The stock slotted 904 torque-converter...
The stock slotted 904 torque-converter pump drive is on the left. The flat-machined unit (right) is from a late-model A500 torque converter. The A500 unit is much stronger. This is a common upgrade on performance torque converters.
Probably the most problematic feature of the 727 is the overrunning clutch in the back of the case, sometimes incorrectly referred to as the sprag. Simply put, the overrunning clutch, a steel housing splined into the aluminum case, acts to stop the gear train and lock up the rear planetary in low and Reverse gears. Failure is often caused by driver error while performing a burnout in First gear. The problem can arise after the water burnout is completed and the car rolls onto dry pavement. The resulting high-shock loads can be transmitted directly to the overrunning clutch, overstressing it and damaging the case. In order to eliminate this weakness, the design of the transmission would have to be completely reengineered, but durability can be improved by pinning or bolting the overrunning clutch to the case, which provides better support than stock soft aluminum splines. Both A-1 and Turbo Action perform this modification to their 727 TorqueFlites. The best way to avoid overrunning clutch stress is to always perform burnouts in Second or high gear.
The output shaft of a stock...
The output shaft of a stock A518 overdrive trans offers inadequate lubrication to the overdrive unit. JET drills out the openings approximately 30 percent to increase the oiling capacity.
For the ultimate in race 727 technology, A-1 offers its ProFlite transmissions for use in NHRA's Comp Eliminator and Super Stock Modified cars, regardless of the brand of transmission the car originally came with. ProFlites are designed to fit wherever a Powerglide once resided. Based on smaller AMC 727 casings (which are narrower in the bellhousing region by 1.5 inches) and featuring light-weight 904-based internal components, these transmissions are so efficient they require only 125 to 150 psi of line pressure to function compared to the 225 psi required in the race 'Glides. The lower the pressure, the less power is wasted turning the pump. A-1 ProFlites are available with 25 different gear-ratio combinations, are available with a billet aluminum adapter to fit Chevrolet engines that allow the use of Powerglide torque converters, and are able to withstand up to 1,300 hp.
A-1's ProFlite transmissions...
A-1's ProFlite transmissions feature ultralightweight innards like these aluminum drums, but that doesn't mean they're weak. These transmissions live behind 1,300hp NHRA Comp Eliminator cars.
Automatic Overdrives
The A500 transmission, introduced in 1988, was the first light-duty Chrysler four-speed automatic. It is literally a 904 transmission with a fourth Overdrive gear bolted to the rear of the case. Similarly, the A518 is a 727 trans with an overdrive unit tacked on. In both cases, lack of adequate lubrication to the overdrive unit is the primary cause of failure. Jet Performance Products, a leader in automatic overdrive transmission technology, performs a number of modifications to enable both versions to live in abusive environments. In all cases, JET replaces the roller clutch and the sun gear with new OEM pieces. These two components are the most likely to have been damaged by the lack of lubrication to the overdrive unit, which leads us to the next round of modifications performed by JET: improving the oiling to the overdrive unit. The three rearmost lubrication holes on the output shaft are enlarged approximately 30 percent (the exact amount is proprietary) to increase the flow of life-giving lubrication to the overdrive unit. JET also offers a shift-improvement kit that allows you to tailor shift quality from mild to wild. The kit also redirects crucial lube to the overdrive. With these modifications, JET is confident that either version is capable of withstanding up to 450 lb-ft of torque, and if the user avoids full-throttle up-shifts into Overdrive, the transmission's life expectancy increases exponentially.
A-1 offers a bolt-in overrunning...
A-1 offers a bolt-in overrunning clutch for 727 TorqueFlites that offers better support for this inherently weak area. The piece begins life as a stock unit, which is then drilled and tapped. Even when beefed up, it's never a good idea to do a burnout in First gear with a TorqueFlite transmission.
Early versions of the A500 were produced with a five-clutch drum (in the overdrive unit); later versions were updated to six-clutch drums, but all A500s can be upgraded to the A518's beefier eight-clutch drum. While often maligned for not being up to the task of handling large amounts of torque, the fact that the A518 is standard equipment (in A618 form) behind Chrysler's torquey turbo-diesel trucks is testimony to its true capacity. The designation A618 is used for diesel and V-10 applications with corresponding calibrations (in the diesel's case, lower rpm shifts).
Glendora Dodge's James Schagel clued us in to the particulars of DaimlerChrysler's newest offering, the 45RFE, also known as the multi-speed transmission. Introduced in 1999 in the Jeep Grand Cherokee behind the 4.7L V-8, it made its way into the Dodge Dakota lineup in 2000. This coincided with the introduction of the 4.7L and the phasing out of the 5.2L (318) as the base V-8 engine. The 45RFE features two Second gears. The computer, sensing load, shifts the trans to either Second gear. In the '03s, the 45RFE is a true five-speed automatic without the multiple Second gears. This trans is available behind 4.7L V-8s as well as Chrysler's new 5.7L Hemi, but it's still too new to have much of an aftermarket following. CC
The 904 lockup input shaft...
The 904 lockup input shaft is on the top. The input shaft on the bottom is a 904 nonlockup unit.
| Mopar Automatic Transmission Guide |
| This list is not conclusive or absolute, but provides general guidelines with respect to power ratings. |
| Trans | Year | Small-Block | Big-Block | Stock | Modified |
| 904/998/999 | '60 | X | -- | D | B |
| 727 | '62 | X | X | A | A |
| 500 | '88 | X | -- | C | C |
| 518/618 | '90 | X | -- | A | A |
|
| Note: In place of a vacuum modulator, Chrysler automatic transmissions use a rod or a cable to control throttle pressure and kickdown. |
|
| *Ratings: A = High torque, heavy car; B = High torque, light car; C = Low torque, heavy car; D = Low torque, light car |
Another breakage-prone area...
Another breakage-prone area of the 727 are the drive tangs (arrows) on the inner pump rotor. The tangs can break off if an engine kicks back after shutoff. High-compression race engines are more prone to cause this than low-compression street pieces. A-1 makes inner pump rotors with larger, heavier-duty tangs.
| Gear Ratios of Popular Mopar Automatic Transmissions |
| Trans | First | Second | Third | Fourth |
| 904/999 | 2.45/2.74 | 1.45/1.54 | 1.00 | -- |
| 727 | 2.45 | 1.45 | 1.00 | -- |
| A500 | 2.74 | 1.54 | 1.00 | 0.69 |
| A518 | 2.45 | 1.45 | 1.00 | 0.69 |
| 45REF | 3.00 | 1.50/1.67 | 1.00 | 0.75 |
Special Thanks
We have to give special thanks to transmission guru Mike Maravelas without whom this series could not have been completed. Mike didn't want credit, but he gave us his undivided attention, shared his knowledge and parts books, and let us use his shop. Thanks, Mike. We appreciate all of your help and promise not to give out your phone number.