Results 1 to 5 of 5
  1. #1
    RC Qualifier Calebs0615's Avatar
    Join Date
    May 2020
    Location
    Maine
    Posts
    693

    Low Shock Oil? No Rebound

    I bought a linear set of springs for the rear of my slash and as I was dissembling the shocks, i noticed i compressed a shock a little by accident. Well it didn't come back at all, so i pushed it in all the way, and it still didn't come back even a little bit.

    Could this be from low or dirty fluid? It had fluid when I emptied it. To be honest im not sure how much though.. Also it was pretty dark. Not black, but for sure a darker tint of gray.

    Could it have been my own error? I bought the big bore shock kit and i had to fill them myself if i remember right.

    This time i filled them too much I think, cause i couldn't even compress them to the bump stop. Not even close really. It was a good 15mm or more away. All i did to fix it was, I'd soak up little bits of oil at a time with the corner of a piece of paper towel until it was low enough where it would actually compress without a fight. Now were good.

    Hard telling how long i had no rear shock absorbers. The progressive spring seems to do a good job at hiding that.

    Sent from my LGL722DL using Tapatalk

  2. #2
    RC Qualifier
    Join Date
    Aug 2015
    Posts
    744
    The shock will not extend unless there is a pressure differential on the piston. Shock extension (or rebound) is mostly spring function. Thick oils or a small orifice opening will increase this rebound time, if your shocks are low on oil or use a very light oil it will not rebound hardly at all without the springs assistance. Shocks are dampers to reduce spring oscillation (bounce).

    Sent from my VS996 using Tapatalk

  3. #3
    RC Qualifier
    Join Date
    Aug 2015
    Posts
    744
    Also if your shocks are low on oil it will cause the oil to foam which moves through the piston orifices easier and lessens dampening because of no resistance to piston movement.

    Sent from my VS996 using Tapatalk

  4. #4
    RC Enthusiast
    Join Date
    Sep 2020
    Posts
    43
    The no rebound would be from old oil that has lost its viscosity. Shock oil wouldn't or shouldn't get dirty unless there is a slight leak. Which would in turn cause no rebound from being low as you mentioned.
    When I replace shock oil I focus on bleeding air first. Fill the shock body about a quarter of the way full. Bleed the air by pushing the shock shaft up a little then pull back forcing air through the holes of the shock piston. Don't push the piston above the level of the oil. Once there is no more air, add a little more oil and repeat. Continue until the oil is almost to the top of the body.
    At this point just add drop by drop until the oil just starts to crown above the shock body. Get a towel, and slowly screw the cap on. The cap bladder will force some oil out as you screw it on so have the towel ready. Clean up and tighten the cap. Check rebound to be sure you didn't overfill and lock the shock as you mentioned. If it's locked, bleed a little out. Any rebound means you have a nice full shock body. Don't worry about 1/16" difference in rebound. Some rebound, and no shock lock means you should be good to go. Also check a-arm movement while the shocks are off. Make sure no pins are bent and everything moves freely.

  5. #5
    RC Turnbuckle Jr. rag6's Avatar
    Join Date
    Mar 2008
    Location
    Accepting requests for bashing at GREENWOOD BASHPLEX in Pittsburgh PA!! Check the thread in the track buddy forum and reply there or pm
    Posts
    15,587
    In my experience, it's usually a small collection of things when a shock sags while on the truck while it's on the ground. Either springs do not match the oil (progressive springs start soft then get stiffer, so it can be a too soft prog spring, too soft linear spring, oil too thick, or piston holes too small) or even possibly a bent shock shaft.


    I think your talking about the shock after refilling... No spring on it right? And if you compress it all the way, it didn't pop back out? Then you overfilled it and it would not compress all the way.

    I do what you did in the end. I overfill a little bit, then remove some, button it back up. And see how the shock responds when compressed. I want no rebound, but I also want no air between the bladder and the oil. Your method of removing oil, then checking rebound matches my method.

    Between the bladder and shock cap, your supposed to have air, but none below it. The bladder, and the air above it is there because as the shock compresses, the shock shaft enters the shock body. It adds volume within the shock body. That volume pushes the bladder up to compensate for the shock shaft entering. At some point, too much oil will push the bladder up to the limit, causing the locked up shaft you experienced when compressing it.

    Many MANY years ago I read an article in RCCA magazine by an accomplished pro racer about rebound shock tuning. The affect of static shock shaft rebound on the real life handling of a car is so small, that mostly top level suspension guys will be able to feel it on the track. He said what I said above. No rebound, absolutely no air under the bladder. He also said no suction when you pull it out. Neutral. You can feel if there is air in the oil when compressing a rested shock. It will compress a few mm before you feel it dampening.

    I've done that for every bladder type oil shock I've owned in the last few decades. My all plastic ultras rarely ever pop caps off even with 50 wt oil. If your shock shaft is pushing out after a refill, you may have a bit too much oil. If you feel the shaft move easily for a couple mm before the dampening happens, then there is too little oil.





    Sent from my moto e5 cruise using Tapatalk
    Ya can't polish fertilizer...

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •