How to find the right Automotive Performance Automatic Transmission Lines AI guide
Written by an AI model from its trained knowledge.
What the AI looks for in Automotive Performance Automatic Transmission Lines
- Fitting type at the transmission and the cooler
- Identify the end fittings before buying: inverted flare, AN flare, pipe thread, or OE quick-connect. Use adapters made for that exact port. Mismatched sealing styles are the main cause of cooler-line leaks. AN flares seal on the 37-degree cone, and pipe threads seal on the threads.
- Line size
- Match or exceed the OE line inside diameter. Performance builds commonly use -6 AN; heavy-tow or high-stall setups may step up. An undersized line restricts cooler flow and raises fluid temperature, which shortens transmission life.
- Hose rated for ATF and heat
- Choose hose and liner specified for transmission fluid and underhood temperatures. Braided stainless or PTFE-lined hose suits high-heat routing. Generic rubber hose softens and swells in hot ATF and can burst under line pressure.
- Routing and support
- Route away from exhaust and moving parts, clamp at intervals, and leave slack for engine and trans movement. Chafed or heat-soaked lines fail suddenly. A loss of cooler flow can burn a transmission quickly.
- Hard line vs flexible
- Use OE-style formed steel lines to replace originals on stock vehicles. Use flexible braided lines for swaps, custom coolers or relocated plumbing. Pre-bent replacement lines bolt in without guesswork. Flexible kits solve fitment the OE lines cannot.
Brands that matter
- Earl's: Long-standing AN hose, fittings and adapters for custom cooler plumbing.
- Russell: Braided hose and AN fitting systems widely used for transmission lines.
- Fragola: AN hose ends and adapters, including transmission-specific fittings.
- Derale: Transmission coolers with matching line kits.
- Hayden: Cooler and line kits aimed at towing and heat management.
- Dorman: OE-style pre-formed replacement cooler lines for many vehicles.
- TCI: Transmission-focused line kits and fittings for popular performance automatics.
What to avoid
- Fuel or heater hose that is not rated for ATF
- Teflon tape or thread sealant on AN flare connections
- Hose clamps on lines without barbs or beads to retain them
- Routing within reach of headers or the exhaust crossover
Questions
Which port is the feed and which is the return?
It depends on the transmission model, so check the service info for yours. Coolers generally work either way, but many builders route the return to the bottom cooler port to help purge air.