Servicing the “non-servicable” OneUp Dropper Cartridge

If you have a few OneUp Droppers like myself, it’s possible you’ve had issues with the non-serviceable cartridges. OneUp are extremely good with their warranty and usually replace the cartridges if they’ve failed during the warranty period, also the replacements are relatively cheap. But if you’re in a pinch and desperately need to service your cartridge then this Instructable shows you how to do that.

Thank you @piciu256 for finding the IFP!

Also, the Race Face Aeffect Dropper has a very similar (almost identical) cartridge and there is a great write up here about tearing it down: https://nsmb.com/articles/race-face-aeffect-dropper-post-teardown/

Supplies

Bent Inner Circlip Pliers or 3d printed tool to remove base of cartridge (or can be made out of 3mm steel/aluminium plate) and four old threaded 2mm spokes
8mm spanner
Syringe (Not entirely necessary but helps with fluid)
Light Grease
Bike Specific Suspension/Damper Fluid (about 30-40mL)
4mm hex tool
Soft Jawed Clamp
A set of o-ring removal tools
17mm wooden dowel
Isopropanol and shop towels

Step 1: Remove the Cartridge

Follow OneUps instructions to remove the cartridge.

It's really easy and everything is on their website.

Step 2: Depressurise Cartridge

Remove the pressure from the cartridge by releasing it from the Schrader valve.

Use a shock pump with an air release button to let the air out.

Step 3: Assemble Your 3D Printed Tool If Not Using Circlip Pliers

Skip this step if you are using circlip pliers

3d print the tool, it’s a 9mm hole in the center with 2mm holes spaced 10mm apart in a square pattern (Spokes are 2.5mm x 1mm thread pitch, so if you are making this out of steel you will need a tap about that size)
Assemble your 3d printed tool
Cut the J-bend ends off the spokes
Using a drill, sand the threaded ends to a tip
Using a drill, thread the spokes into the 3d printed tool

Step 4: Remove Bottom of Cartridge

Remove the bottom of the cartridge with the 3d printed tool or inner bent circlip pliers

Remove the plunger by actuating the plunger and pulling (push down on rod through center and pull out at the same time)

Drain fluid into a container

Step 5: Remove Top of Cartridge

Remove top of the cartridge using a 8mm spanner

Step 6: Remove Inner Tube

Insert a 17mm dowel, into the bottom of the outer tube. The bottom is the end that has writing on it.

Remove the inner tube from the outer tube by pushing the inner tube through the top of the outer tube with the 17mm dowel.

The inner tube can get stuck, try wiggling the top end whilst pushing with the dowel.

The Internal Floating Piston (IFP) can get quite stuck, quite a lot of force can be required to remove it. Try holding the outer tube and banging the end of the dowel on the ground.

NOTE: the IFP can only be removed from the top of the outer tube.

Step 7: Inspect All Parts

Pull plunger from cartridge and clean everything with isopropanol

Inspect all parts.

It's common for these cartridges to have a broken spring and o-ring on the plunger which causes the plunger to slowly extend after being depressed fully. I used a soft jawed clamp to hold the shaft and removed the end with a 4mm hex tool and removed the tip to replace them. The spring was 5mm Diameter x 9mm length and the o-ring was 7.65mm OD with a 1.5mm thickness.

Feel all o-rings, o-rings tend to go hard if they are too old.

Step 8: Assembly - Insert IFP Onto Inner Tube

Grease the IFP and the outside of the inner tube with slick honey (or similar light grease such as slickoleum) and insert the IFP onto the inner tube.

Whilst putting pressure on the IFP into the inner tube, use an o-ring removal tool to squash the o-ring into the inner tube. Pay attention not to damage the o-ring (try and push it in, don't stab it with the sharp tip)

Step 9: Insert the IFP and Inner Tube Into the Outer Tube

Follow these steps exactly to get the IFP position correct!

Insert the IFP and Inner tube into the outer tube from the top of the outer tube (remember that the bottom of the outer tube has writing on it). IFP should be fully inserted into the outer tube.

Push the inner tube into the outer tube, the IFP, inner tube and outer tube should all be flush at the top.

Using the dowel from the top of the outer tube, push the IFP and inner tube all the way to the base of the outer tube. You should feel the IFP o-ring pop into the bottom when you have it all the way to the bottom.

Now push the inner tube back into the the outer tube. Using the dowel push both the IFP and inner tube back towards the top until the inner tube is flush with the outer tube.

What you should see at this point is the inner and outer tubes are flush at the top, at the bottom the inner tube should be flush with the IFP and about 20mm inside the outer tube.

See the picture for this step showing the inner tube flush with the IFP about 20mm inside the outer tube at the bottom, and the second picture showing the inner and outer tubes flush at the top.

Step 10: Install the Schrader Valve Assembly

Grease the Schrader valve assembly liberally around the o-rings and insert into the top of the outer tube. The bottom o-ring should slide into the inner tube and as you screw in the assembly it will push down the inner tube.

Watch the IFP and make sure it doesn't side with the inner tube as you screw on the assembly, if it does you'll need to push the IFP down so it's about 20mm inside the outer tube. If the IFP did not move and the inner tube has slid down to the bottom, no adjustment is required.

Tighten the assembly with a 8mm spanner. Take extreme care clamping the base as you could deform the tube. Remember the o-ring performs the seal so the assembly doesn't have to be super tight.

Step 11: Fill With Fluid

Turn the outer tube up-side down.

From the base, completely fill the inner and outer chamber with 30ml of suspension fluid. The fluid should be level with the outer tube. NOTE the IFP should prevent fluid from entering the outerair chamber, the IFP should still be about 20mm from the bottom of the outer tube if previous steps have been done correctly.

Whilst pushing the plunger valve actuator to open the plunger valve, insert the plunger so that the tip is just inside the inner tube.

NOTE: after this step, do not move the plunger until the lower seal assembly is installed.

Step 12: Install Lower Assembly Seal

Liberally grease the lower assembly seal.

Insert onto plunger shaft and slide down and start screwing into the outer tube.

Note that some fluid will be lost when first screwing on the assembly, this is normal. When the o-ring starts entering the outer tube take care to ensure it's going into the outer tube correctly and not getting caught. When the o-ring is in it will start pushing down the IFP so you may feel more resistance whilst you are screwing it in.

As with the Schrader valve assembly, don't overtighten, remember the o-ring does the sealing not the threads.

Step 13: Test the Cartridge

Test the cartridge. Pump to 300PSI and compress the cartridge as far as it will go.

If the cartridge won't compress, either the IFP is getting stuck or the plunger valve is not being actuated properly. Either way the cartridge needs to be disassembled again and inspected. Ensure there is no damage to any of the inner or outer tubes and all o-rings are not damaged or twisted.

If the cartridge won't stay compressed and slowly rises, either the plunger valve is not sealing or the outer o-ring around the plunger is not sealing. Either way the cartridge needs to be disassembled again and inspected. Disassemble the plunger valve and recheck the spring and inner o-ring, I recommend to replace both of them as the spring loses tension when aged, also the o-ring hardens meaning it doesn't provide an effective seal.

Do not do the test with the shock pump attached. The additional air volume will make it easier to to compress the cartridge and performance will change drastically when you take the shock pump off. You may also damage your shock pump if it not rated for around 600-700PSI as the pressure will increase when you compress the cartridge.

Step 14: Optional, Long Term Test

With the cartridge fully depressed, apply some electrical tape to mark the base of the plunger. Leave this for several hours or days (however long you need to prove to yourself the cartridge is holding it's position). If the cartridge stays in the same position you know you've fixed it.