and 2nd to 3rd gear.
if you want to increase these shift points,
you need an adjustable modulator.
Some Olds came stock with these, they often have a red circle on the outside of the adjustable modulators.
Using a flat head screwdriver, and by removing the black vacuum hose, turn the inner setting clockwise about quarter turn, to increase your shifts by about 200 RPM.
Don’t go crazy, this is not the thing to increase your shifts, if you want to chirp your tires, between shifts.
The modulator is for normal acceleration.
DO NOT confuse a modulator with a Governor!
The Governor will change the shift points under WOT (wide open throttle) for racing!
You’ll want to purchase the B&M Governor kit or one made by TCI.
Ideally, you want to leave the car in drive and floor it and have the tranny change gears at around 5,500 RPM on a 455 / 400 or 425 Rocket.
Providing your engine is stock or slightly modified.
5,500 RPM is usually the best time to shift gears because this is when the Horsepower curve peaks on most big block Oldsmobile’s that are stock or slightly modified. Shifting at 6,000 RPM is a waste of time and can damage your engine, if repeated.
If you want to manually change gears, then you need to bypass the tranny settings.
TH-400’s are designed to automatically change from 1st to 2nd gear, as a safety feature, so you don’t blow up your engine!
The best kit to purchase is the Trans-Go Reprogramming Kit.
It will allow you to manually hold gears for as long as you want. Do so with caution.
People often call this a shift kit, but it’s more than that. Trans-Go provides you with beefier springs, plates and hardware that strengthens your tranny.
Its worth it to have installed by a professional.
Lastly, make sure your Kick-down switch is working properly. It’s often located either just above your gas pedal or by your carb.
400 kick-downs are electronic, 350 TH are manual.
Spray it with a cleaner designed for electronic components to get rid of any gunk.
Ensure the electrical wire that runs to the tranny is good.
Another component that may fail, is the solenoid for the kickdown switch. It’s located inside the tranny pan, despite being an electronic switch.
I hope this clarifies many misconceptions about shift kits and how to properly optimize a TH-400.
3 speed automatic transmissions…
For normal driving, (light acceleration),
most TH-400’s shift at around 1,600 - 1,800
RPM. From 1st to 2nd and 2nd to 3rd gear.
if you want to increase these shift points,
you need an adjustable modulator.
Some Olds came stock with these, they often have a red circle on the outside of the adjustable modulators.
Using a flat head screwdriver, and by removing the black vacuum hose, turn the inner setting clockwise about quarter turn, to increase your shifts by about 200 RPM.
Don’t go crazy, this is not the thing to increase your shifts, if you want to chirp your tires, between shifts.
The modulator is for normal acceleration.
DO NOT confuse a modulator with a Governor!
The Governor will change the shift points under WOT (wide open throttle) for racing!
You’ll want to purchase the B&M Governor kit or one made by TCI.
Ideally, you want to leave the car in drive and floor it and have the tranny change gears at around 5,500 RPM on a 455 / 400 or 425 Rocket.
Providing your engine is stock or slightly modified.
5,500 RPM is usually the best time to shift gears because this is when the Horsepower curve peaks on most big block Oldsmobile’s that are stock or slightly modified. Shifting at 6,000 RPM is a waste of time and can damage your engine, if repeated.
If you want to manually change gears, then you need to bypass the tranny settings.
TH-400’s are designed to automatically change from 1st to 2nd gear, as a safety feature, so you don’t blow up your engine!
The best kit to purchase is the Trans-Go Reprogramming Kit.
It will allow you to manually hold gears for as long as you want. Do so with caution.
People often call this a shift kit, but it’s more than that. Trans-Go provides you with beefier springs, plates and hardware that strengthens your tranny.
Its worth it to have installed by a professional.
Lastly, make sure your Kick-down switch is working properly. It’s often located either just above your gas pedal or by your carb.
400 kick-downs are electronic, 350 TH are manual.
Spray it with a cleaner designed for electronic components to get rid of any gunk.
Ensure the electrical wire that runs to the tranny is good.
Another component that may fail, is the solenoid for the kickdown switch. It’s located inside the tranny pan, despite being an electronic switch.
I hope this clarifies many misconceptions about shift kits and how to properly optimize a TH-400.
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