With the number of miles the AMSOIL/STREET RODDER Road Tour car accumulates in a short period of time we’ve learned what it takes to combine drivetrain components that provide the performance we want with the reliability we demand. Backing up our four-cam Ford are components in which we have complete confidence: a transmission from Gearstar, a Strange rearend, and a driveshaft from Dynotech.
There are a host of reasons for using an automatic transmission in a street rod; first and foremost they make the car easy to drive particularly in traffic. There are other advantages as well – obviously clutch linkage isn’t required, which makes chassis construction easier and the lack of a third pedal provide more foot room for the driver. And let’s not forget performance - converters provide torque multiplication - and automatics don’t miss gears.
AUTOMATICE TRANSMISSION BASICS
While automotive automatic transmissions may have two, three, four, or more gears, manual or computer controls, and vary in complexity, the basic internal parts remain the same, there are just more of those parts in some transmissions. Here’s a look at the major components of an automatic transmission and some of the usual performance upgrades.
This is what connects the engine to the transmission. Not only does it allow the engine to keep running while the car is stationary, but it can also provide torque multiplication when accelerating from a standstill. For a simplistic explanation of how a torque converter works, picture what would happen if two electric fans were facing each other and one was turned on. As the one under power began to turn and move air, the other one would also begin to turn. If you can visualize that, you’ve got the basic idea of how a torque converter works. In a torque converter, both fans are in a container: one is connected to the engine and the other to the transmission, and oil is used rather than air.
As might be expected, there is some slippage inherent with a torque converter; so many overdrive automatics now have converters with a hydraulically applied internal clutch that hooks the transmission directly to the engine for increased efficiency. While better fuel mileage is often considered to be the advantage of a lockup converter there is another, often overlooked, purpose. The higher ratio provided by an overdrive Fourth gear can put an additional load on a conventional converter, causing excessive slippage even in light-throttle, cruise conditions. That slippage creates heat and heat’s the enemy of an automatic transmission. When used with an overdrive automatic, a lock up style will lower engine speed in cruise conditions and lengthen the transmissions life. Overdrive automatics and lockup converters are made for one another.
As gears go, planetaries can do it all. Made up of three elements – a sun, ring, and planet pinion gears – they can provide forward or reverse rotation, a speed increase, constant speed, or a speed reduction.
Three things are necessary to make planetary gears operate: an input (power from the engine), an output (power going out), and a reactor (one of the elements is held stationary). The gear ratio and the direction of travel depend on which element is performing each function. Most transmissions have more than one planetary gear set to provide a variety of gear ratios.
BANDS AND CLUTCHES
Bands and clutches hold the reactors stationary. An automatic transmission goes into gear by holding one part of a planetary gear set stationary with a band or a clutch that is applied by hydraulic pressure. One reactor is released and another applied when the transmission shifts gears; the transmission is in Neutral if no reactor is applied. If you’ve ever been in a car and the transmission felt like it was slipping, that’s exactly what’s was happening – the band or clutch pack wasn’t holding the reactor stationary and it was slipping and not transferring full power. In an extreme case, the clutches, or band, don’t hold at all, and one or more gears (and in some cases, every gear) stops working as a result.
The valvebody is the hydraulic “brain” of the transmission: it controls the shifting of gears by controlling which reactor is applied and when. Some transmissions use hydraulic pressure from a governor, throttle valve, or vacuum modulator to determine shift points, while many contemporary versions use computer controlled electromechanial servos.
Let’s start with the torque converter. In many cases, the stall speed of the converter is increased. Simply put, stall speed is the rpm that the engine will reach with the transmission in gear, the brakes applied, and the throttle held with open. The higher rpm that the engine will reach with the transmission in gear, the brakes applied, and the throttle held wide open. The higher rpm simply allows the engine to produce more power, which will launch the car harder from a standstill. The downside is that higher stall speed converters will slip more in “normal” use. That can create excessive heat, which is what damages transmissions. Of course the perfect solution is a lockup converter with increased stall speed – that’s the best of both worlds.
Most stock automatics are designed to be seamless; that is the shifts are smooth to the point of being hard to detect. This is done by timing the release and application of the various reactors. One may begin to apply as the other begins to release so there is a split second of overlap. While this results in a smooth shift, there is a certain amount of slippage that takes place in the process, which wears the friction surfaces.
Shift kits generally do two things: They change the timing of the release and application of the reactors, which results in a firmer, more noticeable shift and may also lengthen the life of the transmission. In addition the hydraulic pressure to apply the reactors is often increased too, which means the clutches and bands have more holding power, thus increasing the torque capacity of the transmission.
With many transmissions today using computer controls, a variation on the shift kit theme is the hopped-up computer. It can and will do the same things as a conventional shift kit, but changes can often be made without dropping the trans pan.
A common method to increase an automatic transmission’s torque-carrying capacity is to improve the friction surfaces that hold the reactors. This may be done by using improved materials, more clutch plates, wider bands, or a combination of them all.
Just as with manual transmission, an automatic has mechanical components that are susceptible to damage when overstressed. As the horsepower applied to its is increased, it is often necessary to increase the strength of an automatic transmission’s shafts, clutch drums, planetary gear sets, sprags, and other internal parts.
All performance transmissions can benefit from a cooler, as heat is the number-one enemy of an automatic. The cooler core should be mounted in front of the radiator, where it will receive direct airflow under all driving conditions. If that is not possible, a cooler with an integrated fan can be mounted along the frame as long as it has direct airflow. Gearstar recommends at least a 20,000 GVW capacity cooler for their Level I and 2 packages; Level 3, 4, and 5 packages require a 30,000 GVW cooler due to the more aggressive driving they will encounter. Gearstar’s Zack Farah adds, “Optimal operating temperature for transmissions is 175 degrees F.”
Ford was working on an automatic overdrive as far back as 1962, however initial attempts weren’t considered worth the expense, until higher gas prices came along and government mandated mileage standards got tougher. As a result, by 1979 Ford, was offering their first modern automatic overdrive transmission, dubbed the AOD. Over the years the AOD was redesigned and electronic controls were added, the new version was the AODE. It was followed by the improved 4R70W and then came the 4R70E and 4R75E transmissions that were developed for throttle-by-wire applications
GEARSTAR’S OVERDRIVE AUTOMATIC
Gearstar has devoted years to finding the weaknesses in the popular automatic and spent a considerable amount of money developing the parts to correct them. These improved components increase the transmission’s capacity to handle more horsepower and improve longevity. In addition, when a transmission is ordered from Gearstar the customer is asked for information about the car, including engine displacement, horsepower, torque, weight, rear gear ratio, tire size, type of speedometer drive, and the intended use of the vehicle. All these specs are then used to calibrate the transmission’s shift feel for that application.
In stock from Ford’s overdrive automatics are controlled by a system referred to as the EEC-IV, it’s a processor that controls both the engine and transmission. To operate the transmission in an other-than-stock environment, a stand-alone controller is required. Through Gearstar we found just what we needed, the CompuShift II form HGM Automotive Electronics, a specialty equipment manufacturer that designs and supplies leading-edge electronic systems for automotive aftermarket use. CompuShift II operates automatic shifting, paddle shifting, and torque converter clutch lockup for a wide variety of transmissions, including the 4R70W.
For the AMSOIL/STREET RODDER Road Tour’40 we chose Gearstar’s 4r70W Level IV transmission with a lockup torque converter. Rated to handle 750 hp and 550 lb-ft of torque, these transmissions have a long list of improvements and improved parts, including:
Custom-built 10-inch billet torque converter with lockup and 2,600-4,500 stall
Master Overhaul Kit with Alto Hardened Kolene Steels
Raybestos Gen II Racing Frictions
High Performance Valve Body Reprogramming Kit
New electronics – includes updated EPC, Shift Solenoids, Lock Up Solenoid,
Internal Wiring Harness, Output Sensors
High Flow Filter
Complete Torrington Bearing Kit
New Bushing Kit
New Reverse Band
Carbon Fiber Wide O.D. Band
300M Hardened Intermediate Shaft
Heat treated and stress relived input shaft
High Capacity 4 Plate Intermediate Clutch
Direct Clutch Pack (8 Frictions)
Wide Rev. Drum w/Mechanical Diode
Updated Sun Shell with Gear
New Low Spring and Roller
High Capacity Pump Assembly with New Gears
Updated O.D. Servo Pin and Piston
Updated Dual O-Ring 3rd Accumulator Piston
Extra Capacity Aluminum Pan
Custom 360 degree Adjustable Shift Linkage Arm
30,000 GVW Cooler
GETTING IN GEAR
To select the cogs in our Gearstar transmission we chose a floor shifter from Lokar.
Manufacturing quality products exclusively in the United States for over 24 years, Lokar has been recognized for many award-winning products and is dedicated to providing the highest possible quality. For a comprehensive viewing of Lokar Products online, visit www.lokar.com.
Along with the Lokar Floor shifter, HHR installed a Twist steering wheel-mounted paddle shifter called the Shrifter. Here are a few FAQs that explain its operation:
Q: Does the Shifter replace the mechanical column or floor shifter in the vehicle?
A: No. As with any OE manu-matic system, such as Corvette Tapshift, a mechanical PRND shifter is still required. The paddle shifter only controls the forward gears: First, Second, Third, Fourth, and Fourth, Third, Second, First. Gear selection is a safety critical function. It is important to isolate the paddle shifter from Neutral, Reverse, and Park.
Q: How does the Shrifter work?
A: The paddle shifter is nothing more than an input device. When you tap a paddle, a wireless signal is sent to the transmission control unit (TCU). The TCU decides if and how hard to shift and then hits the transmission shift solenoid. It is an all-electronic solution. There are no mechanical levers or separate motors.
Q: How long does t take for the paddle shifter to complete a shift?
A: It doesn’t. The Shrifter merely asks for the shift, and it completes that request in a mere 125 milliseconds. The TCU and transmission are responsible for completing the shift. Actual shift time varies with throttle angle and gear as well as shift firmness calibration, presence of a mechanical shift kit, and even converter selection.
Q: Why is the Shrifter wireless?
A: The Shrifter is a wireless design that greatly simplifies installation. Battery life is at least four years. One “23A” Battery is required. Batteries are readily available from sources like Radio Shack. Test lights on the paddle shifter as well as on the receiver confirm proper operation.
Q: How do I engage paddle shifter mode?
A: With CompuShift you simply squeeze a paddle. Other systems may require a separate toggle switch.