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Bullet-proofing the 4L60E with help from Sonnax and STS Transmissions

Posted By: Steve Baur
The 4L60E and 4L65E transmissions served duty behind GM’s muscle and sports cars for over 20 years, and with an LS powerplant that readily accepted modifications and churned out plenty of power, it wasn’t a surprise when the transmissions behind these engines began to show their weak points. Though the transmissions were much maligned for their inadequacies, Sonnax has come to the rescue with a slew of great upgrades that fortify these automatic overdrive transmissions and keep the gears shifting with vigor.
Sonnax is a leading provider of transmission, converter and driveline components to the automotive aftermarket. They offer a 4L60E series build guide to help make sure you choose the correct Sonnax parts for specific levels of engine performance. Whether you are looking to bolster the transmission in your work pickup or need anything else from mild to wild, Sonnax has the parts for your build. 
Our subject vehicle was trailered to STS Transmissions, as the 4L60E transmission had failed leaving only a couple of gears functional. STS made quick work of the removal process and had the transmission dismantled for inspection in short order.

The subject vehicle for this 4L65E build is an LS-swapped Chevy S10 that has so far received a number of exhaust and tuning mods to boost the stock power output. Combined with some occasionally rowdy driving, it was enough to see the stock transmission’s gear shifting ride off into the sunset after a few years. With additional engine modifications on the horizon, it was determined that the truck would need something more than a stock rebuild to remain fully functioning for years to come.
For many enthusiasts, this is the time where they choose to move to the larger 4L80E transmission, but its size can present some drawbacks depending on the application, and it may require additional modifications to the transmission cross member and driveshaft. With that, we spoke with Gregg Nader, the high performance product line manager at Sonnax, to get his opinion on the two options and this is what he had to say.
“The 4L60E series is—in my opinion—the most popular performance transmission in the world. Even though it does take parts and dollars for it to hold up, it’s everywhere and a great unit when built right. Of course, the 4L80E is also a very popular unit, with the benefit of needing fewer upgrades. For the majority of builds it should always be an option, but the reality is, for most common street rods, the 4L80E is a bit big and heavy. That means installation can involve cutting up the tunnel to make room. There are a few places selling pre-formed tunnels, but it’s still a lot of fabrication, etc., when a properly spec’d and built 4L60E—which is a little smaller and lighter—fits right in and is more than capable at the 400hp-850hp range and even higher for some.”
One thing to note before tearing into the transmission is this wiring harness connector on the side of the transmission. It will vary based on the year of your transmission and you’ll need to know which one you have as it will dictate which EPC solenoid you’ll need for the rebuild. STS Transmissions sources its replacements from Rostra.

These two transmissions, of course, aren’t the only options, as the Powerglide and 2- and 3-speed GM transmissions are still strong and supported, but having the added overdrive and the ability to support big horsepower and torque is often the path most street-based enthusiasts take.
“Roughly speaking two-speeds these days are more likely to be track cars that are trailered,” Nader told us. “There are a fair amount of three-speeds at the track and cruising, but the overdrives are great for street driving/cruising and can still perform acceptably at the track. Their greatest benefit is lower cruise rpm to settle the car down. The reality is most street rods have more than enough power to overcome traction at lower speeds, so having more than four speeds doesn’t really gain anything. That’s why for this build, we actually converted the 1st gear ratio from 3.06/1.63 to a 2.84/1.55, as this takes away a bit of the excessively steep 1st gear and with this power level, it allows for better burnouts, etc. with less need to shift to 2nd. Folks debate how much this improves ET, but it’s effectively about the same amount of ratio change as switching from a final drive ratio of 3.73 to 3.42, or 3.55 to 3.23, but that change affects mostly just 1st gear. The bottom line is an overdrive gives more options to optimize SLR, while still being able to cruise at 70 mph at a lower RPM than a two- or three-speed.”
The Fortification Plan
Sonnax’s success in developing the parts necessary to properly fortify the 4L60e/4L65e transmissions comes from identifying the key failure points and problem areas that need to be addressed.
One of the most common problems with them is inadequate and/or inaccurate fluid pressure. The higher the pressure goes, the more important it is that it be stable so it can do its job properly. There are a number of moving parts within the 4L60e responsible for managing the fluid and its pressure throughout the transmission, and oftentimes excessive wear results in fluid loss, which forces the variable pump in the 4L60e to work harder. 
These are the 3-4 clutches and steels out of the transmission, and as Wilk noted, “They’ve been in the smoker for a while.” The clutches on the ends manage to survive and remain bright orange/red because of the thick steels they have to help dissipate the heat. Their indicates that they are Alto Red clutches, and that this transmission has been rebuilt once already.

Leading the list of possible leakers contributing to unacceptable fluid loss is an excessive amount of wear in the actuator feed limit valve bore, which is located in the transmission valve body. The actuator feed limit (AFL) valve is responsible for supplying fluid to the electronic pressure control (EPC) solenoid, which in turn supplies oil to the boost valve in the pump. This all ultimately controls the pressure output of the regulator valve in the pump. The pressure regulator valve itself is the next offender. Located in the transmission pump cover, the pressure regulator valve bore often shows wear in high-mileage cores, and that allows fluid to sneak past under high pressure situations, reducing pressure control. Sonnax offers an Oversized Pressure Regulator Valve to eliminate leakage and restore proper pressure.
“A worn valve/bore can contribute to pressure instability, which can destroy a pump, so we recommend checking the aluminum bore for wear with a vacuum test,” Nader explained. “If wear is detected, then we do have a reamer and oversized repair. “The reamer is required, as it allows transmission builders to refurbish this pump cover bore and guarantee a precise valve fit.
“You have to control valve body bleeding,” Nader said. “If the valve bores in the body begin to wear, it causes changes in the timing of the bands and clutches and that can have real effects on transmission performance. If you have all these leaks, the pump has to work harder to compensate, and the amount of time the oil spends in the pan is shorter. The oil doesn’t have time to de-gas and the leaks aerate the oil reducing the integrity of the fluid. These are all negative outcomes for the general health of a hydraulic system. If you look at 90 percent of Sonnax valve body products, they are about controlling leaks.”
These are the forward clutches, and its plain to see that they have suffered a good bit of heat stroke, where as the bright and clean clutches in the back of the photo are the reverse clutches, which do not get strained nearly as much.

Other areas to check for leaking transmission fluid are the accumulator pistons, and of course, the valve body itself. Sonnax offers a free vacuum test guide on its website to help you check the integrity of the valve body and pump cover, and provides you with a list of parts to solve any issues you may encounter.
Internal fluid or pressure leaks in transmissions is not really the first thing you hear of when fortifying an automatic gearbox. Oftentimes the first thing you hear about are upgraded clutches and steels, which are directly responsible for managing the distribution of driveline forces through the transmission. Just as you have a clutch and metal  flywheel (single or multi-disc dry clutch) in a manual transmission application, you have a similar setup in an automatic gearbox, but instead of one large clutch , you have several smaller clutch discs that do the work referred to as multi-disc wet clutch packs. An automatic transmission typically has several multi-disc wet clutch packs.
This is the 2-4 band which is clearly showing a burn mark and thus uneven wear that would allude to another problem. 

The common practice in a performance application is to use clutches and steels of high quality, and sometimes using additional pieces to increase the surface area and thus the power-holding capability. The number of clutches and steels that you can add is limited by the original equipment input housing, however, so in some cases thinner clutches and steels are used. These thinner steels, however, are a trade off because there isn’t as much metal to dissipate heat.
To solve that dilemma, Sonnax offers its patented Smart-Tech Input Housing Kit that provides ample room for a larger clutch pack, which in turn ensures you have an adequately sized and capable clutch pack that eliminates the common 3-4 clutch burn up.
Here we have the drum and you can see burn marks on this as well. Wilk also pointed out the sanding marks on it, “People scuff the drum up to increase the coefficient of drag for the band, but it actually reduces the holding power.”

Another common issue that leads to clutch pack failure is flexing of the input housing apply and backing plates. These pieces secure the clutches and steels in the housing and when pressure is applied to the clutch pack, the factory backing plate tends to flex. This causes uneven wear and friction that increases the amount of heat on specific parts of the clutches rather than its entire surface, leading to premature clutch failure. You can check out Sonnax’s informational video on this by clicking this link. To remedy this issue, the Sonnax Smart-Tech Input Housing Kit features upgraded apply and backing plates that are stiffer and resist the flex altogether.
Previously Nader mentioned changing the First gear ratio, and while that can offer a number of performance benefits to the vehicle, it also reduces the chances of damage to the band, input/output shafts, and the sprag as it reduces the impact of the 1-2 gear change. Sonnax’s 2.84 Ratio Input Carrier Kit offers less ratio drop between gears, which in turn requires less work of the clutches and band to complete the gear change.
In this photo, we’re looking at the stator half of the pump, and you can see some grind marks, but Wilk said that being noted, it overall is in not too bad of shape.

Sonnax also notes that the input sprag clutch should be checked and/or replaced, as it is a critical piece in the transmission’s operation. It is a wear item and high-mileage cores car show wear in the clutch races. Furthermore, old transmission fluid can transmit particles that can contribute to the wear of the input sprag as well. Sonnax recommends installing a new sprag assembly and changing the fluid regularly, as well as employing magnets in the transmission pan to catch any particles in the fluid that may wear the input sprag or affect other parts of the transmission such as the EPC solenoid. Along those lines, Sonnax recommends a change to a deep aftermarket transmission pan that allows the filter to be placed deeper in the fluid, which will provide a healthy supply of fluid during hard launches and acceleration.
Just as adding additional clutches and steels provides more surface area to distribute the applied forces to, adding an additional planet pinion to increase the count from 4 to 5 will further distribute the load on the sun gear and around the ring gear. This reduces the stress or flexing of the ring gear, which in turn increases the durability of the existing component.
Programming the Electronic 4L60E Transmission
As we are indeed talking about an electronically controlled transmission, it should go without saying that transmission tuning is an essential part of transmission performance and longevity. Just as a bad engine tune can lean out the air/fuel ratio to the point of detonation, so, too, can a poor transmission tune be detrimental to your gearbox. 
Now that you’ve done all you can on the inside of the transmission to stabilize and provide adequate transmission line pressure, it’s important that the transmission tuning follows suit, and Sonnax recommends any transmission tuning to be done with a pressure gauge to alert the tuner to any accidental changes that would lower the pressure when a higher pressure is called for.

Here we have the other side of the pump and it’s clear to see the scoring on the bushing in the center. This is indicative of improper pump alignment. In the photo below, you can see that there is no wear on the opposite side of the bushing. The snout on the torque converter showed considerable wear as well. General guidelines are. . . If there is wear all the way around the converter hub, but only one side of the bushing, there is misalignment between converter and transmission. If there is wear only on one side of the converter hub, but all the way around the bushing, then the converter hub is welded off center.

Another aspect of transmission tuning is torque management, which is a feature written into the calibration from the factory that cuts power to the transmission during the shifts.  Oftentimes, tuners remove or turn off this function completely, but it is still possible to leave it slightly engaged to add a little longevity to the transmission, without it being detrimental to the performance of the vehicle. Each vehicle application and combination will be different and this should be managed accordingly.
Continuous slip (EC3) torque converter control (TCC) is regulated in the ECM while relying on a number of mechanical parts to manifest the strategy. Over the years, GM has sought to reduce noise vibration and harshness in the drivetrain, and torque converter lockup strategies often produced unwanted characteristics. The ensuing changes to alleviate this issue constitutes enough content to be its own tech piece—in fact, Sonnax has a web page solely devoted to this topic (HERE)—but to keep this transmission build somewhat reasonable in length, we’ll simply note that Sonnax has extensively researched the topic, the common “fixes” that many shops use to solve it, and has its own calibrated strategy. Ultimately, it becomes a direct control strategy that prevents excessive fluid pressure build up in the converter.
Taking a look at the 2-4 servo, we can see that the capsule has been removed and replaced with a plug (top left). The capsule can become worn, however, and some rebuilders will remove the capsule and insert a plug to prevent the fluid leaking past. The capsule that is normally employed allows air to escape and just like with your brakes, air in transmission circuits is a bad thing. Wilk said plugging this is a Band-Aid fix at best, however, and also pointed out the nick in the side of the case at around 9 o’clock, and that you can see someone attempted to sand it out. For these reasons, Wilk replaced the case with a viable unit.

Lastly, Sonnax recommends not mixing and matching components from various manufacturers, as the products may not be designed to work the same from manufacturer to manufacturer, and that can lead to poor performance from your transmission. Oftentimes this is the case for many components of the car in general, so sticking with one company which has developed a plan and products to execute it will usually produce the best results.
Choose Your Build Level
To help people understand the options, Sonnax developed four different build levels for its 4L60E parts ranging from beefing up the transmission for your heavy duty truck to a Performance Level 3 build with all the upgrades needed for applications making over 450 horsepower and 650 lb-ft of torque. After discussing our goals for the vehicle build, Sonnax recommended the Level 3 build.
“What we spec’d here is definitely overkill for the power you are currently at. For your truck, it seemed like a great opportunity to showcase all we have and more upgrades is better than too few, especially since your early descriptions indicated this thing can get beat on pretty ruthlessly,” Nader told us. Indeed, the truck has been driven with “fun” in mind, and that shall continue as we upgrade the powertrain.

The Sonnax Level 3 build calls for the Performance Pack shift upgrade kit (HP-4L60E-01), the SmartShell Heavy Duty Reaction Shell Kit (77749-02K), the Heavy Duty 2-3 Shift Valve (77754-41), the 4th Gear Super Hold Servo Kit (77767K), 2nd Gear Super Hold Servo Kit (77911-03K), the Kevlar Extra Wide Intermediate Band (77700-01K), the Smart-Tech Input Housing Kit with Heavy Duty Input Shaft (77733-10K, 77733-11K or 77733-12K), either the 4WD/AWD Heavy Duty Output Shaft (74678S-HD) or the 2WD & Corvette Heavy Duty Output Shaft (74678L-HD), the Heavy Duty Reaction Shaft Kit (74602-01K), and the 2.84 Ratio Input Carrier Kit (77284-K).

In researching this article and talking with Sonnax’s Gregg Nader, it became evident that the company not only knows the engineering side, but it also has extensive knowledge and experience in the field as well. 

“We as an aftermarket company have to reverse engineer everything,” Nader told us. “One of the most gratifying rewards is that GM uses a number of these upgrades in their performance transmission offerings.” 
With the wear on the pump, there was certainly an alignment issue and taking a look at the back of the block, one can see that the alignment pins have been pushed back into the block. This obviously prevents them from doing their job, which is to locate the transmission precisely to the block.

Pick Your Builder
With the parts picked out, it was time to find a local, and reputable, transmission shop to perform the rebuild and installation. With that, Sonnax recommended STS Transmissions in Sarasota, Florida. STS Transmissions has 43 years of experience in OE and performance transmission work, and the company has expanded from a meager 1,500 sq-ft shop to a 5,500 sq-ft building. Proprietor Steve Wilk started with AAMCO Transmissions in 1979 and eventually opened his own shop. STS Transmissions has been at its Sarasota, Florida, location for 8 years now and is a full-service facility that works on both domestic and foreign applications.
Check out the photos and captions to see the diagnosis of the transmission’s failure, and the rebuild process. If you want to learn more about transmission tech, the Sonnax website has a plethora of information available, and of course, the staff can answer any questions you might have about Sonnax products.
(800) 843-2600
STS Transmissions
(941) 812-1648
TCI Automotive
(888) 776-9824

Now that the transmission has been disassembled and the damage assessment is complete, STS Transmissions' Steve Wilk broke down the internal components, including the valve body and its internal components which are displayed here. All of the cylindrical items are valves that move within the valve body. This movement ultimately wears on the bores in the valve body and they must be checked to ensure proper fluid management.
Here we have a number of factory components as well as Sonnax pieces that are ready for assembly.
Wilk begins with fastening the stator shaft to the transmission pump to the recommended torque specification.
After mounting the valve body to an acrylic test plate, he then vacuum-tests each circuit. “Fifteen inches of vacuum is a low reading, and you’ll find 20-25 on a good circuit. A low reading means the valve body circuit needs to be reamed out to prevent a leak.”
Next up for testing is the transmission pump. It produced a very low reading of 12-13 on the pressure regulator valve. This means it will need to be reamed out and fitted with the Sonnax oversized valve.
As important as it is to ensure that the valves in the valve body fit to the correct specification, the valve body itself must also seal properly to the transmission case. To accomplish that, Wilk flat sands the face of the valve body using a diamond stone.
The corresponding location on the transmission case, the channel plate, also gets dressed ensure flatness.
As mentioned before, the pressure regulator valve in the pump was below spec, so Wilk is reaming out the bore here in this photo to fit the new oversized Sonnax valve.

Pump assembly then begins with pressing in the pump bushing and pump seal.
Next up is the Sonnax spring, which is placed on the pump slide to maintain pressure at high RPM. A special spring compressor helps fit the spring into the pump, much like a piston ring compressor.

A ring clamp used to align the pump halves and then the sealing rings on the stator shaft can be installed using a ring expander. The sealing rings provide the oil to apply the clutch pack. A sizing tool is then used to decrease the size of the sealing ring to the appropriate size.
Wilk moves on to assembling the forward clutch accumulator with the Sonnax pin-less piston, which uses rubber and Teflon seals for improved wear and locating to reduce wear.
The reworked valve body is retested and now shows circuit integrity.
A new Sonnax rear sun gear bushing will be installed and as you can see, it is larger and more robust than the factory piece, which will allow it to remain in better alignment.
Moving to the transmission case, Wilk installs the Sonnax inner sprag race for the Sonnax SmartShell Heavy Duty Reaction Shell Kit (PN 77749-02K). The SmartShell uses an improved design and manufacturing process to produce a unit that is lighter than most aftermarket shells whose design can often lead to breakage under stress.
Next up is the installation of the reverse input drum shaft into the case. 
Here, Wilk is checking the band clearance on the 2-4 servo. The Sonnax servo pin is manufactured to longer than factory specifications and requires grinding down by the transmission builder to provide around .060-inch clearance for optimum band clearance. This will ensure that the 2nd and 4th Sonnax Super Hold Servo’s push on the band correctly and hold the drum as expected.
After to torquing the valve body to the case, Wilk then fastens the pressure switch and torques it to spec. The pressure switch allows the computer to see what pressure is on the clutch pack. That concludes the transmission assembly and the unit is now ready for installation.
Reinstalling a used torque converter is never a good idea, as it is near impossible to remove all of the fluid and contaminants from within it. To that end, we contacted TCI Automotive and ordered one of the company’s Street Fighter torque converters (PN 242931). This unit is a lock-up converter with a stall speed of 3,000-3,500 rpm. 
During the transmission removal process, Wilk and his staff noticed that the transmission shifter cable needed to be better routed. It was spaced down and angled to keep the cable from folding over the transmission crossmember and prematurely wearing the inside of the cable. Here you can see the B&M aluminum deep transmission pan that STS Transmissions recommended we add to the build.
Tending to every detail, Wilk also noticed that the driveshaft slip yoke was worn and he replaced it due to excessive wear. With that, the truck can be fired up and STS Transmissions performed the necessary programming as recommended by Sonnax to the ECM. After a test drive, this LS-swapped S10 was ready for the road and has logged several thousand miles to date without issue. Time to turn up the power!

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