Transmission Bellhousings & Components

What Does A Transmission Bellhousing Do?

A transmission bellhousing bolts between the engine block and the transmission and encloses the rotating parts between them. In a manual car, it covers the flywheel and clutch. In an automatic, it surrounds the flexplate and torque converter.

That job means fitment drives every purchase. The bellhousing has to match your engine's bolt pattern, your transmission's case and the parts spinning inside it. If you're building a stick-shift car, start with manual transmission bellhousings and pair them with manual transmission flywheels that suit your clutch.

Automatic builds use a different set of parts. Flywheel and flexplate dust covers close off the opening below the bellhousing, and street torque converters need to suit your engine and gearing. Not sure which converter fits? Read how to choose a torque converter before you order.

SFI 30.1 Certified Vs. Non-SFI: Which Bellhousing Do You Need?

If you race at a sanctioned track, you'll likely need an SFI-certified bellhousing once your car passes certain performance levels. The cutoff varies, so check your sanctioning body's rulebook before you buy. SFI 30.1 is the certification you'll see on the automatic bellhousings in this category.

The JW Performance Ultra-Bell line includes SFI 30.1 bellhousings for TH350 and TH400 transmissions. Versions fit Chevy, Buick, Pontiac and Olds engines, plus small-block Ford and Ford Modular engines. The ATI 200044 is SFI 30.1 certified for GM 350/400 transmissions with an OEM case.

Running an aftermarket GM Powerglide or TH400 case? JEGS offers an SFI 30.1 certified bellhousing built for those cases. Non-SFI bellhousings are a common choice for street cars and builds that won't go through tech inspection.

Aluminum Vs. Steel Bellhousings: How Do They Compare?

Aluminum bellhousings save weight and usually bolt up with a cleaner fit. Steel bellhousings add weight, but many racers choose them for their strength. Your choice comes down to how you use the car and what your rules require.

On the aluminum side, the McLeod 8520 is a non-SFI bellhousing for small-block and big-block Chevy engines, also sold as the 8520K kit. JEGS offers an aluminum bellhousing kit for 1955-1985 Chevrolet small-block and big-block engines. For Ford automatics, the TCI 513300 is a case-filled aluminum bellhousing for the C4 with a small-block Ford pattern.

For steel, Quick Time Bellhousing makes units for Ford 289, 302 5.0L, 351C and 351W 5.8L engines. It also offers a steel bellhousing for RX7 13B and 20B rotary engines. Plan on test-fitting any steel bellhousing, since some need trimming and you'll want to confirm starter fit.

How Do You Match Bolt Pattern, Transmission And Flywheel Tooth Count?

Match three things before you buy: the engine's bolt pattern, the transmission case and the flywheel or flexplate tooth count. Miss one, and the bellhousing won't bolt up or the starter won't sit where it should.

Bolt pattern follows the engine family, so a small-block Chevy bellhousing won't bolt to a small-block Ford. Transmission fit follows the case. Some bellhousings cover both TH350 and TH400 cases, while others fit a single case like the Powerglide or C4.

Tooth count affects where the starter has to sit. The JW Performance Ultra-Bell for small-block Ford to TH350/TH400, for example, is listed for a 157-tooth flywheel. If you're also changing the flywheel or flexplate, confirm your engine's balance with the engine balance cheat sheet.

Which Block Plates, Spacers, Bolts And Adapters Do You Need?

Most bellhousing installs need a few supporting parts to finish the job. Lakewood, for example, offers both the 15000LKW bellhousing for Chevrolet and a safety block plate. Use this list to fill in what your build is missing:

• Block plates sit between the engine and bellhousing, like the Lakewood safety block plate for most Chevy 90-degree V6 and V8 engines.
• Multi-fit block plates cover more than one engine, like the JEGS block plate for Ford 289, 302 and 351W.
• Spacers sit between the bellhousing and transmission, like the Quick Time Bellhousing T56 Magnum bellhousing-to-transmission spacer.
• Bolt sets secure the transmission to the block, like the JEGS set for GM Powerglide, TH350, TH400 and 700R4 transmissions.
• Adapters pair an engine and transmission with different patterns, so browse engine swap transmission adapters for plates and kits.

How Do You Install And Align A Transmission Bellhousing?

Check bellhousing alignment with a dial indicator before final assembly. Dial-indicating measures bore runout, so you know the transmission will line up with the crankshaft centerline. It's a quick check worth doing on every new bellhousing install, whether the car is built for street or strip.

Mount the indicator to the crankshaft, sweep the bellhousing bore and compare the reading to the spec in your instructions. If runout is out of spec, correct it before the transmission goes in. Then test-fit the starter and confirm clearance around the block plate.

For the full process, follow our guide on how to install a new transmission. When you're ready to finish the drivetrain, shop all performance transmission and drivetrain parts at JEGS.