Servicing Your Fox FLOAT CTD Boost Valve Rear Shock: A Comprehensive Guide

Your Fox FLOAT CTD Boost Valve rear shock is a sophisticated piece of equipment designed to enhance your riding experience. However, like any mechanical component, it requires regular maintenance and occasional servicing to perform at its best. This guide will walk you through the essential procedures for rebuilding a 2013-2015 FLOAT CTD Boost Valve rear shock, ensuring its longevity and optimal performance on the trails. Remember, safety is paramount, so always wear safety glasses and protective gloves.

Important Safety Warnings

Before we dive into the technical aspects, it's crucial to understand the safety precautions associated with servicing Fox suspension products. These shocks contain pressurized air, oil, and sometimes nitrogen, and improper handling can lead to serious injury or death. Always adhere to the following:

• Never attempt to service a "stuck down" shock. A stuck down shock indicates a failure in the internal air seals. If your shock retracts into the air sleeve after releasing air pressure, or fails to extend fully when pressurized, contact FOX or an authorized service center. Improper servicing of a stuck down shock can be extremely dangerous.
• Use only authorized service procedures. Modifications or the use of non-approved aftermarket parts can cause the shock to malfunction, leading to accidents. Stick to the instructions provided by FOX.
• Protective Gear is Essential. Always wear safety glasses and gloves to protect yourself from potential injury from pressurized fluids or flying parts.
• Do not puncture or incinerate. Fox suspension products contain pressurized components. Never attempt to puncture, burn, or crush any part of the shock.

Disassembly: Getting Started

The process of rebuilding your FLOAT CTD Boost Valve shock begins with careful disassembly. Ensure you have a clean workspace and all the necessary tools, including a pick tool, hex wrenches (5/32", 5/64", 9mm, 8mm, 1.5mm), a 3/4" wrench, a vice, a clean lint-free towel, and of course, a Fox high-pressure pump.

Step-by-Step Disassembly:

1. Release Air Pressure: Begin by releasing all air pressure from the shock. Then, carefully remove the air sleeve.
2. Access Pellet Screw: Using a pick tool, remove the nylon plug to expose the pellet screw. Use a 5/32" hex wrench to release any remaining nitrogen pressure and remove the pellet retaining screw. Extract the pellet with your pick tool.
3. Remove Bleed Screw: Clamp the shock vertically in your vice. Use a 5/64" hex wrench to carefully loosen and remove the bleed screw. Observe the oil that leaks out; foaming is an indicator of aerated oil, suggesting a potential issue.
4. Ball Bearing Removal: Invert the shock over a clean towel and tap out the bleed screw ball. Alternatively, slightly compress the shock. Be cautious, as the oil and ball bearing can eject forcefully.
5. Body Bearing Removal: Clamp the shock body eyelet in the vice. Use a 3/4" wrench to remove the body bearing.
6. Drain Oil: Tilt the shock body to drain all the old oil into a suitable container.
7. IFP Removal: Carefully use applied air pressure to remove the Inertial Fluid Piston (IFP). Inspect the shock body for any signs of damage or excessive wear.
8. IFP O-ring Replacement: Remove the old IFP o-ring. Inspect its gland on the piston for damage or contamination. Apply a small amount of Slick Honey grease to the new IFP o-ring from your service kit and install it onto the piston.
9. Lubricate IFP O-ring: Apply a small amount of shock oil over the IFP o-ring. This helps to displace any trapped air.
10. Set IFP Depth: The IFP needs to be set at a specific depth depending on your shock's eye-to-eye and stroke length. Consult the following table:

11. Install New Pellet and Prefill: Insert a new pellet from your service kit, ensuring the flat side faces upwards. Secure it with the pellet screw. Prefill the shock body with fresh shock oil, pouring it down the side to minimize oil aeration. Let the body sit vertically to allow any trapped air to escape while you proceed with the eyelet assembly.

Eyelet Assembly: The Heart of the Shock

The eyelet assembly houses the intricate valving and adjustment mechanisms. If you're working on a FLOAT CTD Boost Valve Remote shock, you'll need to consult the specific remote eyelet section, but the general principles apply.

Step-by-Step Eyelet Assembly:

1. Remove Piston Nut: Using a 9mm wrench, carefully remove the piston nut. Be mindful of the 4x10 valve shim that might stick to the nut.
2. Piston and Shim Inspection: Remove the piston and lay out all the shims in their original assembly sequence on a clean, lint-free towel. Inspect each shim for any signs of damage or excessive wear. Consider upgrading to new Inner and Outer Boost Valve parts if you're experiencing sealing issues; check the FOX Technical Service Bulletin for details.
3. Replace Boost Valve O-rings: Replace all boost valve o-rings and the piston glide ring using parts from your service kit. Don't forget the o-ring located beneath the glide ring. Some CTD BV shocks may already have updated Boost Valve parts installed.
4. Reassemble Valve Stack: After replacing seals and any worn shims, reassemble the valve stack precisely as shown in the diagrams. Set it aside for now.
5. Remove Piston Post and Propedal: Use a chamfer-less 8mm socket to remove the piston post. Follow this by removing the Propedal piston and spring. Set these components aside.
6. Replace Eyelet O-rings and Seals: Remove the body bearing. Replace the o-rings, quad ring, and backup rings from your service kit, lubricating them with Slick Honey. Ensure the ends of the quad ring and backup rings are properly aligned during installation.
7. Bottom-Out Bumper and Shim: Remove the bottom-out bumper and shim. Invert the eyelet assembly and clamp it securely by the shaft using appropriate shaft clamps.
8. Eyelet Removal from Shaft: Apply gentle heat to the outside of the eyelet to soften the red Loctite®. Carefully remove the eyelet assembly from the shaft.
9. Rebound and Compression Rods: Remove the rebound and compression rod assembly. Inspect the compression/rebound rods and the end of the shaft for any corrosion or scratches. If damage is found, replace the part with a current revision. Replace the shaft o-ring.
10. Replace Rebound Rod O-ring: Remove the compression rod and spring. Be extremely careful not to lose the ball on the rod tip. Replace the o-ring located inside the rebound rod.
11. Lubricate and Reassemble Rods: Apply a small amount of Slick Honey to the non-ball end of the compression rod. Slide it back into the rebound rod, either end first. Install the rebound assembly spring. Apply Slick Honey to the rebound assembly and install it into the shaft assembly. Lubricate both ends of the rebound/compression rods where they interface with the CTD compression cam with Slick Honey.

Rebound and Compression Knobs and Final Assembly

The final stages involve reassembling the adjustment knobs and bringing the shock back together. Precision and careful attention to detail are key here.

Step-by-Step Final Assembly:

1. Remove CTD Lever Cam: Using a 1.5mm hex wrench, remove the set screw from the top of the eyelet assembly. This allows the CTD lever cam assembly to be removed. Keep the detent ball and spring for the CTD lever safe.
2. Install New O-rings: Install new eyelet shaft and air sleeve o-rings from the service kit, lubricating them with Slick Honey. Clean any old Loctite® from the shaft threads using alcohol.
3. Separate Rebound and CTD Cams: Separate the rebound knob from the CTD compression cam using a 1.5mm hex wrench. Inspect both cams for corrosion or damage after cleaning.
4. Reassemble Cams: Reassemble the rebound and compression cams, ensuring they spin freely. Set them aside temporarily to focus on the CTD lever assembly.
5. Remove CTD Lever Lock Ring: Use a small tool, like a .004" valve shim, to remove the CTD compression lever Smalley lock ring.
6. Clean and Inspect: Thoroughly clean all parts and inspect for wear or damage. During reassembly, ensure the black knob's indicator aligns with the middle slot of the blue lever.
7. Reassemble CTD Lever: Reassemble the CTD compression lever assembly as per the diagrams, ensuring the retaining ring is fully seated in its groove.
8. Install Rebound Knob: Install the rebound knob onto the CTD lever using a 1.5mm hex wrench.
9. Install Detent Spring and Ball: Place the CTD knob detent spring and ball into the eyelet, using a bit of grease to hold them in place while you install the control knob assembly.
10. Set Screw Installation: Install the set screw with a 1.5mm hex wrench until lightly seated, then back it out a quarter turn. Verify that the lever assembly moves freely and smoothly.
11. Loctite and Shaft Alignment: Apply red Loctite® to the eyelet shaft threads. Carefully thread the shaft into the eyelet assembly, ensuring the rebound and compression rods are correctly oriented with their respective cams, as shown in the diagrams.
12. Torque Eyelet Assembly: Clean the shaft and clamps with alcohol. Clamp the shaft just enough to secure it without causing damage. Tighten the eyelet assembly onto the shaft to a torque of 80 in-lb.
13. Install Bottom-Out: Invert the eyelet assembly in the vice and install the bottom-out plate and bumper.
14. Install Body Bearing: Lightly install the bleed screw into the body bearing without the ball to plug the bleed hole. Install the body bearing onto the shaft, lubricating the shaft o-ring with Slick Honey.
15. Propedal Check Valve and Piston: Install the Propedal check valve and spring, then coat with red oil. Place the piston post over the Propedal check valve and coat with red oil.
16. Snug Piston Bolt: Using an 8mm wrench, gently snug the piston bolt. Do not torque it fully at this stage.
17. Install Valve Stack: Install the pre-assembled valve stack. Tighten the piston nut finger tight. While pressing the Propedal piston check valve down with a 2mm hex wrench, pre-fill the piston bolt area with red oil. This aids oil flow beneath the valve stack.
18. Torque Piston Nut and Bolt: Tighten the valve stack piston nut into the piston bolt to a torque of 60 in-lb. Ensure both the piston nut and bolt are tightened simultaneously to this value. Continue pre-filling the piston area to thoroughly evacuate any trapped air.
19. Fill Shock Body: Ensure the shock body is completely filled with fresh 10wt red shock oil.
20. Join Body and Eyelet: Holding the oil-filled body in one hand and the eyelet assembly in the other, join them together in a single, swift motion.
21. Install Body Cap and Bleed: Keep the combined parts held together. Remove the bleed screw. With the bleed hole positioned at the highest point, hand-tighten the body into the body cap from below. Watch for any air bubbles escaping from the bleed hole. Tap the body as you thread the parts together to help trapped air escape.
22. Tighten Body Cap: Clamp the shock by the body eyelet. Tighten the body cap onto the body. Avoid applying wrenching force directly to the flat side adjacent to the bleed hole.
23. Install Bleed Screw: Install the bleed hole bearing and screw, tightening to approximately 12 in-lb torque.
24. Pressurize IFP and Dyno-Test: Pressurize the IFP chamber according to the boost valve tune indicated on the air sleeve decal. After pressurizing, perform a dyno-test to ensure proper function.
25. Install Air Sleeve: Set the CTD Compression lever to the 'Descend' mode and then install the air sleeve.
26. Install New Plug: Install a new nylon plug from your replacement parts kit.

General Maintenance and Pre-Ride Checks

Beyond a full rebuild, regular maintenance is crucial for your Fox shock's performance and longevity.

General Maintenance Tips:

• Clean Regularly: Wash your shock with mild soap and water only. Avoid high-pressure washers, solvents, or degreasers, as these can damage the finish and anodized parts. Do not spray water directly at the seal/shock body junction.
• Air Sleeve Lubrication: A small residue of air sleeve lubricant on the body is normal. If it's absent, it's time to re-lubricate the air sleeve.
• Service Intervals: If you ride in extreme conditions (e.g., mud, dust, heavy rain), you'll need to service your shock and air sleeve more frequently than the standard schedule.

Before You Ride:

• Clean Exterior: Wipe down the exterior of your shock with a soft, dry cloth.
• Inspect for Damage: Check the entire exterior for any signs of damage. Do not ride if parts appear compromised; contact your dealer or FOX for inspection or repair.
• Check Fastenings: Ensure quick-release levers or thru-axle pinch bolts are properly adjusted and tightened. Check your headset adjustment and brake cables/hoses.
• Brake Test: Test the proper operation of your front and rear brakes on level ground.

Setting Air Pressure and Sag

Correct air pressure and sag settings are fundamental for optimal suspension performance. The CTD (Climb, Trail, Descend) system allows you to fine-tune your shock's characteristics for different terrain.

Setting Sag:

Sag is the amount the suspension compresses under your weight. Aim for approximately 25% sag.

• Measure and set sag using the guidelines in the table below.
• If your measured sag differs from the target, adjust air pressure in 5 PSI increments.
• To decrease sag (increase pressure): Add air.
• To increase sag (decrease pressure): Release air slowly.
• Re-measure and repeat adjustments until the target sag is achieved.

CTD Lever Explained:

• Climb Mode: Engages the firmest low-speed compression for maximum pedaling efficiency.
• Trail Mode: Provides a moderate low-speed compression setting for a balance of pedaling efficiency and bike control on varied terrain.
• Descend Mode: Offers fully open low-speed compression for plushness and maximum control on steep descents.

The blue CTD lever controls these modes. Rotate it 120° between settings: Descend, Trail (lever inline), and Climb (lever fully clockwise).

Trail Adjust (CTD BV models): Fine-tune your Trail mode setting to soft, medium, or firm using the black Trail Adjust knob.

Adjusting Rebound

Rebound damping controls how quickly the shock extends after compression. Finding the right setting is personal preference and depends on rider weight, style, and conditions.

• Rule of Thumb: Set rebound as fast as possible without causing the rear wheel to pack down or bounce erratically.
• The red adjuster knob typically has 12-15 clicks of adjustment.
• Slower Rebound: Turn the red knob clockwise.
• Faster Rebound: Turn the red knob counter-clockwise.

Frequently Asked Questions

Q: How often should I service my Fox shock?
A: For general riding, an annual service is recommended. If you ride frequently in harsh conditions (mud, dust, salt), consider servicing it more often, perhaps every 6 months.

Q: What type of oil should I use?
A: Fox recommends specific suspension oils. For this rebuild, 10wt red shock oil is indicated for certain parts. Always use oils recommended by FOX for optimal performance and compatibility.

Q: My shock feels "stuck down." What should I do?
A: Never attempt to service a stuck down shock yourself. This indicates a serious internal seal failure. Contact FOX or an authorized service center immediately for professional repair.

Q: Can I use automotive shock oil?
A: It is strongly advised against using automotive shock oils. Bicycle suspension oils have specific viscosity and lubrication properties tailored for the demands of mountain biking, and automotive oils can damage internal components.

Q: What if I don't have all the special tools?
A: While some steps can be improvised, using the correct tools, especially for torque specifications and precise component removal/installation, is crucial for a successful rebuild and to avoid damaging your shock. Investing in a basic suspension service kit or taking it to a professional is recommended.

By following these detailed steps and safety guidelines, you can confidently service your Fox FLOAT CTD Boost Valve rear shock, ensuring it performs reliably and efficiently on all your adventures.

If you want to read more articles similar to Fox Air Shock Rebuild Guide, you can visit the Suspension category.