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CAT D6N transmission problem

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

  1. Mobiltech

    Mobiltech Senior Member

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    Have you tried swapping the first speed modulation valve with 3rd speed?
     
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  2. ugis

    ugis Member

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    No but i could give it a try. Before i do that i need to know what is what and what to change places.
     

    Attached Files:

  3. Nige

    Nige Senior Member

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    Following Mobiltech's suggestion you should interchange Modulating Valves "G" (1st speed) and "E" (3rd speed).

    upload_2021-10-9_18-56-31.png
     
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  4. ugis

    ugis Member

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    i swapped these two places but nothing changed.

    Sorry for the stupid question, but how exactly do speeds work. i mean, there's 1.5-> 2-> 2.5-> 3-> 3.5 possible shifting gear, but as far as i understand there are 3 solenoids and 3 clutch discs for gears.
    How it is possible that when clutch disc collapse, the bulldozer first (1.5) speed suddenly does not work at all, but all others operate normally. (2/2.5/3/3.5)
    how exactly does it work?
     
  5. Nige

    Nige Senior Member

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    There are actually 5 clutches in the transmission, each one of which is controlled by a separate solenoid valve.
    To select any gear in the transmission two clutches have to be engaged. A direction clutch (forward or reverse) and a speed clutch (1st, 2nd, 3rd).
    The clutch numbers and what they do are listed below.
    #1 - Reverse
    #2 - Forward
    #3 - 3rd speed
    #4 - 2nd speed
    #5 - 1st speed

    You have no 1st speed in either forward or reverse which is consistent with a problem in #5 clutch.
    You interchanged the solenoid valves for clutches 3 & 5 with no difference, so it cannot be a solenoid valve problem. the conclusion is that #5 clutch has burned out and the next step is to remove the transmission for repair.
     
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  6. Mobiltech

    Mobiltech Senior Member

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    There are really only 3 transmission speeds or ratios. The 1.5 and 2.5 are achieved by automatic engine speed limitation. In other words smoke and mirrors.
    It does sound like you have internal problems. The good thing is if you have no winch on this you can have the transmission out and tore down before lunch!
     
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  7. ugis

    ugis Member

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    the gearbox has been successfully removed. The biggest trouble was that I didn't know about the third axis. * facepalm *
    Anyway, I visually looked at the gearbox and didn't notice anything special.
    As far as i understand the condition of the clutch discs is determined by their thickness. How much should be? Would it be wiser to change all at once?
    What else needs to be done / replaced so that the gearbox problems can be forgotten for a while?
     
  8. Nige

    Nige Senior Member

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    Before attempting to answer the “what to replace?” question, how many total hours are on the machine and does it look as though the transmission has ever been removed before.?
     
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  9. ugis

    ugis Member

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    About 15100h.
    Almost all the screws that needed to be unscrewed were with damaged paint and everything showed that it had already been done before.
     
  10. Nige

    Nige Senior Member

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    In that case a lot will depend on what you find inside the planetary transmission when you disassemble it.
    There are two kits (aatached) available for the transmission:-
    345-9110 Bearing Kit
    345-9112 Gasket Kit
    Also attached a parts breakdown of the transmission and the control valve.
     

    Attached Files:

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  11. Nige

    Nige Senior Member

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    Here is a Disassembly & Assembly procedure for the transmission.

    My thoughts about what you should consider replacing as an absolute minimum:-
    1. Clutch piston seals in all 5 clutches.
    2. Friction discs/separator plates in #2 & #5 clutches. The clutches are for forward direction and 1st speed.
    3. Friction discs in reverse (#1) & 2nd speed (#4) clutches.
    3. Every gasket & seal.
    4. Every bearing.
    Check condition of - and replace if they do not meet specification. (Specifications are attached.)
    1. 3rd speed (#3) clutch friction discs/separator plates (3rd gear doesn't get used that much)
    2. Reverse (#1) & 2nd speed (#4) clutch separator plates. Replace if they show any signs of heat (blue colour)

    Hopefully others will offer their opinions as to how you should move forward on this, but remember that nobody apart from you can see the condition of the parts that you are removing.
     

    Attached Files:

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  12. ugis

    ugis Member

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    Good morning,
    I dismantled the planetary gear of the transmission and found the damage. There was a horrible view and I could only wonder how I could do it at all and how I got out of the pond on my own.
    Attached pictures.
    I don't really know why the disc springs broke (mby heat?). The first gear fiction discs are in critical condition, but the dozer was still able to drive. The first gear disappeared due to damage to the piston seal and loss of pressure. Other fiction discs look like new, with minimal wear.

    Thank you very much Nige for the information which was very helpful to me. I am currently waiting for the spare parts to be delivered and then to be able to put them together.
     

    Attached Files:

  13. Nige

    Nige Senior Member

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    A couple of suggestions after seeing the damage in your photos.

    1. Check all the piston housings (and especially the 1st speed one) for scoring or anything that could cause a piston seal to fail. You should consider the possibility that a piston seal failure might have been the cause of the clutch failure. It is not unknown for the housing to be damaged when a clutch fails like that because the piston travels too far and literally "falls out of the end" of the housing bore.
    2. I would personally still replace the discs/plates in both the 1st speed & forward direction clutches. 1st speed forward is when the machine does most of its hard work.
    3. How did the disc/plate stacks for 2nd, 3rd, & reverse clutches compare to specification and are you planning to renew anything in any of those three clutches other than piston seals.?
     
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  14. ugis

    ugis Member

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    I checked the piston housing and did not notice any damage or wear. However, the piston is badly damaged and I will put it new along with piston seals, rotating rings (?), All first speed friction discs, seperator plates and disc springs.

    i measured the other disc / plate stacks. Carefully cleaned the discs before measuring. Forward stack- 40.1 mm, Reverse 40.2 mm, 3rd gear 24.3 mm, 2nd gear 15.9mm. Forward stack had one slightly bluish points on disc plate. Think of replacing this from 3rd gear.

    My colleague and I could not agree on whether it is possible that these discs have been changed before. i don't want to believe they could last 15k engine hours and wear so little.

    We figured out how to save on expensive gearbox costs by placing a gear pressure gauge in the cab. Or the pressure should be measured regularly for preventive purposes. As far as i know there are no sensor for each gear, only main pressure sensor.
     
  15. Nige

    Nige Senior Member

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    I think based on your reports of their condition then it is almost certain they have been changed before. As you said earlier there were signs that the transmission had been removed previously.

    Others may have a different opinion but I think placing a pressure guage in the cab is going to achieve very little. You also need to be careful that the tube you use to take the pressure from the transmission cannot get damaged somehow and fail. That would dump all your transmission oil on the ground. To take pressures on a regular basis by hooking up an external gauge when doing maintenance might be a good idea.
     
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  16. Nige

    Nige Senior Member

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    I would put all new plates (and discs) in the forward clutch and lleave the exisitng ones in the 3rd gear clutch. As mentioned previously the 1st speed and forward direction clutches are the ones that take the most load and are used most frequently.
     
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  17. Nige

    Nige Senior Member

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    Just thinking out loud. Is it possible the failure you have now is the result of someone who repaired the transmission previously "trying to cut corners" and save a few dollars on the cost of parts by re-using stuff that was not really fit to re-use.? If that is potentially the case are you in danger of falling into the same trap by trying to do the same thing.?

    You can either do it right or do it cheap. If you do it cheap you run the risk of having to do it again in the near future.
     
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  18. kshansen

    kshansen Senior Member

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    The old "Pay me now or Pay me latter" deal! What will suck is that some of the things you replaced the first time will need replacing again the second time. And this does not even take into account the labor and down time!
     
  19. ugis

    ugis Member

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    I will replace all parts that are worn, scratched, or otherwise damaged and all rubber / plastic parts. As well as parts that Nige recommended to replace - forward discs / plates. I also consulted with the dealer and they could not recommend anything else. I also don't think it would be wise to change the parts for good luck, which costs a lot of money. I also do not have any clue as to why this damage occurred. It is possible that the previous owner made careless repairs. It is possible that this is simply a failure.

    I'll measure the pressure from time to time and hope for the best. There is nothing more I can do right now.

    I have been working in agriculture for a long time, I use different brands of equipment and sometimes it just breaks for no reason. New or old- doesn't matter.
     
  20. Mobiltech

    Mobiltech Senior Member

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    Also make sure you inspect the friction discs for wear in the tooth are not just thickness. Check steel plates for wear at the dowel pin contact area.
    When replacing planetary gear needle bearings also replace the rubber/steel retainer pins.
     
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