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Cat 931B No Forward Reverse Normal

Discussion in 'Track Loaders (NOT CTL)' started by Mike AL, Sep 5, 2022.

  1. Mike AL

    Mike AL Member

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    Need some input on a 931B that has no forward movement but reverse is normal.
    This is a 29Y02??? with 3 forward and 3 reverse. Had been using it with no issues
    for about 6 hrs when pushing a pile of brush I stopped and went in reverse to get a different angle, shifted to forward and nothing.
    I have checked the filter and it was clean, disconnected the forward – reverse shift cable
    and shifted it by hand to make sure the linkage was not a problem, replaced the seals in the transmission control valve with no change since it was easy.
    Have not tested pressure at top of the transmission yet but for what it’s worth did test at
    the port on top of the filter.
    When in neutral had 25 to 30 psi
    Shift to any gear in reverse: pressure goes to 100 then a few seconds later to 350
    Shift to any gear forward: pressure goes to 100 and holds.

    Suggestions to do next.
    Is this a transmission problem?
    Did not notice any slipping just working then not, I have had this machine for about
    10 years so it’s not new to me.
     
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  2. Nige

    Nige Senior Member

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    Does the drive shaft between the converter and the transmission spin in neutral but stop when you engage any forward speed.?
    What does it do in when shifting from neutral to reverse.?
    You said you checked the filter. Did you replace it and cut the old one open to inspect for particles.?
     
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  3. Mike AL

    Mike AL Member

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    Hey Nige
    Does the drive shaft between the converter and the transmission spin in neutral but stop when you engage any forward speed.?
    The only drive shaft I see is the short one between the transmission and the bevel pinion. It only moves when the loader moves.
    Does it have another drive shaft?

    What does it do in when shifting from neutral to reverse.?
    drives normal in all reverse gears, no problem.

    You said you checked the filter. Did you replace it and cut the old one open to inspect for particles.?
    Have not replaced the filter yet since reverse was working OK
     
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  4. Nige

    Nige Senior Member

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    Sorry. i was thinking of larger models where the transmission is mounted on the rear case and the shaft connects the converter to the transmission.
    The particles tend to be very small because of the screen on the pump suction side. They would generally not be visible without cutting the filter to look in the bottom of the pleats.

    From your pressure test results of the forward direction clutch not maintaining a pressure above 100psi it has gone AWOL. That clutch, along with the 1st speed clutch, are the usual ones to fail.
    What does the oil look like.? Clear & bright or darker & opaque.?
    Maybe it would be worth draining the oil and removing the suction screen on the bottom of the transmission case to inspect that for particles.
     
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  5. Mike AL

    Mike AL Member

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    The oil is dark.
    Is there anything else I can test before draining the oil. If I'm going to drain the oil I think I will put it on blocks and prepare for the worst.
    I believe the engine and trans come out together, on a loader should the arms be down or are they in the way.
    I'm trying to understand how the transmission works when shifted, are there seals in the forward clutch that can let go and keep it from going
    to full pressure (350psi) when shifted. My thought is if all the material is gone from the disk it still shifts to full pressure but would not move or would slip.
    Keep in mind I'm no mechanic and have no experience working on this loader (have not needed to until now), but if that's what it comes to I guess we'll try it.

    Thanks
     
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  6. Nige

    Nige Senior Member

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    There are two possibilities I can think of off-hand.
    The first is a simple clutch piston seal failure. If the seal fails oil will leak past the piston, the system pressure will drop, and the clutch will not engage.
    The second is wear of the friction material on the clutch disks that when it reaches a certain level the clutch piston moves so far in order to engage the clutch that it pops out of its housing, so pressure will be lost and the clutch does not engage.
    That is an indicator but what colour was the oil generally in the past.?
    Not as far as I know. Putting it up on blocks will give you more space to work.
    Usually on a loader the arms should be raised to give space to work. Others can probably give you more guidance. One thing though, the safety prop on the lift cylinder MUST be installed to prevent any unwanted movement of the lift arms while working underneath them.

    You might find the attached information regarding how the machine powertrain works useful. Information pertaining to the 29Y machine starts on about Page 13.
     

    Attached Files:

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  7. Dave Neubert

    Dave Neubert Senior Member

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    100 psi is pretty low should be at least 250 psi
     
  8. Mike AL

    Mike AL Member

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    Nige thought i would give you an update. Before removing the transmission I did find an air test I could try and here is how that went.
    When applying air to the port for the reverse clutch, the clutch engaged and it held air.
    When applying air to the forward clutch, the clutch did not move and just blew air in the area of the forward clutch.
    Even though I don't use 3rd gear I wanted to see what would happen. 3rd has been weak since I have owned the loader, it would drive on flat ground but would almost stop on an incline.
    When applying air to the 3rd gear clutch the clutch would engage but still pass a lot of air witch made sense to me.

    Based on that I'm guessing the piston seal sense it failed all the sudden. At this point I have the transmission separated and ready to pull from the case. I am hoping that someone who has never worked
    on these before can do this repair. I guess I will give it try unless someone out there tells me otherwise. ( special tools needed ect.)
    As for disk replacement, OEM or aftermarket? This loader is used around the farm less than 100hrs a year.
    Also attached pics of the trans screen which was last cleaned about 8 years ago. Did not find anything big, I guess that is clutch material in the screen.

    upload_2022-10-9_21-4-55.jpeg upload_2022-10-9_21-5-34.jpeg
     
  9. Nige

    Nige Senior Member

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    My opinion. If you are going to all the effort of pulling the transmission apart in the first place are you willing to take a chance on parts of potentially dubious quality.?
    Try contacting Offroad Equipment in Alcoa TN - www.offroadeq.com/
    They come recommended and if you deal with them on the phone they can give you good advice regarding what might be the best parts solution for your particular cricumstances. They sell both OEM & aftermarket parts.

    IMHO the first thing you need is a Parts Manual for all the little seals, gaskets, O-Rings, etc, etc that you are bound to need in addition to a set of discs/plates and piston seals for the 5 clutches.
    You might even find that there are shaft and/or planetary gear bearings that need to be replaced.
    Here's one, new they are $150 for a paper manual so this one is good value, plus it is the latest version available.
    https://www.ebay.com/itm/1436112735...55-0&campid=5338722076&customid=&toolid=10050

    You'd also be well advised to re-seal the transmission control valve while you have the transmission disassembled.
    Attached are the gasket/seal kits listed for the transmission of a 29Y-prefix machine
     

    Attached Files:

    Last edited: Oct 10, 2022
  10. Nige

    Nige Senior Member

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    I guess it all depends how extensive your tool kit is and your confidence in your own ability. The "book way" is to remove the engine & transmission as a unit and split the transmission off once it's on the floor. I have no idea if it's possible to remove the transmission on its own leaving the engine in place.

    The transmission is not that complicated but it needs a clean work space and to work in a disciplined fashion through the component during both disassembly and reassembly. A smart phone camera is your friend, take loads of photos during the disassembly as memory-joggers to make reassembly easier.

    You have already tested the clutches with air so now you know exactly what you are looking for in order to test the rebuilt ones as the transmission is reassembled. It's not unknown to trap a piston seal and have it leak if you're not careful, testing with air will at least give some confidence that the clutch pistons are sealing correctly before the transmission is reinstalled.
     

    Attached Files:

  11. Mike AL

    Mike AL Member

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    Here's what I have found so far.
    Piston seal blown in the forward clutches
    Most of the friction material gone in almost all the clutch packs, 1st gear clutches looked to be in good shape.
    The plates that are part of the case (part #9P-7103 & #7G7617) have a lot of metal on metal wear. Is there a spec where this can be resurfaced vs replaced?
    On the cat website these parts say contact dealer instead of available. Does that mean they my not be available?


    upload_2022-10-15_21-22-11.jpeg upload_2022-10-15_21-23-17.jpeg upload_2022-10-15_21-24-4.jpeg
     
  12. Nige

    Nige Senior Member

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    1st gear (along with forward direction) is usually the clutch that gets the most use under heavy loads for obvious reasons. While you're in there a new set of discs and plates for that clutch would be good insurance.
    I'd also suggest replacing all the springs, or at least check them against the specification (attached).
    There is no specification anywhere that I can see. I would say that if they are scored then they are toast and would need to be replaced.
    They are both current Part Numbers so the "contact dealer" message might potentially indicate a supply problem. The best I can suggest bearing in mind your location is to give Offroad Equipment in Alcoa TN a call, 1-888-299-8432 or www.offroadeq.com/
    They supply both OEM and aftermarket parts and in the unlikely event they don't have stock would likely be able to point you in the right direction.
     

    Attached Files: