My 79 GMC Sierra wont shift past 2nd,its a th350 and 305 engine.any ideas as to why?
- Thread starter lloyd b
- Start date
Molson02536
New member
It sounds like you may have a missed-adjusted throttle valve cable, or a vacuum modulator problem still. In most GM cars with the TH350 there is a stamped steel button on the cable where it clips into the bracket on the intake, hold this button in with your thumb and pull the cable back toward the firewall, this is the tightest setting. Now get in the Sierra and push on the gas pedal hard to the floor! You should hear a ratcheting sound. The cable is adjusted! If this doesn't help, recheck the vacuum line to the modulator for leaks. It should be connected to manifold vacuum.
TH350 class 101
TH350 are controlled by governor pressure, the governor is a centrifugal device that opens a spool valve, based on speed. The modulator & throttle valve are used to supplement the governor by "sensing" engine load and throttle angle. This is what makes the trans shift later, or down shift when you floor it.
If you are getting normal 1-2 shifts, but no 2-3 shift, you may have a sticking governor, or a missed-adjusted manual valve,(the shifter cable). There should be a cover on the side of the trans you can take off & remove the governor. As you lift the weights on the governor, the spool valve should move freely through its entire travel & return when you let it go. If it's sticking, try cleaning it with brake cleaner.
These are just about all the "easy" things that can be checked before you bring it to the transmission shop. Hope this helps and keep us posted.
http://turbo350only.com/