D6t torque convertor failure analysis

[rpm.miedema]

Hey everyone,
I was wondering if your guys minds could help me figure out some failure analysis on this cat d6t convertor (prefix djg) I had rebuilt this converter 1300 hrs ago with all cat parts no aftermarket. Before pulling this unit out I checked stall speed it was correct 1600rpm. Until the housing would flood and then stall would be lower say 1470 or so. Interesting this unit had low WOT speed, you could feel the housing was flooded (machine in n) park brake set. I originally leaned to scavenge issues because of the torque flooding at all times not just under heavy load. Pressure inlet and outlet were in spec no more than 130 when cold and 70 inlet when warm, 60 outlet. No aluminum or steel in torque screen. But failed torque drain test way more than a pail in under a minute. When machine turned off warm there was at least 40 litres in housing. So removed torque and found the housing had large crack. No signs of heat damage anywhere . No broken oil seals. I have to measure all the clearances in the morning. But typically when there is enough oil to flood the torque I find the damage fairly obvious. Just wondering if others have seen this. View attachment IMG_9601.jpegView attachment IMG_9604.jpegView attachment IMG_9603.jpeg

 

[pittsburgh cat man]

Looks like over pressure to me In my experance you only see the 130 max for a split second on a very cold start Also I think those are pretty impressive pressures with that big crack dumping oil into case

 

[rpm.miedema]

I agree on the pressures that’s why I originally assumed a scavenge issue for sure. My mind just can’t comprehend how say If the outlet or inlet relief stuck. The pressure to crack that case would take a lot wouldn’t it? I more thought bad transmission modulation or something causing shock load to the converter. But I could be way off , I just want a good theory to make my brain happy lol I will change inlet valve and pull outlet relief to check condition of spool and bore

 

[pittsburgh cat man]

I'm thinking it prob takes less pressure than you think to split the pot if they put a max pressure at 130 pound. the old 955s had a alum. pot back in the day test and adj book just said 130 inlet pressure people would shim the spring to get the 130 when if was warm and slplit the pot to be honest i saw very few of dozer style pots cracked but i learned long ago nothing is impossible Could have even started at a small crack at one or the bolt holes and grew over time and pressure cycles

 

[D6 Merv]

TC inlet relief valve is just that ! It is purely there to provide a safety valve in case of a blocked oil outlet passage from converter. That is why they say to bench test only.
Internal converter pressure is set by outlet relief valve which normally controls the internal working pressure.
If something goes wrong with that, or if it gets blocked or assembled incorrectly and outlet oil is blocked, from escaping from converter, that is when inlet relief valve comes into play to save converter.

 

[rpm.miedema]

TC inlet relief valve is just that ! It is purely there to provide a safety valve in case of a blocked oil outlet passage from converter. That is why they say to bench test only.
Internal converter pressure is set by outlet relief valve which normally controls the internal working pressure.
If something goes wrong with that, or if it gets blocked or assembled incorrectly and outlet oil is blocked, from escaping from converter, that is when inlet relief valve comes into play to save converter.

With the being said, wouldn’t I need two falures for this to occur? Blocked torque out let say a totally plugged cooler or stuck closed outlet valve. Then at the same time the inlet valve would have to be stuck closed and not relief pressure? Then the torque would receive main pressure.

 

[rpm.miedema]

also it not say the 300 psi cracking the case it’s the pressure/force generated by the TC with double the oil pressure causing that failure correct?

 

[.RC.]

Faulty casting?

 

[pittsburgh cat man]

I doubt it 1300 hours on your rebuild and how many hours on tractor

 

[rpm.miedema]

15000 hours on tractor,that housing was new cat oem I would have to look back on my notes I think it was changed because I didn’t like the amount of heat and colour change from the previous torque failure

 

[pittsburgh cat man]

now I'm curious what happend to torque last time? Was it overheating on gauge? was there any chunks?

 

[rpm.miedema]

Ya original failure was major overheat and they ran it for a long time I don’t think the torque outlet sensor was working correctly or they didn’t care about it lol major bearing wear and lots of internal wear. Pretty much every component was changed I think the shaft and yoke were okay. Replaced sensor and wiring for torque outlet, resealed and installed new torque inlet valve. I removed and had cooler cleaned and tested. Then I removed rad cores and cleaned because I think that was reason for the main heating problem . Usually is the root cause of all over heating issues on these d6t sized machine.

 

[pittsburgh cat man]

I was just thinking if there was chunks it could of been stuck some where and causing a restricion

 

[rpm.miedema]

That’s a very good point, how would a person try to prove or test that tho? Just pig the handful of powertrain lines? I think this machine has ports of cooler lines to check pressure drop

 

[pittsburgh cat man]

We used to always shoot pigs thru the lines after a failure

 

[rpm.miedema]

I resealed/new bearings/sealed this convertor, with a new housing. Resealed and inspected outlet relief(zero signs of damage in spool) changed inlet relief, removed and inspect trans pump and replaced there was signs of wear. Removed cooler had my rad shop clean and test. Pigged all lines .Everything appears normal and operates correctly. Good torque stall speed, temps drop fast after stall. Guess we will see what happens but I feel like I have done everything in my power to provide a successful repair. Also download the product report 3 counts for overheat . All within the same hour, 1 hour less than current hour meter. So I don’t think it was crack that developed I think it happen instantly. If that make sense. Thanks for everyone help on this! Sometimes as individual contractor you feel alone but having knowledgeable people to bounce ideas off is much appreciated.

 

[Nige]

Removed cooler had my rad shop clean and test.

I think if it was me, after a failure as expensive as the one you had, I would be throwing a new cooler at it. As a matter of policy if we were doing a converter or transmission we would install a new pump and cooler as insurance, certainly would with 15k smu on the tractor. YMMV.

Of course the big unknown in your case is that you have no information at all to go on regarding how the machine was behaving in the time frame leading up to it going bang.

 

[C5Land]

I resealed/new bearings/sealed this convertor, with a new housing. Resealed and inspected outlet relief(zero signs of damage in spool) changed inlet relief, removed and inspect trans pump and replaced there was signs of wear. Removed cooler had my rad shop clean and test. Pigged all lines .Everything appears normal and operates correctly. Good torque stall speed, temps drop fast after stall. Guess we will see what happens but I feel like I have done everything in my power to provide a successful repair. Also download the product report 3 counts for overheat . All within the same hour, 1 hour less than current hour meter. So I don’t think it was crack that developed I think it happen instantly. If that make sense. Thanks for everyone help on this! Sometimes as individual contractor you feel alone but having knowledgeable people to bounce ideas off is much appreciated.

man I need some assistance here. I think you’re having the same issue I am and it has me torn between the TC and the Trans pump scavenge section being faulty.

Bit of a read but I will buy you a steak dinner if you invest the time.

Original issue started after we replaced the engine. Did not reseal or rebuild anything power train related. 6000 hours of the machine, D6T SN SLJ00295. Installed engine and after 100 hours or so of operation noticed it was making oil in the engine. Sampled to verify it was not fuel, all samples passed fine. Transmission was the only case losing oil. Went for the rear main. Pulled TC, installed rear main.

Bit of info to keep here. Upon pulling the TC to access the rear main, noticed the TC scavenge screen MIA. 100 percent sure we installed when swapping the engine.

Installed TC along with a new screen. Ran 5 hours and had oil coming out of the Trans breather. Would only get 1450 RPM when oil started puking, nevertheless, before the oil puke, or signs of a loss of power. Zero power loss.

Pulled back in shop and found TC had about 12 gallons of oil in the case. And guess what….. no TC scavenge screen. Gone. No signs anywhere. On top of that, when pulling the Transmission case fill cap, it had a lot of pressure. Equivalent to what you see on a hot hydraulic tank if you pull that cap.

So, here’s where I am at. I have a spare TC. But like I think I read, your questions were the same as mine. If the scavenge pump is not scavenging at a fast enough rate, and the fact that it has eaten two suction screens, Indont know if I have a scavenge pump issue or a TC issue. The outlet of the scavenge pump goes to the case and lubes the diff steer gears. That screen went somewhere. And there is absolutely no sign of any metal I any of the transmission screens or filter. If the outlet of the scavenge was plugged, it wouldn’t remove the TC case oil fast enough. The original issue was that after 100 hours, the engine would overfill. Now, the rear main is good and being that the scavenge section has eaten two screens, the TC begins puking after 4 to 5 hours of operation. Seems to me like the scavenge section was lessened further by the second screen, increasing the TC case fill time.

I did pull the suction line off of the bottom of the TC and cranked the engine. It did pull my hand like it was sucking fine. Just wondering if like a weak water pump, it will still pull oil but not fast enough.

At this point, and due to all pressures being in spec, I guess I will throw a TC and a Trans pump at it. There is no spec or pressure tap for the scavenge section. Additionally, I will pig the outlet tube that runs to the diff steer gears. Only litureature I can fine is that it lubes the diff steer by “spray” oil. So I am hoping that tube is clear and not restricting outlet flow. At which point if it were plugged, I would be pulling the trans in an effort to get to the outlet.

I just don’t like having to throw parts at something. Thanks in advance, scratching my head here.

 

[Simon C]

Where did those screens go and what could they cause for problems in the future. Possibly someone else will chime in with some worthy idea.
Simon C

 

[CRR]

But failed torque drain test way more than a pail in under a minute.

Just curious what the drain test procedure/spec is. I am having a similar issue