TH350 problems galore

[Joe-NC]

I thought everything was fine. My truck drove like it should, etc. I just wanted the leaky rear main seal replaced. My mechanic showed me the flex plate and it was cracked all the way around the shaft bolts. It was so bad you could take a hammer and knock out the center. The transmission support was so worn out it may as well have not been there at all.

1. Do you guys think that was the most likely cause of the cracked flex plate?

He said the torque converter was red hot when he brought it in and after he removed it I could hear loose parts rattling when I shook it. He replaced it with a torque converter from a 400 saying it would give me a little more kick. Now I have a new torque converter and flex plate, everything's put back, and it won't budge. He's worried about the transmission now. Filter and fluid have already been checked. He's taking it back off to check the pump.

Engine is a 305 (one piece rear main seal) with a TH350 transmission.

2. What do you think about the 400 torque converter with this setup?
3. What do you think about the transmission deciding to screw up the day I took it to his shop vs. him doing something wrong?

[zieg85]

I maybe wrong however I thought a torque converter from a TH400 would not properly mate up with a TH350

[beastie_3]

If the torque converter was red hot, I would flush and replace the fluid as well.

Im not sure about swapping the torque converter, either.

[Psycho71]

I'd take my truck to another shop, one I could trust or get good referrences to, and have them tear down the th350 and rebuild it from the torque converter to the output shaft. Do it now while there is, hopefully, no major parts damaged, and it shouldn't cost you much money. I just had a th400 rebuilt for 450, that's with a new heavy duty converter and raybestos friction. Granted, I r&r'd it myself, but the 350's and 400's don't cost much to rebuild.

As for the converters swapping out, I do believe that most 350 and 400 converters are interchangeable.Here's an example http://www.jegs.com/i/B-M/130/20412/10002/-1?parentProductId=748034#moreDetails . Just two different bolt patterns at the flexplate. That's why most flex plates have the two separate bolt patterns. If I am correct on this, and someone will correct me if I'm not, it wouldn't make a difference, as the mechanic you used suggested, which converter you ran in which transmission. They'd both react the same, all other things being equal. That, and the fact you took in a tranny that was working and got one back that doesn't, is why I'd find someone else to work on it from now on.

[VileZambonie]

First off who shakes a torque converter and says it's bad, then puts a used one from a completely different trans in there? Time for a new mechanic.

A cracked flexplate can happen for many reasons and just so you know torque converters gets hot. Maybe he broke the pump when he installed the converter. Do you have a th350 or a th350c?

[Joe-NC]

First off who shakes a torque converter and says it's bad, then puts a used one from a completely different trans in there? Time for a new mechanic.

Sorry, I didn't clarify better. He used a new 400 torque converter. And I'm trying to learn ...if you shake a torque converter and hear loose parts inside, isn't that a pretty bad sign?

A cracked flexplate can happen for many reasons and just so you know torque converters gets hot. Maybe he broke the pump when he installed the converter. Do you have a th350 or a th350c?

He said my old converter was getting too hot (hotter than normal). Turns out I have a th350c after all, so that's why the new torque converter didn't work. He didn't catch that it was a th350c and felt bad about it. He said he's done a lot with other trannys but has only seen a few th350c's.

The guy before me didn't install a kickdown cable and just filled the hole with silicone caulk. Since he replaced the engine with this 305 with no electronic vacuum switch on the carb, he also just left the lockup switch unplugged. So do you think running it with a busted trans mount, no lockup switch, and no kickdown cable is probably why the flexplate cracked and the torque converter went bad?

I'm assuming I'll have to have some type of lockup switch kit, because running it unplugged is not good, right? I'll save up for a 700R4 or something, but for now I'm stuck with what I've got.

[VileZambonie]

Well that explains it... The TH350C has a lock up piston in the converter as well and will be hotter especially if the lock up is not hooked up. Is the plug there to connect it? Have him put the correct converter back in and hook up the detent cable as well. Once everything is hooked up correctly it will probably solve all of your problems. Oh and no, shaking the converter is not an acceptable means of condemning a torque converter.

[Joe-NC]

Yes, I'm getting a new detent cable and the correct converter. Hope that will solve everything. And yes the plug is there for the lockup switch. I'm just trying to decide if I can wire it myself without having to shell out $150+ for a kit.

If it doesn't lock up because the switch is unplugged, seems like it should operate just like a regular th350 ...but I guess transmissions are not that simple.

[VileZambonie]

This may sound like a dumb question but did you plug it in and see if the converter locks?

[Joe-NC]

Unfortunately there is nothing to plug in. Apparently my truck, engine, and transmission all met each other for the first time just before I bought it. As far as I can tell the carb nor the truck has any of the wiring needed for the lockup converter.

Also, it turns out the previous owner cut off the end of the detent cable so short inside the transmission, there's nothing to hook the new cable to.

At least its drive-able right now. Hopefully the new converter will hold out until I can get everything hooked up right.