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That's the part that confuses me. If it feels like it is shifting twice, how could you really not be in 3rd? If the torque converter is slipping like crazy, or the transmission is otherwise faulty, I think we could identify that with a video of you pointing a camera at the speedo and tach and doing some driving under different throttle situations.
-Take off from a stop at 1/4 throttle, again at 1/2, and again at full throttle.
-Find a cruising speed in 3rd gear where the RPMs are around 2,000 rpm. Give 1/2 throttle. Do it again but this time give full throttle.
-Find a cruising speed in 1st gear where the RPM are around 3,500rpm, with the shifter manually placed in 1st (use 2nd if you have to). Left off the gas to decel, then give 1/2 throttle. Do the same thing but give full throttle.
Now if it were me, I would be able to tell the difference between a high stall/slipping torque converter and a standard one almost right away when driving. All of what I listed above may be overkill, but if you posted video of all that, those of us following this subject would be able to really tell whats going on.
Last edited by AboveTheLogic; 09-03-2016 at 04:14 PM.
St. Jude Donor '13-'14-'15, '17-'18-'19-'20-'21-'22
How sure are you that the speedometer is correct? It could have the wrong gear in the transmission, giving faulty readings. Can you have a friend with a newer car drive beside you on the highway at 60 mph, you pace with him and see the reading?
Are you running some weird size tire? Changing tire size without changing the speedometer gear will give you inaccurate speed readings also.
I doubt either of these things alone would give the kind of variances you report. But if you had the wrong tire size in one direction, and the wrong gear in the other, you could get some pretty whacky speed readings.
Just something I would check before I went and pulled a transmission.
The speedometer's had a wheezy leak since I got the car, so I've always tested it with GPS. Excellent accuracy, confirmed with two other, modern cars.
My worry now is that it's got a foreign transmission in it, or some such. Tomorrow's Sunday, which means clear roads, which is perfect for taking video in the car. I'll go ahead and perform those checks you've suggested, and post the results as soon as I can.
Awesome thank you, I'm very interested in seeing just how it is acting. Pictures of the transmission from under the car and from the under the hood would be great too. Looking forward to seeing what you have to share. I really want to know what it is!
Awesome thank you, I'm very interested in seeing just how it is acting. Pictures of the transmission from under the car and from the under the hood would be great too. Looking forward to seeing what you have to share. I really want to know what it is!
You and me both. I was even looking forward to losing a thousand bucks replacing the differential, because at least I'd have known what the issue was. Problems you can't identify -- uncertainty -- are the worst.
I don't know if you've read the entire thread, but I mentioned that the guy who sold me the car rebuilt it from crates and boxes, replacing a few mechanical components as he saw fit during the process. I'm now leaning towards the thus-far-unconfirmed theory that it's a different transmission he decided to go with because it was cheap, or something, when the original THM350 wouldn't work.
You need to look at the transmission data plate (on side) to get model, S/N, and any other info you can. The original trans may have been replaced.
It sure sounds like your torque converter has problems.
Will the plate be visible if I climb underneath the car, or does that inspection require the removal of the transmission?
I'll take a look and report back. Thanks.
could it be torque converter locking up in second gear, making it feel like a 2-3 shift?
Not that I have any real clue about this, but if what you're suggesting is possible, it might explain why my second-to-third shift feels so much softer than the first-to-second shift.
When the torque converter isn't locked up, when you go from approx 1/4 throttle to approx 1/2 throttle, it should feel like giving throttle with a manual transmission as opposed to the RPMs climbing and the vehicle speed catch up to the increase in RPMs. Similar, when letting off the throttle, the RPMs shouldn't drop much immediately, because it is locked up.
I don't know how the TH350 lockup works and in what years it was made available, but if it is electronic and you unplug whatever makes the lockup work, you may be able to turn off the lock up feature and that might help you determine whats going on.
I only base that on my experience with my old '88 Jeep Cherokee that, when the TCU was unplugged, would never lock up and would only shift manually among 1st, 3rd, and 4th gears. That was a learning experience.
His Trans has no lock up and if it did it would be set to lock up only in 3rd gear at a specific vacuum ( it was controlled by a vac switch when introduced in 1980)
You should be able to see what the torque converter is doing by simply standing hard on the brakes and stabbing the gas until the car wants to move. If the rpm's jump way up then it could be the converter slipping.
How many rpm's did it drop when you were holding it steady and then manually shifted to drive?
Does neutral on the shifter actually select neutral so one click back puts it into a forward gear?
Check the vacuum line from the modulator. That could be preventing it from shifting properly because it sure sounds like it's staying in 2nd gear.
\just a thought - He's feeling it hit 3rd but lightly - granted. Is he missing the downshift to 2nd with a poorly adjusted kick-down cable ? Something he isn't feeling regarding 3-2 ?
TV pressure ?
I didn't catch if it was a TH350 or TH400 but food for thought....
09-03-2016, 04:13 PM
