Workshop advice: Automatic transmissions

By: Paul Tuzson, Photography by: Paul Tuzson

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Paul Tuzson explains how to identify the classic auto transmissions...

Workshop advice: Automatic transmissions
Workshop advice: Transmissions



Know your transmissions

Newcomers to the classic car scene wouldn’t be as familiar as seasoned readers with the various automatic transmissions that have been fitted to local cars, but this is important information.

A basic knowledge of the principles and main components utilised in automatic transmissions is extremely useful when speaking with a transmission rebuilder if you’re getting work done. Even casual conversations with more experienced car enthusiasts will be more enjoyable and useful if you have enough basic knowledge to understand what’s being discussed.
So we went and visited Ron and Tony at Pro Automatics in Dandenong to take us through the transmission basics.

Impress your friends! Know your transmission terminology:

Flex plate
The metal disc fitted to the rear of the engine crankshaft. The starter motor meshes with the teeth around the periphery of the flex plate.

A torque converter is the large bulbous component bolted to the flex plate so that it rotates with the engine. It’s also connected to the transmission input shaft and to the transmission pump.

An epicyclic gearset. A cluster of gears in constant mesh with each other. The three types of gears within it are the sun, planet and annulus. The annulus is sometimes referred to as the ‘ring gear’ and the planet gears are often referred to as ‘pinions’.

Flat, ring-shaped plates that carry friction material on either side. Tabs on the inner diameter of clutches key them to hubs.

A component located in the centre of a clutch pack.

Flat, ring-shaped plates located between clutches and against which the friction material on clutches bear. Tabs on the outer diameter of steels key them to drums.

A hollow metal component that carries within it the clutches and steels that make a clutch pack when assembled.

Shift Kit
A selection of replacement components for the valve-body of a transmission and instructions for modifying factory components to create faster transitions from one gear to another.

These grip drums to lock them.

These apply bands. Stronger aftermarket versions are made from billets.


Buying one of these transmissions for rebuilding will likely cost between $450 and $750. Having it rebuilt to standard condition will cost about $1500.

It’s always good to shop around for estimates if your budget dictates your rebuild or servicing, but don’t compromise on quality. Over-estimate your costs in case any problems arise.

A transmission can be disassembled, cleaned and rebuilt with new parts in about a day. Of course, that’s from when your transmission reaches the head of the queue.



The Ford C4 is one of the most common automatic transmissions used in classic cars in America. It was used behind six-cylinder and Windsor V8 engines in Mustangs and other models until 1981. In Australia it was fitted to XT-XY GT models. Like a lot of transmissions, the C4 was available with two spline counts on the input shafts. Earlier models had 24-spline inputs and then halfway through the XW the 26-spline input was adopted. A 24-spline input can be upgraded to the 26-spline unit, but the valve-body of each type is different.

Because C4s were so popular in the US, there are quite a few aftermarket parts available for them. The C4 is a two-planetary transmission and the standard planetaries can be upgraded to take five-pinion and six-pinion gearsets (planetaries). The front planetary is known to wear rather than break, but once replaced you’re on your way again. From the factory, a C4 will handle about 400hp. When fitted with good aftermarket components, a C4 will handle around 650hp. Adaptors are available to fit the C4 to non-factory applications, including rotaries.


The C10 is controversial. Essentially, it’s just a C4 with a slightly different case. In America there’s no such thing as a C10, yet in Australia it’s cited as the most common Ford transmission used.

The name C10 is actually an Australian invention used for what the Americans describe as a ‘pan-fill C4’. In fact, it is identified by the fact that the filler tube (not shown in the shots) is attached to the side of the pan.

On the other hand, what we simply call the C4 is known in America as a ‘case-fill C4’. Again, the filler tube isn’t shown in the shots, but it’s fitted to the case rather than the pan. So, although C10 isn’t an official Ford designation, we’ll continue to use the term because it’s so entrenched.

What can be seen in the shots is the difference between the C4 and C10 cases. The C4 has a more sharply angled, thicker, squarish flange to which the bell-housing is bolted. The C10 has a curved, blended radius on the case where it meets the bell-housing. Also, in the C4 the bell-housing is fixed to the transmission case by the pump bolts. In the C10 a wider circle of separate bolts holds the bell-housing to the case. The internals of the C4 and C10 are virtually the same.


GT Falcons from the XA onwards were fitted with the extremely heavy duty FMX transmission. Unlike the other transmissions shown here, it has an iron case. As with the C4 and C10, it’s a three-speed, but gets its ratios by means of a single planetary known as a dual-compound type.

The FMX is an old transmission design. In fact, FMX internals can be fitted into a Customline case, which is a very early design from the 50s.

The Americans didn’t use them very much, so there aren’t many aftermarket components available. A shift kit and stronger band is about it. Even so, they’re naturally tough and about the only thing that goes wrong is that they wear the second gear band, but that happens mainly in high-performance applications.

The Americans opted for the C6 instead of the FMX, but in Australia we fitted them to XA, XB GTs and 351 Clevelands in general, until the temporary demise of the V8. AMC used a version of the FMX called a Type 12.


As mentioned above, this is the transmission the Americans chose for heavy-duty applications instead of the FMX. I can vouch for the heavy construction of these transmissions from having to move them about for photography.

The FMX is extremely heavy compared with other transmissions of the era, partly because of its iron case. Although the C6 has an aluminium case, it’s also extremely heavy, and it’s about as tough as the legendary TorqueFlite 727. The C6 is easy to spot amongst other classic Ford transmissions because the bell-housing and case are cast as an integral unit.

We never got the C6 in Australian production, although Mustangs did have them. From about ’69 onwards, Ford America fitted them to all their muscle cars. The C6 is used behind 429 and 460 big-blocks, but the example shown here has a small-block pattern.


The Chrysler TorqueFlite transmission is said to be the longest-serving transmission in the world. The first version had an iron case and appeared in 1956 and the alloy type with integrally cast bell-housing seen here replaced the iron type in about 1962.

There are two basic types of TorqueFlite, the 727 and the 904. The 727 was fitted behind big-blocks and small-blocks alike (big-block version shown here). The bell-housings are different, but the internals are similar, except that big-block versions had four-pinion planetaries while small-block models had three-pinion planetaries. Four pinions are always better, but in reality neither type fails in service, particularly in street applications.

The 904 TorqueFlite looks like the 727, but is smaller and designed for use with sixes in standard duty applications. The case shown here is empty because it was being rebuilt. However, it can still be used for identification purposes. The clutch drums at the right show the difference between 727 and 904 components.

Although TorqueFlites are for Chryslers, there are adaptors available to fit them to just about anything, including small-block and big-block Chevs, Windsors, Ford FE blocks and so on. This is because Chrysler was into racing back in the day and this was the first high-power transmission available. Consequently, the TorqueFlite received a lot of development work.

There are a number of uprated components available for it, including stronger input shafts, aluminium clutch drums and Kevlar bands, but these are only needed in performance applications. They’ll take around 800hp with the right components fitted, but a shift kit and replacement servos will be perfectly adequate for virtually any road use. AMC also used a version of the TorqueFlite, with a different bell-housing.


Torque-Power manufactures a range of bell-housings for unusual transmission swaps including: RB30 to Reid Powerglide, RB30 to Turbo 400, Chev Turbo bolt pattern to TriMatic, RB30 to TriMatic, BA 6 to C10, BA 6 to Reid Powerglide, BA 6 to 400, BA 5.4 V8 to C10. Call Craig on 0419 359 143 to see if he has what you’re after.




If you’re going to make a two-speed automatic transmission, it had better be strong, and the Powerglide from GM certainly is. It’s been the backbone of drag racing for decades, yet it was only produced for a fairly limited time.

In Australia it first appeared in HK, HT and HG Monaros behind Chevs. Rod Hadfield told us that in six-cylinder applications it was first fitted to the HD and ran through to the HG in ’71 when the Trimatic and Turbo-400 took over on the 253 and Chevs respectively.

It’s so popular that entire replacement cases are available aftermarket, as are most of the internals required to build race versions. Search for Dedenbear/Reid and TCI to see what’s available from the US.


Strictly speaking, the proper name for Turbo-350 is Turbo Hydra-Matic 350. However, no-one calls Turbo series transmissions by their full name, and no-one cares. This was a very popular transmission in America, but out here we only got them in the HZ and in VB and VC V8 Commodores. They were a heavy-duty option locally and came with long and short tail housings. All OE Australian versions had short housings, but the one shown here must have come from an American car because it has the long tail housing. A well prepared ’box will handle 600-700hp.


The Turbo-400 is stronger again than the 350 and was our most common heavy-duty option from the HQ, in which it first appeared, to the WB. Turbo-400s just last, and in standard service will never break; you’ll simply wear them out.

This is a popular ’box in America and one current modification consists of cutting the cast bell-housing off and fitting a new one that allows the 400 to be fitted behind Ford Cammer engines, of all things. There aren’t many adaptor plates for them out here, but they can be fitted to TriMatic-pattern 308 blocks. Australian 400s had longer tail housings. Again, one wasn’t available to photograph so above is a short tail housing version.


Finally, the TriMatic. This was fitted from Holden’s HG through to the VL Commodore. It’s a good transmission and the Americans also used it, so there are performance components available for it. However, they’re likely to fail beyond about 400hp and hard launches on big tyres can hurt the planetaries. Because they were fitted behind the very popular VL turbos, people worked at finding ways to uprate them, so a unit built with the correct components can handle 500–600hp behind a turbocharged engine. They’re also adapted for use with rotaries.


If the sun gear is held and the planet carrier driven, the annulus will turn in the same direction as the carrier at increased speed.

If the planet carrier is held and the sun gear driven, the annulus will turn in the opposite direction. Remember, two gears in mesh turn in opposite directions.

If the annulus is held and the planet carrier driven, the sun gear will turn in the same direction. The driving arrangements described also work in the opposite directions.


So, that’s most of the classics. The detailed workings of automatic transmissions are complicated, but being able to identify them is the first step in learning about them. That’s about all most people need to do. It’s possible for an enthusiast to work on one at home but it’s probably not wise. Better to leave it to experts like Ron and Tony. You can reach them at Pro Automatics on (03) 9791 5427.


Perform regular services on your automatic transmission. Change oil and filter yearly or bi-yearly, depending on driving frequency.

Periodically check the transmission’s rear seal, which can leak fluid. The old trick of cardboard under a stationary car will warn you of leaks.

If you’re going to be placing strong demands on your transmission because of enhanced performance or towing, fit a supplementary transmission fluid cooler.



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