Unfortunate News

[81GMCSierra1500]

I'll have to take it out again tonight and take a really keen listen to my shifting and see what happens...

[SkinnyG]

Where the shifter sits, what it's pointing to, and what gear is actually selected aren't necessarily the all same thing.

Ron Sessions' book "Turbo-Hydramatic 350 Handbook" says no 2-3 shift could be a valve-body malfunction, a front-pump malfunction, or a direct-clutch-circuit break.

If you are not actually shifting into 3rd, you should probably take the transmission back to whomever built it.

[81GMCSierra1500]

Originally Posted by SkinnyG

Where the shifter sits, what it's pointing to, and what gear is actually selected aren't necessarily the all same thing.

Ron Sessions' book "Turbo-Hydramatic 350 Handbook" says no 2-3 shift could be a valve-body malfunction, a front-pump malfunction, or a direct-clutch-circuit break.

If you are not actually shifting into 3rd, you should probably take the transmission back to whomever built it.

The shift needle is broken (old crusty cluster), so I don't have a needle, but the shifter definitely goes into drive (3 clicks of the lever). I'm thinking maybe a bad vacuum line? I know that if a TH350 doesn't have adequate vacuum pressure, it won't shift correctly or at all... thoughts?

[Bigstevex4]

Pull it down in 1st manually shift 2nd then 3rd or Drive id say your not getting out 2nd

[81GMCSierra1500]

If I have the chance to take it out tonight and drive it, I will do the manual shift test, to see what happens

[Joesjunk]

With a 350 turbo and 3:08 gears you should be able to cruise on the highway no problem. Like the others have said, something's not right. Either your in 2nd, or you don't have a 3:08 rear end.

[81GMCSierra1500]

Originally Posted by Joesjunk

With a 350 turbo and 3:08 gears you should be able to cruise on the highway no problem. Like the others have said, something's not right. Either your in 2nd, or you don't have a 3:08 rear end.

10-4. I'll get an update posted here. I've had some troubles with the vacuum line in the past. I had an episode where it would barely shift from first to second, and bang into 3rd, all because of a leaky rubber mount on the main vacuum line. I'll give it a check and see what it looks like. I'll update as soon as any news is discovered.

[81GMCSierra1500]

This just in! Good news. After much sitting in the dead quiet and eliminating possibilities, I decided to check the main vacuum line. The line to the modulator had partially slipped loose on both ends, and was leaking air out of both ends... A little gentle bending and fiddling, and she's tight as a drum. Went for a good 20km test drive, and the RPM's are at least 1000 lower at cruising around 100km/h. Very good news... Seems much more reasonable as a transition from 2.73ish to 3.08. Thank you all for the help, I find this forum to be an invaluable tool for looking into problems, without the "doctor" having to charge $100 just to look at it... Thanks guys!

[Chaplain]

Thumbs up

[SkinnyG]

And there was much rejoicing.

[tucsonjwt]

I like stories with happy endings.

[Super_Dave]

I had a similar problem on my '74's 350TH. It would seem to shift through all three gears but is was actually skipping a gear. I could manually shift it through all three gears but when in drive it just wouldn't do it. What I ended up with was the throttle linkage snap ring was not seated fully in the throttle cable bracket after doing my engine swap. Once we got that settled out, (a simple 1 minute fix) it has shifted great ever since. Not sure if yours has the same setup, but you are sure describing what I experienced.

[Zane M]

Glad to hear it was something simple.