3 speed Auto stuck in low
Apologize for being off subject ??, but about 10 years ago, my son bought a 67 Firebird with a hacked up chevy 350 + a 3 speed automatic (probably chevy TH350??). Shortly afterwards we replaced the engine with a new chevy crate motor keeping the same transmission. It does not get driven that much but when it is it just performs great, lots of power etc. Last week he attempted to take it for a drive and it would not shift out of low gear. Neutral and reverse are "normal" with some problems. You better have you foot on the brake when you shift it into reverse as it seems to be a hard shift. Manually shifting thru the gears does not bring it out of low. Fluid is clean and full, no smell, linkage is tight etc.
Questions before we either pull it or have it towed for service. I know this is skimpy info, but looking for some guesses as to what it might be.
1. Modulator valve (if it has one)?
2. Gummed up, need a drain/flush
3. TC, valve body or plugged filter if it has one