Posted on by Mac User

How to replace a 3.5″ Hard drive in a 2012 – 2019 iMac 27″

Replacing the hard drive (or upgrading to an SSD) in a 27-inch iMac from 2012 to 2019 is a moderately difficult task that involves carefully separating the display from the chassis (which uses strong adhesive strips), disconnecting cables, and accessing internal components. Apple does not officially support user-replaceable storage for these models beyond RAM on the 27-inch variants, so this is a third-party/DIY procedure.

The process is largely similar across Late 2012 through 2019 models (both non-Retina and Retina 5K versions), with minor variations in adhesive handling or bracket sizes depending on the exact year/EMC number.

Skill level: Medium (not for the faint-hearted)

Important warnings before starting:

  • This will void any remaining warranty (if applicable).
  • Risk of damaging the display, adhesive, or other components—proceed only if comfortable with detailed repairs.
  • The display adhesive is one-time-use in most cases; you’ll need replacement adhesive strips for reassembly (available from iFixit, OWC, etc.).
  • Back up all data first.
  • Work in a clean, static-free environment and discharge static electricity.
  • For Fusion Drive models (common in 2015–2019), there’s a spinning HDD + a small PCIe blade SSD. This guide focuses on the main SATA drive (HDD); the blade SSD has a separate, more advanced procedure.
  • Strongly recommended: replace the spinning HDD with a 2.5″ SATA SSD (e.g., Samsung 870 EVO, Crucial MX500) for massive speed gains. If using a 2.5″ SSD in the 3.5″ bay (most 27″ models), you’ll need a 2.5″ to 3.5″ adapter bracket (often included in upgrade kits).

Tools and Parts Needed

  • Suction cups (strong ones for lifting the display)
  • iFixit or similar display adhesive strips (custom-cut for 27″ iMac)
  • Plastic opening cards/tools or guitar picks (to cut adhesive)
  • T8, T10, T25 Torx screwdrivers
  • Phillips #1 or #2 screwdriver
  • Spudger or plastic pry tool
  • Isopropyl alcohol and microfiber cloth (for cleaning old adhesive)
  • iMac service wedge (to prop display), anti-static wrist strap, SSD mounting bracket/adapter, Temp Sensor Cable

Upgrade kits from iFixit or OWC often bundle the right parts.

The basic parts you will need. Note the anti static mat and wrist bracket is a must.

SSD, Temp Sensor and 3.5 – 2.5 Bracket
  • Preparation
    • Shut down the iMac, unplug all cables.
    • Lay it screen-down on a soft surface (towel/foam). (not idea)
    • Optionally use an iMac service wedge to support the display later. (recommended a lot easy to take the screen off this way)
  • Remove the Display
    • Insert opening picks/cards into the gap and slowly slice through the adhesive around all four edges (it’s very strong—go slowly to avoid cracking the glass).
    • Prop the display top out Do NOT fully remove yet.
    • Disconnect the display cables carefully (power, data, etc.—they use connectors that pull straight up or have tabs).
  • Access the Hard Drive Area
    • Remove screws holding the left speaker (or any obstructing parts).
    • Move/disconnect the left speaker to expose the drive bay.
    • Locate the hard drive (usually bottom-left area when facing the back).
  • Remove the Old Drive
    • Disconnect the SATA data and power cables.
    • Remove any bracket screws.
    • Slide/tilt and lift out the drive + bracket assembly.
Note the bottom rail has not been taken off (Apple Manual recommends this). moving the speaker gives you the leverage to fit the drive without taking the bottom rail off.
  • Install the New Drive
    • Transfer bracket to new drive (or use adapter if SSD is 2.5″).
    • Connect SATA cables.
    • Reinstall speaker and any removed parts.
Hard Drive bracket bottom screw can be a bit tricky (take your time)
OWC Temp Sensor needs to be on the new drive to prevent the fan from kicking in all the time on the iMac
Take the hard drive guide screws from the old drive and put them on the hard drive bracket so it can fit on the bracket.
  • Reassemble
    • Clean old adhesive residue thoroughly.
    • Apply new adhesive strips. (OWC have some with the Temp sensors or use the Apple Part)
    • Line up the Display make sure its level the bottom part use some parcel tape to keep it in place.
    • Peal off the strips on the bottom
    • Reconnect display cables.
    • Peel off the other strips
    • Carefully align and press the display back into place (apply even pressure).
  • After Installation
    • Boot up—may need to hold Option key to select boot drive if new.
    • Use macOS Recovery, Internet Recovery, or a bootable USB installer to format the new drive and reinstall macOS.
    • Restore data from backup.
    • Fusion Drive use the Apple Terminal Command to join the 2 drives together. (click here)

Fixit Guides (excellent photos, rated Moderate to Difficult, 1–2 hours):