I have a 1976 Chevy K20. It has in it a TH350. The issue I have is when accelerating it shifts 1st and 2nd. 3rd gear will shift only when decelerating. Is this a governor and vacuum modulator issue? Any advise is appreciated.

 

If it were vacuum modulator it probably wouldn't shift out of 1st until it was at an engine speed where the governor forced it to shift. A modulator is a cheap and quick solution and if that's not it you're not out much.

You can try pulling and cleaning the governor to make sure it's not gummed up or sticking. Past that could be a dozen things. We've got a couple of transmission guys here who might be able to help more than I can.

Trying to remember on Ks. All K20 are 4wd right? Know the 5 & 10 could go either way.

 

Does it have a good solid reverse? If so, it’s most likely valve body related. The direct clutch serves 2 purposes, obviously it’s the high gear clutch, it’s also the driving clutch for reverse. If reverse is good, most likely the frictions and seals in the drum are good.

Pull the pan. Hopefully there is little debris in the pan and stuck to the magnet. If there is a bunch of crud in the pan, it’s probably best to pull it out.

 

She has a solid reverse. Sounds like a rebuild coming my way. Thank you for sharing your knowledge. Much appreciated.

 

Those both looked good and where in working order. Probably time for a good rebuild. Thank you for the advice.

 

Let us know how things work out. Matt builds transmissions for a living so you can bank on his advice.

Besides, 1st and 2nd gen Blazers are damn cool even if they're not Oldsmobiles!😎