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CAT D6N transmission problem

Discussion in 'Dozers' started by ugis, Oct 5, 2021.

  1. ugis

    ugis Member

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    Hi, i'm new here and my english is as bad as my dozer technical condition right now. :)
    Dozer D6N LGP, serial DJY00951.

    So, all starded when i felt strange gear shifting- short break between, for example, 3 to 4 gear while moving in reverse. And i notice quiet noise from transmission hydraulic pump- buzzing sound at full engine rpm.
    Then i turned down engine and started again and noise was gone and gears shifted smooth for 10 mins.
    Now dozer is not moving in first gear properly- when i switch forward, it moves a bit and stops immediately and then moves again. After a while of not moving in first gear it shows Serv Code 673.02 or sometimes 671.02.
    Other gears shift +/- normally.

    As i know those Serv Codes means problem with speed sensors. Is it possible that all this trouble is because sensor or wiring failure?
    What should i do next?
    Thanks in advance!
     
  2. Nige

    Nige Senior Member

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    You are correct that 673.02 & 671.02 are related to the tranmission output speed sensors. HOWEVER the speed sensor Diagnostic Codes could be the symptom of a different problem, especially when you say that they are only intermittent.

    The buzzing sound you heard could be transmission pump cavitation. Without hearing the noise it is impossible to tell but it is a possibility. This could be caused by either low transmission oil level or a partially blocked oil suction line between the transmission case and the pump inlet port. There is a screen in that line - see Step 3 below.

    I suggest that you should first do some basic checks: -
    1. Check for correct transmission oil level with the dozer on level ground, oil warm, engine idling, & transmission in neutral
    2. Transmission oil colour & smell. Is it dark and cloudy rather than being clear and bright? Does it smell burned?
    3. If the oil is dark or smells burned you should drain it. Change the transmission filter and cut open the old one to inspect for particles (there are plenty of "how to" videos on YouTube). Also you need to remove and inspect/clean the transmission magnetic suction screen for metallic & non-metallic particles. The location of the screen will be shown in your Operation & Maintenance manual.
    4. If you find particles in either the filter or the screen, please take photos & post them here.
    5. I would suggest that you don't refill the transmission with oil immediately. Depending on the findings of steps 2, 3, & 4 above it may have to be removed for repairs.
     
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  3. ugis

    ugis Member

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    i forgot to mention that i bought this dozer a couple month ago and changed all fluids and filters right after, included OEM transmission oil. Now i have worked about 50 hours.
    Oil level seems a bit above max level, oil looks clear.
    Old oil was fine- bright, yellowish color. Didnt check filter inside. I didnt know how many hours was that oil worked.

    I dont have proper operation manual yet. What is exact transmission oil change procedure?
    I consulted with the dealer about what to do, and he told that it is this simple- drain old oil, change filter, fill in new one. Is that really it?
    Where is transmission magnetic suction screen located?
    [​IMG]what is the purpose of these two screws?
    Screenshot_20211005-144331_Firefox.jpg
    [​IMG]
     
    Last edited: Oct 5, 2021
  4. kshansen

    kshansen Senior Member

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    the picture did not come through so no idea on that but see attached file for the magnetic filter:
     

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  5. kshansen

    kshansen Senior Member

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  6. Nige

    Nige Senior Member

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    You can download a pdf Operation & Maintenance manual from Cat for $49.
    Go to - https://catpublications.com/
    Click on the "Continue as Guest" option.
    Type in SEBU8124 in the box and click the Search button. The illustration below should appear. If you buy a pdf download you can have it available in 5 minutes or less. (for CD or paper versions you also have to factor in shipping time.)

    upload_2021-10-5_13-25-54.png
     
    Last edited: Oct 5, 2021
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  7. Nige

    Nige Senior Member

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    Regarding the suction screen it is just before the pump. See the attachment "Power Train oil lines". It is circled.
    There is also a suction screen in the torque converter housing. See the other attachment "converter housing".
     

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  8. Nige

    Nige Senior Member

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    Please confirm that you are checking the oil level with the machine warm, engine idling, and the transmission in neutral..?
     
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  9. Nige

    Nige Senior Member

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    Another thought. While you are removing the screen #11/12 you should make sure the hose #33 is in good condition and that the hose clamps #13 are tight. If those connections are loose or the hose is in bad condition it will pull air into the transmission pump.

    upload_2021-10-5_17-36-7.png
     
  10. ugis

    ugis Member

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    Now i double checked- transmission oil level is between min/max under conditions you mentioned.
    Buzzing sound is exactly the same as when hydraulic oil level is way too low.

    Tomorrow i'll check both suction screen.
     
  11. Nige

    Nige Senior Member

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    Please make sure to check that hose and the hose clips that I mentioned above while you are in the screen.
     
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  12. kshansen

    kshansen Senior Member

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    Yes air in oil going through a pump can make some strange noises and also is not good for the pump!
     
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  13. ugis

    ugis Member

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    while I'm preparing for the suction screen test. is it possible that this case affects the operation of the transmission so much?
     
  14. Nige

    Nige Senior Member

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    If the suction screen is partially blocked the transmission pump will be struggling to suck oil from the transmission case (which is effectively the oil pan). If there is anything in the suction side (e.g. a clamp, O-Ring, hose, etc) that is in the slightest way defective the pump will suck air in through that point rather than suck oil. That could be the cause of the pump cavitation noise you are hearing. If the pump is sucking any air at all the transmission will not function correctly.

    A suggestion of looking for suction air leaks - make a strong mixture of household dishwashing liquid & water, then put it in a hand-operated spray bottle like below. Spray the foam from the bottle on every joint in the suction lines while the engine is running. If you see the foam disappearing into the joint you have found your air leak.

    upload_2021-10-6_13-47-28.png


    There is a distinct possibility that you may find some sort of problem while you are looking at the screen. For example the O-rings #65 & 71 in the illustration above, or maybe the bent tube #20 or the O-rings that seal it. You really don't know what you might find until you remove the floor plates in the cab and start looking around. Before you start cleaning anything take a good look for oil leaks, because if oil is leaking out when the engine is stopped then it is possible that air is leaking in.
     
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  15. ugis

    ugis Member

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    So i removed the suction screen and it looks like this. there was a lot of dirt inside, but I didn't find any large or significant particles. However, I have no idea when it was last cleaned. The suction hose is hard as rock, but I did not find any leaks. I will clear the suction screen and put on a new tube. However, what to do next - pour back the oil and try to test, or is it already clear that the fault is elsewhere?

    Btw, i bought the operation manual and learned some important things.
     

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  16. Nige

    Nige Senior Member

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    That "dirt" is most likely burned clutch friction material. Not knowing when the screen was removed last it's impossible to know if it got there recently or has been there for a long time. If it is a long time since it was last cleaned the quantity of material is not that alarming.

    Personally I would clean the screen, install a new suction hose and new clamps to replace the "hard as rock" existing one (it could be that hose is cracked and sucking air through the hose itself, not at the clamps), put back the oil that you drained and give it a try. At this point you have nothing to lose. As various people said before the cavitation sounds that you reported from the pump are an indication that it is not performing as it should. There are two possible reasons for this, blockage in the suction screen or air leaking into the system - or even both at the same time.

    The hard suction hose may be an indication that the transmission system has been very hot at some time in the past.

    Oh, and when you replace the cover for the screen I suggest to use a new O-Ring. The old one is proably hard by now.
     
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  17. kshansen

    kshansen Senior Member

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    Agree while the amount of stuff in that screen is not good but if it's been several thousand hours since it was cleaned not that surprising!

    Not familiar with the D6N but seem to recall on the D6C I worked on shortly be for retiring in 2015 that there was also a screen in the torque converter or am I thinking of a D8?
     
  18. Nige

    Nige Senior Member

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    The D6N has one also. See the file "converter housing" attached to post #7 above. I did recommend to remove and clean it while the oil was drained.

    Thinking a little more about the material in the screen. I think that if it was from a failure that is in progress right now the transmission oil ought to be dark and smell burned, not clear with no smell as the OP has described it.
     
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  19. ugis

    ugis Member

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    So, i was not as lucky this morning as expected and the test drive turned out to be unsuccessful.
    What exactly did i do these days - I visually inspected the transmission from both the bottom and the top, clean both suction screens, put on a new suction pipe and clamps, check for oil leaks and oil levels.
    The result - the bulldozer moved slightly at first speed and high idle and stopped immediately. Driving normally at other speeds. The same thing happens in reverse. If I start in second gear and switch to first gear, the bulldozer stops in the same way as the brakes are applied quickly.
    When i try to drive at first gear but it doesn't move, then appear Serv code- 113 671.02 and 673.02. The errors disappear if i just drive at some other gear.
    The buzzing sound seems to be gone, only slightly noise when steering.

    ps. since the first day I worked with this dozer- when switching from the second gear to the first at high load, there is a small break / knock and then traction reappears. Break was just 0.5 second long, but i felt it was probably not a good thing. Small or medium load= no problemo.

    i thought of a solenoid problem.
    Is it worth watching, or have I won a ticket to remove the transmission?
     

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  20. Nige

    Nige Senior Member

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    Unfortunately it appears as though you have. It looks as though the speed clutch for 1st speed, which works for both forward & reverse, has failed. The only guaranteed way to confirm it is by checking the clutch pressures using a pressure gauge capable of measuring at least 500psi. It would pay you to measure the clutch pressure in all five clutches.

    upload_2021-10-9_12-15-33.png
    upload_2021-10-9_12-18-19.png
     
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