Manitou Nixon Platinum Fork

Weight: 2185g including IT adjuster cable and 20mm hex axle, but excluding IT bar mount adjuster.

Infinite Travel (IT)

The left leg of the fork has a positive and negative air piston separated by an air valve that can be opened using the IT cable. Opening the air valve equalises the air pressure between the pos and neg pistons. This reduces the length (and travel) of the fork.

The tear down


Disassembly is fairly straight-forward. Only thing to remember is that the air spring rod and damping cartridge rod screw into the lowers, so you unscrew them by turning clockwise.

To remove the air spring rod, you need to remove the valve core and then use a 3mm allen key to turn the air rod in a clockwise direction. Some pliers are needed to hold the 'nut' that screws on the air spring rod. I say 'nut' because this thing is rounded and you need to hold it with a set of pliers.


Damping

The fork has a sealed damping cartridge with IFP in the right leg. The damper features a port-orifice type compression "base valve" with a shimmed "mid valve" and shimmed rebound piston with adjustable rebound and compression. Here's the base valve that is adjusted via the top control knob.


The IFP is spring loaded and the damper needs to be "bled" with under a slight vacuum (achieving using a syringe) on reassembly.


Mid-valve / rebound piston:


Cartridge disassembly requires some clamping blocks. I made some out of hardwood.


Clamp two bits of wood together and drill a hole in the middle of the two pieces. I used a 20mm wood drill bit:


The ideal hole diameter for clamping the cartridge is slightly larger than 20mm so I sanded the holes larger:


Dual air conversion


The IT functionality is great, but not practical on my tandem. You can use the lever to lower the forks travel, but on a tandem there is no way to unweight the front wheel to restore full travel. For this reason I decided the simplify the air spring arrangement slightly by converting it to a "dual air" approach. This involved:

  • removing IT travel rod;
  • modifying top cap by adding a schrader valve for positive air fill;
  • modifying the air piston seal head to compensate for the lack of an IT rod going through the seal head. Mod involved basically blocking off the port left by removing the IT rod.

I also fitting all new o-rings and quad seals while I had the fork apart.

The "dual air" conversion works really well. Like the dual RS forks you fill the positive piston from the top and the negative from the bottom. Having separately tunable pos and neg pistons is really beneficial when using the fork on a tandem because the air pressures are higher than what the fork was designed for. Being able to run a different pos and neg air pressure helps greatly in this case. Definitely a worthwhile mod.

Respray

Gave the forks a respray in a dark metallic grey to better match my tandem. Manitou were kind enough to send me a new sticker kit for free.


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