Vacuum Line Fittings, Automotive Vacuum Hoses & Connectors

What Vacuum Hose Fittings Do in Your Engine

Vacuum hose fittings route engine vacuum from the intake manifold to every system that depends on it. A running engine creates vacuum behind the throttle, and your fittings, tees and hoses carry that suction where it's needed. If one connection leaks, every system downstream loses pull.

On most vehicles, vacuum powers the brake booster, the PCV system, distributor ignition advance and the transmission modulator on older automatics. Classic and muscle cars also use it for pop-up headlights and cowl induction hoods. A leak at any of these points can show up as a hard brake pedal, poor shifting or headlights that won't open.

The PCV system is a common trouble spot, because its hoses and elbows sit near hot engine parts. If you're chasing oil consumption or an uneven idle, compare what you're seeing with these bad PCV valve symptoms before you replace hoses. When you're ready to plumb the rest of your engine bay, browse the full range of fittings and hose.

What Types of Vacuum Line Connectors Do You Need?

Most vacuum line connectors come in a handful of shapes, and each one solves a specific routing problem. Pick the shape first, then match the size to your hose. Here are the types you'll see most often:

• Tees split one vacuum source into two lines
• Straights join two hoses of the same size end to end
• Reducers connect hoses with two different inside diameters
• Elbows turn a line 90 degrees to clear tight spots
• Caps seal unused ports on a manifold or throttle body
• Barbed aluminum fittings grip hose tightly in high-heat areas
• Soft-mount aluminum fittings add a vacuum port to a silicone coupler
• Vacuum manifolds and distribution blocks feed several accessories from one port

Assortment kits with 100-plus pieces bundle tees, straights and reducers, so you can fix heat-cracked connections without a parts run. Shop individual pieces and kits in vacuum fittings and manifolds. You'll find options from brands including Dorman Products and Mr. Gasket.

Silicone vs. Rubber Vacuum Hose: Which Should You Use?

Choose silicone vacuum hose if your lines run near headers, turbos or other high-heat areas. Choose rubber if you want an OEM-style, budget-friendly replacement on a stock engine. Rubber works well, but it hardens, cracks and dry rots with age and heat.

Silicone holds up longer in those conditions, and color options make it easier to trace lines. Vibrant Performance silicone vacuum hose meets SAE J20R3 and resists collapse under high vacuum, plus peeling, cracking and swelling. It's sold in Pit Packs and Bulk Packs, such as a 3/16" (5mm) I.D. 25 ft bulk pack.

Some idle air control hose kits use 3-ply reinforced silicone for added strength. Because silicone is slicker than rubber, secure it with a clamp on barbed fittings. For silicone couplers and hose, check out Mishimoto, or compare every size and material in automotive vacuum hose.

How Do You Choose the Right Vacuum Hose Size?

Measure the inside diameter (I.D.) of your old hose or the outside diameter of the fitting barb, then buy hose and connectors that match. Vacuum hose is sized by I.D., so a 3/16" hose fits a 3/16" barb. A snug fit is what keeps the connection from leaking.

Common vacuum hose sizes include 1/8", 5/32", 3/16", 1/4", 5/16" and 3/8". Smaller sizes usually run to sensors, gauges and ignition advance, while larger sizes typically feed the brake booster and PCV system. Metric hose is close but not always exact, and 3/16" is roughly 5mm.

If two lines don't match, use a reducer, such as a 1/4" x 3/16" or 3/8" x 1/4" fitting. Don't stretch a small hose over a big barb, since it'll split once heat cycles set in. If your build also uses braided lines, our guide to AN fittings and hose sizes explains how dash sizes differ from vacuum hose I.D.

How Do You Fix a Leaking Vacuum Line?

To fix a leaking vacuum line, find the leak, replace the damaged section and reconnect it with a matching fitting. Most repairs take basic hand tools and a few minutes per connection. Work with the engine off and cool, then use this process:

• Inspect each hose for cracks, splits and loose ends
• Trim cracked hose ends back to clean, solid material
• Replace any hose that's hard, brittle or soft and swollen
• Join or reroute lines with a straight, tee or reducer that matches the I.D.
• Secure each connection with a clamp, then listen for hissing at idle

Spring clamps and small worm-gear clamps keep hose from creeping off barbs, and you'll find them in line clamps and separators. A connector kit keeps common sizes on hand for the next repair. For threaded vacuum ports on boosted or custom builds, follow our steps on how to assemble AN fittings and hose so each joint seals.