Classic Mustang Bellhousing, Flywheel and Clutch Guide

The block, bellhousing, flywheel, clutch and starter on a manual-transmission Mustang come as a matched set. Ford built two sets for the six-cylinder and two for the small-block V8, and parts from one set don't work with the other: the starter won't reach the flywheel, or hits it, or the clutch doesn't fit the flywheel. Mixing them is the most common mistake on a transmission swap.

This guide covers the 170 and 200 six and the 260, 289, 302 and 351 V8 in 1964½–1973 Mustangs. It starts with how to tell which set you have by measuring, since casting numbers are often unreadable and parts have been swapped between cars for decades.

Six-cylinder: the 8.5" and 9" set-ups

The 144, 170 and 200 six used one of two set-ups, named for the clutch diameter. Everything in the set has to match: the block, the block plate, the flywheel, the clutch disc and pressure plate, and the starter.

• 8.5" set-up: 8.5" clutch, 132-tooth flywheel with a dished center (a "dog dish"), three-bolt starter.
• 9" set-up: 9" clutch, flat 136-tooth flywheel (some have a small machined lip), two-bolt starter.

The starter is the quickest check: three bolts holding it to the bellhousing means the 8.5" set-up, two bolts means the 9".

Which one an engine takes depends on the block:

• 144 and 170: 8.5" only. These blocks have three freeze plugs on the passenger side; the 200 has five.
• Early 200s: 8.5" only. Block casting C5DE-6015-H is an early 200 with five freeze plugs and the 8.5" pattern only.
• Mid-1960s 200s: some blocks from about 1965 to 1968 are "dual pattern" and take either set-up.
• Later 200s: 9" only. From 1967 on, most cars have the 9" set-up.

Measuring a six-cylinder block

Four bolts hold the bellhousing to the block. The bottom two, level with the crankshaft, are in the same place on both set-ups. The top two are not. Measure across between the centers of the top two bolt holes:

• 4 3/4": 8.5" set-up.
• 5 1/2": 9" set-up.

A dual-pattern block has both pairs of holes. Wear marks in the paint around the holes show which bellhousing was last bolted on.

Six-cylinder bellhousings

The transmission names in this table are bolt patterns. The 2.77 and 3.03 are three-speeds; the numbers are the distance in inches between the input shaft and the countershaft, not gear ratios. The Dagenham is a light-duty British-built four-speed, not a Toploader, and came in early (1962–1965) and late (1965–1966) versions with different bolt patterns, plus an "oddball" with the late pattern and a short input shaft, probably behind the 170. Mustangs used the early Dagenham behind the 170 and 200 in 1964½–1965 and the late one behind the 200. The Toploader takes the Ford narrow pattern on cases built through early 1965 and the wide pattern after that; the Toploader guide covers the difference.

C0DD-6394-A and C3DA-6394-A look nearly alike; the early Dagenham bell (C3DA-6394-A) has a different transmission bolt pattern, and it's the only one here whose transmission bolts go in from inside the bellhousing and thread into the transmission. C1UU-6394 is an Econoline 170 bellhousing. There is also an iron version of the 9" wide-pattern bell.

Adapter plates to bolt a T5 to a stock six-cylinder bellhousing are widely made for the two 9" bells, C6OA-6394-C and C7ZA-6394-A. Options for the 8.5" bells are limited, and none is made for the early Dagenham (C3DA-6394-A). The 1968 Mustang 200 T5 swap uses the 9" set-up.

Small-block V8: 157-tooth or 164-tooth

The 260, 289, 302 and 351 use one of two flywheel sizes, and each has its own bellhousing:

• 157-tooth flywheel: 10" or 10.5" clutch.
• 164-tooth flywheel: 10", 10.5" or 11" clutch.

The bellhousing holds the starter in place for one ring gear size. Put a 164-tooth flywheel in a 157-tooth bellhousing and the starter hits the flywheel and won't go in. Put a 157-tooth flywheel in a 164-tooth bellhousing and the starter spins without reaching the teeth. The block plate between the engine and the bellhousing is also made for one size.

Mustang V8s by year

• 1964½ 260 and early 289: 157-tooth, with a five-bolt bellhousing pattern on the block. The six-bolt pattern arrived around August 1964, at the start of the 1965 model year. A six-bolt bellhousing doesn't fit a five-bolt block.
• 1965–1967 289, including the Hi-Po: 157-tooth, six-bolt.
• 1968: the changeover year. Ford listed both 157-tooth 289s and 164-tooth 302s.
• 1969–1973 302, Boss 302, 351 Windsor, 351 Cleveland and Boss 351: 164-tooth. The Boss 302 and Boss 351 used a 10.5" clutch.

Measuring a V8 bellhousing or block plate

Counting the flywheel's teeth settles it, but if the engine is together, measure instead. The 164-tooth bellhousing holds the starter about 1/2" further out:

• Bellhousing: from the last bellhousing-to-block bolt on the passenger side to the top starter bolt is just over 1 1/2" on a 157-tooth bell and about 1 13/16" on a 164-tooth bell.
• Block plate: from the mounting bolt on the far side to the top starter bolt hole is 16 27/32" on a 157-tooth plate and 17 5/16" on a 164-tooth plate.

Small-block bellhousing castings

Casting numbers on small-block bellhousings end in 6394. Many lists online are incomplete or unconfirmed, so this table has only the castings two independent sources agree on.

Flywheel balance: 28 oz or 50 oz

Small-block Fords are externally balanced, so the flywheel carries a set imbalance that has to match the crankshaft and the harmonic balancer. Small-blocks up to about 1981, including the classic Mustang V8s, are balanced at 28 oz-in. The exception is the 289 Hi-Po, whose flywheel and flex plate are weighted differently; buy a Hi-Po flywheel for a Hi-Po. The 5.0 from 1982 on is 50 oz-in. A 50 oz flywheel from a later 5.0 on a 28 oz 289 or 302, or the other way round, makes the engine vibrate. Check the balance before buying a flywheel for a swap.

The FE and 385-series big-blocks (390, 427, 428, 429) use larger flywheels and their own bellhousings, and aren't covered here.

Toploader bellhousings

Behind a V8, a Toploader needs a car bellhousing 6 1/4" deep; a 6 3/4" truck bellhousing is too deep. The bellhousing's transmission pattern also has to match the case: cases built through early 1965 have the narrow four-bolt pattern, and later cases the wide eight-bolt one. The Toploader identification guide decodes the tag, the ratios and the output spline.

Before you buy parts

1. Identify the set-up you have: count the starter bolts on a six, or count the flywheel teeth or measure the bellhousing on a V8.
2. Buy the flywheel, clutch, block plate and starter for that set-up, and on a V8 the flywheel for your engine's balance.
3. Match the clutch disc to the transmission's input shaft. The T5 guide and the Toploader guide list input shafts.
4. Match the driveshaft's slip yoke to the transmission's output shaft. See slip yoke specifications.