Ask the experts

[Muggydude]

I just rebuilt my 2019 Fox 36 Factory Fork. Grip2 Damper and NA2 Airspring.

I did a complete rebuild of everything. New seals, went to the longer 170mm air shaft (coming from 160mm) as well, and put on a Luftkappe. I used Push Industries low friction dust wipers.

everything seemed to go well, followed all the Fox service shock instructions to a T as far as I know.

Fork feels smooth, it has a bit of a air sucking/squishing sound when compressed. When I first had it Re- assembled, operated great. But the first time I got back on the bike and weighted the fork, it seems like the lower air chamber gets negative pressure? And now Fork doesn’t want to go to full extension, it will suck back down about a cm from full extension due to the negative pressure (if I pull the fork to extend it first).

I released the pressure inside the air spring with the top valve, inverted the shock and removed the lower air spring nut to release the negative air pressure by breaking the seal, so it seems like the negative pressure is in the lower chamber?

After I filled the air spring back up and re-assembled, the fork operated normally again and would go back to full extension… until I weighted it hard. Same thing again, won’t stay at full extension. I assume flexing the fork is causing a seal to allow air to be pushed out of the lower chamber? Causing the negative pressure.

Removing all the air from the top valve, fully extending the fork, and refilling with air also “fixes” the issue until I weight the fork again.

Any ideas? Bad dust wiper seals? Bad seals on the air spring? Not sure what else to do. This is my first time rebuilding a fork so I certainly could have messed something up.


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[bamboocoreONLY]

I just rebuilt my 2019 Fox 36 Factory Fork. Grip2 Damper and NA2 Airspring.

I did a complete rebuild of everything. New seals, went to the longer 170mm air shaft (coming from 160mm) as well, and put on a Luftkappe. I used Push Industries low friction dust wipers.

everything seemed to go well, followed all the Fox service shock instructions to a T as far as I know.

Fork feels smooth, it has a bit of a air sucking/squishing sound when compressed. When I first had it Re- assembled, operated great. But the first time I got back on the bike and weighted the fork, it seems like the lower air chamber gets negative pressure? And now Fork doesn’t want to go to full extension, it will suck back down about a cm from full extension due to the negative pressure (if I pull the fork to extend it first).

I released the pressure inside the air spring with the top valve, inverted the shock and removed the lower air spring nut to release the negative air pressure by breaking the seal, so it seems like the negative pressure is in the lower chamber?

After I filled the air spring back up and re-assembled, the fork operated normally again and would go back to full extension… until I weighted it hard. Same thing again, won’t stay at full extension. I assume flexing the fork is causing a seal to allow air to be pushed out of the lower chamber? Causing the negative pressure.

Removing all the air from the top valve, fully extending the fork, and refilling with air also “fixes” the issue until I weight the fork again.

Any ideas? Bad dust wiper seals? Bad seals on the air spring? Not sure what else to do. This is my first time rebuilding a fork so I certainly could have messed something up.


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I've fixed a lot of negative air issues by pulling the air spring out of the uppers and making sure there isn't loads of grease/slick honey on it. There's little dimples in the uppers that allow air to move from the positive chamber to the negative chamber and if there's too much grease, it doesn't allow the air to pass through using those dimples. So I usually just clean it all with iso and reassemble with just enough slick honey to coat all seals, etc.

[Whiteroom_Guardian]

Ok, so I'm still confused as to how 50 psi, 30% sag, (I'm 175ish pounds kitted up on the bike) and not even getting close to full travel is "too soft".

That much sag would suggest too soft for sure, but the o-ring never gets any closer than about a full inch away from max travel. Even with brand new seals/oil the stanchions don't slide very well....so maybe there is something to the misaligned lowers/bad bushings theory.

Damping seems very bad or blown. It feels like too much compression when all the way open (this is the RC lowest end one with just one setting/knob).....yet all the way closed doesn't really feel any different lol.

I'm on some Reynolds TR carbon wheels. Second owner. Very very stiff. Laced to Hydras.

[Dromond]

OK so I put down a pretty good time on my local "test track" today. Bike still shudders like it wants to throw me off the track.

I made one adjustment before the dh. Slowed down fork rebound a few clicks. Maybe it helped a bit....idk.

How much of this crazy shuddering could be damper related?

Airspring? I'm running one token. 50psi. 30% sag.

I'm fucking mystified.

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You need to test for undersized bushings! I had symptoms like this on a brand new Fox 36 2 years ago. It was a grip 2 but the problem was irrelevant to the damper. I tried every combination of pressure and tokens but no matter what, even with very low pressure and no tokens I couldn’t get close to full travel and I weigh 180lb. The fork felt harsh and my front end traction was poor. It was driving me nuts!

It was difficult to figure out what was wrong. One test I did was to disconnect the air spring and damper so I could just slide the lowers up and down on the stanchions without any resistance. The bushings and seals should have only the slightest friction, allowing them to easily glide up and down, but instead it was tight and almost notchy with noticeable static friction.

Another test is to see if the fork sags slightly under the weight of the bike when you gently rest down the front wheel. It should, but the static friction of stiction from bushings that are too tight will prevent it. I also jumped on a friends bike with the same fork and could immediately tell it could compress under very small bumps in a way my could not.

The fix was to send it back to Fox for warranty. It can back the most supple, tuneable, best riding fork I have had! Chalk it up to terrible quality control at the factory.

A friend of mine was struggling with a similar fork problem recently, it was also on a 36 but could happen to any fork. He couldn’t figure it out, but the second I did the sag-under-own-weight test and tried compressing it manually I new it was a stiction/bushing problem. He sent it in to warranty and it came back performing super well.

[Andeh]

I have wore their underwear for 15+ years, and I have a few of their chamois. They are great, give them a try!

Yeah, their chamois is great. I own 3 pairs. What they say about them running cooler than you'd expect is 100% accurate.

[Andeh]

Ok, so I'm still confused as to how 50 psi, 30% sag, (I'm 175ish pounds kitted up on the bike) and not even getting close to full travel is "too soft".

That much sag would suggest too soft for sure, but the o-ring never gets any closer than about a full inch away from max travel. Even with brand new seals/oil the stanchions don't slide very well....so maybe there is something to the misaligned lowers/bad bushings theory.

Damping seems very bad or blown. It feels like too much compression when all the way open (this is the RC lowest end one with just one setting/knob).....yet all the way closed doesn't really feel any different lol.

I'm on some Reynolds TR carbon wheels. Second owner. Very very stiff. Laced to Hydras.

Not using max travel at super low pressure is because of the pile of tokens. Take them all out, set pressure for 20% sag, go ride. If you bottom out on moderate stuff, add one back. Repeat as necessary.

I wouldn't stress about the lack of damping yet if your air spring setup is completely out in left field. A lot of people (pros included) run their compression wide open with proper air spring setup and quick rebound, and are quite happy with that. Damping only controls shaft speed, not the amount of support you have (within reason... obviously a fully closed LSC will feel like it's got support since the oil can't go anywhere).

[t.odd]

<shudder> seeing rick's (onecut) mug in here...but those chamois are indeed legit and I have a pair in my dresser.

[Whiteroom_Guardian]

Not using max travel at super low pressure is because of the pile of tokens. Take them all out, set pressure for 20% sag, go ride. If you bottom out on moderate stuff, add one back. Repeat as necessary.

I wouldn't stress about the lack of damping yet if your air spring setup is completely out in left field. A lot of people (pros included) run their compression wide open with proper air spring setup and quick rebound, and are quite happy with that. Damping only controls shaft speed, not the amount of support you have (within reason... obviously a fully closed LSC will feel like it's got support since the oil can't go anywhere).

I have one token in there right now. It's been that way since day one. I guess I should just take that one token out and see how it runs.

[Eluder]

I'm on some Reynolds TR carbon wheels. Second owner. Very very stiff. Laced to Hydras.

You are gonna hate me for saying it, but IME this is part of your problem. Those use Reynolds old rims, they shipped the molds to Asia and do the lay up there. They are stiff as fuck, I am a little lighter than you, but I can not ride that rim. They shoot me offline and are sketchy on high-speed chunder. I ended up selling the two pairs I had and went in a different direction. Try throwing a different front wheel on there, alloy or something known to be compliant. My buddies that are over 200lbs don't seem to have as drastic of issues with them for what it's worth... my hands hurt thinking about them.

But yes, your fork seems to suck.

[Eluder]

I just rebuilt my 2019 Fox 36 Factory Fork. Grip2 Damper and NA2 Airspring.

I did a complete rebuild of everything. New seals, went to the longer 170mm air shaft (coming from 160mm) as well, and put on a Luftkappe. I used Push Industries low friction dust wipers.

everything seemed to go well, followed all the Fox service shock instructions to a T as far as I know.

Fork feels smooth, it has a bit of a air sucking/squishing sound when compressed. When I first had it Re- assembled, operated great. But the first time I got back on the bike and weighted the fork, it seems like the lower air chamber gets negative pressure? And now Fork doesn’t want to go to full extension, it will suck back down about a cm from full extension due to the negative pressure (if I pull the fork to extend it first).

I released the pressure inside the air spring with the top valve, inverted the shock and removed the lower air spring nut to release the negative air pressure by breaking the seal, so it seems like the negative pressure is in the lower chamber?

After I filled the air spring back up and re-assembled, the fork operated normally again and would go back to full extension… until I weighted it hard. Same thing again, won’t stay at full extension. I assume flexing the fork is causing a seal to allow air to be pushed out of the lower chamber? Causing the negative pressure.

Removing all the air from the top valve, fully extending the fork, and refilling with air also “fixes” the issue until I weight the fork again.

Any ideas? Bad dust wiper seals? Bad seals on the air spring? Not sure what else to do. This is my first time rebuilding a fork so I certainly could have messed something up.


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The Luftkappe increases the size of the negative chamber (duh) and sucks the fork down a bit because of it.

[Whiteroom_Guardian]

I have heard others say those Reynolds are just too stiff. I have thought about getting some of the new I9 Enduro 305s. Have heard good things and I can get a good price on them from a buddy who works there.

[Andeh]

I have heard others say those Reynolds are just too stiff. I have thought about getting some of the new I9 Enduro 305s. Have heard good things and I can get a good price on them from a buddy who works there.

It's definitely another possible factor. Even carbon wheels that are relatively compliant are very stiff compared to aluminum. I had a pair of LB wheels ~4 years back that were painful to ride. This winter I did some back to back rides on my ebike and my Megatrail, riding a set of WAO Unions (regarded generally as a good balance of stiffness and compliance) and the mediocre Roval aluminum wheels that came on the ebike. The Unions felt noticeably harsher in brake bumps than the alu wheels when riding the Megatrail. On the ebike, the stiffer carbon wheels didn't cause the same feedback but the added precision to counter the sled-like nature of the heavy bike felt better. So I put the Unions on the ebike, and got of Reserve AL for the enduro bike.

[Whiteroom_Guardian]

My favorite carbon wheels were the Enves I had (which I did not pay full price for and never would have). They had a great feel until I broke one. The "cheap" DT Swiss alu wheels that came on my SB120 actually had a really nice feel. I think you are onto something here.

I want to believe in this bike. Softer wheels and a new fork and it might totally change the way it rides.

[Eluder]

My favorite carbon wheels were the Enves I had (which I did not pay full price for and never would have). They had a great feel until I broke one. The "cheap" DT Swiss alu wheels that came on my SB120 actually had a really nice feel. I think you are onto something here.

I want to believe in this bike. Softer wheels and a new fork and it might totally change the way it rides.

I did a back-and-forth on a Yelli Screamy with some Reynolds and Enves that Toast was reviewing 6-7 years ago. The Enves were amazing, but the Reynolds just hurt. Thankfully Enve made everyone up there game in this regard.

[toast2266]

Agreed with all of the above on wheels. I don't think the wheels are the real problem for WRG, but they probably aren't helping things either.

[Muggydude]

I just rebuilt my 2019 Fox 36 Factory Fork. Grip2 Damper and NA2 Airspring.

I did a complete rebuild of everything. New seals, went to the longer 170mm air shaft (coming from 160mm) as well, and put on a Luftkappe. I used Push Industries low friction dust wipers.

everything seemed to go well, followed all the Fox service shock instructions to a T as far as I know.

Fork feels smooth, it has a bit of a air sucking/squishing sound when compressed. When I first had it Re- assembled, operated great. But the first time I got back on the bike and weighted the fork, it seems like the lower air chamber gets negative pressure? And now Fork doesn’t want to go to full extension, it will suck back down about a cm from full extension due to the negative pressure (if I pull the fork to extend it first).

I released the pressure inside the air spring with the top valve, inverted the shock and removed the lower air spring nut to release the negative air pressure by breaking the seal, so it seems like the negative pressure is in the lower chamber?

After I filled the air spring back up and re-assembled, the fork operated normally again and would go back to full extension… until I weighted it hard. Same thing again, won’t stay at full extension. I assume flexing the fork is causing a seal to allow air to be pushed out of the lower chamber? Causing the negative pressure.

Removing all the air from the top valve, fully extending the fork, and refilling with air also “fixes” the issue until I weight the fork again.

Any ideas? Bad dust wiper seals? Bad seals on the air spring? Not sure what else to do. This is my first time rebuilding a fork so I certainly could have messed something up.


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https://youtu.be/zSZaew4XCzk

Here’s a video of what’s happening. You can hear the air equalizing a bit at 9 seconds in.

I don’t think there’s too much grease on the piston, it wasn’t very generous. Certainly way way less than from the factory.

So is this normal with the Lufkappe?

I did just go from 160mm to 170mm travel, so the 10-15mm of lost extension isn’t the end of the world, I’m more concerned about if the fork is going to perform properly.

[Spencer123]

Ride wrap: I know it’s been covered before; but the ride wrap we ordered is going to be a week behind our parts coming in for a build.

Is it way easier to wrap the frame before building it, or is it reasonable to wrap it later and just pull the wheels and cranks?

Thanks!

[MegaStoke]

It's definitely another possible factor. Even carbon wheels that are relatively compliant are very stiff compared to aluminum...

Zipp 3zeroMotos are the most compliant rims I’ve ever been on, by a large margin. They’re also heavy and really expensive, but they sure do ride nice.

[joetron]

Ride wrap: I know it’s been covered before; but the ride wrap we ordered is going to be a week behind our parts coming in for a build.

Is it way easier to wrap the frame before building it, or is it reasonable to wrap it later and just pull the wheels and cranks?

Thanks!

Yes, best time to Ride Wrap is before building/riding.



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[Boissal]

I have one token in there right now. It's been that way since day one. I guess I should just take that one token out and see how it runs.

Definitely worth trying, along with running much higher pressure for sag at or below 15%.
I've never been on a Zeb but couldn't get my Pike into the last inch of travel with 2 tokens, and with 1 token it won't go into the last cm, even when test riding it around the house with 20 PSI below what I should be running (35% static sag). Now I run it without tokens, it feels stiff and weird at low speed but the second I get moving sensitivity is there and I'm finally at a point where I'm considering keeping the fork it on the bike. I've also removed a lot of LSC (HSC is almost always wide-opened) and it really improved things. I can bottom out if I really ham on the front, which is what's supposed to happen, mid-stroke support is much better due to the higher pressure, and high speed chatter is no worse than it's been with all other settings.

I've read a number of threads with people experiencing the same issue on various forks: a weird feeback cycle of decreasing pressure to get better small bump/chatter compliance, resulting in less mid-stroke support and a dive-y fork, which they address by adding tokens and making the fork crazy progressive, and before they know it the fork only lives between 50 and 70% of its travel and feels like absolute shit.
Not saying that's what you're experiencing, and clearly you know enough about suspension to avoid that pitfall, but starting at 0 tokens is the ticket for us light people. I have complaints about the Pike's airspring with no tokens, but with 2 tokens in the only thing I want to do it use the fork as a gardening tool because it's an absolute POS that can be optimized for more that 1 thing.

If you can't get the Zeb to work without tokens then move on, the properties of the air spring are just not working for you and not amounts of fucking with the fork will get you where you want to be.

[Roxtar]

I have heard others say those Reynolds are just too stiff. I have thought about getting some of the new I9 Enduro 305s. Have heard good things and I can get a good price on them from a buddy who works there.

I've run the Carbon Enduro 305s on my last three builds so you know where I stand on them. If you're worried about too much vertical stiffness, go with the 24H.
What I love about them is the lateral stiffness when stuffed into a turn. "Normal" spoked wheels feel like noodles now.

[Andeh]

One other reason to ditch the tokens: you said you really liked your old 36 with coil conversion. Coil is linear, so you should be trying to make your fork more linear, not more progressive (tokens).

[D(C)]

Just chiming in on the Zeb discussion, the Luftkappe is what made the fork work for me. Before that, I was choosing between good support but overly tall/firm initial stroke, or good initial stroke but lack of general support. With the Luftkappe, I can run proper pressure for support without such a tall initial ride height. The main downside is that it’s harder to use full travel. It takes up the space of 2 tokens and you’re running higher pressure, so it can be hard to bottom even with all tokens removed.

I haven’t tried the newest Debonair+ air spring but it also looks to be an improvement over the previous one.

[skinipenem]

WRG, it's been said, but ....

Try 15% sag. Try 20% sag. Try 25% sag.

One inch from full travel with 30% sag means the fork might be running low in the travel which will make it 'harsh', choppy and unpredictable. The fork is operating in a steeper sloped section of its curve... in other words, a very progressive section.

This might not be your problem, but is the first and most likely issue.

Could also be too slow Rebound (too much ground damping) causing the fork to run deep in the travel.

Could also be too much compression

Could also be poorly aligned stanchions or a bushing issue.

Could also be your dick shrinks on long rides and looks like willy, the one-eyed midget optometrist.

Could also be I don't know what the heel I'm talking about and you should either send your fork to a pro for service and turning or buy a different fork.

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[toast2266]

^^^ that, and really, go somewhere with lift served riding. It's a shitload easier to dial in suspension when you can run 10 laps on the same terrain and make minor tweaks. At the very least, go somewhere with short, ~200 vert laps that you can run repeatedly so you can make incremental changes instead of just swinging for the fences with your setup.