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.jpeg View attachment IMG_9604.jpeg View attachment IMG_9603.jpeg
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
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
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
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.
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?
Faulty casting?
I doubt it 1300 hours on your rebuild and how many hours on tractor
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
now I'm curious what happend to torque last time? Was it overheating on gauge? was there any chunks?
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.
I was just thinking if there was chunks it could of been stuck some where and causing a restricion
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
We used to always shoot pigs thru the lines after a failure
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.
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.
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.
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
Just curious what the drain test procedure/spec is. I am having a similar issue
What model of machine are you dealing with.? There isn’t really a spec per se but someone will at least be able to give you an idea.
D6T. KJL01024
So here's my swing at it. As I said earlier there is no spec that I'm aware of. You'll need a few bodies to do this test. Two as a minimum but an extra one ot two probably wouldn't hurt. Whoever is under the machine during the test needs to be well aware that the machine could potentially move. 1. Run the machine and warm up both the engine & transmission oil to normal operating temperature. Stop the engine. 2. Remove the plug from the bottom of the converter housing and drain all the accumulated oil from it. Leave the drain plug out. 3. Place an empty bucket under the converter. Make a mark in it that approximates to around 8-10 quarts. 4. Start the engine and immediately shift the transmission into 3rd speed. 5. Stall the converter against the brakes with the governor control at the max setting. 6. Measure the time taken for the measured amount of oil from Step 3 to dump into the bucket. Shift to neutral, shut down, and replace the drain plug.
What an easy way to do a live convertor test with tangible results. Hard to argue with what is in the pail. So does Cat have a spec., for how many quarts in 30 seconds or 1 minute. Thanks for sharing. Simon C
It's all anecdotal handed down through the ranks over the years AFAIK. There is no spec and it all depends on how big the converter is. The leakage on a D6 converter would be expected to be far less than that on a D11. Another thing to look at is the size of the oil stream falling out of the drain plug hole. if it looks as though the oil is "backing up" in the converter housing it's leaking too much internally.
Its kind of what I thought as when I worked at Finning in McMurray on D11N,R they are a whole lot more torque than a D6,7. If a heavy stream probably has some heavy wear inside. Easy enough to compare one from another if you have 2 machines. Thanks Simon C
The part with the crack? What is the material, and wall thickness? Its more like a high stress point is the reason.
Nige your test/steps in post 23 jogged my memory I had seen a video of a guy doing the bucket test (on old D8)…the difference is it appeared he was by himself, which meant he had to do the test based on time (1 minute at stall) to then see what he had in the bucket. I suspect your test is smarter since the machine won’t lose as much oil given the observer can wave off the test once the bucket is half full… If you start at the 26-27 minute mark he shows the test. Certainly a quick way to fill a 5-gallon bucket!!!
She should have an apron on and holding a pan of cookies.