transmission control module replacement

[taskunitbruiser]

My transmission doesn't shift well, and after eliminating everything else I can think of I feel the TCM is just garbage. I had the transmission rebuilt, new OEM throttle position sensor, and zero reason to believe the RPM sensor is bad. Aren't the only things not IN the transmission the TPS, rpm sensor, and TCM?

Should I buy a US Shift Quick 2 TCM or get a military replacement TCM? I have the box under the seat so I assume I could just disconnect the batteries and swap out the module inside the box, correct? This seems easier than rewiring things for the Quick 2 TCM and a more stock look (which I prefer), but it seems some TCM pulled from units are untested and sort of a gamble, particularly if without a return policy. Does anyone know how I can test mine?

 

[Retiredwarhorses]

Just what does “not shift well” mean?

 

[taskunitbruiser]

Just what does “not shift well” mean?

The torque converter stopped locking, the shift from 1st to 2nd makes "squoosh" noise, and the shift into third is very late. Fourth gear shifts smoothly right around 40mph. When I first got the truck the transmission was slipping and shifts were horrible, eventually just only would run in limp mode. Trans fluid was black, I posted it to the forums at the time. It would shift better with the TPS unplugged but the problem worsened overtime (sort of expected). The torque converter would never lock if TPS was unplugged. I had the transmission rebuilt but the 2nd and 3rd gear shifts were late and just felt wrong. TC did lock. Unplugged TPS and lost any ability to lock TC but the vehicle was drivable but still not fun because of 2nd and 3rd issues, esp 1st to 2nd.

Long story on TPS with ebay, etc, but eventually got a new one from either Mac or HPG (would have to check records). Dialed in the voltage and no limp mode issues until just recently. Unplugged versus new TPS about the same performance, TPS slightly sooner 3rd gear. Still no TC lock.

The rebuilder checked or changed any internal sensors and zero slipping or such issues after. New TPS dialed in. I just think a faulty TCM, probably combined with Middle East heat, armor, young Marines, and possibly pulling a trailer burned it up originally. The military auctioned it and made it my problem. I just want smooth normal shift patterns and TC to lock so I can go much faster and lower RPMs (which also saves me money! ha). When I had gotten TC to lock before I got it to 80mph, without it about 65mph is more like the limit. Not really sure how people are getting 65mph out of the TH400 though. I do have the ECV which has a lower gear ratio.

Seeing how unplugged TPS is (after rebuild) about as good as plugged in I just suspect the TCM is not calculating anything. Mike at Black Dog was surprised I could even drive around with TPS unplugged. Anyway I am going to trailer it over to BDC soon, but would like to get some insight here and maybe fix this issue myself. Seems like a TCM replacement would be simple, but US Shift controller would take some work. If anyone thinks something else could be the problem, knows how to test my TCM, or could recommend OEM TCM vs US Shift, I would really appreciate it.

 

[Mogman]

First you should never knowingly drive without TC lock, the torque converter makes a tremendous amount of heat when it is driven out of lock.
Second do you have a working trans light and if you do when was the last time you read the codes?

 

[taskunitbruiser]

First you should never knowingly drive without TC lock, the torque converter makes a tremendous amount of heat when it is driven out of lock.
Second do you have a working trans light and if you do when was the last time you read the codes?

I think I need a new TCM to get the TC to lock.

Yes the trans light works. In the past I would get codes about the ratios being low, high, unexpected. I will see if anything different this time.

 

[Retiredwarhorses]

The torque converter stopped locking, the shift from 1st to 2nd makes "squoosh" noise, and the shift into third is very late. Fourth gear shifts smoothly right around 40mph. When I first got the truck the transmission was slipping and shifts were horrible, eventually just only would run in limp mode. Trans fluid was black, I posted it to the forums at the time. It would shift better with the TPS unplugged but the problem worsened overtime (sort of expected). The torque converter would never lock if TPS was unplugged. I had the transmission rebuilt but the 2nd and 3rd gear shifts were late and just felt wrong. TC did lock. Unplugged TPS and lost any ability to lock TC but the vehicle was drivable but still not fun because of 2nd and 3rd issues, esp 1st to 2nd.

Long story on TPS with ebay, etc, but eventually got a new one from either Mac or HPG (would have to check records). Dialed in the voltage and no limp mode issues until just recently. Unplugged versus new TPS about the same performance, TPS slightly sooner 3rd gear. Still no TC lock.

The rebuilder checked or changed any internal sensors and zero slipping or such issues after. New TPS dialed in. I just think a faulty TCM, probably combined with Middle East heat, armor, young Marines, and possibly pulling a trailer burned it up originally. The military auctioned it and made it my problem. I just want smooth normal shift patterns and TC to lock so I can go much faster and lower RPMs (which also saves me money! ha). When I had gotten TC to lock before I got it to 80mph, without it about 65mph is more like the limit. Not really sure how people are getting 65mph out of the TH400 though. I do have the ECV which has a lower gear ratio.

Seeing how unplugged TPS is (after rebuild) about as good as plugged in I just suspect the TCM is not calculating anything. Mike at Black Dog was surprised I could even drive around with TPS unplugged. Anyway I am going to trailer it over to BDC soon, but would like to get some insight here and maybe fix this issue myself. Seems like a TCM replacement would be simple, but US Shift controller would take some work. If anyone thinks something else could be the problem, knows how to test my TCM, or could recommend OEM TCM vs US Shift, I would really appreciate it.

But of course you can drive without a TPS, but you will get funky issues, at my shop, we fix issues, we don’t bypass them…
last time I had this type of issue, the TPS was wired wrong near the fuel filter where it plugs in the harness, an hour with a schematic and a meter? I had it fixed as 2 of the wires were backwards when the reset facility spliced the connector back on for some reason.
Many times you will not get coeds on these trucks, but you still need to check for them to narrow it down.

 

[taskunitbruiser]

But of course you can drive without a TPS, but you will get funky issues, at my shop, we fix issues, we don’t bypass them…
last time I had this type of issue, the TPS was wired wrong near the fuel filter where it plugs in the harness, an hour with a schematic and a meter? I had it fixed as 2 of the wires were backwards when the reset facility spliced the connector back on for some reason.
Many times you will not get coeds on these trucks, but you still need to check for them to narrow it down.

I know I was getting the 5V ref, ground, and the variable 0.4-4.5V. Did the truck with the fuel filter harness wiring issue get these at the TPS plug end?

 

[Retiredwarhorses]

I think I need a new TCM to get the TC to lock.

Yes the trans light works. In the past I would get codes about the ratios being low, high, unexpected. I will see if anything different this time.

till you get the transmission shifting accordingly, the TCC is on the bottom of the list…these issues work themselves out many times when you fix major issues, TCC doesn’t happen till you are at about 40-45mph and off the accelerator, that’s a separate test, and 99% of the time the brake switch is the problem…best way to test is to short connection with a jumper while you are driving at lower speeds and watch the tachometer for the rpm spike when you remove the 12v.

 

[Retiredwarhorses]

I know I was getting the 5V ref, ground, and the variable 0.4-4.5V. Did the truck with the fuel filter harness wiring issue get these at the TPS plug end?

every TPS I install is just bolted on and set midway…generally in the same spot as the one I took off.
ive had the them just plugged in and laying on top of the pump and the truck shifts fine…

 

[Retiredwarhorses]

And what model truck do you have?

 

[taskunitbruiser]

And what model truck do you have?

M1151A1