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American Automatics

Specialising in Classic American Transmission Rebuilding

Technical Info for Ford C4 gearboxes

The Ford C4 is a popular gearbox due to its simple, reliable and compact design. However it is very easy to come a cropper when buying one or swapping parts. The reason for this is mostly due to the fact that it was fitted in so many different vehicles from Mustangs, to Trucks and Vans. Also 6 cylinder and V8 engines. Such a variation requires a number of different parts. Coupled with this, there have been 4 major design stage changes over its life from 1964 to 1986! The advantage of the C4 is the bolt on bellhousing, but this is also where the trouble starts......‚Äč

Design overview

The C4 is called a C4 because it was brought out in 1964 and the Ford part number for 64 year is C and 4 and so the name stuck.

There are 2 main style differences - Case fill and Pan fill. Case fill has a dipstick tube entering the front of the main casing, (most common) Pan fill has a dipstick tube entering the side of the sump pan. 

All varieties are 3 speed only. A version called the C5 was brought out in 83 that had a lock up torque converter. Essentially it is the same but had better lubrication design. Servo sizes varies greatly and is dictated by the letter on the housing such as H or C. The gearbox operates by a combination of clutches and bands which are adjustable. A whole range of performance upgrades are readily available. These are generally dependable gearboxes that normally only fail due to old age and hard lives, coupled with good old fashioned neglect. 

Major design change steps

There are 4 major design changes in distinct year blocks which can create problems with parts interchange so you have to pay close attention to the exact year and type of gearbox you have. They are as follows

1964-69 (mostly case fill) Vent tube on side by rear servo. Small 24 spline input shaft. 24 spline hub.

1970 on its own (either case or pan) An odd ball year having a Small 26 spline input shaft and 26 spline hub.

1971-82 (mostly pan fill) Vent on tail housing. Larger 26 spline input shaft 24 spline hub

1983-86 (C5 version supersedes C4 name) Mostly Pan fill. Tail vent. 26 spline input. Fine thread band adjuster.

Internal variations

Internally there are plenty of parts that change over the years and also change due to the application they were made for. For example, externally a 6-cylinder gearbox will look exactly the same as the V8 version but internally it will have clutch hubs that have fewer plates, therefore less strength than is needed for a V8 engine torque level. They cannot be upgraded to V8 as the snap ring groove is in a lower spot. They must be totally replaced with V8 versions. It's not uncommon for unscrupulous folks to bolt a V8 bellhousing to a 6 cylinder case!! Been caught out myself.

Valve bodies changed alot. Early ones in 64 had a shift style called 'Green Dot'. This had two types of D range, D1 and D2. Essentially D1 started out in 2nd gear for driving in the snow. D2 was normal. There was no '2'. Quickly this was dropped as a confusing bad idea and replaced with a PRND21 that we now no as normal!

Filters also changed alot to suit the valve bodies they bolt to. Trucks with deeper pans have a funnel shape filter. This won't fit the shallow car pans.

Pumps vary by style and year and can't be swapped between case and pan fill. 

Bellhousings, flexplates, Block plates and torque converters

This is a nightmare area where most folks gets themselves in a right pickle, often costing them money on parts that are completely incompatible.

Bellhousings - there are 2 main types with further variations. Case fill bellhousings and pan fill bellhousings. They don't swap with each other. One bolts through the pump to the case and the other bolts to the casing separately. Apart from this main difference you then have the size and depth that is right for your engine and other parts. C4 bellhousings were made for Small blocks with 5 bolt blocks, small blocks with 6 bolt blocks, Big blocks, 6-Cyl blocks. There are no FE blocks.

Flexplates and torque converters have 3 main sizes - 157 tooth, 164 tooth and an oddball 143 tooth for Mustang II, due to the small floor pan in this car. 157T torque converters are known as '10 1/2 inch' and 164T are known as '11inch'. This refers to the bolt pattern diameter. Not the outside diameter of the doughnut. The 164T torque converter will not fit within the 157T bellhousing nor will it fit the flexplate bolt holes. Both 157T and 164T torque converters come in either 24 or 26 spline input shaft sizes. (I feel you holding your head in your hands right now :-) Stay with me!

Just as it can't get any worse we have the block plate! This is the seemingly pointless sheet of steel hanging off the back of your block. It is actually to locate the starter motor in the exact position and is required. Annoyingly a 157T block plate is therefore useless for a 164T bellhousing as this puts the starter in the wrong location for engagement with the flexplate. Ford you utter bastards!! Also starters are different for autos and manuals.

So to sum up. Be careful, do you research. For a correct installation you need a set up that matches like this 157T block plate, 157T flexplate, 10 1/2 inch converter with the splines that match your gearbox input shaft and bellhousing of 157T style. Even though a 157T torque converter will fit inside a 164T bellhousing it is deeper and therefore will not fit. Trust me I have already made these mistakes.

I hope you found this section interesting and informative. It certainly taxed my brain to write it! It is by no means a definitive list. There are shift lever variations to consider !!