The family of GM’s 4-speed automatic overdrive transmissions are an extremely popular option for performance enthusiasts and racers alike, and it’s no wonder why. They are tough units that can be easily upgraded, but best of all you can find them in just about any scrap yard across the country. Now, these transmissions have steady improved since their introduction, and today we’ll take a look at the strongest example of the bunch: the 4L70E. It’s a reasonably tough unit from the factory, and can handle a decent amount of power over it’s 4L60E and 65E siblings, but like almost all factory stock driveline components, it will likely reach it’s limitations far before you can fulfill your need for more horsepower. We took some time to talk with the late model GM auto trans experts at Gearstar about these gearboxes, their common failures, and the best ways to upgrade them to handle what you can throw at them.

Building A Better 4L60 Series Box – The 4L70E

Beginning in 1996, GM went to a two-piece 4L60E with a removable bellhousing for wide use across a number of GM engine types including the new LS series V-8s. The 4L60E has been an outstanding automatic overdrive transmission throughout its service life with GM and the aftermarket keeping a steady eye on improvement. Internal improvements have brought greater load and torque capacity along with improved performance.

• 
• 

This is the 4L70E, basically the same externally as the 4L60 and 4L65E. Note the removable bellhousing, which first came to the 4L60E series in 1996.

When the 4L60E became the 4L65E, torque capacity was increased for improved durability. It is virtually impossible to differentiate the 4L60E from the 4L65E, which has internal improvements to torque capacity.

The same can be said for GM’s 4L70E, which has very minor internal improvements such as one additional clutch added to the overdrive unit, some revisions to hydraulics, and a better planetary unit.

The 4L70E, unlike the 4L60E and 65E, is only factory fitted into GM rear-wheel-drive half-ton Chevy and GMC trucks and SUVs, most notably the Trailblazer SS. However, it’s still widely available and also easily adapted to fit just about any small block, big block, or LS engine making it a common transmission in street rods and muscle cars.

Where to find a 4L70E Transmission

• Half-ton RWD Chevy and GMC trucks from 2006 and up
• Chevy and GMC RWD sport utilities from 2006 and up (Trailblazer SS)

Stock Torque Ratings

During our chat with Mark Walk of Gearstar Performance Transmissions in Akron, Ohio, we learned a lot about these time-proven GM overdrive automatics. Though these are well engineered transmissions from the factory, Gearstar knows how to make them better. “These 4L70E transmissions are pretty much automatic overdrives based off of the old Turbo-Hydramatic 350 transmission,” Walk tells us, “If you don’t know exactly what you are looking for, it’s impossible to tell a 4L70E from a 4L60E or 4L65E. There aren’t any physical differences externally in the case. Even the cases are still stamped 4L60E.”

 “Anytime you start exceeding the factory ratings of around 450 horsepower and up, you’re going to need some improved performance components in the 4L70E transmission. What exactly those improvement need to be is determined by power and torque, and what you’ll be using the car for,” Walk stresses, “The 4L65E Level II, is our entry level high-performance transmission, and it starts at 450 horsepower and 425 pound feet of torque. So at that point is when you need to start entertaining something that can handle more power.”

Upgrading the 4L70E To Handle More Power

Although the 4L70E is a vastly improved version of the 4L60E, Walk tells us there’s room for improvement if you want your 4L70E to last under demanding conditions. Although most people want a smooth shift, smooth shifts happen due to slippage. Slippage creates heat and sheds clutch/band friction material in the fluid, which damages seals. You want a firm upshift and a smooth, unnoticeable downshift.

Less Slippage Means Less Heat

The first way to upgrade the 4L70E is to cut down on the heat. “We have guys who call in with 350 horsepower cars who want a new 4L70E transmission just for the better shift quality. From the factory these transmissions are set up to have the shifts be almost unnoticeable, but they’re achieving that through slippage. Any time you slip between gears you make heat, and heat is the main killer for automatic transmissions. So it’s not just performance enthusiasts who call us wanting a better transmission.” Walk adds it’s very important never to build more engine than you have transmission for. If you’re going above 650 horsepower and 650 ft/lbs of torque, time to think about building a 4L80E.

Reduced Friction Means Efficiency

Upgrading the friction materials in a 4L70E can go a long way in improving it’s durability and power rating. “Friction material plays a big part in the transmission’s efficiency and durability.” says Walk. “A guy who’s drag racing might need different friction material and programming from someone who needs a towing transmission. Again, it’s all determined by what the vehicle will be used for. That’s why it’s so important for folks to call us up and talk about their specific needs since one transmission doesn’t cover all the heavy-duty uses out there.”

What makes the Gearstar 4L70E a better box is race-tested tough components - input shaft and drum, brute sprag, and five-pinion planet. Translated, more working surface area to bear the load. An already heavy duty automatic only gets better.

Building In Durability With The Best Parts

The Gearstar 4L70E (Stage 4 only) is fitted with:

• Custom Built Lock-up 10in or 11in Billet Racing with 2600-4000rpm stall
• Master Overhaul Kit with Alto Hardened Kolene Steels
• Raybestos Gen II Racing FrictionsFilter
• New 28 Element Input Sprag High Capacity Upgraded Pump Assembly
• New Hardened Pump Rings
• New 10 Vane Pump Rotor
• New Vanes
• New Stator
• .500 Boost Valve
• Pressure Regulator Valve
• Updated Boost Valve
• Transgo Reprogramming Shift Kit with Shift Command
• Bushing Kit
• New Thrust Washers
• Complete Torrington Bearing Kit for reduced friction
• Heavy Duty Hardened Sun Shell
• Heavy Duty Expanded Capacity Input Drum with Reinforcing Sleeve
• High Rev Spring Kit
• Heavy Duty 5 Pinion Front and Rear Planetary Gear Set with Sun Gear
• 300mm Hardened Output Shaft
• 300mm Hardened Reaction Shaft and Hub
• Super Hold 4th Servo
• Corvette Servo
• Wide Carbon-Fiber 2-4 Band
• New Valve Body Spacer Plate
• New Shift Solenoids
• New EPC Solenoid
• New PWM Solenoid
• New 3/2 Solenoid
• New Manifold Pressure Switch
• New Internal Wiring Harness W/New TCC Solenoid
• New Electronic Speed Sensor
• Inspection Cover (Polished Aluminum)
• Extra Capacity Polished Aluminum Pan
• Transmission Mount
• 30,000 GVW Hayden Cooler
• Gear Ratios:  3.06/1.62/1.00/0.70

When Do You Need The 4L80E?

“The 4L80 was introduced in 1990 and was designed for ¾ ton to 1 ton trucks, and was strictly a heavy-duty unit. The basic 4L80E design was taken from the heavy-duty TH400. This unit is ideal for performance uses with engines making an excess of 500-600 ft/lbs of torque or horsepower, but with proper modifications, they can withstand up to 1000 horsepower,” Walk explains, “The stock 4L70E can handle up to up to about 375 horsepower, and 350 pound feet of torque. Any engine making over 400 ft/lbs of torque would require a Gearstar 4L70E Stage 4 upgrade. Anything beyond 500-600 ft/lbs of torque needs the 4L80E.”

Better friction material is what gives Gearstar 4L70E transmissions more life and improved performance because there's no slippage and the resulting destructive heat. Heat breaks down fluid, seals, and frictions. You want your Gearstar unit to perform better. However, you also want durability.

Benefiting from Electronic Control

“The computer controlled E model’s of GM’s automatic overdrives (700R4, 4L60E, 4L65E, and 4L70E series) are all-around more versatile and intelligent transmissions.” says Walk.  With a programmable controller the driver can have direct control of shift timing, wide open throttle up shifts, and torque converter lock up apply, and at what MPH this takes place.

Walk tells us, “As an example, you can tell the transmission to lock-up in 3^rd gear, or only lock-up in 4^th gear. Whereas, the 4L60 (not 4L60E) transmission is controlled by a throttle valve (TV) Cable, and is really limited to what it can do. Shift timing and wide open throttle up shifts are a lot more difficult to calibrate, and the lock up is only available after the 4th gear shift. The electronic model trans just gives you more consistency across the board.”

Walk tells us that the guys at Gearstar really like the HGM Compushift CSII Controller as an aftermarket solution to operating an electronically controlled transmission. “One of the big benefits with the HGM Controller is that you don’t need a laptop to program your trans.” Walk commented.

In Conclusion…

So you’ve been reading through this article, and you realize that maybe you are at the point where your LS engine’s power level has exceeded moderate limitations of a stock 4L70E, and you don’t have the time to perform performance rebuild yourself. Well, Gearstar can help you out on that front as well.

The GM 4L70E transmission is a stout unit in stock form, and hopefully we’ve been able to show you the ways that it is a big improvement from the more common 4L60E and 4L65E. With a few improvements in hard parts and friction materials, and the 4L70E can easily stand up to the type of power that today’s engines are capable of producing along with maintaining the benefits of overdrive and electronic shift control.