Replacing a garbage disposal under an older kitchen sink

Quick answer

A humming disposal is usually jammed, and a silent one has often tripped its reset button. If it leaks from the body, it is worn out and should be replaced. We match the new unit to your sink, drain height and dishwasher connection.

Kitchens in older Alhambra homes have usually been updated more than once. That means the disposal under your sink may be sitting on a mix of drain parts from different decades, and a vintage cast-iron or deep porcelain sink can add its own quirks.

Here is how to sort out the common problems.

Quick checks before you call

• It hums but does not spin. It is jammed. With the power off at the switch, use the hex wrench that fits the socket in the center underneath to work the plates back and forth.
• It does nothing. Check the reset button, the wall switch and the breaker. Some disposals plug into an outlet under the sink that may be on a tripped GFCI.
• It drains slowly. The clog may be past the disposal in the trap or the line.

When replacement makes sense

• Water drips from the bottom of the unit itself
• It trips its reset button again and again
• It jams constantly even with ordinary use
• It is loud, rusted or more than about a decade old

Older-kitchen details we watch for

Deep or thick sinks. Vintage cast-iron and porcelain sinks have thicker drain openings, which affects how the mounting assembly seals.

Drain height. A new disposal can sit lower or higher than the old one. If the outlet ends up below the drain in the wall, water collects in the pipe, so we adjust the trap to keep it flowing downhill.

Dishwasher connection. If a dishwasher drains through the disposal, the knockout plug inside the new unit has to be removed first. Forgetting this is a classic cause of a dishwasher that will not drain.

Old drains and new disposals

Older Alhambra kitchens often have cast-iron or galvanized drains, sometimes with sinks that have been replaced several times. A disposal adds food solids to those drains, so the drain needs to flow well. If the sink already drains slowly, have the drain cleaned before adding or replacing a disposal.

Sink and flange

Vintage sinks, especially cast iron or porcelain, may have thick bowls or an unusual drain opening. Disposals need a standard 3-1/2 inch opening. Most sinks have it, but some old sinks need an adapter or extended flange. We check before buying.

Electrical

Disposals need power. Many older kitchens have no outlet under the sink, or the disposal was wired directly. A GFCI-protected outlet under the sink and a wall switch or air switch make the setup safer. If there is no switch, an air switch on the counter avoids opening walls.

Choosing a disposal

A 1/2 or 3/4 horsepower continuous-feed disposal suits most kitchens. Stainless steel grinding parts last longer. Sound insulation helps in open kitchens.

Our steps:

• Turn off power and disconnect the old unit
• Remove the old mounting ring and clean the flange
• Install a new flange with plumber's putty
• Mount the disposal, connect drain and dishwasher
• Connect power and test for leaks

Dishwasher connections

If the kitchen has a dishwasher, its drain hose connects to the disposal. Knock out the dishwasher plug inside a new disposal before connecting the hose. Use a high loop or air gap.

Avoiding clogs

Run cold water while grinding and for a few seconds after. Keep grease, coffee grounds, eggshells, and fibrous vegetables out. See low water pressure at one fixture for other kitchen plumbing issues.

Noise and vibration

Old disposals can rattle loudly, especially when mounted to thin stainless sinks. Newer models have better sound insulation and anti-vibration mounts. A quieter disposal makes a big difference in open kitchens.

Smell

Odors come from food stuck under the splash guard and in the chamber. Clean the rubber guard, and grind ice and citrus peels occasionally.

When to replace

Disposals typically last around ten years. Leaks from the bottom, frequent jams, or a motor that hums but will not turn after clearing mean it is time to replace.

Disposal-free option

Some homeowners prefer no disposal and use a sink strainer and compost. That is easier on older drains.

Sizing for the cabinet

Older sink cabinets can be shallow or crowded with pipes. Measure the height from the bottom of the sink to the cabinet floor and the distance to the drain outlet in the wall before choosing a disposal. Compact models fit tight spaces.

If the new disposal's outlet sits lower than the wall drain, the trap will not drain properly, so a shorter unit or a lower drain connection may be needed.

What our replacement involves

We shut off power, disconnect the old unit and the drain, and remove the mounting ring. We clean the sink flange, set the new flange in fresh plumber's putty, mount the new disposal, and reconnect the drain and dishwasher line. Then we run water through it and check every joint for leaks.

See our garbage disposal replacement page.

Keeping it running

Run cold water while the disposal is on and for a few seconds after. Keep grease, rice, pasta, coffee grounds and fibrous peels like celery out of it. And run it every few days so the parts do not seize.

Kitchen jobs off Main Street often end with a basket of har gow at Lunasia before we head to the next call.

Want us to handle it?

Call or text (626) 684-3505, Mon–Sat 8:30 AM–7 PM. Send a photo and we will give you an upfront quote.

Call or text (626) 684-3505