Problem putting the shock cap back on after changing oil

[Skadar]

Hey everyone, I disassembled a shock in order to fix a sticking piston. That worked out just fine... however, putting the shock back together was very problematic. I watched a few tutorials online, so I was prepared for everything except what I kept experiencing. Here's what happened...

I would fill the shock with fluid and then place the diaphragm on top. I would then make sure to eliminate any air under the diaphragm. Then I would gently compress the shock a bit in order to force out extra oil that prevented the diaphragm from seating in its proper spot. This was all fine.

The problem came whenever I tried to screw on the cap. A natural seal formed between the diaphragm and the cap with a pocket of air as I screwed it down. This forced the diaphragm to collapse into the shock barrel.

I tried assembling the shock about 6 times. I would screw on the cap and then unscrew it to check the diaphragm, and every time I would find it floating sideways in the oil. I kept having to fish out the diaphragm, clean it, clean out the inside of the cap, and then try again.

I'm pretty sure I finally solved the issue by compressing the shock about half way as I screwed the cap on. I'm too afraid to check the cap one last time and the shock seems to be working normally.

How to you guys avoid this? I only ask because nobody in the videos seemed to have this issue, but when you think about how the cap is designed, the issue appears to be unavoidable!

[meatmonkey]

I had a similar issue with one of my Kit's shocks. I kept finding that the bladder wouldn't stay in it's home when the cap was threaded on.

Does anyone know if your supposed to put the bladder in the cap and then thread it on, or put it onto the top of the shock body and then thread the cap on?

And if it goes into the cap, do you press it down so it is half compressed before you put in onto the body, or leave it fully "bubbled"?

If it goes onto the body, then you want the body full of oil when placing it on, right? So, what position should the shock shafts be in when placing the bladder ontop of the body?

Maybe I'm over-thinking this, because three of my shocks went together with perfect rebound (about 1/8"") and no air inside, but the last one didn't cooperate and I ended up tearing a small hole in the bladder. My replacements will be here tommarrow and I don't want to screw another one up.

If you've had the bladder come out of position several times, you might want to closely inspect it for tears around the outer diameter.

On traxxas plastic shocks I've had good luck with placing the bladder in the cap and then pressing it down a little to "burp" the air out under it so it has a little vacuum to prevent excess rebound once assembled. Not sure if the ratio of body volume/shock shaft displacement on the Wraith shocks requires a different order of operations.

[muddywaters]

The way that I did it was to put the diaphragm into the shock cap put aside. Then fill my shock with oil before it over flows then pump the shock up and down to get the air bubbles out. Once the air is out compress the shock, fill to the top and screw the shock cap on. If the oil over flows its ok just clean and that should do it. Hope this helps Cause it worked for me.

[bbking9]

As a tag along to this thread - one of my bladders is torn and my LHS doesnt have any Axial parts. What other bladders can i use - any 1/10 truck bladder (ex -traxxas)??

thanks.

[slickwillie]

Here's a good writeup:
Shock Building Tips

I built mine this way & didn't have any problems.

[bbking9]

Traxxas 1765 bladders work fine.