Rock Shox bottoming out on top of the tire, help needed

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    • #78873

      Hello everyone, I picked up a bike with Rock Shox Magnesium forks, Mag 20. After finally finding that the air fill is the center screw on the dampening dial (three local LBS did not know this even after seeing the bike, thanks to Jesus I found a thread with the Rock Shox Mag 21 service manual). I’d like to know how much air to add. Air starts to escape from the shock as soon as I remove the air needle, but I’ve managed to set the screw under a little pressure but I can’t tell how much. Not nearly as much as indicated in the Mag 21 manual, 30 + lbs. Most of the air escapes before I can set the air inlet screw. Must I set the air inlet screw faster, or is there some better way to fill and actually tell how much air is in the Mag 20 shock?
      I’m feeling very tentative about riding this bike after going over the handle bars during my first test ride when the shocks bottomed out on top of the front wheel, causing the front wheel to come to a abrupt stop. I would hate to have the air leak out during a ride and get hurt.
      I’m not sure if I have enough air in the shock and certainly don’t want another trip over the handle bars. Help this Noob out, and tell me what I need to know about using and maintaining.these shocks.
      After adding air the shocks SEEM ok. They do not bottom out and when I put my full weight of 208lbs. on the handle bars. I’m hopping they will not bottom out after taking a bump or a jump hard and fast. The bike has 26" x 2.2" knobby tires.
      Does anyone have a link to the Mag 20 User’s manual?
      After thinking about the Rock Shox bottoming out on top of the tire, this fork appears very dangerous, if the one that I have is installed correctly. If the shock losses pressure the rider can be ejected from the bike, if the fork bottoms out on the tire, resulting in serious injury or death. Please see photo.

      http://www.flickr.com/photos/[email protected] … 7/sizes/o/

      http://www.flickr.com/photos/[email protected]/3536623357/

    • #78874

      Try this for your tuning charts…

      [url:2jmj704e]http://www.sutherlandsbicycle.com/files/RSSection4.pdf[/url:2jmj704e]

      But beware of this shock. I believe it may have been recalled.

      [url:2jmj704e]http://www.cpsc.gov/cpscpub/prerel/prhtml95/95136.html[/url:2jmj704e]

    • #78875

      Thanks very much Jeremy. According to Sram my bronze color fork was not included in the recall, I’m still leery about using this fork. If it would have been in the recall, they would replace it with one of their Dart branded models. I find it offensive that Sram would replace a defective upper tier item with a lower tier item.
      I can’t seem to get more than about 25 PSI of air into this shock because most of the air that I have pumped in rushes out, after I remove the fill needle, and before I can replace the set screw, regardless of how much I pump in. Do you have any suggestions?
      With the dampening set to the lowest, I can get the shock to bottom out on the top of the tire if I put all of my weight, 208lbs. on the handle bars and press down with all of my strength. With the dampening set to the highest, I can not get the shock to bottom out on to the tire. I will feel more comfortable if I can get about 40 lbs of air into the shock. I’m using the gauge on my floor type bike pimp to estimate the air PSI in the shock.
      Thanks again,
      Uni

    • #78876
      I will feel more comfortable if I can get about 40 lbs of air into the shock. I’m using the gauge on my floor type bike pimp to estimate the air PSI in the shock.

      Somthing dont sound right herre dude.First you say you cant keep the air in the fork once you pump it up which is normal but not in the amount and way your stating.And then you say your using a floor pump to pump up a suspension fork????
      First of all,suspension forks and shocks have there own pump called a "SHOCK PUMP",do you have one of these or did I read your post wrong and miss somthing??
      Second of all,pumping up suspensions even with the right kinda pump will not keep all the air in that you pumped into it,theres always a little that excapes from unscrewing the pump from the shock.You have to over pump it to reach the desired psi. and that takes a little getting used to because it doesnt always come out the same everytime.

    • #78877

      From reading the charts I am definitely thinking you need to be in the high 40’s range on the fork. Some of the pressure will be lost in the hose when you release the pump from the fork so you will probably need to over fill it and get a good guess at how much rushes out.

      A couple of people were mentioning using a shock pump but I don’t think you need one for your specific fork because it allows you to use the needle rather than having to screw the pump onto the fork like newer forks.

    • #78878

      Thanks guys for your help. This 1990’s Rock Shock Mag 20 only takes 35-48lbs of air. I’ve read that most fill this shock with a basketball type fill needle rounded at the fill end so as not to damage the seal. Please explain how a suspension specific pump will help in this situation, will the fill hose even fit this older type fitting? My problem seems to be that I am unable to replace the very small fill screw, about 1/8" diameter, before the air pressure drops to about 25 PSI, even though I inflate the shock to about 60 PSI. The air rushes out so fast after I remove the fill needle. I do not want to bust the seal by over inflating. May be there is a better technique to replace the fill screw without losing so much air pressure? I’ll try removing the needle and then covering the air inlet with a finger while trying to replace the air inlet screw.
      I’m glad to read that what I’m experiencing is normal. I think I just need to develop the technique for filling the shock without losing so much air pressure, or maybe there is a better way?
      All suggestions are appreciated.

      I appreciate your help and comments.
      Uni

    • #78879
      "Jeremy_Green" wrote

      From reading the charts I am definitely thinking you need to be in the high 40’s range on the fork. Some of the pressure will be lost in the hose when you release the pump from the fork so you will probably need to over fill it and get a good guess at how much rushes out.

      A couple of people were mentioning using a shock pump but I don’t think you need one for your specific fork because it allows you to use the needle rather than having to screw the pump onto the fork like newer forks.

      Thanks Jeremy. Even though I pump the PSI to about 70, when I remove the fill needle the air pressure drops to about 25, in about 2 seconds, before I can replace the fill screw and stop the air loss. Any suggestions?
      Thanks again,
      Uni

    • #78880

      I wish I had some great tip for you here other than "use your ninja-like reflexes to plug it super fast." I’m guessing that might be one of the "upgrades" Rock Shox has figured out over the years. New forks use a shrader valve or a presta valve instead of a needle. Good luck.

    • #78881
      First of all,suspension forks and shocks have there own pump called a "SHOCK PUMP",do you have one of these or did I read your post wrong and miss somthing??

      Way to stay on the ball dude,I am not familiar with those older rock shox and it now sounds like your on the right path with the needle thing.Keep on trying to figure it out on your own,but there might be someone here on singleracks familiar with that older fork and could tell you exactly how to pump up that fork.Or you might be able to find an online service manual to show you exactly how to pump up the older rock shox.

      My problem seems to be that I am unable to replace the very small fill screw, about 1/8" diameter, before the air pressure drops to about 25 PSI, even though I inflate the shock to about 60 PSI. The air rushes out so fast after I remove the fill needle. I do not want to bust the seal by over inflating.

      Yeah,dont bust anything or any seals,it sounds like there is a trick to this fork getting the air in there or a way thats just not that obvious at the time.

    • #78882

      Thanks Jeremy and Steve, I think it’s filled to the low 40’s.
      As I remove the fill needle I cover the fill hole with the thumb of the opposite hand, then pickup the screwdriver previously loaded with the fill screw, then as I uncover the fill hole, I quickly replace the fill screw.
      It’s definitely a Ninja move, Lol.
      Now with the index adjusters on the lowest setting I can barely force the fork to move, only about 1/4" as I jump on it with my full weight. When the index adjusters are on the highest setting I can not get the fork to budge, I have to thank Jesus for this.
      I picked the bike up at a yard sale Friday, and am very pleased with it.
      At the same time, I’m also concerned that I can be injured if a seal in this fork fails. Has anyone ever heard of a bike injury due to the seals in the fork failing?
      My rigid frame seem much safer.
      Let me know what you think.
      I appreciate everyone’s viewpoint.
      Thanks,
      Uni

    • #78883

      [url:27vg4k5r]http://www.bikeman.com/content/view/1089/47/[/url:27vg4k5r]

      I searched this fork and found this link for you to check out,it looks like you need a new seal where that needle goes into the fork to fill it with air,like a basketball as far as I can tell.???Anyway,check it out and read it.At any rate,the article has some pretty cool stuff about your fork.

    • #78884
      "steve32300" wrote

      [url:1yb2m4rp]http://www.bikeman.com/content/view/1089/47/[/url:1yb2m4rp]

      I searched this fork and found this link for you to check out,it looks like you need a new seal where that needle goes into the fork to fill it with air,like a basketball as far as I can tell.???Anyway,check it out and read it.At any rate,the article has some pretty cool stuff about your fork.

      Thanks Steve, I will.

    • #78885

      Thanks everyone. The fork height was the cause of the fork bottoming out. Now the fork legs are flush with the crown and I have 1/8"-1/4" clearance even after removing all the air in the shock, and it does not bottom out.
      Uni

    • #78886

      So it was "stuck" in it’s travel at a certain point??I’m just curious,I’m all interested in just how this fork works now,and would love to learn more about how this fork works with the needle thing and the current problem you were having with it.It’s old technology but makes me curious.

    • #78887

      Hi Steve, the upper fork legs were not flush with the fork crown. They were actually above the fork crown by about 1/4". Take a look a this picture and you will be able to see what I mean.

      http://farm4.static.flickr.com/3628/353 … e90f_o.jpg

      When The fork legs were lowered I had enough clearance so that the fork would not bottom out on the top of the tire.

      I have not fully learned how these works myself. Filling them with air is like filling a basketball with air, or so I’m told. However with these, the air rushes out of the fill valve which is located in the middle of the index adjuster knob. Funny thing, if I cover the fill valve opening with my thumb for a second after removing the air needle, then remove my thumb, the air does not escape nearly as fast. Moreover, after replacing the fill valve screw, and then removing the screw the next day, the air does not readily rush out. I have to insert the air needle to depressurize the shock. Go figure! I need to get in touch with someone that has actually used, and knows how this fork should work. The people that I spoke with at Sram are too young. This fork was before there time.
      Ask, and I will try to answer any questions.
      Thanks again,
      Uni

    • #78888
      "Unicornz0" wrote

      Hi Steve, the upper fork legs were not flush with the fork crown. They were actually above the fork crown by about 1/4". Take a look a this picture and you will be able to see what I mean.

      http://farm4.static.flickr.com/3628/353 … e90f_o.jpg

      When The fork legs were lowered I had enough clearance so that the fork would not bottom out on the top of the tire.

      I have not fully learned how these works myself. Filling them with air is like filling a basketball with air, or so I’m told. However with these, the air rushes out of the fill valve which is located in the middle of the index adjuster knob. Funny thing, if I cover the fill valve opening with my thumb for a second after removing the air needle, then remove my thumb, the air does not escape nearly as fast. Moreover, after replacing the fill valve screw, and then removing the screw the next day, the air does not readily rush out. I have to insert the air needle to depressurize the shock. Go figure! I need to get in touch with someone that has actually used, and knows how this fork should work. The people that I spoke with at Sram are too young. This fork was before there time.
      Ask, and I will try to answer any questions.
      Thanks again,
      Uni

      It’s pretty lucky that you were able to figure that one out. Never seen that before in a fork but I can see how it could happen. Be careful to make sure that a hard drop doesn’t cause the same problem in the future.

      On another note, I wonder if you do not have a worn out seal or some sort of valve seal failure that is causing the air leak you mentioned when you fill the fork. Some of the seals are nothing more than a rubber loop that squeezes down around the needle that you insert. If those rubber seals were to harden, they wouldn’t resort back to their original shape as well and would lead to leaks. The manual mentions using "Judy Butter or Slick Honey" to lubricate the valve needle and prevent valve wear. I’m not sure exactly what these two lubricants are exactly but I wonder if they don’t also serve some sort of conditioning purpose for the seal, keeping them soft. It might be worth a try to attempt to insert your needle using one of these and see if it helps recondition your seals any. If not, well at least you are following your manufactureres guidlines for fork upkeep. Good luck.

    • #78889

      Thanks Steve, one of the things than baffles me about this shock, is that the air valve seals after it has been filled with air for a while. I’m going to try Slick Honey and hope that it solves this problem of the valve sealing right after removal of the air fill needle, when other lubricants did not.

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