Transmission Torque Converter - Tech

OK, enough of the history lesson. Here's the crux of the issue. The finger points to the coarse 19-spline input shaft used through the '66 model year. The fine 24-spline input shaft (on right) arrived in 1967. These shafts engage inside the torque converter and because the 19-spline input shaft has a smaller diameter than the 24-spline shaft, it is possible to accidentally install a '67-and-up torque converter in a '62-'66 727. If you do, the car won't move an inch. More than a few Mopar builders have been stymied by this detail. Conversely, the input shaft diameter difference prevents '62-'66 converters from accidentally being installed in '67-and-up 727 transmissions. Thankfully, they just won't go in all the way. The parts in the middle are reaction shaft supports. While they both share a common 27-spline configuration, they are machined for different input shaft support bushings and are not interchangeable between cable and lever-operated 727 transmissions.

The design of the front clutch retainer is critical, so study yours carefully to make sure its compatible with the new parts you're swapping in. The '62-'70 front clutch retainers have round oil feed holes (pen points) and use a narrow 9/16-inch-wide bushing. If you see these features on yours, you must use a '67-'70 style input-shaft/rear-clutch piston retainer assembly and reaction shaft support. Late-style '71-'78 front clutch retainers are quickly identified by machined oil feed slots (rather than holes) and are only compatible with '71-'78 input conversion parts.

Here are the components you need to change to upgrade a cable-operated transmission to accept a '67-and-up torque converter. You're looking at the input shaft/rear clutch piston retainer assembly and the reaction shaft support. These goodies are hidden behind the front pump cover in an assembled transmission, except for the two splined extensions, which are visible after you pull the torque converter. Beware, these parts come in two varieties: narrow bushing, used from 1967 to 1970, and wide bushing, used from 1971 through 1978. You cannot mix parts between the narrow and wide bushing versions. The component set must be from the same-vintage donor transmission. Your best bet is to scavenge them from an unmolested donor or source them from a competent transmission rebuild shop that's aware of such intricacies. Expect to pay around $100 for clean used parts.

Identifying the conversion parts for mutual compatibility with the front clutch retainer is a simple matter of taking careful measurements and observing details. On this reaction shaft support, the tape measure shows the 9/16-inch contact journal used on '62-'70 transmissions. If yours measures greater than 9/16-inch wide, it's for a '71-'78 wide bushing application and must be matched with a '71-'78-style front clutch retainer and input-shaft/rear-clutch piston retainer assembly.

A classic hassle with TorqueFlite of all types is limited access to the bolts attaching the flex plate to the torque converter drive lugs. An excellent remedy is to cut an access area in the bottom of the case using a hole saw and pneumatic cutoff wheel (or reciprocating saw). The opening eliminates wrench-to-case interference, which leads to rounded bolt heads, inaccurate tightening, busted knuckles, and wasted time. The gap has no impact on case strength as long as the cut line intersections are gently curved to prevent crack-inviting stress risers. While you probably wouldn't want to do this to the numbers-matching transmission case in your Hemi Super bird, it's super practical for the average street and strip stormer.

Identifying the input-shaft/rear-clutch piston retainer assembly is a simple matter of counting the number of sealing rings present on the area indicated by the pen. If you see two (like the model shown here), it's a '67-'70 unit. If you see only one, it's a '71-'78 item. Naturally, you also must confirm that the splined end of the input shaft has the desired 24-spline count, thus opening the door to modern torque converter offerings. We won't bog you down with the installation process as it's no different from a typical 727 build . . . as long as you follow our tips and use the properly matched components we've outlined.

Mosher's Steve Benoit uses a punch to gently drive the stock race out of the empty transmission case. It's important to work in a gradual circular pattern to keep the race from getting wedged. Always be sure to remove the set screw located at the 6 o'clock position of the race prior to any removal effort.

While you're inside your TorqueFlite, take the opportunity to replace the stock-over running clutch assembly with a quality bolt-in replacement from A&A Transmission. The stock unit (left) is press-fit into the case and is prevented from rotating by a shallow serrated interface with the case and a small set screw. If the rollers and springs are upset from their proper positions in the outer race due to driveline breakage or improper burn out technique, the steel race can easily break loose and spin in the soft aluminum case, triggering catastrophic-and potentially deadly-transmission destruction. Bolt-in over running clutches, also known as sprag assemblies, eliminate the threat. We installed the standard A&A 12-roller bolt-in sprag (right). It's available as PN K22961E for about $110. Even greater insurance is provided by A&A's $175 Ultimate Sprag (center). Notice the upgrade from four to six retainer screws and 16 instead of 12 rollers for greater load capacity. Recommended for all-out TorqueFlites, it's sold as PN K22961EVS-6.

A soft-bristle wire wheel is used to knock down the high spots, stake marks, and burs where the old race was pressed and staked into the case. This process smoothes the receiver cavity and eases the installation of the bolt-in race. Benoit warns, "Unless you are upgrading to a bolt-in sprag, never disturb the original race. Just leave it in place during the input shaft swap process and rebuild".

The bolt-in race is installed by gently pulling it down using bolts and stacked nuts to serve as spacers. Work in a criss-cross pattern to apply even force. Never use a hammer or brute force as you can crack the aluminum case.

This close-up shows the business end of the shift cable. It snaps into a pivoting sleeve that bolts to the valvebody rooster comb inside the transmission. Installation is a simple matter of pushing the cable through the case and into the sleeve. You'll hear it click past the lock spring once it is fully seated. Always make sure the rubber O-ring is fresh to prevent fluid leaks. Disconnecting the shift cable from the valvebody sleeve requires dropping the pan so you can access the retainer spring.

A quick, sure-fire method of getting correct shift cable adjustment is to have a helper fully depress the Neutral shift button inside the car while you manipulate the external adjuster ring. When the indicated arm (pen points) is aligned with the Neutral safety switch and the ring is flush against the case, you're done. A small lock bolt threads through the adjuster ring into the case to prevent disruption. If a reverse-pattern valvebody is used, remember to mark the shift buttons accordingly. The Neutral position remains the same regardless of valvebody type or modification.

The street manners of Max Wedges and Race Hemis are compromised if you're stuck with a low-stall speed torque converter. Off-idle bogs and hiccups are par for the course unless you add some stall to mask the awkward transition from idle to power when those big quads open up. Thanks to the upgraded '67-'78 fine-spline input shaft and related parts shown in this story, your early B-Body's push-button TorqueFlite is ready to accept commonly available high-stall torque converters like this 10-inch unit. Drivability and off-the-line performance will improve immediately.