RockShox Pike sucked down.

PB Forum :: Mechanics' Lounge
RockShox Pike sucked down.
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flag down1111
Posted: Feb 5, 2016 at 8:57 Quote
Hi,

Hoping someone can offer some assistance.

Did a lower leg service on my Pikes today (Solo air/RCT23, 160mm).

Followed the instructions on a well known magazines YouTube and got them back together, they feel 100% plusher for sure; better than they did from new.

The issue is they know sit at 20% sag unless I pump them up to 140psi (run them at around 80psi with 4 x volume spacers usually). I’ve tried letter some air out, cycling them etc, pumping them up and cycling them etc…. as soon as I set them back to 80psi they sit down to around 10/20% saga again.

Not sure how to resolve. The only “air” considerations I considered when putting them back together was, as per the video to make sure when I assembled the push rods was to compress the lowers all the way with the screw in the bottom (loosely, pushing it in) so any air could escape from the lowers before tightening the bottom bolts.

This essentially meant the forks were “sucked down” all the way until I added air on the positive chamber. When I let all the air out of the positive changer now, the forks automatically compress 100%.

Any help/suggestions would be greatly appreciated, supposed to be riding tomorrow!!!

Thanks!
flag bigburd
Posted: Feb 5, 2016 at 9:51 Quote
you may get more/quicker help posting on the mechanics Q+A thread at the top of this sub forum.
flag el-booto
Posted: Feb 5, 2016 at 10:47 Quote
Sounds like the "equalization port" in the bottom of the spring side stanchion is blocked and there's a big whack of air in the negative side, how much grease did you put on the air piston?
flag Dirtlabs
Posted: Feb 5, 2016 at 11:45 Quote
You may heave created too much of a vacuum in the lowers which acts as a secondary negative spring causing the fork to suck up. could also just be a clogged air transfer port in the air chamber.
flag sheldonuvic
Posted: Feb 5, 2016 at 14:22 Quote
I am surprised you didn't find this mentioned when doing your rebuild research.

The seals used on the Pike are surprisingly strong, and will trap air creating a negative spring in the legs of the fork. Easiest thing to do is to slip the tapered end of a small zip tie under the seal while pulling up on the fork to release the pressure and bring things back to full travel.

Not uncommon for myself to have a ziptie in the pack when riding high in the alpine to even the internal pressure to the ambient air pressure in order to eliminate "fork suck". Some people have taken to drilling and tapping motocross micro-bleeder valves into their forks to make this more convenient (I am planning to on my next rebuild as I am out of warranty).

Hope that helps!
flag RickDraper
Posted: Feb 8, 2016 at 8:52 Quote
The well known magazine video is totally wrong in the way they installed the lower legs.
flag hainman
O+ FL
Posted: Feb 9, 2016 at 11:35 Quote
I had similar issue's.someone told me to get the smallest tie strap and slide it gently in between the washer seal and the stanchion and slide it up and down gently,it will release some if not all of the air vaccum,Worked for me
flag Dirtlabs
Posted: Feb 9, 2016 at 16:31 Quote
Here is a video to show you how to do it. http://www.dirtlabs.com/burping-pressure-fork-lowers/
flag sjacklin
O+
Posted: Jul 10, 2020 at 14:44 Quote
Here's an update with my personal experience:

2017 RCT3 140mm was sitting around the 20% sag mark.

Tried the zip tie trick, with air and without, cycled it a few times, but still kept coming back to about 20% unless I put 140 PSI in the chamber.

Before giving up and calling the shop, I put my foot on the top the tire and gave it a good yank to see if I could "unsuck" it.

Sure enough, the fork returned to full travel. A blocked channel, as mentioned by others, must have released.

Hope my experience helps. Just yank it!
flag rahrider
O+
Posted: Jul 10, 2020 at 21:28 Quote
sjacklin wrote:
Here's an update with my personal experience:

2017 RCT3 140mm was sitting around the 20% sag mark.

Tried the zip tie trick, with air and without, cycled it a few times, but still kept coming back to about 20% unless I put 140 PSI in the chamber.

Before giving up and calling the shop, I put my foot on the top the tire and gave it a good yank to see if I could "unsuck" it.

Sure enough, the fork returned to full travel. A blocked channel, as mentioned by others, must have released.

Hope my experience helps. Just yank it!

Did this once, but I sat on the tire and grabbed the fork crown and lifted hard as I could. Apparently you can make it easier to equalize the pressure between the neg and pos Chambers by equalizing them numerous times when inflating and deflating the fork.

Try deflating the fork 5-10 psi at a time then cycling the fork 5 times pulling the fork to full extension with each cycle. Apparently cycling the fork every 5-10 psi prevents the trapped air problem. Also, the too much grease on the airshaft causes troubles.
flag Thorjensen
O+
Posted: Jul 11, 2020 at 11:25 Quote
down1111 wrote:
Hi,

Hoping someone can offer some assistance.

Did a lower leg service on my Pikes today (Solo air/RCT23, 160mm).

Followed the instructions on a well known magazines YouTube and got them back together, they feel 100% plusher for sure; better than they did from new.

The issue is they know sit at 20% sag unless I pump them up to 140psi (run them at around 80psi with 4 x volume spacers usually). I’ve tried letter some air out, cycling them etc, pumping them up and cycling them etc…. as soon as I set them back to 80psi they sit down to around 10/20% saga again.

Not sure how to resolve. The only “air” considerations I considered when putting them back together was, as per the video to make sure when I assembled the push rods was to compress the lowers all the way with the screw in the bottom (loosely, pushing it in) so any air could escape from the lowers before tightening the bottom bolts.

This essentially meant the forks were “sucked down” all the way until I added air on the positive chamber. When I let all the air out of the positive changer now, the forks automatically compress 100%.

Any help/suggestions would be greatly appreciated, supposed to be riding tomorrow!!!

Thanks!

The well known online mag compresses the lowers compleatly when they install the two bolts into the lowers. That's NOT the way to do it. You created too much of a vacuum when you pump air into your fork. You only have to compress the lowers so much that you can reach both treads in the shafts.
You can try the easy fix with the pointy end of a cable tie and ease it down between the wiper and stanchion. Keep on doing that until you dont hear any more air hizzing out. If that doesn't work remove your lowers check your air piston is max extended when you slide on the lowers again. Enjoy
flag Blownoutrides
O+
Posted: Dec 2, 2021 at 9:54 Quote
Thorjensen wrote:
down1111 wrote:
Hi,

Hoping someone can offer some assistance.

Did a lower leg service on my Pikes today (Solo air/RCT23, 160mm).

Followed the instructions on a well known magazines YouTube and got them back together, they feel 100% plusher for sure; better than they did from new.

The issue is they know sit at 20% sag unless I pump them up to 140psi (run them at around 80psi with 4 x volume spacers usually). I’ve tried letter some air out, cycling them etc, pumping them up and cycling them etc…. as soon as I set them back to 80psi they sit down to around 10/20% saga again.

Not sure how to resolve. The only “air” considerations I considered when putting them back together was, as per the video to make sure when I assembled the push rods was to compress the lowers all the way with the screw in the bottom (loosely, pushing it in) so any air could escape from the lowers before tightening the bottom bolts.

This essentially meant the forks were “sucked down” all the way until I added air on the positive chamber. When I let all the air out of the positive changer now, the forks automatically compress 100%.

Any help/suggestions would be greatly appreciated, supposed to be riding tomorrow!!!

Thanks!

The well known online mag compresses the lowers compleatly when they install the two bolts into the lowers. That's NOT the way to do it. You created too much of a vacuum when you pump air into your fork. You only have to compress the lowers so much that you can reach both treads in the shafts.
You can try the easy fix with the pointy end of a cable tie and ease it down between the wiper and stanchion. Keep on doing that until you dont hear any more air hizzing out. If that doesn't work remove your lowers check your air piston is max extended when you slide on the lowers again. Enjoy

Just wanted to say thanks for posting this... definitely over compressed the spring when I put my lowers back on and had the fork stuck down in a big way. Pulled the lowers and reinstalled the air spring (shaft was stuck in, big POP when it came out). Sorted. Thanks again.
flag GBangShredder
Posted: Jun 29, 2022 at 18:39 Quote
That was exactly my issue, fork was sucked down... the zip tie into the dust seals fixed it! Thanks pinkbike!
flag Thorjensen
O+
Posted: Jun 30, 2022 at 6:20 Quote
GBangShredder wrote:
That was exactly my issue, fork was sucked down... the zip tie into the dust seals fixed it! Thanks pinkbike!

You are welcome ☺️
flag GBangShredder
Posted: Jul 1, 2022 at 0:09 Quote
I have to say I'm really impressed that those dust seals hold that kind of pressure. No wonder they make the fork feel like poop once they are dirty. It all makes sense now!
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