TH-400 Shift points and how to do it right!
Thread Starter
GT73
Joined: Nov 2014
Posts: 6
From: Toronto
TH-400 Shift points and how to do it right!
I swapped my original 350 Rocket with a TH-350, to a 455 Rocket (modified) with a TH-400 from a ‘70 Delta 98.
Couldn’t figure out why it still wasn’t that fast?
Until I did some research and did the following.
Man, what a difference!
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.
Modifying the Governor with lighter weights and springs is how to increase your shift points in drive, this kit is available separately.
TMI offers this kit and mods should be done by a professional, you’ll have to test varying springs to get it exactly right - shifts automatically under WOT at 5,400 - 5,600 RPM.
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, when you manually have it in 1st gear, 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.
Couldn’t figure out why it still wasn’t that fast?
Until I did some research and did the following.
Man, what a difference!
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.
Modifying the Governor with lighter weights and springs is how to increase your shift points in drive, this kit is available separately.
TMI offers this kit and mods should be done by a professional, you’ll have to test varying springs to get it exactly right - shifts automatically under WOT at 5,400 - 5,600 RPM.
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, when you manually have it in 1st gear, 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.
Last edited by GT73CS455; Oct 17, 2024 at 08:21 AM.
Registered User
Joined: Feb 2013
Posts: 15,432
From: Phoenix, AZ
I suspect a lot of folks on the forum would have a heart attack if their transmission shifted at 5500 RPM. Most are timid about "pushing" it to 5000 RPM.
Registered User
Joined: Jan 2010
Posts: 6,116
From: central Indiana
It’s easy enough to disable the automatic 1-2 upshift if you’re comfortable removing the valve body. You basically need to grind a flat onto the shift valve and plug a hole in the valve body.
At most, you can move shift points 2-4 mph with an adjustable modulator. If you need a bigger change than that, you need to play with the governor.
You will never get the full throttle shift points dialed in if the kickdown system isn’t functioning. The trans will always tend to “short shift”.
this article has some good tech tips.
https://nastyz28.com/threads/th400-r...tricks.131600/
At most, you can move shift points 2-4 mph with an adjustable modulator. If you need a bigger change than that, you need to play with the governor.
You will never get the full throttle shift points dialed in if the kickdown system isn’t functioning. The trans will always tend to “short shift”.
this article has some good tech tips.
https://nastyz28.com/threads/th400-r...tricks.131600/
Registered User
Joined: Dec 2024
Posts: 1
Originally Posted by GT73sdsCS455;159sdsds0679
I swapped my original 350 Rocket with a TH-350, to a 455 Rocket (modified) with a TH-400 from a ‘70 Delta 98.
Couldn’t figure out why it still wasn’t that fast?
Until I did some research and did the following.
Man, what a difference!
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.
Modifying the Governor with lighter weights and springs is how to increase your shift points in drive, this kit is available separately.
TMI offers this kit and mods should be done by a professional, you’ll have to test varying springs to get it exactly right - shifts automatically under WOT at 5,400 - 5,600 RPM.
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, when you manually have it in 1st gear, 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.
Spoiler
Until I did some research and did the following.
Man, what a difference!
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.
Modifying the Governor with lighter weights and springs is how to increase your shift points in drive, this kit is available separately.
TMI offers this kit and mods should be done by a professional, you’ll have to test varying springs to get it exactly right - shifts automatically under WOT at 5,400 - 5,600 RPM.
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, when you manually have it in 1st gear, 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.
Last edited by SadieWalker; Dec 26, 2024 at 05:42 AM.
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