Inverted block and tackle balances support the sash in many tilt-window systems. Unlike a standard block and tackle balance, the spring is positioned toward the bottom of the channel, while the cord and pulley system are located toward the top. A T-lock shoe attached to the balance engages the pivot bar at the bottom of the sash.

Before You Start

Clear the area around the window and prepare a padded, stable surface for the removed sash.

Tools you may need:

• Phillips-head screwdriver
• Flat-head screwdriver
• Tape measure
• Safety glasses
• Cut-resistant work gloves
• Phone or camera for reference photos
• A second person for a large or heavy sash

Safety Warning: Inverted block and tackle balances contain stored spring tension. Always maintain control of the balance and T-lock shoe when the shoe cam is unlocked.

Do not remove the upper mounting screw while the balance remains extended. Guide the balance toward the top of the jamb first so the spring tension can be reduced.

Inverted balances are available in several series and configurations. Parts that appear similar may use different channels, T-lock shoes, cams, mounting arrangements, or weight ratings.

Before ordering, record:

• The complete stamp printed on the metal channel
• The length of the metal channel
• The channel width and depth
• The balance series or channel shape
• The T-lock shoe width and thickness
• The color of the puck on the back of the shoe
• Whether the T-lock cam is open or closed
• The upper mounting-hole location
• The original balance orientation

If the balance has no readable stamp, you may also need the sash weight to determine the correct spring strength.

Unlock the window and raise the sash approximately 2 to 3 inches before tilting it inward.

1. Support the sash evenly from the lower rail.
2. Raise it several inches above the sill.
3. Release both tilt latches.
4. Pull the top of the sash gently toward you.
5. Tilt the sash inward until it is nearly horizontal.

Raising the sash before tilting helps reduce unnecessary pressure on the pivot bars located at the lower corners of the sash.

With the sash tilted inward, lift one corner slightly higher than the other. This allows the first pivot bar to disengage from the T-lock shoe.

1. Keep both hands on the sash.
2. Lift or angle one corner upward.
3. Release the first pivot bar from its T-lock shoe.
4. Shift the sash carefully and release the opposite pivot bar.
5. Place the sash on a padded surface.

Do not pull the sash straight outward while both pivot bars remain seated in the shoes.

Before moving or removing the balances, photograph both jambs and record the installed position of each balance.

Confirm:

• The height of each T-lock shoe
• The direction of the channel and shoe
• The upper mounting-screw position
• The stamp on each balance
• Whether both sides use matching balances
• The condition of the pivot bars and T-lock shoes

The cam inside the T-lock shoe holds the balance in position when the sash is removed. A flat-head screwdriver is used to rotate the cam and release the shoe.

Locked position: The cam opening normally faces upward.

Unlocked position: Rotate the cam approximately one-quarter turn while maintaining control.

1. Insert a flat-head screwdriver securely into the cam opening.
2. Maintain a firm grip on the screwdriver and balance.
3. Rotate the cam away from you approximately one-quarter turn.
4. Confirm that the balance can move within the jamb.

After unlocking the T-lock shoe, slowly guide the balance upward toward its mounting point at the top of the jamb.

1. Keep control of the balance as it moves upward.
2. Do not allow it to snap toward the mounting screw.
3. Guide it upward until the spring is no longer heavily extended.
4. Confirm that the balance is stable before removing the mounting screw.

Repeat the process on the opposite side of the window.

Once the balance has reached the top of the jamb and the spring tension has been reduced, remove the upper mounting screw.

Tilt the upper portion of the balance outward after removing the mounting screw.

Rotate the balance and T-lock shoe as needed to clear the jamb opening.

1. Support the balance while removing the mounting screw.
2. Tilt the top of the channel outward.
3. Rotate the balance and shoe within the jamb.
4. Guide the T-lock shoe through the available opening.
5. Remove the complete balance assembly.

Do not force the T-lock shoe through the jamb. If it will not clear, adjust the angle and rotation of the balance rather than prying against the vinyl.

Install the replacement balances by reversing the removal process.

1. Compare the new balance with the original before installation.
2. Confirm the channel, stamp, length, T-lock shoe, and mounting location match.
3. Rotate the T-lock shoe and channel so they can enter the jamb opening.
4. Tilt the balance into its installed position.
5. Align the upper mounting hole.
6. Install and tighten the original mounting screw securely.
7. Maintain control of the balance while guiding it downward toward its original position.
8. Use a flat-head screwdriver to rotate the cam back into the locked position.
9. Repeat the process on the opposite jamb.

1. Hold the sash nearly horizontal.
2. Insert the first pivot bar into its T-lock shoe.
3. Angle the sash slightly and insert the opposite pivot bar.
4. Confirm that both pivot bars are fully seated.
5. Level the sash and tilt it upward into the frame.
6. Press the sash closed until both tilt latches engage.

Operate the window several times and confirm that:

• The sash raises and lowers smoothly
• The sash remains open at several positions
• Both sides move evenly
• The sash does not drop or bind
• The tilt latches engage correctly
• The sash closes and locks properly

A damaged balance may not be the only issue. Inspect the hardware that connects the sash and balance system.

• Cracked or distorted T-lock shoes
• Worn, open, or damaged cams
• Bent, loose, or broken pivot bars
• Cracked sash corners
• Loose upper mounting screws
• Damaged jamb tracks
• Frayed cords or damaged pulleys
• Uneven wear between the two sides

• Tilting the sash without raising it first
• Allowing the sash to hang from one pivot bar
• Unlocking the T-lock shoe without controlling the balance
• Allowing the balance to snap toward the top of the jamb
• Removing the mounting screw while the balance remains under heavy tension
• Forcing the T-lock shoe through the jamb opening
• Ordering a replacement based only on channel length
• Ignoring differences in shoe size, puck color, or cam style
• Installing the left and right shoes at significantly different heights
• Discarding the original balances before confirming the replacements

Watch the video below for an overview of identifying and repairing vinyl tilt windows that use inverted block and tackle balances.

Replacing an inverted block and tackle balance requires safely removing the sash, controlling the T-lock shoe, guiding the balance upward to reduce the spring tension, and matching the replacement by more than appearance alone.

Record the stamp, channel dimensions, balance series, shoe measurements, puck color, cam style, and mounting arrangement before ordering.