History of A500/42RH, A518/46RH 618/47RH
In the late 1980’s and early 90’s there was a big push by Detroit auto makers to get better fuel economy from their vehicles. Other than improving the engine's efficiency, there was a lot of room for improvement in the hydraulic transmissions of the time.
The development of overdrive gears and lockup torque converter clutches in transmissions immediately led to a huge improvement in fuel economy whilst improving the overall performance and driving experience.
Torqueflight, the manufacturer of Chrysler’s automatic transmissions released their first light-duty automatic overdrive transmission in 1988: the A500. It was based on the A904 transmission and contained an extension housing bolted onto the rear of the case which contained the overdrive gear.
Soon afterwards, the A518 transmission was released in 1990, which is a stronger, medium-rated overdrive transmission, and later in the middle of the 1990s, the A618 was released which is essentially a stronger A518.
Like the A500, the A518 was also based on another transmission: the A727. It too has an extension housing bolted onto the rear which contains the overdrive gear.
In this guide, we’ll be talking about the specifications and how to control the hydraulically controlled versions of A518, A618 and the A500.
Specifications of the TorqueFlight A500/42RH, A518/46RH 618/47RH
All the three transmission models came in multiple variations over the years. To differentiate between the variations, Chrysler assigned each variation a code name which reveals key details about how it functions and its capabilities.
The hydraulic A518’s code name for instance is 46RH. The 4 refers to four forward gears, and the 6 represents the torque strength on a scale 1 to 9. The R signifies rear wheel drive, and H signifies it is controlled by a hydromechanical operation with a governor mechanism.
As the A518 is a medium rated transmission, it is better suited for trucks and heavier applications. It can handle up to 400 lb-ft of input torque and can be splined with a 5.9L engine, however in stock form, it can only handle 250 to 350 rwhp at most.
The A618 on the other hand has a different bellhousing shape. It can be paired with bigger diesel and V10 engines, and can handle up to 450 lb-ft of input torque.
For light duty applications such as light pick-up trucks and light vans, the Chrysler A500 transmission would be the better pick. Its code name 42RH tells us that it is an overdrive transmission with 4 forward gears and a low torque capacity (2 out of 9).
The A518 and A618 came with both lockup or non-lockup torque converter clutch (TCC) options, whilst the A500 only came with a lockup TCC.
Weight-wise, the A518 is heavier than the A727 due to the additional overdrive unit mounted to the end of the transmission, and its length is also about 4 inches longer than the 727.
Dry Weights of the Transmissions
Strengths of the Transmissions
The A518 transmission, excluding the overdrive unit, is almost exactly the same as the highly popular A727. The A727 was very popular for nearly 30 years due its reliability, strength and versatility, making its way into various different trucks, vans and jeeps.
Where the A727 was known to fall short was its engine power losses through the transmission, which got converted into excess heat. In this area, A518 is a lot better thanks to the introduction of the overdrive gear on the output shaft. The overdrive gear provides a drop of 30% in RPM and subsequent fuel savings. The lower RPMs also leads to less wear on the engine and less noise.
In the 618/47RH, the internals are stronger allowing it to handle more torque and horsepower. It is rated to have among the highest torque capacities of any one-ton series of trucks produced by any manufacturer.
The A518 and A618 came with lockup and non-lockup converter clutches, whilst the A500 only came with a lockup torque converter clutch. The lockup TCC when locked, prevents slippage and this lowers the required engine rpms to maintain the same speed. Overall a lower rpm improves fuel economy and reduces engine noise and wear.
Weaknesses of the Transmissions
Torque Converter problems are the most common issues faced by users using the A518/A618 lock up torque converter clutches. They can get damaged more easily under high stress, whilst the non-lockup torque converters tend to be more durable and resilient under high torque loads.
Lack of 2 nd gear engagement is another issue commonly caused due to a faulty band. The band that engages 2 nd gear is known to break, so many owners often upgrade to stronger aftermarket bands if they plan to do some power upgrades
Gear Ratios of the A500/42RH, A518/46RH 618/47RH Transmissions
Popular Custom Vehicles that use the A500/42RH, A518/46RH 618/47RH Transmissions
The A518 is most commonly seen in Dodge trucks and vans, which is also owned by Chrysler. They’re commonly referred to as “Mopar” vehicles, which gets its name from “ Motor Parts”.
In vehicles that originally came with the A727. However, this can be upgraded to the A518/46RH given their similar size.
If you desire to do a manual to automatic transmission switch, from a similarly capable manual transmission such as the Getrag 360 which came in Dodge trucks, the
A518 should be a good option too.
The A518 mainly came in Dodge Ram and Dodge Dakota trucks, while the A618 / 47RH only came in the 1994 to 1995 models of the Dodge Ram 2500 and 3500 series trucks, before being subsequently replaced by electronically controlled 47RE.
A 1994 Dodge Ram that could feature a TorqueFlight A518/46RH or A618/47RH Transmission depending on the engine.
A First-Gen Dodge Dakota which later came with the option to have an A500/42RH transmission
By far the majority of A500 and A518 transmissions were used in Dodge vehicles, however some of those transmissions were also used in the Jeep Grand Cherokee’s of the nineties, as Jeep is also owned by Chrysler.
In the custom vehicle scene, the A518 and A618 is often internally upgraded to be used in hot rods and drag racers.
Controlling the Torque Converter Lock-Up and Overdrive Engagement
The shifts between the first 3 gears need to be adjusted with the hydraulic governor.
However, activating overdrive and the torque converter clutch (TCC) engagement can be done electronically.
There are different ways you can control the TCC lockup and overdrive, such as with a delay timer that engages the TCC after a set time in 3 rd or 4th gear. Some owners also use a manually operated switch in the cockpit to engage overdrive or the TCC.
Many existing methods of controlling the overdrive have their downsides. For instance, on a manually controlled TCC, if one forgets to unlock the TCC, it could lead to shuddering and a stall when coming to a stop.
These methods also don't consider moments when you need more torque and acceleration such as when trying to execute a pass. This is where a transmission controller like the COMPUSHIFT Mini works very well.
Torqueflight A518/46RH, A618/47RH, and A500/42RH Transmission Control with the COMPUSHIFT Mini
The COMPUSHIFT Mini works only with the hydraulically operated TorqueFlight overdrive transmissions. It can control the overdrive as well as the torque converter clutch engagement based on information from the throttle position sensor and speed sensor.
At lower speeds the TCC should be unlocked to multiply torque, whilst when driving at high speeds and lower loads, the TCC should be locked to provide a direct drive from the engine to improve efficiency and reduce power losses. The overdrive gear engagement also works very similarly, akin to a regular upshift or downshift.
The COMPUSHIFT Mini has the ability to drive a speedometer and provide diagnostics such as trouble codes. All this can be viewed via the app which connects to the COMPUSHIFT Mini via Bluetooth. Compared to many other overdrive and TCC engagement methods, the COMPUSHIFT Mini is a very comprehensive solution.
The COMPUSHIFT Mini’s overdrive and TCC application strategy can be easily customized using the app. You can always start with the default calibrations provided by HGM electronics which work right out of the box. The defaults can be easily adjusted as per the provided instructions.
To learn more on transmission control of the hydraulically operated Chrysler A500, A518 or A618 transmissions, head over to the COMPUSHIFT Mini’s Product Page.