Introduction: Why Upgrade to a Mopar Performance Torqueflite?

Few transmissions are as iconic in the muscle car world as Chrysler’s Torqueflite 727. When paired with a big-block B-body like a 1968–1970 Dodge Charger, Plymouth Road Runner, or a 1971 Plymouth GTX, the factory A727 delivers decent performance for stock applications—but it leaves plenty of room for improvement. Installing a Mopar Performance Torqueflite transmission (often a remanufactured or upgraded unit sold under the Mopar Performance banner) takes your B‑body’s drivetrain to the next level. These transmissions feature hardened internals, higher-capacity clutches, improved valve body calibration, and better torque converter options designed to handle 500–700 hp while still providing crisp shifts and daily-driver civility.

This guide covers a full installation of a Mopar Performance Torqueflite A727 into a B‑body. Whether you’re replacing a worn-out three-speed or upgrading from a smaller A904, the process is similar. We’ll walk you through every step—tools, preparation, removal, installation, and final tuning—so you can complete the swap with confidence. Always refer to the specific instructions included with your transmission kit, as details vary by model year and engine combination.

Tools and Materials Needed

Having the right tools on hand before you start saves frustration and prevents unnecessary trips to the parts store. Below is a comprehensive list. Where possible, note recommended brands or part numbers for a B‑body application.

  • Mopar Performance Torqueflite Transmission – Choose the correct model for your engine (big-block versus small-block bellhousing pattern) and your performance goals. PN P4876830AB is a popular pre‑built unit for 440/426 Hemi apps.
  • Transmission fluid – Use ATF+4 or a high‑performance alternative like Dexron III/Mercon (check the converter manufacturer’s spec). Genuine Mopar ATF+4 is recommended for longevity; expect 10–12 quarts for a dry installation.
  • Basic hand tools – 3/8” and 1/2” drive socket sets (metric and SAE), combination wrenches (8mm to 19mm), Phillips/flat screwdrivers, needlenose pliers, and a breaker bar.
  • Torque wrench – Essential for tightening bellhousing bolts and transmission mount fasteners to manufacturer specs (e.g., bellhousing bolts: 50 ft‑lbs; crossmember bolts: 40 ft‑lbs).
  • Jack and jack stands – A low-profile transmission jack is ideal; otherwise a floor jack with a piece of plywood works. Use four jack stands that support at least 3 tons each.
  • Transmission cooler lines – Pre‑bent stainless steel lines (e.g., Magnum Tru-Cool) or custom rubber hose with AN fittings. Get a 6‑an hose kit for easy routing.
  • New gaskets and seals – Fel-Pro gasket set for A727 includes the pan gasket, front pump seal, rear seal, and extension housing gasket. Replace the tailshaft bushing if installing a new transmission.
  • Torque converter – Your Mopar Performance transmission may come with a converter; otherwise use a 2,800–3,200 stall unit from TCI or Hughes for street/strip use.
  • Safety equipment – Safety glasses, mechanic’s gloves, and rags. Transmission fluid burns easily, and hot exhaust parts are sharp.
  • Miscellaneous – Pilot bushing (if old one is worn), antiseize compound, Loctite Blue 242, and a transmission dipstick and tube (the tube length varies by B‑body year, e.g., 1970 Charger uses a 16” tube).

Preparation: Setting Up for Success

Before you touch a wrench, prepare your workspace and vehicle. A clean, well‑lit area with room to move on all sides of the car makes the job safer and faster. Secure the B‑body on four jack stands placed at the frame rail pinch welds (not the rear axle). The transmission will drop straight down, so you need clearance under the car—at least 24 inches from the floor to the transmission pan rail.

Disconnect the battery negative terminal to avoid accidental shorts or engine cranking. Drain the old transmission fluid by removing the pan (if still attached) or using a suction pump through the dipstick tube. While the pan is off, inspect it for metal debris—excessive glitter may indicate internal wear that could affect the new transmission. Also drain the torque converter if it’s a stock unit—most Mopar Performance transmissions come with a new, empty converter, but if reusing an old converter, drain it completely to avoid mixing fluid types.

Now remove the starter and the inspection cover on the bellhousing. This gives you access to the torque converter bolts and the flexplate. Mark the flexplate orientation relative to the crankshaft; the converter bolts are typically 3/8” and require a 15mm socket. If your transmission has a kickdown cable (mechanical linkage for throttle pressure), disconnect it at the carburetor. For 1970‑later B‑bodies with electronic speedometers, unplug the VSS connector.

Removing the Old Transmission

The removal process follows a logical sequence. Take your time, label any disconnected wiring, and keep fasteners organized in trays.

Step 1: Driveshaft Removal

Place wheel chocks at the front wheels (if raised only at the rear). On a B‑body, the driveshaft is a two‑piece design on most big‑block cars (1970–74). Start by unbolting the rear u‑joint straps at the differential yoke (two 9/16” bolts per strap). Slide the rear shaft forward slightly to release the slip yoke from the transmission tailshaft. Then unbolt the center bearing support (two 9/16” bolts) and remove both halves of the driveshaft. This prevents damage to the transmission tailshaft bushing during removal.

Step 2: Transmission Support

Position a transmission jack under the transmission pan (place a piece of 2x4 between the jack pad and pan to distribute weight). Raise the jack just enough to take weight off the crossmember. Remove the rear crossmember bolts (usually four 15mm bolts) and lower the crossmember. The transmission will now be supported only by the engine bellhousing and the jack.

Step 3: Disconnect Everything Else

  • Cooler lines – Use a line wrench to disconnect the two lines at the transmission case. Plug the ports with rubber caps to keep dirt out.
  • Speedometer cable – Unscrew the cable housing from the tailshaft housing (7/8” hex). If it’s stuck, use penetrating oil.
  • Kickdown linkage – Remove the clip and slide the rod out of the trunnion on the transmission lever.
  • Neutral safety switch wires – Unplug the connector near the shift lever on the driver’s side.
  • Starter – Unbolt the starter (two 13mm bolts) and move it aside. You don’t need to remove the battery cable from the starter; just tuck it away.

Step 4: Lower the Transmission

Using a long extension and a swivel socket, remove the four bellhousing‑to‑engine bolts (typically 3/4” 12‑point, torqued to 50 ft‑lbs). With a helper, rock the transmission back and forth to break the torque converter loose from the flexplate. Slowly lower the jack while pulling the transmission rearward until the input shaft clears the flexplate. Be careful not to let the transmission tilt forward—the converter may slide off the input shaft and spill fluid. Once the transmission is free, lower it completely and slide it out from under the car.

Inspecting and Preparing the New Mopar Performance Transmission

Your new transmission should be inspected before installation. Look for shipping damage: dents in the pan, bent cooler line fittings, or cracks in the bellhousing. If the transmission came pre‑filled, check the fluid level with the dipstick supplied; otherwise, fill with 4–5 quarts initially (see final fill step).

Torque Converter Installation

The torque converter must be fully seated before installation. Lubricate the converter hub with transmission fluid and slide it into the pump splines while rotating it clockwise. You should feel three distinct “clicks” as the pump gears engage. Measure the distance from the converter mounting pads to the flexplate face: it should be approximately 1/8” clearance. If the converter is too deep, it will bind when you bolt the transmission to the engine; if too shallow, the pump may not engage. Use a depth gauge or a straightedge to verify.

New Seals and Gaskets

Replace the front pump seal (in the bellhousing) if it looks dry or cracked. Use a seal driver or a suitably sized socket to tap it in flush. Similarly, install a new rear seal on the extension housing. Apply a thin coat of transmission assembly gel or ATF to all seals to prevent dry start damage. Also replace the pan gasket—aftermarket fiber or rubber gaskets work well; avoid using excessive sealant.

Check Pilot Bushing

Inspect the pilot bushing in the crankshaft. It should be snug, not worn, and free of burrs. If the old transmission had a vibration issue, replace the pilot bushing with a new bronze unit from Mopar Performance (PN P3690934). Tap it in with a bushing driver until it bottoms out.

Installing the New Transmission

With the new transmission prepped, it’s time to go back under the car. This stage requires patience to get the alignment right.

Step 1: Raise and Align the Transmission

Place the new transmission on the jack (again with a board to protect the pan). Lift it until the bellhousing is just below the engine. Guide the torque converter into the flexplate while rotating the converter to match the bolt holes. The flexplate bolt holes are asymmetrical—note that one is offset from the others. Use a small screwdriver to rotate the converter until all three bolts can be started by hand. Do not force them.

Step 2: Bellhousing Bolts

With the transmission flush against the engine block, install the four bellhousing bolts (top two first, then bottom two). Torque them to 50 ft‑lbs in a cross pattern. If your application uses a dust shield between bellhousing and block, install it now.

Step 3: Flexplate to Converter Bolts

Rotate the engine using a socket on the crankshaft bolt to access each converter bolt. Apply Loctite Blue to the threads and torque to 40 ft‑lbs. Reinstall the inspection cover.

Step 4: Crossmember and Mount

Lower the jack until the transmission mount lands on the crossmember. Install the crossmember bolts (torque to 40 ft‑lbs), then the transmission‑to‑mount bolts (usually two 15mm, torque to 35 ft‑lbs).

Step 5: Driveshaft, Cooler Lines, and Electrical

  • Driveshaft – Slide the slip yoke into the tailshaft until it seats, then install the center bearing support and rear u‑joint straps. Torque u‑joint bolts to 20 ft‑lbs.
  • Cooler lines – Connect the lines to the transmission ports. If using AN fittings, ensure they are tight but not overtightened (30 ft‑lbs maximum). Route lines away from exhaust manifolds; use heat sleeve where necessary.
  • Kickdown linkage – Reconnect the rod to the transmission lever. For factory cable systems, adjust the cable so that throttle return spring force is not pulling on the transmission. A properly adjusted kickdown is critical – too loose and the transmission will upshift too early; too tight and it will hold gears.
  • Speedometer cable – Screw the cable into the tailshaft; if the cable is too short, use a speedometer adapter.
  • Neutral safety switch – Plug in the connector; check that the engine starts only in Park or Neutral.
  • Starter – Reinstall the starter with two bolts torqued to 35 ft‑lbs.

Final Checks and Filling

Before lowering the car, double‑check all fasteners, especially bellhousing bolts, torque converter bolts, and crossmember bolts. Reconnect the battery negative terminal.

Fill the Transmission

Using a funnel with a long tube, add approximately 6 quarts of ATF+4 to the transmission through the dipstick tube. Start the engine and let it idle in Park for 2 minutes. Shift through each gear (P‑R‑N‑D‑2‑1) for 5 seconds each, then return to Park. Check the fluid level on the dipstick; it should read between “Add” and “Full” when the transmission is at operating temperature. Add fluid in 1‑quart increments until the level is correct. Total capacity for a dry A727 with a 12” converter is about 10 quarts.

Check for Leaks and Test Drive

With the engine running, inspect all connections—pan gasket, cooler lines, rear seal, and front seal. Any dripping must be addressed before driving. Once satisfied, lower the car, set the parking brake, and take a short test drive. Drive gently through all gears, then perform a few full‑throttle upshifts to verify shift points. Adjust the kickdown cable if the transmission shifts too early or too late. Refer to this Mopar DIY forum guide on kickdown adjustment for fine‑tuning.

Troubleshooting Common Issues

No swap goes perfectly every time. Here are the most frequent problems and solutions.

  • Transmission won’t go into gear – Check fluid level first. If the converter wasn’t fully seated before installation, the pump may be damaged. Remove the transmission and reseat the converter.
  • Severe vibration at highway speed – Verify the driveshaft angle. The transmission tailshaft should be level within 1 degree; if not, adjust the transmission mount or install shims under the crossmember.
  • Fluid leaks from the front pump seal – This usually means the converter is not correctly seated, causing the pump bearing to be side‑loaded. Replace the seal and ensure the converter is fully home.
  • Transmission slips or doesn’t shift – Low fluid, blocked cooler lines, or a misadjusted kickdown. Also check that the transmission cooler is not air‑locked; if using an external cooler, purge air by filling the cooler before connecting lines. Summit Racing has a good article on transmission cooler installation.

Performance Gains and Next Upgrades

A properly installed Mopar Performance Torqueflite transforms your B‑body. You’ll notice firmer, quicker shifts that put power to the ground without slop. The upgraded internals mean the transmission can handle repeated abuse at the track or on highway pulls. To maximize the new transmission’s potential, consider adding a deeper transmission pan (adds 2–3 quarts of capacity and lowers fluid temperature), a stacked‑plate external cooler (mounted in front of the radiator), and a transmission temperature gauge. Keeping fluid below 200°F dramatically extends transmission life.

Conclusion

Installing a Mopar Performance Torqueflite in a B‑body is a rewarding project that dramatically improves both street manners and track capability. By following this expanded guide—paying attention to torque converter seating, bellhousing alignment, kickdown adjustment, and thorough leak checks—you can ensure a reliable installation. Every B‑body owner who makes the switch reports more confident driving and fewer “headaches” compared to a tired factory unit. For ongoing tips and community support, join the B‑Bodies Only forum where seasoned builders share specific tuning advice for Chargers, Road Runners, and Satellites. With your new transmission in place, you can focus on enjoying the roar of a properly built Mopar—without worrying about whether the next gear change will hold.