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  1. #1
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    Traxxas Slash Ultra Shock Leaks

    My Ultra shocks have been leaking from the shock caps ever since I upgraded to aluminum caps. I have purchased multiple rebuild kits to replace to bladders in the ultra shocks that create the seal. After going through 3 rebuild kits and still having leaks, what are best route to stop leaks?


    I have Losi 2.0" and Losi 2.5" 4.1 rated springs that I would like to keep.

    New Bladders that are not traxxas brand? HPI Racing? Tamiya 50600?
    Switching to Aluminum Shock Bodies? Such as STRC
    Switch out shocks and go with Losi 3.0?


    THANKS

  2. #2
    RC Qualifier Calebs0615's Avatar
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    This may seem obvious but are the caps cross threaded? Its easier than you think being the threads are plastic.

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  3. #3
    RC Champion RCWilly's Avatar
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    Also, make sure the bladders/diaphragms are seated properly (flat against the cap).
    Everyday's a gift, thus now is called the present.

  4. #4
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    Definitely not cross threaded, caps seem to screw on very easy. Also everything looks straight without any imperfections in the threads on the plastic bodies.

  5. #5
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    Yes ive been doing that and using squeezers to make sure they are seating all the way down in the shock cap.

  6. #6
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    When I service mine I seat the bladder on the shock body then slip the cap on...seems to work for me.

  7. #7
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    Try using the stock ultrashock bladders and see if it stops the leaks.

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  8. #8
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    The aluminum caps are proper ones and made for Traxxas? Perhaps it screws on easily, but too easily and the oil ist just creeping through the threads...
    In case yes: perhaps it just doesn’t go all the way down and the sealing seat is not compressing the bladder...

    Did you go back and test the stock plastic ones? Just to rule out the cap as roof cause.

  9. #9
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    Quote Originally Posted by Dad of a son View Post
    The aluminum caps are proper ones and made for Traxxas? Perhaps it screws on easily, but too easily and the oil ist just creeping through the threads...
    In case yes: perhaps it just doesnít go all the way down and the sealing seat is not compressing the bladder...

    Did you go back and test the stock plastic ones? Just to rule out the cap as roof cause.
    I found the same trouble when I went to alum caps. Since I donít do much jumping anymore, I just use the plastic.
    My theory is the alum cap has zero ďgiveĒ and are subject to over tightening and squashing the bladder seal.
    I think this makes proper seating that much more important. The plastic caps will give a little...

  10. #10
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    Are you lightly oiling the bladder and cap? Tightening it dry can also skew the bladder.

  11. #11
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    I have not yet tried to see if switching back to the plastic cap would resolve the issue. I have put a light coat of oil on both sides of the bladder. Seems like the bladder when shock is compressed in wont rebound and stays concaved inward. I'm going to buy more bladders, try seeing if the plastic caps are leak proof with new ones. Also maybe using less oil? I try and aim for around 3/4 rebound. Maybe should try for 1/3 to 1/2?

  12. #12
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    Quote Originally Posted by Ace911 View Post
    I have not yet tried to see if switching back to the plastic cap would resolve the issue. I have put a light coat of oil on both sides of the bladder. Seems like the bladder when shock is compressed in wont rebound and stays concaved inward. I'm going to buy more bladders, try seeing if the plastic caps are leak proof with new ones. Also maybe using less oil? I try and aim for around 3/4 rebound. Maybe should try for 1/3 to 1/2?
    Rebound preferences will vary...
    More important is having some rebound, and also not having it hard as a rock.
    Trying to force too much oil can skew the bladder and crush it while tightening.
    That squished bladder may never be the same again... I chuck any suspect bladders.
    Screw the caps on tight, but not too tight.

    Are you putting the bladders into the caps first then screwing them on?
    I run the little Allen key around the edge of the bladder in the cap to make sure it’s seated nice.
    Sometimes you can trap a bit of excess air under the cap, which will skew it on tightening.
    Seating the bladder into the shock body first works too. Try that way, might work better for you!
    Last edited by fortunespoonz; 02-23-2021 at 09:30 PM.

  13. #13
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    Quote Originally Posted by fortunespoonz View Post
    Rebound preferences will vary...
    More important is having some rebound, and also not having it hard as a rock.
    Trying to force too much oil can skew the bladder and crush it while tightening.
    That squished bladder may never be the same again... I chuck any suspect bladders.
    Screw the caps on tight, but not too tight.

    Are you putting the bladders into the caps first then screwing them on?
    I run the little Allen key around the edge of the bladder in the cap to make sure itís seated nice.
    Sometimes you can trap a bit of excess air under the cap, which will skew it on tightening.
    Seating the bladder into the shock body first works too. Try that way, might work better for you!
    Iíve gotten to understand that tightening these screw caps is very important to not have it too tight or too loose. My LHS unfortunately didnít have any more rebuild kits cause I purchased them all already. I feel like the bladders swell up and expand. Because of this itís near impossible to put the bladders directly on the shock housing. Putting it inside the cap is much easier to have it appear level when tightening the cap

    Bladders seam to do any of the following:
    Fold/kink
    Concave inward and never regain original form
    Tear around seal edge
    Swoll up and become larger/less dense
    Leak around and oil get behind bladder
    Leak around threads but not behind bladder


    How tight do these things need to be?

    When itís plastic against aluminum?
    When itís aluminum against aluminum?
    When itís plastic against plastic?

  14. #14
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    Not sure whether or not you saw it already, but in terms of filling volume: did you see traxxas’ video?
    https://m.youtube.com/watch?v=YGM55LEeC4Q

    Bladders swollen up:
    give it a try: take one bladder put it into the oil and leave it there for 24h. If not expanded that’s most probably not the reason

    The Al caps are proper ones (where you could expect it’s good quality and tolerances fit) or cheap ones (where you don’t know anything about it)?

    Tear around seal edge:
    You got access to a microscope or magnifier? Just take a look and rule it out

    How tight?
    I strongly assume the outer flat part of the bladder is made to seal. So it should not matter how tight the threads are...
    Just give it a try and use 2 bladders on top of each other and check if they get tight. If so you know the cap is not compressing it down to the shock body.
    Last edited by Dad of a son; 02-24-2021 at 04:27 PM.

  15. #15
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    Quote Originally Posted by Dad of a son View Post
    Not sure whether or not you saw it already, but in terms of filling volume: did you see traxxasí video?
    https://m.youtube.com/watch?v=YGM55LEeC4Q

    Bladders swollen up:
    give it a try: take one bladder put it into the oil and leave it there for 24h. If not expanded thatís most probably not the reason

    The Al caps are proper ones (where you could expect itís good quality and tolerances fit) or cheap ones (where you donít know anything about it)?

    Tear around seal edge:
    You got access to a microscope or magnifier? Just take a look and rule it out

    How tight?
    I strongly assume the outer flat part of the bladder is made to seal. So it should not matter how tight the threads are...
    Just give it a try and use 2 bladders on top of each other and check if they get tight. If so you know the cap is not compressing it down to the shock body.

    So last night I finally got my Blitz bladders. Also received my front aluminum bodies. These bladders are much denser material and almost more of a plastic than a rubber. Anyways, I installed it on the plastic body and still had a leak. I think this might be because I didn't tighten it past finger tight and may need to do hand tight? As for the Aluminum bodies its very hard to tell if they are leaking, deffenitally not as much as the plastic bodies though.

  16. #16
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    Quote Originally Posted by Ace911 View Post
    So last night I finally got my Blitz bladders. Also received my front aluminum bodies. These bladders are much denser material and almost more of a plastic than a rubber. Anyways, I installed it on the plastic body and still had a leak. I think this might be because I didn't tighten it past finger tight and may need to do hand tight? As for the Aluminum bodies its very hard to tell if they are leaking, deffenitally not as much as the plastic bodies though.

    So I decided to make then hand tight this time and 1/8-1/4 turn with the help of an align key. The plastic bodies are still leaking, the aluminum bodies its hard to tell but are definitely leaking less or maybe it was oil that slowly went down the threads after 8 hours of sitting?

  17. #17
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    depending on how much it is, but I also some oil on the threads when replacing the shock oil. Reason is fairly easy: when closing the oil flows over the rim down the threads and threads are not fully tight. So the oil left in the thread might flow down further.

    But that would also mean that waiting 1 day, cleaning it off and waiting another day you shouldn't see more oil. Is that the case?


    As the root cause seems to be hard to figure out online: did you ever go to a local store and have them show you how to do it? Let them fill it up, close it and then you just go back and show them what you see and they can comment in person.

  18. #18
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    Quote Originally Posted by Dad of a son View Post
    depending on how much it is, but I also some oil on the threads when replacing the shock oil. Reason is fairly easy: when closing the oil flows over the rim down the threads and threads are not fully tight. So the oil left in the thread might flow down further.

    But that would also mean that waiting 1 day, cleaning it off and waiting another day you shouldn't see more oil. Is that the case?


    As the root cause seems to be hard to figure out online: did you ever go to a local store and have them show you how to do it? Let them fill it up, close it and then you just go back and show them what you see and they can comment in person.
    I have an update of how I was able to stop the leaks finally. After I upgraded my shock bladders to Tamiya 50600 Green shock bladders. These bladders fit much better as are snug/hard to remove once seated. So far Iíve had them dry for about 12 hours.

    This bladder worked with the aluminum shock caps. On both the ultra plastic shock bodies and the strc aluminum shock bodies. I donít recommend STRC shock bodies as they no longer come with o-rings for shock cap seal. They also have large gap on bottom seal that can lead to a large leak. Also no customer service is a big negative.

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