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  1. #1
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    T-Maxx Classic Restoration (TRX 2.5 Nitro) - Help with Transmission Issues!

    Hello,

    This is my first post here, and this is also my first Nitro RC Truck.
    This T-Maxx Classic was given to me, and it didn't run at all when I got it. I got the engine running, and it seems to run fine.

    However, the servo for the forward/reverse shifting is missing, and when I try to pull on the rod that engages fwd/rev. operation, it is stuck. It takes a LOT of force to even move it.

    If I were to get a replacement servo for it, I'm afraid it wont be able to move the rod. It's stuck there pretty good.

    I also noticed they sell "Forward Only" kits online, how do I check to see if this has been installed?

  2. #2
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    I think you should open up the transmission, inspect all your gears for wear
    and install a Forward Only kit.
    Heres an exploded view of the transmission. It shows how the gears mesh together
    the part you need for a FOC kit, and the gears replaced by adding a FOC kit.
    It also has step by step instructions for adding an FOC if you decide to go that route.
    http://traxxas.com/sites/default/fil...INST%20FOC.pdf
    Last edited by NitroTrout; 12-09-2012 at 09:29 AM.
    Bash, Crash, Upgrade, Repeat..

  3. #3
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    The thing is I want Reverse... But it currently doesn't have the servo or anything for it.

  4. #4
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    I am in a similar boat but not exactly. Mine sat for 8 years and when I went to get it going again it didn't want to shift so I was hesitant to take the trans apart to clean it. If you follow the diagram on the traxxas website it's actually a pretty straightorward process to take it apart and inspect/ clean....parts are cheap at your LHSbut it might just be some dirt needs to be cleaned out. prob take about 2-3 hrs start to finish if it's just dirt. p.s. I am by no means a hobbyist or mechanic so you should be fine...

  5. #5
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    Quote Originally Posted by Dr. Bogger View Post
    The thing is I want Reverse... But it currently doesn't have the servo or anything for it.
    Tear down the tranny, I've done it and it isn't a problem. Take pictures as you go if it'll help you to reassemble it.
    You probably got some dirt in the internals, check for wear and clean it out. Then you can install a new shift servo.
    If the forward only kit was installed, you won't be able to roll the truck while holding the spur gear if I am correct.
    Hope that helps you out
    Last edited by 1979chevy.; 12-09-2012 at 07:39 PM.
    Matthew 7:7

  6. #6
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    Quote Originally Posted by Dr. Bogger View Post
    However, the servo for the forward/reverse shifting is missing, and when I try to pull on the rod that engages fwd/rev. operation, it is stuck. It takes a LOT of force to even move it.

    If I were to get a replacement servo for it, I'm afraid it wont be able to move the rod. It's stuck there pretty good.
    If the shift fork rod is hard to move there is most likely an internal problem.

    Quote Originally Posted by Dr. Bogger View Post
    I also noticed they sell "Forward Only" kits online, how do I check to see if this has been installed?
    Since the shift fork rod is still installed, there would be no forward only conversion.
    If you want to keep reverse (for the time being), you will need to open up the tranny and have a look to see what is the problem(s). You can always install the FOC at a later date.
    No slipper/tall gearing/power = broken parts.

  7. #7
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    Okay, well I got the tranny apart, and found out that the "4989 Shift fork-shaft" was all bent out of shape.
    So I replaced it, and now the shaft wont move when the engine is running. However, it'll move freely when the engine is off.

    So my guess would that the two gears that have the slipper clutch type thing is not set properly, and is pushing out too far with the engine on idle.

    Does anyone have any suggestions on how to properly set them? There's an adjustment screw on each one.

    The two parts I'm talking about are: 4998, and 4997. They can be adjusted.

  8. #8
    RC Turnbuckle Jr. Snook Man's Avatar
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    Generally the adjustment screw will be adjusted to where the head of the grub screw is about even with the start of the bevel section of the threads in the gear.
    That being said, the most common reason the shift fork can’t be moved when the engine is running is a high idle speed. If you feel the idle speed is good and the problem persists, adjust the screws clockwise in small increments. Adjusting too far (more tension on the spring) will cause the pawl to engage at a higher rpm than normal and slam into gear when the pawl opens.
    No slipper/tall gearing/power = broken parts.

  9. #9
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    I ended up just replacing them. Now I'm having Carburetor Issues... So I have a new carb on the way.. Should be here tomorrow.

  10. #10
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    Okay, what would make a TRX 2.5 start fine, idle fine, but when you rev up the engine, it doesn't wanna idle back down very well?

    I checked all the linkages, and the carburetor is brand new. The carburetor is retracting back fully, so it's not a servo / linkage issue. The engine starts almost instantly from a cold start, after sitting overnight, without any problems at all! (within 1 - 2 seconds).

    The issue that I'm having right now is getting the engine to idle back down when the throttle is released.
    Anybody have any ideas?

    Could this be caused by a compression leak?
    Could it be caused by improper tuning? (too lean or too rich?)
    Any other ideas?

  11. #11
    RC Racer
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    Good read from the Best Nitro Tuner in the Sport. Read Carburetor Needle balance:

    http://www.rctech.net/forum/onroad-n...ing-bible.html

    One tell tail sign of this is if after reving up the completely warmed up engine it tends to idle fast for a few seconds then drops to lower idle speed. If you start leaning the bottom end a little at a time [then repeat the reving up and idle test] and it takes longer before the idle drops your going in the right direction.


    Eventually as you keep leaning the bottom the idle will stay too high, now it is time to lower the idle to were it belongs by re adjusting the idle screw!
    Last edited by BAD RC; 12-13-2012 at 07:11 PM.

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