Introduction
The 700R4 automatic transmission, commonly referred to as the 700R4 “trany,” is a four‑speed torque‑converter automatic gearbox that was produced by the American automobile manufacturer Chrysler from 1979 through the late 1990s. It was originally designed for front‑engine, front‑wheel‑drive (FF) vehicles and was intended to offer improved fuel economy and durability compared to its predecessors. Over its production life the 700R4 saw widespread use in a variety of Chrysler, Dodge, Jeep, and Plymouth models, becoming one of the most recognizable automatic transmissions of its era. Its robust construction and straightforward design contributed to a long service life and a large aftermarket support base. This article examines the development history, technical specifications, applications, common issues, maintenance practices, and legacy of the 700R4 transmission.
History and Development
Origins and Design Philosophy
In the late 1970s, the automotive industry faced increasing pressure to improve fuel efficiency in response to energy crises and evolving emission regulations. Traditional automatic transmissions of the era, such as the 4L60 and early 4L80, were heavy, complex, and often failed prematurely under higher torque loads. Chrysler sought a solution that would combine the reliability of a manual gearbox with the ease of an automatic, leading to the development of the 700R4. The transmission was engineered around a simple four‑speed planetary gear set, with a torque converter providing the primary connection between the engine and drivetrain.
Production Timeline
The 700R4 entered production in 1979 for use in the Chrysler K platform, specifically the Dodge Dart, Plymouth Reliant, and Chrysler LeBaron models. The initial iteration, the 700R4A, was a low‑torque version tailored to the 2.2‑liter inline‑four engines that powered these cars. In 1984, the 700R4B was introduced with increased torque capacity and a revised torque converter for the larger 3.0‑liter engines. The 700R4C appeared in 1986, featuring further improvements in durability and a modified shift pattern that accommodated the higher output of the 3.5‑liter V6 engines. Production continued through 1998, with the transmission being replaced by the 4L60 and later the 4L65H and 4L80 in Chrysler’s lineup.
Variants and Modifications
Several variants of the 700R4 were produced to accommodate different engine configurations and drivetrain layouts. The most notable variant is the 700R4B, which was adapted for use in the Chrysler PT Cruiser and the Dodge Intrepid models, receiving an updated torque converter that matched the increased horsepower of the newer engines. In addition, aftermarket companies produced conversion kits to allow the 700R4 to operate with higher torque outputs, such as those found in the Jeep Grand Cherokee’s 4.7‑liter V8. These kits typically involved upgraded input shafts, stronger bearings, and revised gear ratios to reduce stress on internal components.
Technical Specifications
Mechanical Layout
The 700R4 is a multi‑plate, hydraulic automatic transmission that relies on a torque converter, a set of planetary gear assemblies, and a series of hydraulic valves controlled by an electronic or vacuum actuator. The transmission is mounted at the front of the engine, with the input shaft connecting to the engine’s crankshaft via a flexible coupler, and the output shaft connecting to the differential through the driveshaft. The gearbox is typically mounted on a cast aluminum frame, providing a rigid mounting surface for the internal components while also containing the cooling system and hydraulic reservoirs.
Gear Ratios
Below is a representation of the standard gear ratios for the 700R4B variant. Variations exist for the 700R4A and 700R4C, but the overall structure remains consistent.
- First gear: 4.28:1
- Second gear: 2.33:1
- Third gear: 1.00:1
- Fourth gear: 0.79:1 (overdrive)
- Reverse: 3.44:1
These ratios provide a balance between low‑speed torque for acceleration and high‑speed efficiency for cruising. The overdrive ratio of 0.79:1 allows the engine to operate at lower RPMs on the highway, thus improving fuel economy.
Clutch and Torque Converter
The torque converter is a critical component that manages the transfer of power from the engine to the transmission. The 700R4 employs a two‑stage torque converter with a primary, secondary, and tertiary clutch assembly. The converter’s lockup clutch was available only in the 700R4C variant and provides a direct mechanical connection between the engine and transmission, eliminating slip and reducing heat generation during high‑speed cruising. The lockup feature is typically engaged automatically at around 3,000–4,000 RPM, depending on the engine load.
Input and Output
The input shaft of the 700R4 is typically 7.5 inches in length, with a splined bore that interfaces with the engine’s flex coupler. The output shaft, 6.0 inches in length, is mounted on a universal joint that connects to the driveshaft. The driveshaft length and angle are chosen to provide a direct path to the differential while maintaining adequate clearance for the transmission housing and related components. The gearbox is designed to handle continuous torque loads of up to 400 lb‑ft in the 700R4C variant, although typical operating conditions rarely exceed 200–250 lb‑ft.
Materials and Construction
The transmission housing is made of cast aluminum alloy, chosen for its favorable strength‑to‑weight ratio and thermal conductivity. The internal gears are forged steel, machined to precise tolerances to reduce wear. The planetary gear sets use a mixture of hardened steel and alloyed brass for the sun, ring, and planet gears, which are arranged in a standard epicyclic configuration. The use of a single planetary set, as opposed to multiple stages, simplifies the design and reduces the number of moving parts.
Compatibility and Applications
Vehicle Models
The 700R4 was employed across a range of Chrysler, Dodge, Jeep, and Plymouth vehicles. Key models include:
- Dodge Dart (1979–1983)
- Plymouth Reliant (1979–1983)
- Chrysler LeBaron (1979–1983)
- Chrysler PT Cruiser (1984–1991)
- Dodge Intrepid (1991–1995)
- Jeep Cherokee (1984–1994)
- Jeep Grand Cherokee (1993–1995)
- Chrysler 300 (1997–1998)
In addition, the transmission was used in some non‑Chrysler vehicles that had sold Chrysler engines, such as the 1987–1990 Lincoln Mark II and the 1994–1998 Lincoln Navigator. Its widespread adoption across multiple brands made the 700R4 one of the most common automatic transmissions in North America during the 1980s and early 1990s.
Performance Characteristics
The 700R4 was designed to provide smooth operation under typical automotive loads. With its single planetary gear set and well‑balanced torque converter, the transmission offers relatively quick shifts and a low likelihood of “shift shock.” However, its four‑speed layout limits the potential for performance tuning compared to modern five‑ or six‑speed units. The overdrive gear, while beneficial for fuel economy, can feel sluggish during acceleration from a standstill if the vehicle’s engine is not configured to deliver adequate torque at low RPMs.
Common Modifications
Enthusiasts and mechanics have often modified the 700R4 to enhance durability or performance. Typical modifications include:
- Replacing the stock torque converter with a high‑torque unit that features a larger lockup clutch area.
- Installing a revised valve body that increases hydraulic pressure during shifts, reducing shift times.
- Upgrading the input shaft to a thicker, higher‑strength alloy to accommodate higher horsepower.
- Replacing the stock gear sets with forged steel or alloyed components that offer better wear resistance.
- Adding a custom cooling system that increases the coolant flow rate, mitigating overheating during heavy use.
Such modifications are often employed in Jeep off‑road applications, where the transmission may encounter extreme torque loads during off‑road climbing or towing.
Common Issues and Troubleshooting
Fluid and Cooling Problems
Transmission fluid in the 700R4 is susceptible to degradation over time due to high operating temperatures and prolonged use. Common symptoms of low or contaminated fluid include rough shifting, delayed engagement, or failure to shift into higher gears. Fluid level must be checked with the engine running and the transmission in neutral or park; a low reading may indicate leaks or excessive consumption. Overheating is a frequent cause of transmission failure, particularly in high‑torque vehicles. Overheating can be prevented by ensuring the cooling system operates correctly, that the coolant temperature remains below 200°F, and that the fluid cooler is free of blockages.
Valve Body Issues
The valve body of the 700R4 is responsible for directing hydraulic pressure to the clutches that engage or disengage gears. Wear or contamination in the valve body can lead to inconsistent shifting or failure to shift. Symptoms include delayed first‑gear engagement, slipping out of first gear, or a “floating” gear sensation. The valve body is often replaced with a refurbished or aftermarket unit that incorporates improved seals and improved valve design to enhance shifting performance.
Overheating and Seal Failure
Repeated exposure to high temperatures can cause seals to weaken, leading to fluid leaks. The input shaft seal, the output shaft seal, and the differential flange seal are all common failure points. A leaking input shaft seal may produce a low fluid level and a high‑pitch whining noise due to the loss of hydraulic pressure. Replacement of the seal and a thorough inspection of the shaft for damage are required to restore normal operation. Overheating can also cause the transmission’s gear mesh to become misaligned, leading to a grinding noise or a failure to engage gears. In severe cases, the transmission may seize entirely, requiring a rebuild or replacement.
Rebuilding and Replacement
When the 700R4 fails, rebuilding the unit is often the most economical solution. A rebuild typically involves disassembly, cleaning, inspection, and replacement of worn or damaged parts. Key components replaced during a rebuild include the torque converter, input and output shafts, bearings, clutch packs, valve body, and gear sets. A rebuild kit typically includes a new gear set, new clutches, new seals, and a new torque converter. After a rebuild, the transmission is reassembled, filled with fresh fluid, and subjected to a short test drive to confirm proper operation.
Maintenance and Service
Fluid Change Intervals
Chrysler’s recommended fluid change interval for the 700R4 is typically 30,000 miles or 36 months, whichever comes first. However, many service manuals advise more frequent changes, particularly for vehicles that are frequently driven in severe conditions, such as towing or off‑road use. When changing fluid, it is advisable to flush the old fluid completely to remove metal shavings and sludge that can compromise performance. After the new fluid is added, the transmission should be run for at least 10 minutes to ensure proper circulation.
Inspecting Components
Routine inspections should focus on the following areas:
- Transmission fluid level and condition: Check for the presence of metal particles or a burnt odor.
- Seal integrity: Inspect the input shaft, output shaft, and differential flange seals for leaks.
- Torque converter operation: Verify that the lockup clutch engages correctly by monitoring the engine’s RPM drop during highway cruising.
- Valve body condition: Look for wear or blockages in the valve body or the pressure lines.
Any issues identified during inspection should be addressed promptly to prevent more extensive damage.
Rebuilding Process
A typical rebuilding procedure for the 700R4 includes the following steps:
- Remove the transmission from the vehicle.
- Disassemble the housing, separating the input shaft, output shaft, and planetary gear set.
- Clean all components using a solvent or degreaser, ensuring removal of all old fluid and debris.
- Inspect bearings, seals, and clutch packs for wear; replace as necessary.
- Install new gear sets, clutches, torque converter, and valve body.
- Reassemble the housing, making sure all components are seated properly and all fasteners are torqued to specification.
- Fill with fresh transmission fluid and perform a diagnostic test on a bench or in the vehicle.
- Verify shift quality and torque converter lockup operation before returning to normal service.
Historical Impact and Legacy
Market Position
The 700R4 represented a significant step forward in automatic transmission design for Chrysler. At the time of its introduction, it was one of the few units that combined a relatively lightweight cast aluminum housing with a robust four‑speed planetary gear set. Its ability to handle up to 400 lb‑ft of torque made it suitable for a broad spectrum of engines, from the 2.2‑liter inline‑four to the 4.7‑liter V8 in certain Jeep models. This versatility contributed to its widespread adoption and longevity.
Comparison with Contemporaries
When compared to other automatic transmissions of the era, such as the A904 and A727, the 700R4 offered a more balanced approach to torque handling and fuel efficiency. The A904, used primarily in larger Chrysler V8 applications, was heavier and less efficient in fuel economy due to its higher gear ratios. The A727, a two‑speed automatic, was simpler but offered limited versatility and poor acceleration. In contrast, the 700R4’s four‑speed layout allowed for better acceleration without compromising cruising efficiency.
Influence on Future Designs
Elements of the 700R4’s design can be traced into later Chrysler transmissions. The 4L60, introduced in the early 1990s, adopted many of the 700R4’s casting techniques and hydraulic systems while expanding the gear ratios to five speeds for improved performance and efficiency. Additionally, the use of a single planetary gear set as a core concept influenced the development of the later 6L80 transmission, which offered six speeds and improved torque capacity.
Modern Perception
Collector Interest
Collectors of classic American muscle and daily drivers often seek the 700R4 for its reliability and ease of maintenance. Its straightforward mechanical design makes it an attractive choice for restoration projects, particularly for models that originally shipped with this transmission. The availability of aftermarket parts and a robust community of rebuild specialists has made it possible to maintain the transmission well into the 21st century.
DIY Rebuild Culture
The 700R4 has become a staple project for hobbyist mechanics. Detailed manuals and step‑by‑step rebuild guides are widely available, facilitating the learning process for those who wish to gain hands‑on experience with automatic transmissions. Building or rebuilding a 700R4 from scratch allows individuals to experiment with alternative torque converters, valve bodies, and gear sets, providing a practical learning platform for transmission mechanics.
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