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Teardown

Öhlins RXF 36 m.2 Spring Swap

Words AJ Barlas
Photos AJ Barlas
Date Jul 15, 2020
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Coil sprung forks used to be the best performance option available. Since that time air springs have improved by leaps and bounds and major brands like RockShox and Fox stopped producing top of the line coil forks. More recently aftermarket options have begun popping up allowing you to retrofit your air fork into a sweet spring. This makes them a great update for riders interested in a coil-sprung fork. Many of these options have a downside, though; they typically weigh more than the original air-sprung fork and often more than a stock coil-sprung option.

But perhaps the biggest disadvantage is that most, if not all retrofits, are stuck as a coil once the change is done. It’s not impossible to switch back to an air spring but in most situations, a minimum requirement involves the costly process of replacing the CSU to do so successfully.

Öhlins opted for a self-contained air spring for the new RXF36 m.2, making it possible to switch from coil to air and back again. I recently posted my review of the Öhlins RXF36 m.2 coil fork and have now been on the air spring for awhile. I thought it would be worthwhile sharing the process of the change. I visited Vorsprung Suspension in Whistler, a local authorized Öhlins Service Centre, to get the change done professionally.

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The m.2 coil fork cleaned, loaded, and ready for surgery.

Swapping About

While it can be as simple as a straight forward spring swap, Öhlins sells forks with different compression tunes in the damper. The coil-sprung m.2 comes with Öhlins' C60 damper tune but the air-sprung fork comes with a lighter C50 tune. Öhlins feels the different characteristics between an air and coil spring necessitate adjusting the compression to provide a comparable ride quality, regardless of an individual's spring choice. For each spring the rebound tune remains the same at R40.

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First things first, remove the lowers.

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With the lowers off, Tom at Vorsprung gives everything a rinse clean.

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The lowers were hung to dry while we got stuck in.

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With the damper and coil spring removed, we were now ready to change the shim stack to Öhlins' C50 compression tune for the air spring.

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Öhlins' TTX18 damper is a cartridge system. In the vice ready to be opened.

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The top and bottom of the cartridge were opened to reveal the inner tube of the twin-tube damper cartridge.

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The tubes split out. From here we begin to get into the depths of the damper. But first, we needed a set of clamps made.

The parts for the air spring were mostly contained within the air spring cartridge assembly, the exception being a replacement end cap for the spring system. For the coil setup, the end cap has a smaller relief for the piston rod but because the air spring piston rod is larger, it requires a different part to secure it in the stanchion. Apart from this and the required special "Coil kit tool,” anyone capable of a lower leg service shouldn't have any problem changing the springs in either direction. Öhlins has also started releasing service manuals and video to help capable at-home and shop mechanics access the information needed to successfully perform these services.

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A new set of clamps to hold the inner cartridge was needed so while Steve set up the CNC machine in the back of the shop to make the part, we moved onto the spring swap. You can see the different inner diameter on the two spring end caps (the silver pieces in the image).

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With the coil spring assembly removed, we were ready to slide in the air spring cartridge.

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The air spring end cap in place. This part requires a special Öhlins tool to complete the job.

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At this point, I was feeling a bit sad about the exceptional coil spring feel being gone, but was interested in seeing how the air spring compared.

Where things get tricky is changing the shim stack to match Öhlins’ specifications. Removing the damper cartridge is no more difficult than the spring swap but digging into its internals is more complicated. Öhlins appears to do a good job of applying Loctite to their threads and each step required a little heat to loosen things up. Once inside, the inner workings of the TTX damper are visible. Steve at Vorsprung informed me that the damper uses a variable diameter clamp system. A downside is it can be finicky to put together to specifications thanks to the assembly requiring a very precise torque. Get it wrong and oil won't be able to adequately flow through the valves, degrading performance.


The variable diameter clamp system basically stiffens or softens the shim stack, and when it reaches the firmest position it also closes off the LSC circuit. It's a very good system in the sense that it allows for you to "revalve" the compression damping in a very similar way to a softer or stiffer shim stack. – Steve Matthews, Vorsprung
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Now with freshly manufactured clamps, Tom moved onto the rest of the damper tear down.

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With the inner tube open, we got to see how the system was dealing with everything after 800km of abuse. The damper fluid was clean and aside from the need to revalve, didn't need to be touched. Öhlins use a good amount of Loctite on the threads throughout the fork and the damper required a bit of heat to help it loosen up.

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Steve shows me the variable diameter clamp system and the current shim of the compression valve assembly. I understand the basics of shims and dampers but things quickly went over my head. Steve enjoys getting tech!

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Shim stacks and damper ready to go. We were ready to switch the compression tune from the coil sprung C60 down to the lighter C50 for the air spring.

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The compression valve assembly mid way through the revalve.

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Tom carefully removes the first of the shims of the check valve assembly.

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With everything done, Tom carefully secures the nut to the check valve assembly. Getting the torque on these nuts wrong at either end will cause the damper to function incorrectly.

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With the damper done, Tom fills the system back up with the recommended damper fluid, cycling the piston rod as he does.

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The damper is finished and the cartridge put back together. Now we could give the lowers a proper clean and put everything back together.

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Everything received a good clean to make sure things would run as new, or better, after the service.

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Final inspection! The lowers did have some contaminants in them when we first pulled them apart, somewhat to be expected after a solid amount of use. We wanted to be sure everything was gone before putting the fork back together.

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After 800kms of use, new seals were installed. Öhlins' seal kits also include new bottom bumpers, which I haven't seen from other service kits. Tom noted that it's quite rare for the bumpers to need replacing but we replaced them anyway.

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With everything back together, Tom airs up the spring…

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And checks the damper to make sure everything is functioning as it should.

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From coil to air in a service.

It is possible to perform the spring swap without changing the compression tune in the fork. Doing a straight swap makes the process much faster but to properly review the air-sprung fork, I had to change it to reflect what Öhlins sells to consumers. So far everything feels great and with the lighter damper tune my settings are very close to the coil with heavier compression valving. Before completing the review I will swap out the air spring for the coil but test the current C50 tune with that to see how it affects things. Look for that review soon.

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Comments

GiveitsomeWelly
0
Karl Fitzpatrick  - July 14, 2020, 12:53 a.m.

I read somewhere recently that Formula forks can be changed from coil to air by swapping the damper from one leg to the other. 

Sounded like an awesome way to swap my RockShox back and forth until I realised that there's a teeny tiny dimple in the air side the equalizes the pressure between the pos/neg chambers as it moves through its stroke. 

If anyone here can tell me if this is possible or what small mod can be done to make it so, I'm all ears.

Reply

AJ_Barlas
0
AJ Barlas  - July 14, 2020, 8:17 a.m.

That is interesting. Not sure how it’s possible, if it truly is, with Formula forks but the dimple to equalize chambers is very important! Perhaps those you heard it from run the coil in the damper side and when switching back to air, run the air back in the stock spring side?

Reply

albadistribution
+2 AJ Barlas Andrew Major
albadistribution  - July 14, 2020, 10 a.m.

Hey guys, it's possible with the Formula as the fork uses either a coil negative spring (Selva S) or a separately adjusted negative air chamber (Selva R).  Both options mean that you can run your spring side in either fork leg. So, if you started with an air fork (R or S) you could swap to coil, run the coil in the same side, but if you ever wanted to switch back to air, you'd have to run the air in the damper side now, as the previous spring leg would be marked inside from the coil spring.

Those negative spring transfer ports wouldn't be easy to add to an existing fork leg, I doubt.

Reply

AJ_Barlas
0
AJ Barlas  - July 14, 2020, 1:06 p.m.

Awesome info, thanks heaps for chiming in and confirming this for us guys!

Reply

velocipedestrian
0
Velocipedestrian  - July 15, 2020, 2:59 a.m.

This makes me wonder if this trick could work with dimpled forks... Any reason a Fox or RS damper can't be moved over to the spring side?

Reply

GladePlayboy
0
Rob Gretchen  - July 14, 2020, 6:03 a.m.

Nice... I am riding the M.2 Air right now alongside the TT Air shock and really enoying it.   My son has the previous gen coil fork on his bike and I am impressed with how sensitive my air sprung fork is compared to the coil... and nice job with the Hope split ring crown race.    Why aren't all headsets like this?

Reply

AJ_Barlas
+1 Rob Gretchen
AJ Barlas  - July 14, 2020, 8:20 a.m.

Like you, I’m certainly finding it to work damn impressively with the air configuration, Rob! 

Not sure about the crown race? There may be a mechanical/engineering reason I’ve not heard but I’ve not had a problem with the Hope split race in three years now. It makes things easy when switching the front end, that’s for sure.

Reply

kekoa
+1 AJ Barlas
kekoa  - July 14, 2020, 11:07 p.m.

That Hope crown race is invisible. Been running Hope headset and crown race for over three years and it’s great.

Reply

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