No TCC lockup

[hear]

Helping TJ Buddy with his TCC lockup. This was a jeep we got for CHEAP because it didn't have reverse. I rebuilt it (I can't remember what was wrong with it now) and it's been running ok-ish. The TCC would never lock up, and he had some weird shifting issues. Turns out there were a few external things wrong.....and I stress that because we ain't about to blame the rebuilder here.

First, the bracket that holds the tv cable in place at the back of the trans was not remotely tight, so there was a ton of play there. I think that means that it wasn't always pulling on the valve along the right axis, so the throttle input didn't map cleanly to the TV input.

Second, the cable itself had slippage inside the piece that attaches to the throttle bracket. So now the throttle was not really 1:1 with the TV cable.

Third, when he replaced the TC a few weeks back, it would appear that the TV valve return spring did not take part in the reassembly, so even if all that other stuff was ok, he had a situation where if you let off the throttle, the throttle valve would not return to zero....making the trans think that you were still giving it gas. This might hydraulically be enough to not allow the TCC to lockup....but I'm not sure about that.

Fourth, and this should be ancillary, but the new solenoid I put in had a bare spot in the wire when we looked at the valve body. I had cause to look at the VB because it was popping a fuse. I had the same problem on my very first rebuild, and I was able to temporarily solve it by just flipping the plug over. It's the only plug on the whole jeep that can go either way, and if you orient it such that the bare ware is the switched ground, it shorting out against the trans case turns it into a nothing burger.


I tightened the bracket. He replaced the cable. He replaced the return spring. No more fuses blowing on the TCC. But still no lockup. What is very curious is that there is no P0740, which is the code for "no RPM drop from TCC lockup." It's not locking up so the RPM's aren't dropping, but since there is no code maybe it's because the PCM isn't telling it to lock up? This is where the trail ends for me. Hoping somebody has some insight. About the only thing I know to do next is wire in a test light to the solenoid circuit so I can see if it ever actually requests lockup, but I feel like the lack of P0740 already tells me it isn't.

 

[hear]

Well it gets worse. This thing has been rebuilt & running for 18 months, but he finally decided that the torque converter not locking up was worth fixing, so a few weeks ago we replaced the TC. On his way over here tonight (in the 100F+ heat) it started slipping and when he finally got out front of my house it was puking up a ton of ATF on the street. The vent hose (we did the vent relocation) had steam/smoke coming out of it. It sure seems like the leak is coming from inside the bellhousing, and I'm willing to bet he didn't lube up the seal & TC snout before he installed. 99% chance I reminded him before we got to that step, but I should've just done it and the we wouldn't wonder.

At any rate, he's got a heat problem & almost certainly a seal problem. The question is did he have a seal problem that spit out enough fluid to create a heat problem, or did he have a heat problem that created a seal problem? There isn't any hard evidence that the vent tube had any fluid spit up through it; the tube seemed dry near the top, but there was ATF all over the starter. Driving 60 can cause leaks to blow everywhere so there's no telling.

This rig is supposed go on our overlanding trip next week so we're under the gun to resolve it. He doesn't run a temp gauge, but I did point my laser thermometer at the pan and it was 250F after sitting for 10 minutes. I don't know enough about where heat generates to know if I should expect it to cool down immediately or if the lack of circulation should actually cause it to initially get hotter at the pan. Meanwhile its getting towed back to his house and I expect a late night scramble to drop it & replace the seal. Just what I was hoping for.

 

[hear]

Trans dropped, there is a trail of tears from the bottom of the seal, so I'm confident we found at least one problem.

I also forgot, Fifth, he had a cooler line "come off" a few weeks back too. It looked like the quick release broke, but maybe it was blown off due to massive pressure/heat? The thing had been driven plenty, so I can't imagine what would have happened to suddenly generate enough heat to cause a problem. But then again, this summer has been MUCH hotter than last summer, and it hasn't been driven that much during the hottest months. And the cooler lines were replaced at the same time as the new TC went in, so there haven't been any miles on them.

So maybe those new cooler lines aren't actually flowing properly? I'm gonna make him disconnect the hot line from the radiator to ensure we're getting good flow, that seems like a likely reason for a sudden increase in heat.

 

[hear]

Since we all love pics. That’s more hemorrhaging than he ever seen from a pump seal but it’s pretty obvious the cause of *this* problem.

What I don’t know is the root cause.

 

[hear]

The square looking pin on the lower left is the kickdown band apply lever pivot. It's one of those things that could easily be the source of a leak but never is. It's not held in by anything other than 2 little o-rings that hold it in snug. The next time I see fluid weeping from there will the the first time. I guess because they're lubed up on the way in and never actually move once in place and not exposed to hot fluid they tend to not break down. IDK, one of life's mysteries I guess.

 

[hear]

Not that anybody cares, but we've got a real mystery on our hands now.

He replaced the pump seal, that appears to have stopped the leak. It was probably advisable to replace the pump bushing too, but that was more than he was gonna do on his own and I couldnt' get out there to help. This might be important later.

Test drive last night, he lets it idle for 20 mins (in park, because he doesn't believe me that N & P use different fluid circuits) and then drove off. Was ok for ~20 mins but then basically fell out of D, and no amount of moving the shifter could restore power. He waited on the side of the road for maybe 20 mins, and was able to limp it to a better spot (not very far at all) but it was slipping hard during that little drive. It acts like either the TC is starved for fluid or there is insufficient pressure to apply the forward clutches. There is also a rattle at the front that sounds like a loose inspection plate, but there are no coincidences in this world.

Then we jacked with it for 90 minutes or so, and at various points along the way we ran it through the gears and you could feel the torque being applied in R & D. Eventually he put it back out on the road. Right out of the gate, it had all the power in the world, no slipping. So the clutches are not spent. And the fluid has been clean every time we've had to look at it. But 30 seconds into that drive it all happened again. No power, changing gears changes nothing.

Possible causes?

• when the cooler line blew, it got debris and now it doesn't flow. Eventually starves the pump?
  • would explain the heat problem we had on Sunday
  • Fluid level at the time of failure was fine
  • We tested flow on the pressure side and then also the return side. All good.
• Deep pan was also installed
  • the spacer behind the filter is there
  • fluid level is fine
  • and we see flow from the cooler lines
  • it drove for 20 minutes fine, if it wasn't able to pull from the sump it would've happened sooner
• New torque converter
  • it has been in for 2 failed drives now, the first one was the low fluid/overheat event from post #2
  • low fluid/heat could have damaged the pump bushing, no way to know w/o removing the pump
  • Maybe the new TC just sucks? Hardest thing to prove without just putting another one in there.
    • Among the next moves, I want him to put the old one back on
    • He replaced it because the old one wasn't locking up...likely was unrelated
• Torn up pump bushing
  • this is allowing some chatter there
  • somehow causing pressure to bleed off
  • Need to run a pressure test to see what the line pressure does during a failure
• Valve body issue
  • We took a VB out of one of my cores and threw it into his jeep. No obvious change, but my VB wasn't known to be good either.
  • But it would have needed to be bad in basically the same way
• Gunked up filter theory
  • ChatGPT came up with this
    • Fluid has crap in it. At idle the fluid demand is low. Under load the fluid demand is higher and it sucks up crap from the pan and/or the filter is clogged so it cant deliver enough fluid. Eventually there is not enough pressure to hold the clutches.
    • When things settle back down it works ok again
    • counter evidence: the pan isn't full of crap, and just letting it sit at idle for a while should allow it to go back into gear but I'm not sure we've seen that happen.

Just thinking out loud here. Feel free to play along at home.

 

[hosejockey61]

Let us know when we can start blaming the rebuilder!!

Seriously, that sucks. Especially before a trip. I wish I had something of value to add.

 

[hear]

Let us know when we can start blaming the rebuilder!!

Seriously, that sucks. Especially before a trip. I wish I had something of value to add.

Oh i'm taking it in the shorts in our group chat, don't you worry.

I have a few troubleshooting steps but it's gonna wait until after we get back. We leave on the 23rd, return on 27th. Looks like one of our friends is going to loan him his JKU (!!!) that he used to wheel until he got a new one to wheel. Or our Sami friend will bring one of his 40+ samis or trackers. Either way, he's covered so the trip is no longer a concern.

 

[hosejockey61]

Oh i'm taking it in the shorts in our group chat, don't you worry.

I have a few troubleshooting steps but it's gonna wait until after we get back. We leave on the 23rd, return on 27th. Looks like one of our friends is going to loan him his JKU (!!!) that he used to wheel until he got a new one to wheel. Or our Sami friend will bring one of his 40+ samis or trackers. Either way, he's covered so the trip is no longer a concern.

I just picked up another 32rh from the junkyard ($120) as a spare. Hell, I can get my money back just selling the dipstick and tube. As much time as you guys are putting into that thing, if you have the option of pulling one for cheap I would go that route.

 

[Rickyd]

Doesn't running a lockup trans without it at highway speeds create more heat than it can deal with?

Are there seals in the pump that can get cooked?

Lockup seems easy to figure out. Voltmeter to the actuating wires at speed. Is ground from pcm applied? Is power to the solenoid?

 

[hear]

Lockup is now the least of his problems. But yes, it can add heat. Not for nothing, I ran mine for a long time with some bad wiring so the TC would never lock up. It's not the end of the world, especially since I know the driving habits of the owner.

@hosejockey61 I have several cores here, all need rebuilt. I even have the rebuild kits on hand, I really only lack motivation. The challenge is that just swapping a new one in doesn't give us an RCA, and if I rebuild it again can I say with certainty that I fixed it? I mean, I would sure expect that would fix it but that's not giving scientfic method. Of course scientific method involves a whole lot of drop trans change one variable, re-install trans & test. I would figure I have at best 2 more shots at that. And I had better be getting that new trans prepped in the meanwhile.

That also reminds me, I got a core over the winter from a guy in OK but I forgot to get the dipstick. Talked to the guy, he had it waiting for me next time I came through. Well next time was a failure because I was trying to beat OK big weather and I couldn't get to his property because of a train. Several months went by but i'm still in touch with the guy (have bought lots of parts from him). Last month we connect, except on my way there he tells me he can't find it. That tube alone is like $200 on ebay motors.

 

[Mike_H]

Go back to the old TC. Most of your problems started when that was replaced. Not an easy elimination, but that is the first thing that changed to start the cascade of bad.

 

[hear]

Go back to the old TC. Most of your problems started when that was replaced. Not an easy elimination, but that is the first thing that changed to start the cascade of bad.

I tend to agree. The lack of any lockup codes could easily be attributed to some other CELs that apparently can block the lockup request. There's no hard evidence that anything inside the trans is blown or burned up. It CAN generate & hold pressure, something is causing it not to after a time.