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  1. #1
    RC Qualifier
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    need some shock advice

    hey guys, I have a 3906 maxx with twin KD 820's on it. took me a few months to get it all together after the wide track kit and the steel shafts and the idler as well. Now my rear shocks are drooping really bad, almost to the point where the rear skid drags the ground. ive went as far as putting 3 shock collars on all four rear shocks and it doesnt seem to help. Also, I had it outside today...first time in about 3 months, and it seems like my rear A-arms dont want to rebound like the front does. I literally have to push the tires back down in place with my hands to make them reset into position.


    Now here is my question...

    Is it the shocks or is it something wrong with my rear arms? I dont know how in the world something could be wrong with the arms, but to explain it lightly would be like a rusty car door, it will still move but you have to give it a shove before you can shut it...kind of that same idea. I re oiled the shocks with 50w oil thinking heavier oil would be better for those gigantic motors. I bet with the swamp dawgs and those KD 820's that truck weighs every bit of 10-15 pounds.


    So what should I do? Order a set of piggybacks with the heaviest springs I can find...or...do the double spring method to help with the rebound. Any info on this would be greatly appreciated, I am not sure what to do in this situation...in all the years ive played with RC's I've never had a-arms "stick" I tried to loosen them some but it just made the set screw start to back out at high speed runs. If you guys want some pics, or maybe even a video, let me know and ill do what I can...Thanks.

  2. #2
    RC Competitor
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    Mar 2012
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    I'm not sure what shock &/or spring to recommend to you because I'm not familiar with the motors you referred to. How heavy are those KD 820s?? As for your a-arm problem, I'd suggest making sure your hinge pins aren't bent.

  3. #3
    RC Champion
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    820's are heavy, having two and heavy weight oil the springs won't be able to extend the shocks back up. mine weighs at 11lb with one 820
    Guide books aren't part of the packaging.

  4. #4
    RC Champion
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    Test if you have an A-arm binging issue by disconnecting the shocks and move the arms. If you feel it "catching" then try to remedy it. When I got my set of RPM A-arms I had to shave the mating surfaces so it would free move.

    I don't think it's the shock thats the problem if you are having to push the A-arm into a full position. Although if your shock shafts are bend bad enough they will catch at the bend.

    With the shocks removed, push the shaft up into the body. The shaft should be pushed smoothly out by the springs. You can further test the shock by removing the spring and pushing the shaft into the body. If your bladder is good and you have the right amount of oil, the air trapped in the bladder should push the shaft back out of the body.

    For a heavy truck like yours I'd try 60 or 70 wt oil with heavy springs and use 2 hole pistons.

  5. #5
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    that was the first thing that I checked. I even bought a new set thinking that the new A-arms might have had a different inner shaft dimension, both pins do it...with or without the little plastic clip on washers.

  6. #6
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    its not exactly catching...its hard to explain. its like the links at the bulkhead are pressed against each other really hard and rubbing, which they arent. About an hour ago I sprayed them down with some penetrating fluid then a very thin coat of 10w40 motor oil. I figured the viscosity of the motor oil would stick into the jointed area a little better than wd40, wd40 will dry out over a very short time.

    I dunno, im confused. it rips all over my yard...was doing some nasty donuts on some ice out back right before dark. Im thinking im going to wait till tax time then buy either some 100 mm piggy backs or order some custom ones from the LHS down the road.

    any other ideas? lol.

  7. #7
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    ok guys i made a video of the suspension setup. this is after I moved the shock locations to the inner most postion making the shock almost straight up and down.

    Here it is, tell me what you think.
    http://www.youtube.com/watch?v=kPW1S...ature=youtu.be

  8. #8
    RC Champion
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    that is bad, looks like something is binding on all 4 sides. Remove the hinge pins on the arms to bulks to see if they are bent, or remove the shocks and compress them to see how smooth they return, which ever is easiest to do first.
    Guide books aren't part of the packaging.

  9. #9
    RC Champion
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    I thinks it's the arms are to thick for the bulkheads. We're they tight to fit into the bulkheads? Take the -arms off and shave or sands the surface's that touch the bulkheads. You want them to fit freely but don't shave them too much as to create a gap that will cause front to rear movement. Ideally the A-arm should move free enough that without shocks mounted, the A-arm will flop around under its own weight.

  10. #10
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    Quote Originally Posted by M n M View Post
    I thinks it's the arms are to thick for the bulkheads. We're they tight to fit into the bulkheads? Take the -arms off and shave or sands the surface's that touch the bulkheads. You want them to fit freely but don't shave them too much as to create a gap that will cause front to rear movement. Ideally the A-arm should move free enough that without shocks mounted, the A-arm will flop around under its own weight.
    Ya I notice today those RPM a-arms are a lot thicker for the bulkheads compared to the traxxas brand arms. After watching that video it would almost have to be the rpm arms in the bulkheads

  11. #11
    RC Champion
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    if it was the arms he would of noticed when he put them on originally that they was tight.
    Guide books aren't part of the packaging.

  12. #12
    RC Turnbuckle Jr. Wildman4910's Avatar
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    Sand the RPM arm pin ears till the arms move freely, they should catch or be stiff in their movement, they should be very free & smooth.

    Stay away from anything Intgey except for their shock spring kit, everything else is junk.

    Traxxas BigBores with stiffer springs are the ticket, unless you want to spend more to go to a 4 buggy shock setup.
    Look out for the tree/crunch!

    LiPo? Naw NITRO!!

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