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  1. #1
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    cv shaft problem

    Hi all I broke my right front a-arm and replaced both sides with rpm ones. my problem is on the right front which is the one that broke. the cv shaft keeps coming out of the drive cup. I replaced the cup and shaft but it still is happening. anyone have any ideas what could be the issue? Thanks

  2. #2
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    Something else broke in that crash that you haven't found yet. Whatever that something is, it's allowing the wheel to flex away from the differential giving the axle shaft room to slide out.

    Unfortunately, you're going to have to go piece by piece through the right side suspension looking for cracks or other damage until you find what it is.

    My guess, since you broke the lower control arm is that it may be the upper control arm, which now allows the suspension to droop too much when the suspension is unloaded, and the axle shaft can then fall out of the drive cup. That's where I'd start poking my nose.

    Let us know what you find.

  3. #3
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    Oh, some helpful troubleshooting questions to answer which can help you narrow down which parts to examine:

    Does the shaft fall out when the suspension is compressed or extended?

    Does the shaft fall out when steering?

    What is the vehicle usually doing when the shaft falls out? Landing a jump? Accelerating forward? Turning? Those can help you figure out what parts of the suspension or steering are moving when the failure is happening.

    Happy troubleshooting!

  4. #4
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    The RPM arms seem to be the problem. Had the exact same situation. Broke a stock arm and thought RPM's would be an upgrade. But not so! Fully tore down the whole front end and carefully inspected everything couldn't find out why they kept falling out. Got tired of it and went back to all stock and CV's never popped out again. In fact I had problems with both CV's falling out with the RPM arms.

  5. #5
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    Dang, that's a bummer to hear that about the RPM arms. Their stuff is usually on point.

  6. #6
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    Have you contacted RPM regarding this? Or can anyone else confirm similar findings?

    I'm interested in a set of the RPMs since they won't trap debris like the stock ones. But this info certainly dampens that interest.

  7. #7
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    The fact that the OP only has it happening on one side, and it's the side that broke, I'm leaning toward what Fallen originally suggested and that something else may be out of whack. I just installed both the lower and upper RPM control arms today. I haven't run it yet but I just took a careful look and everything seems just fine. I don't see how they could fall out.

  8. #8
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    I have an update for my last post... Out of an abundance of curiosity and time, I pulled the new RPMs from one side and installed the old a-arms to compare. HOLY COW! Sure enough, the RPM arm allows for far more droop and nearly expels the dogbone pin at the 12 o’clock position. With enough flex or maybe crash I could absolutely see it popping out. The stock side doesn’t even come close...in fact the pin stays at least halfway into the drive cup. One of the most notable differences between the two lower arms is the lack of a travel stop on the RPM. The stock arms have a slightly longer forward pivot that incorporates an integrated stop for both full compression and full droop....this may be what’s going on. I’ll tell you what though, I put my stock arms back on, bought two spares and have some RPMs I wasted my money on IMHO.
    Last edited by b-mack; 06-05-2020 at 01:52 PM.

  9. #9
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    Thanks for the update, and that is quite a bummer to hear.

  10. #10
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    I keep having this happen on mine but I still have the stock arms. I've taken it apart yet can't see why it pops out. Only on one side does it do it and only when turning it seems.

  11. #11
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    As referenced in b-mack's post, the lower A-arms have an integrated droop stop. It's located on the trailing edge of the front pivot point. I'm just looking at the exploded view to confirm this, as my UDR is away for paint so I don't have my own A-arms on hand.

    Your droop stops might have either worn out, or broken off. Other than shock length, I don't think anything else in the front suspension limits droop other than that little stop. Unfortunately, you might have to remove the A-arm to confirm if it's still there.

  12. #12
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    Quote Originally Posted by Fallen View Post
    As referenced in b-mack's post, the lower A-arms have an integrated droop stop. It's located on the trailing edge of the front pivot point. I'm just looking at the exploded view to confirm this, as my UDR is away for paint so I don't have my own A-arms on hand.

    Your droop stops might have either worn out, or broken off. Other than shock length, I don't think anything else in the front suspension limits droop other than that little stop. Unfortunately, you might have to remove the A-arm to confirm if it's still there.
    Ok just for some information on my own. What would I be looking for. And if they are worn, what would be the best replacement option. Stock? RPM? HR? GPM?

  13. #13
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    Comparing the failing side to the good side would probably answer your question. It'd be ideal to compare it to a new one, but the good (used) one will probably work. Compare the droop stops that b-mack described to tell if one of them is worn or broken.

    And it unfortunately sounds like stock is the best replacement currently from the options you listed. But if you'd like to upgrade, Vitavon or RC4WD are probably your best bet. I'm not a fan of aluminum A-arms though, so stock is my recommendation.

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