RockShox Mag Fork Service Guide

Servicing Your RockShox Mag Suspension Fork: A Comprehensive Guide

Your RockShox Mag suspension fork is a marvel of bicycle engineering, designed to provide a smooth and controlled ride. However, like any sophisticated mechanical component, it requires regular maintenance to ensure optimal performance and longevity. This guide will walk you through the essential steps for servicing your RockShox Mag 21, Mag 10, and Mag 21SLTi forks, covering models from 1993 to 1996. By following these instructions carefully, you can keep your fork running like new.

Understanding Your RockShox Mag Fork

The RockShox Mag series forks, including the Mag 21, Mag 10, and Mag 21SLTi, were revolutionary for their time. They utilise an air-sprung and oil-damped system. Proper servicing involves careful disassembly, cleaning, inspection, and reassembly of internal components. It's crucial to remember that these forks contain oil-filled and pressurised damping units. Therefore, a thorough understanding of the procedures, the correct tools, and a clean working environment are paramount. Always use genuine RockShox replacement parts to ensure compatibility and performance.

Tools and Materials You'll Need

Before you begin, gather all the necessary tools and materials. Using the correct tools will make the job easier and prevent damage to your fork.

Common Hand Tools:

• Small tip external snap ring pliers
• Small tip internal snap ring pliers
• 19mm & 22mm socket and ratchet or box end wrench
• Torque wrench
• Metric ruler (150mm or longer)
• Precision calipers (optional)
• 32mm & 36mm headset wrenches
• #1 Phillips screwdriver
• 1-litre beaker or container for used fork oil
• Safety glasses
• Straight blade screwdriver
• Bench vice

Special RockShox Tools:

• Quadra bushing removal tool (PN 70106)
• RockShox standard pump/air gauge (PN 20109)
• RockShox needle (PN 56991) (no hole on side to tear air valve)
• Upper tube clamping blocks (PN 70101)
• Seal/lower bushing installer (PN 70103)
• Seal puller (PN 70113)
• Valve body tool (PN 70105)
• Drop-out vice blocks (PN 70107)

Miscellaneous:

• High quality bearing grease (e.g., Judy Butter or Non-Lithium)
• Medium strength thread lock (e.g., Loc-Tite 242)
• ROCK SHOX fork oil (5wt. or 8 wt.)

Step-by-Step Servicing Procedure

1. Fork Removal from Bike (Optional but Recommended for Full Service)

While it's not strictly necessary to remove the crown/steerer assembly from the bike to service the damper units, a full service is best performed with the fork removed.

• Disconnect the front brake cable from the brake lever.
• Loosen fork crown bolts alternately to avoid putting too much clamping force on one bolt and potentially stripping the bolt head. Use a 4mm hex key.
• With a slight rocking motion, pull both lower fork tubes out of the crown. (See Figure 2A for 1993 Mag 10 and Figures 2B, 2C, 2D, 2E for 1994+ Mag 10/Mag 21 and 1993 Mag 21 respectively).

2. Fork Brace Removal

The fork brace adds rigidity to the fork and needs to be removed for full access to the lower legs.

• Remove brakes as per manufacturer’s recommendations.
• Using an 8mm open-end wrench, remove both brake posts. (See Figure 2B).
• Using a 4mm hex key, remove both brace screws.
• Clean the exterior of both fork legs. Use soap and water if necessary.

3. Depressurising the Fork

This is a critical safety step. Always point the needle away from yourself and others.

• For 1993 MAG 10: Pry out the upper tube dust cap from the side. (See Figure 2C).
• For 1993 MAG 21: Remove the air filler screw from the top of the air cap using a #1 Phillips screwdriver. (See Figure 2D).
• For MAG 10 (1994) and MAG 21 (1994 and later): Pry off the rubber dust cap from the top of the air cap. (See Figure 2E).
• Insert a RockShox needle (PN 56991) through the exposed hole to depressurise the damper. (See Figure 2F). WARNING: POINT NEEDLE AWAY FROM YOURSELF AND OTHERS.

4. Fork Air Cap Removal

The method for removing the air cap varies slightly depending on the model year.

• 1993 MAG 10: Push the exposed aluminium air cap down into the 10mm upper tube and remove the wire clip. (See Figure 3A). NOTE: DO NOT SCRATCH THE INTERIOR WALLS OF THE TUBE WHEN REMOVING THE WIRE CLIP. Then, pull the air cap out of the tube using a 6mm bolt threaded into the centre hole. (See Figure 3B).
• 1994 MAG 10: Remove the air cap by unscrewing it with an 8mm hex key. Inspect the adjuster head O-ring for signs of wear or damage and replace if necessary. (See Figure 3C).
• MAG 21 (ALL Years): Turn the air cap counterclockwise using a 19mm (for '93 MAG 21) or 22mm (for '94 and later MAG 21) socket or box wrench. (See Figure 3D). NOTE: DO NOT FORCE THE DAMPING ADJUSTER KNOB TO TURN WHEN REMOVING THE AIR CAP. THE SOCKET OR BOX WRENCH MUST NOT GRAB THE ADJUSTER KNOB WHEN REMOVING THE AIR CAP, OR THE ADJUSTER ROD WILL BE DAMAGED.

5. Draining the Fork Oil

Proper oil disposal is essential for environmental protection.

• Drain all oil by pumping the unit upside down into a used oil receptacle. (See Figure 3G). PLEASE RECYCLE!
• For oil changes only, please refer to the “Fluid Level Setting” section (not detailed in this excerpt but would be in a full manual).

6. Fork Boot and Dust Wiper Removal

These components protect the fork's internals from dirt and debris.

• Gently pull up on the fork boots to remove them. Inspect boots for wear or damage and replace as needed.
• Carefully pry up the dust wiper with a flat, blunt screwdriver. (See Figure 4A). This applies to ’93 MAG 10, ’93 MAG 21, ’94 MAG 21, and ’94 MAG 21 SLTi forks. Inspect dust wipers for wear or damage and replace as needed.

NOTE: The following MAG forks will have fork boots installed and no dust wipers: ’94 MAG 10, ’95 MAG 21, and ’96 MAG 21.

7. Main Seal Removal

The main seal holds the upper and lower tubes together. This step requires specialised tools.

• Remove the main seal snap-ring using internal snap ring pliers. (See Figure 4B).
• Extend the upper and lower tubes to their fully topped-out position.
• Place the seal puller (tool #70113) over the tubes, with the larger end over the lower tube.
• Clamp the upper tube in a vice with the vice blocks against the small end of the seal puller (tool #70101).
• Unscrew the seal puller by hand. For hard-to-remove main seals, refer to the special instructions below. (See Figure 4C).
• The upper and lower tubes can now be pulled apart by hand. (See Figure 4D).

Special Instructions for Hard-to-Remove Main Seals:

If you cannot remove the seals by hand, a little heat can help.

• Apply heat to the lower tube at the location of the seal using a hot air gun or blow dryer. WARNING: DO NOT USE OPEN FLAME.
• Carefully continue to unscrew the puller. If necessary, use 32mm and 36mm headset wrenches on the puller flats.
• NOTE: THE SNAP RING ON THE TOP-OUT SPRING CAN FAIL IF TOO MUCH FORCE IS USED TO REMOVE THE MAIN SEAL. PROCEED CAREFULLY AND SLOWLY. APPLY HEAT TO THE LOWER TUBE BEFORE ATTEMPTING TO USE 32MM AND 36MM WRENCHES.

If the top-out retaining ring fails, the upper tube will separate from the lower tube, and the seal, bushings, top-out spring, and top-out retaining ring will remain in the lower tube. In this case:

• Grab the bushings and the main seal with one end of the Quadra bushing removal tool (PN 70106).
• Slide the seal puller over the bushing removal tool shaft.
• Attach the end of the bushing removal tool to a bench vice.
• Use the seal puller to pull the bushings and main seal straight out from the lower tube.
• An alternative method is to use a small, thin, flat-blade screwdriver to pry the main seal from the lower tube, being careful not to damage the lower tube.
• The bushings, spacer, top-out spring, and top-out retaining ring should now slide out of the lower tube. Turn upside down and tap the lower tube on a bench.

8. Upper Tube Parts Explained and Removal

This section details the components on the upper tube and how to remove them for service.

• Slide the seal, bushing washer, main seal O-ring, bushings, bushing spacer, and top-out sleeve off the upper tube. (See Figure 5C).
• NOTE: Only remove the valve body from the upper tube if it needs service or replacement; otherwise, it may be left in the upper tube while overhauling the fork. Skip to Upper Tube Parts Assembly.
• For disassembled forks where the top-out spring retaining ring failed, inspect the snap ring groove on the valve body and replace as needed. Use only genuine RockShox replacement parts.
• Place the inverted upper tube in clamping blocks (PN 70101) and a bench vice.
• Insert the pins on the valve body tool (PN 70105) into the holes on the valve body.
• Turn the valve body tool (PN 70105) counterclockwise with a 19mm wrench. Apply downward force while applying torque to the valve body tool to prevent the tool from pulling out and damaging valve parts. (See Figure 5A).
• NOTE: If service of the top-out spring is not required, the following step may be skipped.
• Remove the top-out snap ring from the valve body using external snap ring pliers. The top-out spring and top-out washer should now slide off the valve body. (See Figure 5B).

Bushing Identification:

Correct identification of bushings is crucial for proper assembly.

• 1993 MAG series forks (Mag 10 and Mag 21): Have identical upper and lower bushings with an outside diameter of 1.126″ (28.60mm).
• 1994 and later MAG series forks: Have different size upper and lower bushings. The upper bushing has a larger outside diameter (1.157″ or 29.39mm) than the lower bushing (1.126″ or 28.60mm). It is recommended to mark the upper bushing to avoid confusion. For MAG series forks, the 1994 and later lower fork bushings are identical to the 1993 upper and lower fork bushings.

Diagram of Upper Tube Parts: (Refer to Figure 5C in the provided images for a visual representation of Top-out Sleeve, Lower Bushing, Upper Bushing, Top-out Spring, Top-out Snap Ring, Valve Body, Top-out Washer, Main Seal O-ring, Bushing Spacer, Bushing Washer, Main Seal, Main Seal Snap Ring, Dust Wiper).

9. Valve Parts Explained and Disassembly

The damping system's valve components require careful handling.

MAG 21 Valve Parts:

• Screw the adjuster rod all the way clockwise into the valve body.
• Remove the E-clip from the bottom end of the adjuster rod using a small straight-blade screwdriver. (See Figure 6A).
• Unscrew the adjuster rod from the valve body.
• Remove the valve spring snap ring using snap ring pliers.
• Remove the valve parts from the adjuster rod. (See Figure 6B).
• Inspect parts and replace as needed.

Diagram of MAG 21 Valve Parts: (Refer to Figure 6C for Rebound Plate, Valve Spring Washer, Valve Spring, E-clip, Adjuster Rod, Valve Body).

MAG 10 Valve Parts:

• Hold the valve body with tool (PN 70105) and remove the valve bolt with a flat-blade screwdriver.
• Remove the E-clip from the valve bolt using a straight-blade screwdriver. (See Figure 6D).
• The rebound washer, valve plate, valve spring, and spring washer will now slide off.
• Inspect parts and replace as needed.

Diagram of MAG 10 Valve Parts: (Refer to Figure 6E for Rebound Plate, E-clip, Valve Plate, Valve Spring, Valve Spring Washer, Valve Bolt).

10. Component Inspection

Thorough inspection of all components is vital for a successful rebuild.

• Valve Springs and Bodies: All 1993 MAG series forks were assembled with stiff valve springs (PN 44103). For 1994 and later MAG series forks, the valve springs were softened (PN 44306) to improve fork responsiveness. The valve springs are a tuning variable. The 1993 MAG valve body had two intake port valves with a compression bleed hole drilled to 0.028″ (0.71mm). 1994 and later valve bodies (PN 42226) had four intake port valves with a compression bleed hole drilled to 0.040″ (1.02mm). The intake port valves and the compression bleed hole are tuning variables. Another change made for the 1994 and later MAG series forks was that the valve plate (PN 42327) was machined with a relief step of 0.005″.
• Bushings: Check the coating on the inside of the bushings and replace if scratched or worn (brassy-coloured). Replace bushings as needed. (See Figure 7A). WARNING: BUSHINGS FROM 1993 REBUILD KITS WILL NOT WORK CORRECTLY AS UPPER BUSHINGS FOR 1994 & LATER FORKS!
• Upper Tube: Check the upper tube for signs of nicks or scratches that could damage the seal or inhibit proper seal function. Replace the upper tube as needed.
• O-rings and Rebound Plate: Check all O-rings for evidence of tears, deformations, or scratches. Check the rebound plate for deformations or scratches. Replace as needed. (See Figure 7B).
• Main Seal: Check the main seal for deformations or scratches. Replace as needed. (See Figure 7C). NOTE: IT IS VERY RARE THAT A SEAL FAILS. THE PRIMARY CAUSE OF SEAL LEAKAGE IS DUE TO DIRT WORKING INTO THE LIPS OF THE SEAL OR A SCRATCHED OR DAMAGED UPPER TUBE AND DISRUPTING THE SEAL’S FUNCTION. IN MOST CASES, THEY MAY BE CLEANED AND REINSTALLED. PROPER MAINTENANCE AND CLEANING OF THE UPPER TUBE AND DUST WIPERS WILL PREVENT LEAKAGE.
• Top-out Spring: Check the top-out spring for correct free length. Measure the spring from end to end. The minimum length is 0.827″ (21.0mm). Replace as needed. (See Figure 7D).
• Fork Brace: Inspect the fork brace at the cable mount area for signs of damage from crashes or misuse. (See Figure 7E). NOTE: IF POSSIBLE, ADJUST THE HANDLEBARS TO HIT THE TOP TUBE BEFORE THE FORK CAN SWING AROUND AND THE CABLE MOUNT HITS THE DOWN TUBE.
• Lower Tubes: Inspect the lower tubes for signs of damage at the drop-out area. (See Figure 7F). Replace as needed.

11. Valve Assembly

Reassembly of the valve components requires precision.

MAG 21 Valve Assembly:

• Slide the following parts onto the adjuster rod in the following order: rebound plate, valve plate, valve spring, and valve spring washers. (See Figure 8A).
• Install the valve spring snap ring on the damper rod using external snap ring pliers. Place the sharp side of the snap ring away from the valve spring washer. (See Figure 8B). WARNING: BE CAREFUL NOT TO OVEREXTEND THE VALVE SPRING SNAP RING WITH THE PLIERS.
• Screw the adjuster rod assembly completely into the valve body.
• Install the E-ring on the bottom of the adjuster rod.
• Slide the top-out washer onto the valve body, followed by the top-out spring, and install the valve spring snap ring (see Figure 9C) with the sharp side away from the top-out spring (Figure 8A) to retain the assembly.

MAG 10 Valve Assembly:

• Slide the following parts onto the valve bolt in the following order: valve spring washer, valve spring, valve plate, and rebound washer. (See Figure 8C).
• Install the E-clip with the sharp side of the E-clip away from the rebound plate.
• Thread the valve bolt assembly into the valve body using a straight-blade screwdriver. Use medium strength threadlock and torque to 36 IN-LBS (3.3 Nm). WARNING: OVERTIGHTENING WILL BREAK THE VALVE BOLT.

12. Upper Tube Parts Assembly

Reassembling the upper tube components correctly is vital for fork function.

• Hold the upper leg in a vice with the upper tube blocks (PN 70101).
• Tighten the valve body into the upper tube (the valve goes into the end of the tube with threads all the way to the edge). Apply three drops of medium strength threadlock to the valve body threads. Torque the valve assembly to 35 FT-LBS (48 Nm) using the valve body tool and a 19mm (3/4″) socket with a torque wrench. (See Figure 9A). Apply downward force while torquing to prevent the tool from pulling out and damaging the valve ports.
• Slide the top-out sleeve onto the upper tube with the shoulder away from the top-out spring. (See Figure 9C).
• Slide the lower bushing onto the upper tube, followed by the bushing spacer, upper bushing, main seal O-ring, and main seal washer.
• WARNING: FOR 1994 AND LATER MAG FORKS, THE UPPER BUSHING HAS A LARGER OUTSIDE DIAMETER THAN THE LOWER BUSHING. PLACING BUSHINGS IN THE WRONG POSITIONS WILL DAMAGE UPPER TUBES. FOR IDENTIFICATION OF UPPER AND LOWER BUSHINGS, SEE THE UPPER TUBE PARTS EXPLAINED SECTION.
• Gently press the above assembly into the lower tube using the seal installer tool (PN 70103). (See Figure 9B).
• Grease the main seal inside and out. Place the main seal over the upper tube. NOTE: INSTALL THE MAIN SEAL WITH THE SMALL SPRING SIDE FACING TOWARD THE INSIDE OF THE FORK. PRESS THE SEAL INTO THE LOWER TUBE USING THE SEAL INSTALLER TOOL. (FIG. 9B) THE END OF THE TOOL WITH THE LARGER BORE SHOULD FACE THE SEAL.
• Install the main seal snap ring (sharp side up, see Figure 9C) into the lower leg using internal snap ring pliers. WARNING: THE SNAP RING MUST FULLY ENGAGE THE GROOVE IN THE LOWER TUBE. IMPROPER INSTALLATION MAY ALLOW THE TUBES TO SEPARATE DURING USE.

Diagram of Upper Tube Assembly: (Refer to Figure 9C for Top-out Sleeve, Lower Bushing, Upper Bushing, Top-out Spring, Top-out Snap Ring, Valve Body, Top-out Washer, Main Seal, Bushing Spacer, Seal O-ring, Bushing Washer, Main Seal Snap Ring, Dust Wiper).

Fluid Level Setting

After reassembly, setting the correct oil level is crucial for proper damping performance. This typically involves adding the specified amount and type of RockShox fork oil to the damping leg. The exact procedure and oil volume can be found in the complete RockShox service manual for your specific fork model.

Frequently Asked Questions (FAQ)

Q: How old are the seals on a MAG 21?
A: If you are using original RockShox seals that have been in storage (NOS - New Old Stock), they are likely at least 25 years old, as the Mag 21 models are from the mid-1990s. It is often recommended to source modern, compatible seals if possible, as old seals can degrade over time.

Q: Can I use modern seals instead of original RockShox seals?
A: Yes, it's possible to find modern seals that match the dimensions of the original ones. This can be a good option for ensuring the longevity and performance of your fork's seals.

Q: What if my bushings are worn?
A: The Mag 21 fork requires specialised tools for bushing service. If your bushings are worn, it might be easier to find a replacement lower leg assembly with good bushings, as sourcing specific RockShox bushing kits can be challenging.

Q: How often should I service my RockShox Mag fork?
A: For regular use, a basic service (cleaning, lubrication of stanchions, and checking air pressure) should be performed every 20-30 hours of riding. A full internal service, as described in this guide, is recommended every 100-200 hours of riding or annually, whichever comes first.

Q: What type of oil should I use?
A: Always use genuine RockShox fork oil, typically 5wt. or 8wt., as specified in the original manual. Using the wrong type of oil can damage the damping system.

By diligently following these steps, you can ensure your RockShox Mag suspension fork continues to provide a superior riding experience for years to come. Remember to work in a clean environment, use the correct tools, and always prioritise safety.

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