TH400 shift points

[84GMCSierra]

I have a question about shift points on my 84 Sierra with the TH400. Taking off from a stop light, it shifts into 2nd at about 17- 18mpg, and into 3rd about 37-38 mpg. Is this a normal range for this trans?
Thanks everyone

 

[Ricko1966]

I have a question about shift points on my 84 Sierra with the TH400. Taking off from a stop light, it shifts into 2nd at about 17- 18mpg, and into 3rd about 37-38 mpg. Is this a normal range for this trans?
Thanks everyone

Depends on tires and gear ratio. I'd want to know what rpms its shifting at. Not so much what speed I was at.

 

[awar]

Turbo 400 transmissions have a vacuum modulator and a governor. It is the relationship between throttle pressure and driveshaft rpm that determine shift points. This transmission also has an electric override kick down switch also in play. Final drive gear ratio and tire size determine the output shaft rpm.
All of this determines when and how firm it shifts to the next gear.
That being said, light throttle yields early softer upshifts. More throttle up to the kick down switch yield later and firmer shifts. Kick down is the latest shifts including holding the transmission in second gear until the governor overrides the kick down command. As an aside manual low will upshift into second without a shift kit, I discovered this in 1974, it was unexpected and very exciting. Almost hit the curb on the outside of that turn.

 

[Frankenchevy]

You may have a th400 with a diesel governor installed. Do you know the history of the trans & truck?

 

[idahovette]

Turbo 400 transmissions have a vacuum modulator and a governor. It is the relationship between throttle pressure and driveshaft rpm that determine shift points. This transmission also has an electric override kick down switch also in play. Final drive gear ratio and tire size determine the output shaft rpm.
All of this determines when and how firm it shifts to the next gear.
That being said, light throttle yields early softer upshifts. More throttle up to the kick down switch yield later and firmer shifts. Kick down is the latest shifts including holding the transmission in second gear until the governor overrides the kick down command. As an aside manual low will upshift into second without a shift kit, I discovered this in 1974, it was unexpected and very exciting. Almost hit the curb on the outside of

Yes and it was a hell of a shift. Mine came out of low about 5400 RPM and really snapped your neck......lotsa fun!!!

 

[xm20k]

Not the topic at hand but for those running a TH400 that like their burnouts.

The 1-2 sprag does not like the upshift with high wheel speed it is the breaking point of even beefed-up race th400s. Its why racers do 2nd gear burnouts and some build turbo glides ie. remove first gear entirely.

Stop your burnout before shifting to 2nd or start in 2nd.

I know a lot of guys run them in these trucks, and most are stock so just a tip so hopefully no one ends up stuck on the side of the road with a busted sprag.

 

[84GMCSierra]

You may have a th400 with a diesel governor installed. Do you know the history of the trans & truck?

As far as I know it's all original. Tires are 235 85R16. It shifts smooth as glass. I was just wondering if the shift points I'm getting are normal.

 

[84GMCSierra]

Not the topic at hand but for those running a TH400 that like their burnouts.

The 1-2 sprag does not like the upshift with high wheel speed it is the breaking point of even beefed-up race th400s. Its why racers do 2nd gear burnouts and some build turbo glides ie. remove first gear entirely.

Stop your burnout before shifting to 2nd or start in 2nd.

I know a lot of guys run them in these trucks, and most are stock so just a tip so hopefully no one ends up stuck on the side of the road with a busted sprag.

I couldn't do a burnout in this thing if I tried unless it was in gravel or a wet surface, it's too heavy, lol. Besides that, I can't afford another set of tires. I just put new ones on 2 weeks ago.