700 R4 Transmission - Overdrive Evolution

[Ed Blown Vert]

700 R4 Transmission - Overdrive Evolution
GM's TH700-R4 four-speed automatic-overdrive transmission and its derivatives have nearly become the universal favorite of hot rodders. Properly built, a good 700 is capable of withstanding at least 450 lb-ft of torque. But that hasn't always been the case. With the help of the experts at B&M and TCI, we traced the 700's initially checkered past and bring you up to date on some of the countless improvements incorporated over the years as GM continually refined the basic design to keep up with the increasing output of the engines it was installed behind.
In the Beginning
The 700-R4 was first introduced in the '82 Corvette. On paper, its specs looked pretty good: The trans had lower First and Second gears (3.06 and 1.63, respectively) than other automatics, its lockup torque converter offered potential fuel-mileage gains, and the 0.7 overdrive decreased the overall drive ratio by 30 percent. But the original design was not considered a strong transmission, with failures behind even a mild 350 not uncommon. The trans was so weak that in its original setup, GM deliberately calibrated it to kick out of lockup and high gear under full-throttle, top-end conditions to avoid burning it up. The original versions had only downsized, 27-spline input shafts, one of many possible and common failure points. By 1984, 700-R4s intended for use behind small-block Chevy V-8s began to receive beefy, 30-spline input shafts similar to those found on classic TH350 and TH400 transmissions. From 1984 to 1987, the most failure-prone internal parts, from the ring-gear to the oil-pump housing, were upgraded. An auxiliary valvebody was added in October 1986. Finally, on performance cars like the Corvette, additional internal lubrication improvements permitted the trans to survive in high-gear, full-throttle, top-end conditions. Many of the improvements can be retrofitted into the earlier, weak transmissions, but the 27-spline versions need so many new parts that it's more cost-effective to swap in a later core. However, it is worthwhile to upgrade the later 30-spline versions to Corvette/IROC-level internals, if they're not already so equipped.
Enter The 4L60E
The next big change was in 1993 with the introduction of the 4L60E in pickup trucks, vans, and SUVs. "E" derivatives are entirely controlled by the computer via electronic solenoids installed on the valvebody.E-type transmissions require a computer to function-either the original factory GM ECM or available aftermarket standalone solutions-but now shift quality can be easily dialed in without having to go into the trans itself. Also, with the computer controlling line pressure, E transmissions eliminate the TV cable and its associated bracket geometry and adjustment issues.
Not all '93 vehicles got the 4L60E. Rear-wheel-drive cars continued to use the 700-R4, but in keeping with GM's new nomenclature, the carryover trans was renamed the 4L60 (without the E). Other than the name, the 4L60 is essentially the same trans as a similar-vintage 700-R4. All GM transmissions use the new identification system: the first digit is the number of forward gears (4), the letter indicates whether the trans is intended for front-wheel-drive (T for transverse) or rear-wheel-drive (L for longitudinal) applications, and the last two numbers provide a guide to the unit's relative torque capacity (60, in this case) compared with other GM transmissions. If both nonelectronically controlled and electronically controlled versions of an otherwise similar transmission design are offered, an E suffix (for electronic) is appended to the designator.
Rear-wheel-drive cars received the 4L60E starting in 1994. Although many internal mechanical components interchange, the cases, electronic controls, and valvebodies are so different that it's not practical to upgrade a non-E to an E (or vice versa)
Many internal electronic changes occurred on 4L60E transmissions between 1993 and 1996. These included the introduction of a pulse-width-modulated torque-converter lockup function on some models starting around 1995. This smoothes out the converter lockup function by pulsing the apply function using a PWM solenoid. There are several unique evolutions on this system with matching solenoids and electrical switches. Although not really important for performance use, it is of concern if you just need a replacement trans with full functionality for a late-model and want to make sure everything works as intended.
Three-Piece Case
In 1996, with the 4L60E in use for most rear-drive applications and with new engine designs on the drawing board, GM began moving to a common main case with a bolt-on bellhousing. Previously, there were just two separate case patterns: a metric case for 60-degree V-6 engines and the classic Chevy case that fit traditional big- and small-block V-8s, straight Chevy L6s, and V6-90 engines. The move to a separate bellhousing let one common core fit a variety of different engine families and also opened up the interesting possibility of aftermarket adapter bellhousings to fit oddball or niche classic engines, such as Keisler Engineering has done with its Mopar conversion kits.
Other changes coincided with the move to separate bellhousings. The input-shaft tip configuration was revised, although the overall shaft diameter and spline-count still remained at 30. When retrofitting, the new spline tip requires a corresponding torque converter to mate with the revised shaft. GM also changed the tailhousing from a four-bolt to a six-bolt design.
The 4l65E
Stock 4L60Es are rated at 360 lb-ft of torque. By 2001, engine output had increased to the point that further internal modifications were needed for Corvette, Hummer, and some other applications. The uprated transmission-in stock form rated to withstand up to 380 lb-ft-is known as the 4L65E (RPO M32). There were significant improvements, including five-pinion planetaries, a higher-capacity input housing, and an induction-hardened input-shaft assembly. Beginning in 2002, many of the technologies from the 4L65 applications that added durability were incorporated into the 4L60, including more robust bushings and bearings. Many of the other durability-enhancing parts can also be swapped into earlier 4L60 transmissions.
The 4l70E
Classified as the 4L70E, the ultimate production evolution of the original 700-R4 trans family is used in selected '07 trucks and includes further refinements over the 4L65E. The 4L70 is a variation of the five-pinion 4L65, with additional strengthening in the output shaft and reaction internal gear to handle increased engine torque. It is doubtful that GM will continue to upgrade the trans any further, as it will be phased out once the new six-speed automatic production lines are ramped up.
On the surrounding pages we've illustrated some of the most important improvements and variations, many of which can be used to upgrade earlier transmissions. But there are so many details that we can only scratch the surface here. If you really want to get into what makes this trans tick and get the lowdown on all the changes, fixes, and improvements, the best sources are Automatic Transmission Service Group (ATSG) Techtran and upgrade handbooks available directly from ATSG's Web site as well as on eBay
1 Planetary Carriers
Planetaries are used both forward (the input planetary carrier) and at the rear (the reaction planetary carrier). Early failure-prone planetary carriers should be upgraded to at least the improved design with batwing washers (circa 1985). The improved four-pinion input carrier carries GM PN 24226173 and bolts in to any trans. The best four-pinion reaction carrier was introduced at about the same time for selected high-perf applications like Corvettes and IROCs. Besides the batwing washers, this carrier also adds a pinion oiling system with internal passages. Even better-although much more expensive-are the late five-pinion carriers introduced on the 4L65E, available from both GM and aftermarket sources.
2 Reaction Sun Shell And Input Shaft
The reaction sun gear shell helps apply both Second and Reverse gears and is a key part for holding all the internals together. It has been a major failure item since the 700's inception. Originally, the Low and Reverse clutch roller race rode against the shell, separated only by a thin thrust washer. Aftermarket beast shells became available made from thicker material around the neck. A Torrington bearing replaced the spindly thrust washer, and better roller races became available as well. Finally, starting in 2001, GM completely redesigned the sun shell. The thrust washer was eliminated, and a new fully rollerized thrust bearing was added to the reaction carrier shaft and front carrier ring gear. The new-design sun gear shell (GM PN 24229604), reaction carrier shaft (PN 24222756), and sun shell thrust bearing (PN 24217328) will back-fit as a complete assembly.
3 Input Clutch Housing (below left and center)
Over the years, both GM and the aftermarket have upgraded the input housing. The material thickness was increased, the input shaft hardened, and the housing depth slightly increased to accommodate additional 3-4 clutch packs.
4 Reverse Input Housing (above right)
The reverse input housing engages Reverse, but it also supports the 2-4 band. Check the drum surface carefully for signs of wear. Because of the nonadjustability of the band that contacts the drum, there is no way to resurface the drum without having adjustment problems or having the drum crack if returned to service. Drums manufactured starting midway through the '86 model year are slightly thicker in the 2-4 band apply area, which improves 2-4 band performance.
5 Front Pump
Overall pump design has been continually upgraded to improve hydraulic pressure. There are three major factory pump designs: one for the early small input shaft and torque converter, one for the '84-'96 large input shaft and torque converter, and one for '97-and-up transmissions. The early style had only a 7-vane pump; the second design (usually cast 732 on the cover) had a 10-vane rotor set, and the beefy, late third-design has 13 vanes. There are subvariants that may affect interchange, but in general, the '84-'95 10-vane pump can replace a 7-vane pump by plugging its auxiliary valvebody port and changing the reverse drum and torque converter. Installing the 13-vane pump in place of an early 7- or 10-vane pump requires considerable machining to back-fit as a complete assembly.
Oil-pump performance may be further improved by modifying control orifice size, altering spool valve land shapes, and adjusting spool valve diameters to meet specific operational requirements. For example, boost-valve pressure-regulator components installed in the pump cover regulate boost-line pressure throughout the trans. Up to a point, higher pressure is better.
6 Valvebody
There are several major valvebody configurations. The early '82-'87 configuration had no auxiliary valvebody; the torque converter clutch (TCC) lockup function was actuated hydraulically at a set pressure without computer input. Although this makes retrofit easy into early vehicles, the first-generation valvebodies often have leaky, low-capacity 1-2 and 3-4 shift valves that produce inconsistent shift quality.
The late '87-'93 second-design valvebody solved the problems. It added an additional auxiliary valvebody to fix a Park/Drive bang/clunk problem. A new abuse valve smoothed out rock-shifting, helping cars get out of snow and mud easier. A new one-piece 1-2 shift valve improved consistency, reduced leakage, and permitted downshifting from Second to First gear at fairly high rpm. The 3-4 shift valve was redesigned to permit WOT 3-4 upshifts. B&M offers the improved WOT 3-4 upshift kit under PN 70249.
Most second-generation valvebodies have a plugged TCC hydraulic lockup port, as GM transferred TCC lockup control directly to the engine computer. The early valve can be installed in place of the port plug to permit locking up the TCC via hydraulic pressure through the '88 models. From '89-'93, the former TCC hydraulic lockup port is completely blocked off, and no valve can be retrofitted. Instead, a computer or electric toggle switch is needed to actuate TCC lockup. Various coordinated aftermarket shift-improver kits are also available to recalibrate the shift feel on pre-4L60E valvebodies.
The 4L60E phased in a valvebody controlled by the computer acting through electric solenoids in lieu of shift valves. There is no interchange between E and non-E valvebodies.
Servo Assembly
The 2-4 servo assembly applies the 2-4 band. Upgraded servo assemblies have more surface area and volume to increase the holding force and yield firmer shifts. The best GM servo was used on C4/C5 Corvettes, as well as '93-and-later Camaros and Firebirds equipped with LT1 and LS1 engines. TCI sells the Corvette servo assembly under PN 376003. Aftermarket Super Hold servos are available with even more holding power. Changing the servo should be coordinated with valvebody recalibration, all matched to the intended application. Production inner (second apply) and outer (fourth apply) servo pistons can even be mixed and matched to fine-tune the feel.
Governor
Valvebody mods contained in typical aftermarket shift-improver kits can alter individual shift points, but playing with the governor weights allows the end user to change all shift points equally. The 4L60E no longer has a governor.

Photo Gallery: 700 R4 Transmission - Overdrive Evolution



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[Hi-Po]

Very good read.