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D6T Torque Converter Problem

John C.

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Long story so have a cup of coffee and some time. I don't fully understand what is going on with this problem and would welcome any input.

I've got a customer with this machine Sn. JML0036. They changed the engine while leaving the torque converter hanging in the machine. They put the replacement engine in the machine got everything running and the converter would barely turn the drive shaft. Machine would go into gear and the drive shaft would lock up and there wasn't any torque applied and the machine wouldn't move. All the transmission pressures checked out as confirmed by the Cat dealer field mechanic who said something is wrong in the converter. They pulled the converter out, tore it down, didn't find anything obvious, put it back together and in the machine with the same result. They checked for an exchange or even a new converter and were told that this particular converter has been discontinued and is no longer available.

They called me for some troubleshooting and opinion and just like before the pressures were there. The only odd thing was torque converter outlet pressure was about the same as torque converter inlet pressure plus the output yoke seal was leaking. I'm figuring that the drive line still should turn but it was just limping along. They tore the converter back out of the machine and I came in to help dismantle the thing again. The output shaft has two seals that seal a land where oil is fed from the torque converter case into output shaft and down its length and up into the stator housing and into the cavities of the impeller and turbine. One of those seals was damaged, possibly when the shaft was installed. We didn't see much of anything else wrong.

I did see one odd thing to me in that the stator is different than any I've worked on in the past. We went into SIS to find that this particular converter has a free floating stator and a lock up clutch. The lock up clutch isn't part of the problem in that it locks the turbine to the output only under certain conditions. On the stator there is basically a sprague clutch inside that will lock it to a hub when the turbine has a load against it. When I checked it as we pulled the converter apart the stator would turn either way on the hub. I'm perplexed by this. Anyway it was torn apart, inspected and reassembled by the instruction in SIS. When done it worked the way the book said it should. I think it could be a problem if oil wasn't directed back to the impeller but think it all should have turned the impeller and drive shaft anyway.

The other perplexing issue is that the turbine connects outside on the flywheel side to a ring gear with a planetary inside it. The hub of the planetary carrier is connected to the output shaft. If you spin the output shaft by hand, the planetary carrier just spins in the ring gear. If you spin the ring gear, I can feel the turbine turning inside the converter housing, but the planet carrier doesn't turn, just the planet gears do. Apparently the turbine is supposed to spin the ring gear which spins the planet carrier and apparently there is supposed to be enough force to make those planetary gears not spin around inside the ring gear? There is no sun gear on the output shaft to positively connect that ring gear to the output shaft? We put the whole thing back together by the book and installed it in the machine yesterday.

They are finishing the wiring and cab stuff and reinstalled fluids today and we are going to fire it up on Monday. I hope it works but am pretty nervous because I don't fully understand all that is going on in this thing.
 

Nige

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When I checked it as we pulled the converter apart the stator would turn either way on the hub. I'm perplexed by this.
The one-way clutch was foobarbed. That's the usual mode of failure - the spring/roller mechanism fails and the stator will not lock in place against the force of the oil flow through the converter when required to do so. It works exactly the same as a ratchet wrench. Locked in one direction of rotation. Click, click click, in the other.

It's just the same as a truck with an LUC. When the LUC is engaged the spring/roller ratchet mechanism permits the stator to "freewheel" so that it turns with the converter. In torque converter drive the mechanism has to lock the stator in place so that it directs oil at the correct angles between the impeller and the turbine.

I've never come across a freewheel stator in a Cat tractor before, but in a wheel loader the failure of the FWS was usually accompanied by first reports of a lack of engine power (in fact nothing to do with the engine) or in an off-highway truck often the complaint would be a failure of the transmission to upshift correctly.

Question: When the converter was rebuilt with new parts did the one-way stator clutch work correctly.?

It's a bit late now but I'd have been looking very closely at the condition of the shaft surface where those two rotating seals you mentioned that were found damaged.
Also the lack of a difference between converter inlet pressure and outlet pressure is strange. I'd be interested to see what the pressures are when it's tested after having been rebuilt.
 

John C.

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Mark250; Your illustration shows a sun gear on that torque divider. I mentioned that on the machine we are working on that there is no sun gear. I checked the parts book first thing because of that and it does not show a sun gear for that planetary or a place to even mount one in there. I checked both the planetary page and the flywheel page and neither showed a sun gear. Perhaps I'm missing something here and maybe someone could check SIS under the serial number and see if we are missing something on that line.

Nice; When I pulled the stator out and unit would turn on the hub either way. I pulled it apart to make sure the springs were in the right orientation and that the hub and cam rings didn't show any wear and that the rollers were in good condition. I reassemble it and it checked out proper in a manual test. I was also thinking that even if that did freewheel that the drive line should still turn. The case would still be flooded and oil would be pushed by the impeller into the turbine. I think the result would be low power and probably overheating.
 

John C.

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That piece didn't show in the illustrations that I've seen in SIS. Do you have an illustration number or something I can go off of in the morning? What is the description for the circled item and the rings on either side?
 

John C.

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Super! That solves the whole mess I think.

I'll keep my eyes open.

Thanks!!!
 

Mobiltech

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I was going to say that I had a customer install a torque but they left the sungear out. It did the same thing as you describe. Somebody has the sungear laying under their bench. It would have come out with the engine. It is snapringed into the flywheel.
 

John C.

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It was swapped with an exchange engine so I think the gear is gone. I’ll know more tomorrow morning. Thank you all for the help!!
 

Nige

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I sent you some more info.
Need the S/N of the replacement engine to check if the flywheel P/N is the same as the one from the engine that was removed. The toothed recess for the sun gear looks deeper, and I'd bet the flywheel on the replacement engine doesn't have a snap ring groove either.
 

Shimmy1

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Can I be the first one to ask why in the hell do these machines have to not only be so complicated, but why this missing gear wasn't being shown in whatever John was referring to?
 

John C.

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It is my understanding that the people who did the swap are not currently working for the owners of this machine. If you look close at the diagram that Nige posted you will see just a plate with no indication of a sun gear showing at all. I don't recall if I looked at it directly and didn't realize what it was or it just wasn't part of the diagram that I saw. I agree on the complexity.
 

Mobiltech

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Make sure there is a pilot bearing in the flywheel too the next time you have it apart. Would be sad to have a torque failure after all this.
 
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