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Mopar Trans ID Guide

Photography by Marko Radielovic

In recent months, we've chronicled the pros, cons, weaknesses, and strengths of the various automatic transmissions offered by General Motors and Ford. This month, the third and final installment in our automatic transmission series focuses on the Chrysler Corporation's TorqueFlites. Mopar guys don't have as many choices, but while their options may be limited, the offerings are a good foundation on which to build a hot street or strip car.



The Three Speeds
Mopar three-speed transmissions can be broken down into two groups: The light-duty 904 transmissions and the heavy-duty 727 series of transmissions. The 904 made its debut in 1960 and the 727 hit the scene in 1962. We've always found it interesting that Mopar was the lone OEM to make a three-speed automatic transmission standard on all cars rather than offer it as a higher priced upgrade for a two-speed. Heck, if you bought a Chevy, you couldn't even get a three-speed until 1965, and then only behind a big-block, and two-speeds were the standard automatic in most GM cars into the early '70s.

Both TorqueFlite transmissions came standard with a ball-and-trunion output yoke through the '65 model year when a more conventional slip-yoke became standard. We'll look at the lighter duty of the two first, noting that the 904 was never offered behind anything larger than a small-block and was never considered a performance option. In the case of automatic-equipped performance small-block applications, such as 340-powered vehicles and heavy-duty applications with 360s, a small-block version of the 727 was standard.

Generally speaking, the 904 and its derivatives are considered some of the most mechanically efficient automatic transmissions offered to the American public.

Introduced in 1960, the light-duty TorqueFlite came in three basic designations--the 904, 998, and 999. The 904 was equipped with three direct friction plates, the 998 had four, and the 999 came with either four or five. They are otherwise dimensionally identical, and beginning in 1980 all were offered with a low gear set (2.74 First and 1.54 Second) as standard equipment. TorqueFlites were also used in some American Motors automobiles from 1972 until AMC's demise, and they even made an appearance in some import applications, including Mitsubishis. Due to its high mechanical efficiency and low weight, 904-based transmissions are a popular choice with drag racers because the light internals eat a minimum of horsepower compared to heavier duty offerings. But there are certain inherent design drawbacks with the light-duty TorqueFlite. A particularly weak link is the spindly, slotted front pump drive of the torque converter. The slots themselves are wide for ease of installation, but the resulting sloppy engagement makes the drive prone to cracking. Many aftermarket torque-converter manufacturers use much narrower slots to reduce the cracking problem. Later 904-based automatic overdrive transmissions (A500 series) have a flat machined pump drive that eliminates the crack-inducing feature entirely.

Turbo Action's Paul Forte tells us his company addresses this weakness by substituting a chromoly pump drive for the weak factory version on its high-performance torque converters. T/A's street and strip (S/S) 904 transmissions receive modifications to their lubrication circuits to improve flow along with a high-performance valvebody. Other than these basic mods and good clutch materials, T/A's S/S units can easily handle 500 eager horses. When moving up to a race unit, a full manual valvebody is standard, a transbrake is optional, and a Torrington bearing is used in the tailhousing instead of a fixed bushing. The cumulative effect of these mods brings the level up to the 600hp range. If the racer is looking to eke out the last 100th of a second and is not concerned with durability, Turbo Action can build an all-out lightweight unit featuring aluminum drums and a plethora of other lightweight parts. These top-dollar units are able to withstand up to the 900-horse range as they are lighter and more efficient, but they are built to go fast and not to last in a street car.

The heavy-duty 727 TorqueFlite was used by Mopar to back up virtually all of its high-horsepower mills from the 426 Max Wedge to the aforementioned 340 high-performance V-8 engines, to the brutal Street Hemis. While not nearly as efficient as its little-brother 904, the 727 can handle an obscene amount of horsepower. Early versions of the 727 ('62 through '65) used a push-button cable-operated shifting mechanism as well as a smaller-spline input shaft that required a corresponding torque converter unique to these model years. The '65 727 did not use push-buttons, but retained the cable-operated shift mechanism. From 1966 on, all linkage was mechanical.



Marv Ripes of A-1 Automatic Transmission has developed many components to make the already stout 727 even stronger. The 727s were produced with both three- and four-pinion front planetary-gear sets, and all were constructed of aluminum. Heavy-duty applications, such as cars and trucks equipped with high-performance big-blocks, got the four-pinion planetary. Light-duty applications received the three-pinion unit. Ripes offers a steel planetary with five pinions for use in all high-performance 727 automatics.

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.

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.

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.

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

Mopar Automatic Transmission Guide
This list is not conclusive or absolute, but provides general guidelines with respect to power ratings.
TransYearSmall-BlockBig-BlockStockModified
904/998/999'60X--DB
727'62XXAA
500'88X--CC
518/618'90X--AA
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
Gear Ratios of Popular Mopar Automatic Transmissions
TransFirstSecondThirdFourth
904/9992.45/2.741.45/1.541.00--
7272.451.451.00--
A5002.741.541.000.69
A5182.451.451.000.69
45REF3.001.50/1.671.000.75

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.

SOURCES
Turbo Action
1535 Owens Rd.
Jacksonville
FL  32218-1639
904-741-4850
Jet Performance Products
www.jetchip.com
B&M Performance Products
8-18/-882-6422
bmracing.com
A-1 Automatic Transmission
7359 Canoga Ave., Dept. KC
Canoga Park
CA  91303
Glendora Dodge
9-09/-451-0022
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