chevygod Posted February 17, 2007 Share Posted February 17, 2007 Hi Gang, Need TH350 help. I have 350C (lockup converter) in my 84 Monte Carlo, trans has 180k miles and is untouched. Trans will not grab second, either upshifting or downshifting automatically or manually. Was fine until shortly after having it smogged on a roller dyno. Fluid is at proper level and smells fine, TV is adjusted correctly, and modulator lines look good (no leaks)and modulator doesn't appear to be leaking internally (no white smoke from exhaust. I am going to swap in a different modulator, to see if that helps. Any other thoughts on things to check, or am I at the service life (long one too!) of the trans? I will rebuild/replace if needed, but don't want to spend the time or money right now if I can avoid it. Thank you for any input, Tom Quote Link to comment Share on other sites More sharing options...
wallaby Posted February 17, 2007 Share Posted February 17, 2007 I'm not any expert, but it sounds as if you might have a band that has stopped working. Either the band itself, or the actuator. I think the gears in a TH350 are controlled by bands grabbing the drum inside the trans. When in 1st or 2nd, bands are keeping the drum from turning, and in high gear the bands are released. Then again, I could be totally wrong. That's the problem when you want to be helpful, but have no idea what you are talking about. Quote Link to comment Share on other sites More sharing options...
kc8oye Posted February 17, 2007 Share Posted February 17, 2007 "won't grab second" do you mean it skips second and straight to third? or permantly stuck in 1st gear? if it won't come out of first, I'd say your vacuum modulator has failed. pull it out.. put a vaccum pump on it. pull down to about 15in-hg.. and see if it will hold it. if not.. a new one is about $11 i'd also take the pan off and make sure the kick-down cable isn't jammed in the full-pull position. if the fluid isn't burnt/discolored, I doubt it's anything major. Quote Link to comment Share on other sites More sharing options...
Mike 57 Posted February 18, 2007 Share Posted February 18, 2007 It could be an issue with the intermediate sprag it it holds the second gear planetary. Thats not good at all and it will not show like burnt clutches or bands. Quote Link to comment Share on other sites More sharing options...
chevygod Posted February 18, 2007 Author Share Posted February 18, 2007 Thank you for the replies. I did not have time to check the modulator today, I must get to that tomorrow. The trans starts out fine in first, and will hold it to redline even with light throttle if I don't let up on the pedal before shifting straight to third. When I manually upshift the trans it does the same thing, 1st straight to 3rd, with nothing while I shift into 2nd. Downshift from third into second and the trans will free wheel until I bring the revs up enough to engage everything and push the car. Pop it into first and it will lock the wheels (I know, that's bad) and go to first. Except for this, the dang thing runs fine. As I said, I will mess with the modulator tomorrow, and report back. But I think it's time for a new trans. But that is a subject for a new topic. Thanks again, Tom Quote Link to comment Share on other sites More sharing options...
Kevin Wiles Posted February 18, 2007 Share Posted February 18, 2007 My TH350 has also become a powerglide: My experience from the 2006 eastern meet: "Rewind to Thursday night. Checking all fluids readying my car for the 3-1/2 hour trip to the Eastern Meet in Bristol. Transmission fluid was nice and red. Fast Forward two days, Saturday night. Now the transmission Fluid resembles the last few drops of your Yoo-Hoo chocolate milk that you forgot to shake up. Oh, and one other little thing THERE ARE CHUNKS OF METAL IN YOUR YOO-HOO beverage. This was the case this weekend for me. 2nd gear is shot. The good news is I now have a rare powerglide 2 spd monte. I tell ya, it shifts from 1st to 3rd just as pretty as you please. It gave no real trouble really. A non-car type wouldn't even know something is wrong. I wonder how long a cheapskate chisler can make this last?" Update, Feb 17, 2007 its still going strong in its new life as a powerglide!!!!! Quote Link to comment Share on other sites More sharing options...
kc8oye Posted February 18, 2007 Share Posted February 18, 2007 ick.. that sounds like a sprag clutch has gone.. that's not good. but id' have to bust out the TH350 book to be sure.. (I'll do that a bit later) Quote Link to comment Share on other sites More sharing options...
chevygod Posted February 19, 2007 Author Share Posted February 19, 2007 OK, findings of today. Changed out the modulator for a known good one, no difference in shifting, no second gear, just 1st to 3rd. Checked old modulator and it looks and operates off the car fine. I have the Ron Sessions TH350 Handbook, and the troubleshooting list has nothing on a missed 2nd gear, or constant 1 to 3 upshift. Any input from anyone is appreciated. Best, Tom Quote Link to comment Share on other sites More sharing options...
Mike 57 Posted February 25, 2007 Share Posted February 25, 2007 Check out the section on the sprag clutch. If it fails no second gear Quote Link to comment Share on other sites More sharing options...
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