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Discussion Starter #1
My TH350 doesn't upshift to 3rd when it gets hot. It shifts fine when running in cooler weather, but when it gets in the higher temps, it does not want to shift. Does anyone have idea what the issue could be? Please let me know.

Thanks!
John
 

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My TH350 doesn't upshift to 3rd when it gets hot. It shifts fine when running in cooler weather, but when it gets in the higher temps, it does not want to shift. Does anyone have idea what the issue could be? Please let me know.

Thanks!
John
Do you have reverse when hot?

Let us know and we will go from there.:thumbsup:

If the high/reverse clutch or high/reverse clutch hydralic circuit is going bad, both 3rd and reverse will have symptoms. You could be having a shift valve stick as the temp goes us. Your govenor could be sticking as the heat goes up, etc.

Let us know!
 

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Discussion Starter #3
Reverse works fine. Additional information is that I had the engine replaced with a 350 at 325 hp or so. The shop also replaced the torque converter with a "high stall" converter. I've had them check it out and of course it ran fine. But this issue has become a problem with the hotter weather or if I have to idle the car in gear for an extended amount of time. Example: idling through a drive through window for 10 minutes or so. Does this info help?

Thanks for the reply.
John
 

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WHere do you have your vacuum modulator connected? It needs to see vacuum right from the manifold not a "timed" source from the carb. Low vacuum at the tranny could keep it from shifting. And if you still have the TCS hooked up, it could be turning the vacuum off to the trans keeping it from shifting. Also check your detent cable- if it's too tight, it may cause the trans to think you're at WOT, and in a forced downshift mode.

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Would heat be a factor affecting these issues? In other words, would the car shift ok when cooler and if one of the issues listed in your post was linked to my car, would heat be a factor in the car not upshifting? Does this make sense?:huh: :huh:

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John
 

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About the only thing heat could affect, as I see it, would be the valves in the valve body. Possibly sticking when really hot. The detent cable may be hanging when hot too. But for that to cause your problems, it would be after a forced downshift. THe TCS has a thermostatic valve, plumbed thru a temp switch usually on the thermostat housing with 3 or 4 lines in and out. That senses both heat and 3rd gear, and then retards the spark for cleaner exhaust. If that is hooked up wrong and the vacuum for the modulator goes thru it it could cause poor vacuum signals to the trans. Past that, I'd have to go with a sticky valve in the trans. One other thing I just thought of. Between the valve body and trans case is a spacer plate. I've seen several spacer plates the check balls have worn grooves in and then won't seal properly, causing a bypass inside the trans. It's possible that may be a problem too.
 

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Would heat be a factor affecting these issues? In other words, would the car shift ok when cooler and if one of the issues listed in your post was linked to my car, would heat be a factor in the car not upshifting? Does this make sense?:huh: :huh:

Thanks,
John
Yes, heat can affect the performance of the clutches. Without doing the standard diagnostics, I will list some possible causes:

1: as the oil thins, "leaks" at sealing rings can increase to the point that the clutch can not stay engaged. If this is the case, the trans needs to be dissassembled and repaired. There will probably be clutch housing damage or sealing ring damage requiring repair parts.

2:The valve body is made of aluminum while the valves are made of steel. They expand and contract at different rates and can cause the shift valves to stick as temps go up. This usually involves removing the VB and buffing the valves and bores. I can also be caused by metal parts impregnated into the aluminum. If that is the case, a new/rebuilt VB is in order.

3:The rubber sealing rings are hard/old and can no longer seal with thinner oil because of the heat.

Those are the most common. TimAT may chime in here with more info as well. To really get a good feel as to what is going wrong, we need to do a pressure test. Cold and hot. It is a realativly simple test but requires a guage, hose and misc stuff.

Does this answer your question?

BTW, does your oil smell burnt?
What color is the oil?
 

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And how many miles does this tranny have on it? It could be as rjent is right in the fact that the seals are dead. A 350 is an easy and cheap build. Even using HP parts, under $125.
 

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Discussion Starter #9
Thanks for the info. I have to admit, I'm not very adept at all concerning transmissions. However, your information gives me a start when speaking to the performance shop that did the engine work and the torque converter. I don't recall having this issue before the engine was changed out and think maybe there could be an issue with how it's hooked up or maybe the valves are sticking.

Thanks again.
 
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