Transmission question/ issue?

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Dino soar, Sep 23, 2020.

  1. Dino soar

    Dino soar Road Train Member

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    RTX 14610

    My transmission shifts smooth and seems like it's 100% like it should be.

    The question I have is that when the truck is in 8th gear there's a certain point or a certain RPM or a certain load that I feel what I probably would be described as of driveline vibration, like if you had a loose pinion or incorrect driveline angle. Driveline angle is probably a good way to describe that. It feels more like it's in the wheels or axle but that's the only gear that I feel that.

    It is a vibration and kind of like a dull sound like a rot rot rot. It is a sound that cycles and you hear it say every two or three seconds.

    Now the tires on my front rear are not matched, and I do have a very very slight amount of up-and-down play in my pinion in the front rear. But I only feel that in 8th gear under certain conditions.

    I have also noticed that sometimes when I Jake brake in eighth gear I hear it a little bit in the transmission. But again that is the only gear.

    My own guess would be that if there was a problem in the bearings on the counter shafts you could feel something like that, but I would think you would feel that in more than just one gear. And by the way the problem is minimal I'm just very anal and I notice it and I'd like to anticipate the problem before it gets worse.

    Can you have a problem like that in just one gear?
     
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  3. AModelCat

    AModelCat Road Train Member

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    What about 3rd gear?

    On that transmission, 3rd and 8th should share the same gearset in the main box. If there was an issue in the main box, I would think you should be feeling it in 3rd as well.
     
  4. AModelCat

    AModelCat Road Train Member

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    Have you tried running it in 7th or 9th but at the same speed as you'd run in 8th? That could help pinpoint if its a driveline problem or not.
     
  5. Cattleman84

    Cattleman84 Road Train Member

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    This....

    If it does it is speed related, it should do it at that same speed in another gear. If it does the same thing at same speed in different gear it would suggest the problem is in the drive train behind the transmission, or possibly an anlignment/tire issue.
     
  6. BoxCarKidd

    BoxCarKidd Road Train Member

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    Gears wear. When they wear as a set they tend to be quite with a lot of wear. Rebuilders pick through the cores for parts to reuse and mix them up. I have personally replaced a mainshaft gear due to wear at the sliding clutch during rebuild. Then I had a similar noise as you describe.
    So yes you can have a problem with that in just one gear and I would not worry much about it.
     
  7. Dino soar

    Dino soar Road Train Member

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    That is what is confusing because I don't feel it at all in the other gear.

    I have a friend that's a mechanic that suggested the same thing. I will try that the next load. It seems more like it's an RPM or load kind of a thing rather than actual speed though. When I feel it if I lay off the accelerator it feels better.

    I'm wondering if maybe the mismatched tires on the front axle and that little bit of play that I have in the pinion up and down could be responsible for that.

    The outer tires on the front rear are a little larger than the inner tires and the inner tires have a little bit of River wear from the truck they came off of.

    I have a matched set on the back rear maybe I should put them on the front rear?

    There are times that I go down the road say in hi gear that I do feel a very small amount of vibration from those mismatched tires. But it's really only enough that it reminds me that I have mismatched tires.

    I would like to buy a nice matched set but it's just not time yet. I'd like to keep running them for a while if I can because they have a lot of meat on them.

    The picture is a little distorted the tire is not that much larger that you see but it does sit a little higher.

    20200611_184437.jpg
     
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  8. lester

    lester Road Train Member

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    Holy crap, get matched tires on there. I doubt that is your issue but you are going tonwear them out in no time flat.
     
  9. Diesel Dave

    Diesel Dave Last Few of the OUTLAWS

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    Wow, that’s a big difference in tire size. I would take care of that first. Not to mentioned it’s gonna put more weight/heat on that bigger tire...... kabooom.....
     
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  10. lester

    lester Road Train Member

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    I'm having trouble figuring this out in my head but I'm trying. Even though those tires are spinning the same speed obviously because they are tied together they dont want to be and the smaller tire will be scuffing or dragging basically. A taller tire takes less revolutions to travel a certain distance than a smaller one. But somehow when I picture them spinning together on that same side they have to be turning the same and they are but yet not. Does that make any sense
     
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  11. Roberts450

    Roberts450 Road Train Member

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    Think of it as rolling a cone on the ground. It will want to go in a circle. The big end and small end are spinning the same speed but the big end will want to travel further.
     
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