Wednesday, April 18, 2012

TECH: Part 4 of 4 - How to bleed Fox FIT cartridge and reassemble a Fox F32 Fork

Once you have dried off all the parts to your fork (overnight or towel dry) we will be installing new seals, changing the oil in the FIT cartridge and reassembling the fork.

For 2012 Fox released these new seals. They make the fork feel like it's night and day compared to the old seals. 

If you are purchasing this seal kit from your local bike store. Make sure they don't try to sell you the old stock at full price. You want the 2012 version. Make sure the part numbers are correct before buying.

803-00-613 Kit: Dust Wiper, Forx, 32 mm, Low Friction
803-00-614 Kit: Dust Wiper, Forx, 34 mm, Low Friction
803-00-615 Kit: Dust Wiper, Forx, 36 mm, Low Friction
803-00-616 Kit: Dust Wiper, Forx, 40 mm, Low Friction

When Fox calls for Fox Red Fluid or Fox Green Fluid. They are pretty much the same thing. The Fox Red is Silkolene Pro-RSF 10wt Suspension Fluid. The Green is Torco RSF Medium. For the FIT cartridge users Fox says you need to use both Red and Green. Red goes into the FIT cartridge itself. Green into the damping leg side oil bath to lubricate the fork going up and down. In my view, just use Red for both. So if you bought Silkolene Pro-RSF Suspension Fluid 10wt just use that for everywhere on FIT forks. Silkolene Pro-RSF 10 wt Suspension Fluid and Torco RSF Medium are both synthetic based oils. By buying one less bottle of oil at approximately 20 dollars a bottle you are getting similar results.

For the other users out there who have open bath Fox forks (meaning non-FIT versions). I would recommend finding Torco RSF Medium from a motorcycle shop, because the cSt @ 40C between Silkolene Pro-RSF 10 wt and Torco RSF Medium are not equal.

For myself I chose to use Redline Suspension oil. I purchased a bottle of their heavy and a bottle of their medium. I mixed them to get the same cSt @ 40C as Silkolene Pro-RSF 10wt.

42% Redline Medium + 58% Redline Heavy = Fox 10wt =  silkolene pro rsf 10wt


I purchased this from a golf shop so that I can hold my FIT cartridge in my vice without it being damaged.

First order of business is to change the oil in the FIT damper cartridge. The Fox service shows them breaking down the FIT cartridge completely. You do not need to do this for a simple oil change unless you had problems with your fork not damping. There is no reason to open it. If you open it up and follow their guide the complexity quickly jumps to a 10/10 on a scale of difficulty.

I'm assuming you have been following the previous 3 posts and are now at the point of all the parts of the fork broken down into their sub-assemblies.

TECH: Part 1 - How to do an annual service on Fox Forks
TECH: Part 2 - Annual service on Fox Forks (reality check)
TECH: Part 3 of 4 - How to replace seals, oils, and re-assemble

We will begin with working on the FIT damper first and change the oil. Unscrew the lockout assembly from the top of the FIT cartridge. You can do this with your fingers.

Once that is off, set it aside and dump out all the old oil. You should cycle the shaft in and out of the FIT cartridge to get all the oil out. Then make sure the shaft is all the way in and squeeze the rubber bladder to get the remaining amounts out.

Hopefully you followed the 1st post and went to Walmart to buy one of these syringes. It was located in the automotive section of the walmart close to my home.The vacuum nipple you will need to cut the tip off with a sharp knife. Choose one that will acts as a plug between the FIT cartridge and the syringe tip.

You are going to need to place the FIT cartridge into a vice so that you can use two hands to work with (This is where the golf shaft rubber grip for the vice is used). Take the plunger out of the Syringe, install the nipple that you cut the tip off of and plug it into the FIT cartridge. Extend the shaft of the FIT cartridge all the way out and pour in the Fox Red 10wt or Silkolene Pro-RSF 10wt or Redline Oil Mix.

The next steps are to bleed all the air out of the FIT cartridge. Unfortunately my hands were covered in oil and I did not have an assistant to take photos for me. So we will be following the Fox service guide here:


The important point to make is do not let the syringe ever go empty. You will then be introducing air back into the FIT cartridge.

Bleeding the Complete Cartridge Assembly

Your next step is to purge any trapped air within the entire assembly. First, remove the lockout lever assembly, and press the syringe body into its threaded opening in the topcap assembly.

Fill the syringe reservoir with 10-15 cc of 10 wt. oil.

Gently squeeze the bladder, progressively rolling the squeeze from your pinkie to your index finger. Sustain your squeezing, and watch for air bubbles rising up from the cartridge into the syringe reservoir. Allow enough time for the air bubbles to rise to the oil surface and escape, before you release finger pressure.

Release your grip on the bladder, to allow it to return to its smooth-sided cylindrical shape.

Repeat this process; gently squeeze the bladder, progressively rolling the squeeze from your pinkie to your index finger. Keep squeezing, allowing enough time for any trapped air to bubble up through the oil reservoir in the syringe. Keep watching for air bubbles; repeat this operation as often as necessary, until no more air bubbles can be seen.

While maintaining your squeezing of the bladder, with your other hand slowly push the end of the shaft up all the way, to further purge any air still trapped internally in the piston and coupler assemblies. Slowly return the shaft end downwards to full extension and release your grip on the bladder, which will draw oil back in from the syringe reservoir.

Take a break and let everything sit for perhaps 30 minutes, to allow a chance for more air to bubble out. If air bubbles are still present, repeat the bleeding process once again. Repeat this process until you see no air bubbles appearing when you squeeze the bladder.

The total time it takes to complete the bleeding process can vary, depending on:
  • the time and care taken during assembling of the parts
  • the time and care taken when adding the oil to all the parts assemblies

Wrapping It Up

Draw the cartridge shaft all the way back down, which will draw most of the oil in the syringe body into the cartridge. The bladder must be back to its natural, cylindrical shape; no dents or dimples. Lift the syringe out while capping the point with your finger, and return the excess oil back into its container.

What you should now have is a cartridge completely filled with 10 wt oil, evidenced by the oil slightly overflowing into the topcap.

Insert the lockout assembly, and screw it into place finger-tight for now. Again, be sure to engage the threads of the lockout assembly, to ensure that the o-ring fully seats and seals the topcap. The lockout assembly o-ring should not be visible.

Note:  Some oil will be displaced into the topcap well when you do this, which is normal and should not re-introduce any air into the cartridge.

Remove the cartridge from the vise clamps and dump the overflow oil in the topcap into a drain pan.

When the lockout is completely closed, a successfully rebuilt FIT cartridge will not compress, or have any air gaps when you compress it. The final step is to test this before installing the rebuilt cartridge back into the fork assembly.

-------------------- (end of Fox service guide)

One point I like to make is that even though I let the FIT cartridge sit for an hour and came back to it, I found that the rubber bladder/reservoir never returned to full shape with the shaft fully extended. This is a problem because when I put the lockout assembly back into the FIT Cartridge and screwed it in finger tight (this effectively closes off the FIT cartridge and gives you "lock out") the shaft could still be pushed into the FIT cartridge. When the FIT cartridge is locked out, the shaft when fully extended should not compress at all (as indicated by the Fox service guide above). If it compresses you have one of two problems. #1 being you still have air bubbles in the FIT cartridge. Or #2 the rubber bladder/reservoir never fully expanded back to original shape (which is ballooned out) and moving the shaft to compress it caused the rubber bladder to balloon. A fully filled reservoir with oil should be ballooned. What I ultimately had to do was to hold the syringe with my left hand and apply force to push the syringe down against the nipple/FIT cartridge, then take the plunger of the syringe in my right hand, re-install the plunger into the syringe and push down gently to force additional oil into the FIT cartridge to fully expand the bladder/reservoir.

Once the lockout assembly/valve is reinstalled and the excess oil on the top cap dumped out, try to push the shaft from the fully extended position, if it can't move you have successfully changed the oil in the FIT cartridge. We can now go and focus on putting the fork back together.

Installing the fork seals

First thing to do is to use fox float fluid to soak the foam rings.

Place some of the float fluid onto your finger and swipe it around the bushings in both legs. Place the new foam rings with them already soaked in fox fluid into the fork legs.

Now take one of the new SKF low friction seals and coat the outer diameter with fox fluid.

Take the lubricated seal and place it onto your fox leg and push down with your fingers as best as you can.

If it doesn't fully seat (which is rare) you can use a Fox fork seal driver. You don't really need this tool. It is expensive. If you can't get it to fully seat and you don't want to spend 30 dollars for this driver which is just machined plastic with a lip, just take the back of a spoon and use it to push around the circumference of the seal until it is fully seated. Alternatively find an old PVC pipe and use it to push the seal down.

Do the same for both sides of the fork.

I lightly coated the left and right stanchions with a light oil (Triflow)

Slide the crown into the fork lower legs.You can slightly tilt the fork stanchions to help ease the insertion.

Now it is time to install the air piston back into the air side. The air side is the left side of the fork when you are looking at your fork with your bum on the saddle.

Take some grease and apply a light coat around the air piston. Make sure the small foam ring around the air piston also is coated with Fox Float Fluid.

Now it is time to push the air piston back into the left side fork bore. Be careful when pushing the air piston back in. Try your best to ensure the piston is going in straight and square. You do not want for the air piston to catch on the threads of the crown. If this happens you can damage the air piston and will cause your fork to not hold pressure later on.

Now invert the fork and add 20cc (Fox F100 RLC FIT) of Fox Red or Fox Green or Silkolene Pro RSF 10wt or your Redline mix into the spring side oil bath.

With the fork still upside down, use one hand to hold the fork leg, while the other hand's finger to push the air piston down in the bore such that the threaded shaft will protrude past the hole. Do not flip the fork back to the upright position. Oil will be spilled everywhere! Install a new plastic crush washer that is part of the Fox seal kit.

Torque the black nut to 50 inch lbs

Now invert the fork and add 10cc of Fox Float fluid into the bore.

Next step is to add a little bit of anti-seize to the crown's threads. This will prevent galling between the crown's threads, and the top cap's threads

Carefully thread the top cap with the shreader valve into the air piston side fork leg.

Tighten the top cap to 220 in-lb torque. For picture purposes I had to use one hand to hold the camera and the other to demonstrate the torquing. Make sure you use your second hand to apply downward pressure to the head/socket of the torque wrench to prevent the socket from slipping on the 26mm hex.

Air up the fork to 80 psi to extend the fork fully.

Re-install the blue cap

Now Re-install the FIT cartridge. You will need to guide the threaded shaft such that it comes out of the bottom of the leg.

Now install the black nut on to the bottom of the threaded section protruding past the fork leg. Use a new plastic crush washer from the Fox Seal service kit. Place the crush washer between the fork leg and the nut and torque to 50 inch lbs.

Now add 20cc (Fox F100 RLC FIT) of Fox Red or Fox Green or Silkolene Pro RSF 10wt or your Redline mix before installing the top cap. This will internally lubricate the FIT cartridge's shaft, and the stanchions.

Now push down on the top cap to start the threads into the crown. You may need to slightly turn the lockout assembly counter clockwise to get it out of "lockout".

Now put the ball back into the hole for that allows for the click when you turn the blue knob. You can apply a bit of grease to the ball and the hole to keep it sliding over time. It is best to pick up and place the ball with a small pair of needle nose pliers.

Apply little bit of grease to the back side of the blue adjusting knob

The installation of the RLC top cap can be quite tricky. This is where I break and I will copy and paste the section from Fox service guide.


Install the RLC Topcap

Before starting the following procedure, The diagram below shows the graphic cross-sectional overview of the RLC topcap hardware.
  1. Place the spring the spring back into the detent, then place the ball bearing on top of the spring.

  1. Place the low-speed compression bezel onto the topcap. Align the multiple divots with the ball bearing; do not align the divots with the low-speed compression adjuster needle.

  2. Place the lockout lever on top of the low-speed compression bezel. Using the lever as a wrench, turn the lockout lever clockwise as far as it will go. Take the lever off, replace it and turn again until you are sure that you have turned the adjuster shaft fully clockwise. Remove the lever one more time and position it near the 6 o'clock position; this is now the locked-out position of the fork. Turning the lever counterclockwise will unlock the fork. However, note that the fork will mechanically be locked out once the lever has past the 3 o'clock position, although it is a good idea to turn the lever full counterclockwise anyway.

  3. Using a 1.5 mm hex key wrench, tighten the three set screws on top of the lockout lever. Do not over tighten these set screws. Doing so will damage the lockout lever and also the low-speed compression bezel. Over tightening the screws cause the associated ball bearings to stress the surrounding aluminum surfaces, causing permanent damage. To be safe, lightly tighten the screws, then back off 1/2 turn. Turn the lockout lever and check for proper, smooth operation.

  4. Place the rebound knob on top of the lockout lever. The lever and adjuster shaft are indexed.

  5. Using a 1.3 mm (0.050") hex key wrench, tighten the hex key on top of the rebound knob.

-------------- (end of Fox Service guide)

Now re-install the red rebound adjust knob. Make sure to line up the set screw with the indent.

The final step is to take the sheet of paper you used to record down all your settings in Part 3 of 4 of these Posts. Air the fork to the desired pressure, set the rebound and compression back to where you had it.


  1. awesome tutorial

    now, how much $ to go through mine?

  2. Please keep on posting about This topic. I want to know more details about it. Anyway, I have read some of posts in your blog here. And all of them are very informative. Thanks for sharing.

  3. A fully filled fit cartridge should NOT be ballooned as you suggest. The reason they appear like this before a service is due to air ingress (bad).

    With damper shaft fully extended, the bladder should be compressed/deformed by vacuum force, this allows room for the bladder to expand/balloon at bottom out.

    If you force oil into it to balloon the bladder at full extension and close the damper like that, it will generate excessive pressure at bottom out and decrease bladder life and increase the risk of rupture and damage to other components. It's nice to see your enthusiasm but this is the type of reason it's best to only repeat Fox instructions verbatim without adding your own information unless you are 100% sure no damage will result.

    Also, Redline is fine, however matching cSt is insufficient, the VI (temperature stability of viscosity) must also be equal or better for low-volume FIT dampers. Redline happens to have a high VI like Silkolene RSF, however many oils don't. Worth noting for anyone deviating from factory spec. For lower lubrication I have tested multiple products and the Fox Green 10wt (custom formulation) is best.

    1. Udi is 95% wrong only oil part is right.

  4. Really nice post about the FIT cartridge damper oil change....

  5. Thanks so much, i found the fox instructions for simple seal and oil change where confusing as i had a fit damper and theirs is open bath requiring 160 ml of fluid in the leg where i really only need a small amount to keep the seals etc moist.
    fit = damper
    Talas = spring

    1. Fit= close cartridge.
      Float = Fix travel
      Talas = Adj. travel
      Springs are in the air leg.

  6. Can the rebound adjuster assembly be replaced without stripping or bleeding the cartridge?

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