There comes a time when spinning that small-block to 3,500 rpm in an attempt to avoid being run over on the freeway becomes tiresome. This quickly leads to contemplating an upgrade to an overdrive automatic. There are plenty of good reasons to choose either the 700R4 or the 4L60E. Both offer the benefits of an overdrive, and deciding between the two, the choice comes down electronics or no electronics. We won’t make excuses, convenience comes at a price. As Mark Twain once wrote “You pays your money, and you takes your choice.”
The good news is that either way, you win. Elsewhere in this story we’ve listed the ratios of both the TH350 and the 700R4/4L60E. While the 3.06:1 First-gear ratio would appear to be an advantage over the TH350’s 2.52:1, the downside with the deeper First is the major rpm drop in the 1-2 and 2-3 gear changes that the 700R4/4L60 force upon you. At part throttle, this is only a minor issue since converter slippage absorbs most of the difference.
The obvious advantage for the overdrive is the 30-percent reduction in cruise RPM. None of this is breaking news, and both transmissions offer the same advantages. Now let’s get into what makes them different by first investigating the 700R4. The advantages start with something that’s important to everybody – price. If you’re searching for a used transmission to rebuild, only the non-overdrive versions are less expensive. The big advantage this “analog” overdrive offers over its digital compatriot is you don’t need a stand-alone controller to operate it. Right away that puts the 700R4 ahead in the price war by $600 to $1,200.
Next, the 700R4 is easier to install since it does not require anything more than the TV cable hookup, shortening the driveshaft, moving the crossmember, and adding a 12-volt source to the transmission. You have the luxury of choosing a lockup converter, and there are kits available to lock the converter when the transmission shifts into overdrive. This does, however, require the use of a special brake light switch. These are cheap and easy to wire into the transmission. This switch cuts power to the transmission when you step on the brake pedal, which unlocks the converter.
Another minor advantage for the 700R4 is that it offers an old-school speedometer cable, so upgrading an older chassis is simple. The transmission fits into most early transmission tunnels fairly well, although, there might be some minor floor pan tweaking required.
This takes care of the advantages. Now, we’ll move to the down sides of this gearbox. The biggest detriment, and the item that most often gets the blame for 700R4’s being disabled on the roadside, is the dreaded TV cable. The 700R4 uses a cable that connects the throttle linkage to the transmission’s throttle valve (TV) in the valvebody.
The TV cable essentially replaced the vacuum modulator valve that was the load sensing device for the transmission. The cable moves the throttle valve in the valvebody and increases transmission line pressure as the throttle opens. This would appear to be a simple operation, and with stock components, it’s rarely an issue. But with aftermarket carburetors, EFI throttle bodies, and various linkage mounts, the opportunity for mistakes is rampant.
There are volumes of material written on setting up the TV cable, and if you get it right, the system works great. But the difficulty comes in setting up the linkage adjustments to accomplish this task. It is not easy, and when misadjusted even slightly, the price is generally a wasted set of 3-4 clutches – an expensive repair. The internet is saturated with sad stories of burned up 700R4 transmissions whose only fault was a poorly adjusted TV cable.
If you are running a late-model engine like an LS with production EFI, there is no factory provision for a TV cable because these engines were equipped with the later electronic 4L60E version transmission. It is possible to adapt a TV cable to an LS2 for example, and it has been done successfully. But, it is yet another reason why the 700R4 is more of a challenge to tune properly.
Another minor annoyance is that wide-open-throttle (WOT) up-shift is mainly determined by the governor that is driven off the transmission’s output shaft. Most rebuilt 700R4’s will use very heavy weights and light springs on the governor that will signal the transmission to up-shift at very low engine speeds. Of course, you can manually shift the transmission at any RPM you desire, but if you want to adjust the automatic WOT up-shifts, this can only be done by modifying the governor.
Several companies like B&M and TCI offer kits to do so, but it is a trial-and-error effort and requires the pressed-in governor cover to be removed each time to access the governor. Expect to spend half a day or more on this process.
There are a few other aspects that accompany a conversion to a 700R4, but these are the main ones that you might consider. Certainly, the biggest benefit to the analog 700R4 is its affordability. But as we will see when looking into the details of the electronic 4L60E family of transmissions, these newer, digitally controlled versions offer some real rewards.
700R4: The Good And The Bad
- Less expensive than 4L60E – no expensive controller needed
- Easier to install with minimal wiring
- Popular upgrade support
- Fits most early chassis
- Transmission has cable speedometer output – no adapters needed
- Limited torque capacity with early transmissions
- TV cable is difficult to adjust for proper pressure and up-shifts
- Must use pressure gauge to set TV cable for proper part throttle up-shift
- Often requires custom TV cable bracket and connection on carburetor or EFI
- Custom WOT shift points require governor changes
- Limited to converter lock-up only in overdrive (4th gear)
- Needs special brake light switch to cut power to unlock converter when brake is applied
- May require additional low-vacuum switch to cut out converter lockup under heavy part-throttle load – and then may cycle back and forth – requiring additional delay relay
Shifting over to the 4L60E side, the main advantage of this transmission is that electronics eliminate the need for a TV cable and that whirling dervish of weights and springs to establish shift control. In the case of a retro-fitted 4L60E, a swapper will need the service of a separate transmission controller. Here is where both the main advantage and disadvantage of the electronic transmission reside. Separate controllers obviously add significantly to the overall transmission cost.
If your next project involves using EFI, consider the latest in electronics that now combine GM transmission control with EFI. For example, several companies now offer 4L60E and 4L80E control as part of their EFI systems. Holley’s Dominator EFI offers this, as does Big Stuff3. Just recently, Holley introduced the Terminator LS EFI system, retro-fit for multi-point LS, that will optionally control a 4L60E transmission. This eliminates the cost of purchasing a stand-alone controller. FiTech also offers a similar control opportunity.
There are distinct rewards for making the 4L60E investment. Most importantly, the controllers make it very easy to establish exact shift points for each up-shift. It will also allow adjustment of shift firmness all within the control of either a simple hand-held device, or in some cases, sophisticated software that can be tuned via a laptop. An example would be the ability to set the exact WOT shift points with a couple of keystrokes, instead of struggling for six to eight hours with a recalcitrant governor.
One requirement for the 4L60E is that it demands input from a throttle position sensor (TPS). If your engine is equipped with any type of modern EFI, TPS is already part of the regime. But, if the engine is carbureted, this will require adapting a TPS. Luckily, HGM Automotive makes a slick TPS adapter that will bolt directly to a Holley, Edelbrock, or Q-jet carburetor. Other companies like Holley and Innovate also make TPS mounts, but we really like the HGM unit called Accu-Link. This is yet another expense that must be integrated into the cost of a 4L60E.
Combining the factory speedometer in your early muscle car with a 4L60E also requires additional assistance. The 4L60E generates only an electronic vehicle speed output (vehicle speed sensor – VSS), but there are various ways to make this work. The simplest is to use an electronic speedometer that either uses GPS for input to convert the VSS transmission signal to the speedo.
If the car’s existing cable-driven speedometer works well, Speedhut makes a very nice electric motor that uses either the transmission VSS signal or a GPS antenna to spin the motor, which drives the speedometer cable. We’ve installed one of these boxes in our ’64 El Camino with a 4L60E, and it has performed well for over a year. Again, this is an added expense that should be considered before deciding on a 4L60E.
4L60E: The Good And The Bad
- Full and finite electronic control over all aspects of shift control, including WOT
- Easy changes to part-throttle shift points and line pressure
- Easy setup for desired converter lockup – can lock in third
- Can tune shift points from the interior – no need to crawl under the car
- Can buy EFI packages with transmission control as part of EFI – saves money
- Increased torque capacity with 4L65-70-75 versions
- LS engines can use the LS 4L60E – no adapters necessary
- Speedometer calibration is simple
- Most expensive – must add separate controller – can cost up to $1,200
- Needs a TPS input – must add with carburetor
- Requires adapter to run either electric speedometer or motor to spin cable speedometer
- Cooler lines use push-in clip connectors that often leak – should replace with a more traditional connector – AN or inverted flare
It’s difficult to offer a cost differential between a typical 700R4 and 4L60E overdrive transmission because there are so many variables that will directly affect the end game. The controllers alone vary from $650 to over $1,400. We priced comparable 700R4 and 4L60E transmissions from Hughes Performance for example, and the price difference on just the transmission was only $100 ($1,834 vs. $1,934 through Summit Racing), so based on that, the 4L60E could run an additional $1,000 to $1,200 more depending upon the component choices.
Hopefully this little dissertation has offered up some useful options and ideas you may not have considered. The rest is up to you.