🔧 GLC300 - Engine Mount Replacement

Your GLC300 uses hydraulic engine mounts to isolate vibration and keep the engine properly positioned. When mounts leak or collapse, you’ll feel extra vibration at idle, clunks on acceleration/braking, or drivetrain “thump” during shifting.

Difficulty Level: Advanced | Estimated Time: 3-6 hours

Assumption: Access is from below with the front safely raised.

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⚠️ Safety & Precautions

• ⚠️ Support the engine before removing any mount bolts (the engine can drop and pinch hands/wires).
• ⚠️ Never work under a vehicle supported only by a jack—use jack stands.
• ⚠️ Keep the jack/engine support off plastic oil pans; use a wide wood block to spread the load.
• ⚠️ Let the exhaust/turbo area cool fully before working near the right-side mount.
• ⚠️ Do not lift the engine high—only enough to unload the mount.

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🔧 Required Tools

You'll need the following tools for this repair:

• Floor jack (rated 3-ton minimum)
• Jack stands (rated 3-ton minimum)
• Wheel chocks
• Safety glasses
• Mechanic gloves
• Engine support bar (specialty)
• Wood block (2x6 or similar)
• Torque wrench (10–200 Nm range)
• External Torx socket set (E10, E12, E14)
• Socket set (10mm, 13mm, 16mm, 18mm)
• Ratchet (3/8")
• Breaker bar (1/2")
• Extensions (3", 6", 12")
• Universal joint swivel adapter
• Trim clip removal tool
• Paint marker
• Work light

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Left engine mount (hydraulic) - Qty: 1
• Right engine mount (hydraulic) - Qty: 1
• Engine mount bolt kit (one-time-use) - Qty: 1

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📋 Before You Begin

• Park on level ground, set the parking brake, and chock the rear wheels.
• Raise the front and support it securely on jack stands at the factory jack points.
• Remove the lower engine undertray/splash shields using a trim clip removal tool and 10mm socket.
• Set up your engine support method:
  • Engine support bar = a bar that spans the fenders/strut towers and holds the engine from above.
  • If you don’t have one, you can carefully support from below with a floor jack and a wood block (only to hold the engine’s weight, not to lift the car).
• Use a paint marker to mark any brackets/fasteners you loosen so reassembly is easier.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Support the engine

• Position the engine support bar (specialty) and take up light tension on the engine lifting point(s).
• If supporting from below, place the wood block on the floor jack pad, then gently contact a solid engine support area (do not crush plastic covers).
• Lift only until you see the mount slightly “unload” (you’re removing weight, not raising the engine).

Step 2: Remove components blocking access (as needed)

• Remove any lower bracing/cover panels that block mount bolts using 13mm socket and E10/E12 external Torx sockets.
• If a heat shield blocks the right mount area, remove it using an E10 external Torx socket.
• Tip: Bag bolts by area (left/right/undertray).

Step 3: Replace the left engine mount (driver side)

• Locate the left mount between the engine bracket and front subframe.
• Remove the mount-to-subframe fastener(s) using an 18mm socket (or E14 external Torx socket, depending on fastener style).
• Remove the mount-to-engine-bracket fastener(s) using an E12/E14 external Torx socket and extensions.
• Slowly raise/lower the engine a small amount with the engine support bar (or floor jack) until the mount slides out without forcing it.
• Install the new left mount in the same orientation as removed.
• Start all bolts by hand first (prevents cross-threading).
• Torque to Mercedes-Benz WIS specification for the left engine mount fasteners using a torque wrench.

Step 4: Replace the right engine mount (passenger side)

• Locate the right mount near the turbo/exhaust side—work carefully around hot/fragile parts.
• Remove the mount-to-subframe fastener(s) using an 18mm socket (or E14 external Torx socket).
• Remove the mount-to-engine-bracket fastener(s) using an E12/E14 external Torx socket, extensions, and a universal joint swivel adapter.
• Adjust engine height slightly to create clearance, then remove the mount.
• Install the new right mount, hand-start all bolts, then snug them evenly with a ratchet.
• Torque to Mercedes-Benz WIS specification for the right engine mount fasteners using a torque wrench.

Step 5: Reassemble underbody panels and braces

• Reinstall any heat shields/braces removed using E10/E12 external Torx sockets and 13mm socket.
• Reinstall the undertray using a 10mm socket and any retained clips with a trim clip removal tool.
• Torque to Mercedes-Benz WIS specification for underbody brace fasteners using a torque wrench.

Step 6: Lower the vehicle

• Remove engine support load (lower the engine support bar tension or gently lower the floor jack).
• Raise the vehicle slightly with the floor jack, remove jack stands, then lower to the ground.

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✅ After Repair

• Start the engine and let it idle in Park. Watch for excessive movement and listen for clunks.
• With your foot on the brake, shift through Reverse/Drive briefly and feel for improved smoothness.
• Take a short test drive. Recheck for any new noises over bumps and during light acceleration.
• Look underneath for any signs something is contacting the undertray or heat shield.
• Tip: Minor vibration change is normal at first.

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💰 DIY vs Shop Cost

Shop Cost: $900-$1,800 (parts + labor)

DIY Cost: $250-$650 (parts only)

You Save: $650-$1,150 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 3-6 hours.

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🎯 Ready to get started?

HowToo makes it easy: same-day/2-day shipping on every part, plus all the tools and specialty tools you need! Check out the parts and tools sections below to add everything to your cart.