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Rebuilding The 904 Torqueflite Transmission - Three Speeds ForwardRebuilding A 904 Torqueflite From the April, 2004 issue of Mopar Muscle By Marko Radielovic Photography by Marko Radielovic
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When we took delivery of project Stealth Bomber, the '89 Diplomat police car, we set a goal that would require a fairly stout drivetrain. The first item on the agenda is the transmission. Even though the mileage was remarkably low, the 58,000 miles showing on the odometer were hard miles. The shift quality wasn't great, resulting in early and soft shifts. This, as well as lots of overlap, and a propensity for freewheeling in reverse until the car was good and ready to move, told us it was definitely time for a rebuild. Normally, we would lean towards the more bulletproof 727, especially in a drag application where repeated hard launches take their toll, but in this situation the A999 derivative of the venerable 904 was deemed more than adequate. Remember, our stated goal is a 150-mph capability, so we will maintain the ultra-high 2.94 rear gear, and upon launch the car will not be subjected to much shock. The '89 A999 our police car was equipped with is a wide-ratio transmission featuring a 2.54:1 first gear ratio, a 1.54:1 second gear, and a 1:1 high gear. An autopsy revealed burned high-gear/reverse clutches from overheating, burned bands, and a slightly-mangled, lower/reverse drum thrust-washer. We were fortunate that our 'Flite didn't require any "hard parts," as everything internal was serviceable.  Here it is, an A999 wide-ratio,...  Here it is, an A999 wide-ratio, 3-speed automatic-slightly used, a bit grungy, but perfectly serviceable.  TransGo provided us with a...  TransGo provided us with a shift kit to help firm up the shifts on our worn-out A999 trans. This kit covers all 904 Torqueflites and their derivatives, including the A500 four-speed, automatic-overdrive units. Included with the kit was this video that shows you how to install the kit from start to finish. It proved invaluable.  Converting Torque Project...  Converting Torque
Project Stealth Bomber has some unique requirements in the torque converter department. We wanted a bit of stall in order to move the less-than-svelte Diplomat off the line with some authority, yet we wanted it to lock up tight on the top end. Having used Continental Converters with great success on past projects, we turned to owner Kris Abrahamson for help with our "unrealistic" goals. We didn't need an off-the-shelf unit, we needed a custom piece to satisfy our performance needs. We brought Kris a slightly-used A500 high-stall converter from an '89 Shelby Dakota we owned nearly a century ago. It differs from other 904-type converters in that it has a high-stall stator inside. This unit was deemed the best foundation, and Kris began by back-cutting the stator to raise the stall a bit more, adding Torrington bearings and a stronger pump drive.  Once all the mounts, linkage,...  Once all the mounts, linkage, and brackets are removed, then remove the plate on the tailshaft housing that covers the snap ring. Having access, open the snap ring and lift the tailshaft housing off.  With the pan out of the way,...  With the pan out of the way, the valvebody is now accessible and can be detached with 10 torx-headed bolts. Hopefully, you drained the trans prior to removing the pan!  With the six bolts holding...  With the six bolts holding the front pump in place removed, you will need a slide hammer to actually take the pump out of the case. There are two 3/8-inch coarse-threaded holes, 180-degrees apart at the 11 and 6 o'clock positions (approximately), made specifically for the slide hammer. After the pump is out, you can now remove the input shaft by grabbing hold and pulling-as long as the forward clutches aren't welded together. Thankfully, ours weren't.  In order to remove the spring...  In order to remove the spring from the high-gear/reverse clutch drum, you will need a good spring compressor. The snap ring needs to be removed first. Be very careful while performing this task because the spring is under a lot of pressure. Our high-gear/reverse clutches were burned up. With the entire transmission apart, it's time to assess the damage. Fortunately, we had no "hard part" damage and would only have to perform a "soft part" rebuild.  A torx wrench and screwdriver...  A torx wrench and screwdriver will be needed to disassemble the valvebody. Be careful not to lose any of the check balls.  Our grimy trans case was dumped...  Our grimy trans case was dumped into a sonic cleaning tank. All other parts received a thorough cleaning in the hot tank. Cleanliness is paramount when rebuilding an automatic transmission.  Our late-model A999 was already...  Our late-model A999 was already equipped with the desirable five-clutch, high-gear/reverse drum. This is a worthwhile upgrade when building an earlier model 904 trans. More clutches equate to more holding power.  These five bushings were replaced:...  These five bushings were replaced: high-gear/reverse drum, front pump, front ring gear, extension housing, and pump stator support.  The High-gear/reverse clutch...  The High-gear/reverse clutch drum has a wave-loc snap ring (on right) that holds the clutches in place. We replaced it with a flat snap ring that will improve the second- to third-gear shift. The wave snap ring was designed to soften the shift on passenger cars. We like our trannies to bark the tires on upshifts. A wave-loc snap ring is also used on the input drum as it softens the engagement into gear from park. You will want to leave that one alone.  The original plastic accumulator...  The original plastic accumulator was replaced with an aluminum piece from an earlier 904 (727s use the same part). Not only is the aluminum unit stronger, it will also provide a better seal than the plastic unit.  Transgo's instructions show...  Transgo's instructions show you what modifications need to be made to the valvebody. These two holes were drilled in the separator plate. Transgo even provides the correct drill-bits.  A new manual valve is provided...  A new manual valve is provided with the Transgo kit. The manual valve directs the trans into gear when you move the selector (shifter). The OE manual valve doesn't allow the transmission to pump oil while in Park, making it necessary to check our trans fluid level in Neutral. Transgo's replacement manual valve makes the transmission pump oil even while in Park. This is a particularly important feature that would benefit any vehicle that spends a good deal of time idling, e.g., emergency and delivery vehicles, because lube will continually flow through the transmission. Now we can check our fluid level in Park.  The band on the left is a...  The band on the left is a standard 904 band and is 1.3-inches wide. The most desirable band is the one that came standard in 904s behind 360 engines and were 1.75-inches wide. While our A999 came equipped with the wider band, we could not get a replacement in time, so we went with the next best option, an A500 overdrive band (right) that is 1.6 inches in width. Will it hold up to the punishment of our Stealth Bomber? Only time will tell.  Here, our buddy and tranny...  Here, our buddy and tranny man Neil Kaukola of Bob's Transmission in Simi Valley, California, hoists our refurbished bullet back under the Diplomat.  When reinstalling the front...  When reinstalling the front pump, torque the six bolts between 18 and 20 lb-ft of torque.  The trans pan on the right...  The trans pan on the right is the original shallow unit, but we opted for the deep unit on the left. The deeper pan is from an A500 and provides increased fluid capacity.
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