1971Chevy Pickup not shifting right

[chazdo2]

I think I have my engine RPM problem figured out. It is a three speed auto tranny. It seems like its only shifting first and second gear. I guess that would explain me running around 4K RPM's at 55 MPH. Any ideas why the tranny is not shifting up as it should? The vacuum line is hooked to the intake manifold and the tranny.

[LockDoc]

Originally Posted by chazdo2

I think I have my engine RPM problem figured out. It is a three speed auto tranny. It seems like its only shifting first and second gear. I guess that would explain me running around 4K RPM's at 55 MPH. Any ideas why the tranny is not shifting up as it should? The vacuum line is hooked to the intake manifold and the tranny.

Are you sure that your linkage is adjusted correctly? Is the indicator in the park position when the trans is in park?

LockDoc

[chazdo2]

not sure about the linkage. Truck doesn't have the transmission indicator on the column. How do you adjust the linkage?

[davepl]

What about the kickdown cable at the carb? If that's disconnected and just pulled taught it'd never upshift, or not till very late. That's about all I can think of.

[chazdo2]

Originally Posted by davepl

What about the kickdown cable at the carb? If that's disconnected and just pulled taught it'd never upshift, or not till very late. That's about all I can think of.

where does the kick down cable hook up to?

[davepl]

Originally Posted by chazdo2

where does the kick down cable hook up to?

Transmission to carb.

[Coley]

...have you checked your trans fluid/fill level?
If you are low on fluid it will not shift correctly or quickly.
The level is often hard to read on the trans dipstick...but this is a quick check and fix if it is low.
My two bits.
Coley

[leftybass209]

Everything said above, and do you know your rear end gearing? What's the story with the transmission? Where did it come from? Is it shifting soft, or firm right now? Does it lunge after it shifts?

[kwmech]

Kick down cable on a T350 does not affect up- shifting

[davepl]

Originally Posted by kwmech

Kick down cable on a T350 does not affect up- shifting

How does it work?

[haycatcher]

Try starting in low gear and manually shift by hand and see how trans responds. Check trans fluid at running temperature with truck in gear with helper so no one gets run over or anything gets run into. Make sure modulator line is not leaking and any rubber on line is not cracked.

Not 100% sure but I think bad modulators will suck out trans fluid.

[Gromit]

Here is the page for service interval - if its been close to this long or this many miles since you changed the fluid and filter I would suggest doing that service since you are experiencing unknown issues.

In other words you were going to have to change the fluid anyway so why not get a better look inside the transmission at what might be happening.

Changing the fluid and filter of course involves removing the transmission pan and you will know right away if you find pieces of metal in the pan you will be glad you stopped driving it.

And if it is something minor then the fluid change might be enough to correct it.

Assuming you have a TH 350 I would check that modulator line first though because it is an easy check - just pop off the rubber elbow at the modulator on the rear of the transmission and see if you can see any transmission fluid. If so you need to change out the modulator with a new one and clean out the line with brake fluid.

[chazdo2]

You guys are the best!!!!!!!!!!!!!!!!!!!!!!!!! Cant thank you enough for your time spent with the less learned!!