Anybody that has ever ventured inside of the fluid-breathing Hydra-matic monster found between the flex plate and rear axle knows this is not a job to be taken lightly. They also know that it really isn’t all that complicated and by doing it yourself at home, you can save loads of cash.
When taking your transmission to a shop, it pays to know what kind of modifications are available and what options you have in terms of parts combination to match the performance and durability desired from your favorite ride. The overdrive transmission first came on the Corvette scene in 1982 with the mighty 700R4. This transmission gave the Corvette a more aggressive first gear, coupled with an overdrive to zip down the highway at minimal rpm. It also featured the already proven torque converter lock-up technology. The early C4 saw the same transmission later evolving to the 4L60E with the LT1 engine models. Finally, the C5 and early C6 both enjoyed the reliability and performance of the 4L60E and later versions, including the 4L65E. All of these generations of transmissions share some of the same basic components or variations of the same and are all susceptible to the same type of failures. As the horsepower goes up, so does the chance for failure. TCI, located in Ashland, Mississippi, has all of these issues covered and can match components to do the job for the performance-minded enthusiast.
Common Parts, Common Failures, Total Solutions
The torque converter is the magic of how an automatic gets the job done. The converter uses a series of fins and vanes to disperse fluid pressure and engage the engine rpm to the transmission input. Heat and poor or old fluid are hazardous to the life and performance of the converter. The converter also holds several quarts of fluid at all times, which makes it impossible to replace all the fluid in a standard service.
Stock converter applications are appropriately balanced to factory specifications and perform well right off of the showroom floor. However, major changes to the engine (including cam, heads, and induction system) require the appropriate balance of torque speed. This allows your ride to harness the horsepower at the peak opportunity to increase acceleration and overall performance. The converter can only be serviced when the transmission is removed, so it is very important to address and match it to your performance needs. TCI has a variety of converters to fill the bill from mild to wild, including custom creations made just for your specific application.
With variations, the 700R4 and 4L60E transmission share a similar pump design. The pump uses a set of vanes that spin in concert with the engine rpm off the tip of the torque converter shaft. These can be found in 7-, 10- and 13-vane variations. The 7-vane rotors were found in the earlier models and were really noisy. The 13 vanes were added later to reduce noise, but also increased the chance for failure due to more parts in the same space as the 10-vane system.
When the pump fails, the transmission doesn’t move since everything that happens inside depends on fluid pressure. While some pumps are broken due to installation errors and usually fail immediately or in the first few hundred miles, others are caused from the additional stress placed upon high-performance applications. TCI has designed a new generation 10-vane billet rotor pump assembly that cures this common problem. The billet rotor is stronger than the OEM part and delivers when you need it most, by staying put during extreme use. The pump sits between the torque converter and the main body of the transmission. Replacing the pump requires removal of the torque converter, input shaft O-ring, pan, TCC solenoid, and pump housing bolts. It can then easily be pried free from the unit.
Moving behind the pump, there are a variety of parts and pieces that work in harmony to transfer the engine rpm into rear wheel action. There are also plenty of areas for improvement over stock. The Sunshell is the crucial link between reverse, 2nd, and 4th gear. The factory version is prone to fail by stripping the teeth out or shearing the rear coupling off the housing. This is especially true in the higher performance applications. TCI offers the Beast Sunshell, which features additional thickness in the casting around the known-to-be-weak areas of the OEM application. As TCI will tell you, this is cheap insurance on the task to putting your car back on the road … and keeping it there. There are two sets of planetary gears in the 700R4 and 4L60E series transmissions that rely on a four-gear system from the factory. The planetary gears actually crawl around within their housing to transfer the torque load. TCI offers a five planetary system that adds the additional gear to increase the input torque capacity by 25 percent. This is crucial when running up the power to keep it all safely harnessed to the rear tires. When matching these hard core internal parts to a complete clutch and rebuild kit from TCI, your car will have the guts to handle whatever kind of performance you expect.
Banging the Gears
Most people associate a shift kit with whiplash-causing, neck-snapping, second gear action. While that may be the case in some applications, the shift kit does much more to improve the longevity and performance of your Corvette transmission. Also, a “shift kit” takes on many forms to different people.
Altering the shifting pattern may include changes to the TV system on a 700R4, servo, valve body, and pressure valves. Ultimately, on 4L60E models final shift firmness and feel is adjusted through computer programming. While the stock Corvette servo has been the standard swap-in performance application for non-Corvette builds, TCI has ramped that up another few notches with their jumbo servo kits. These have large pistons with modified springs to generate ultra-positive, neck-snapping shifts. The idea is to generate a quick, firm shift to reduce slippage between gears, therefore getting more power to the tires faster without bleeding it off through the clutches along the way. Manipulating the valve body is another way to complement other modifications to enhance the shift quality and fluid pressure to where it is needed most during performance applications.
While the 700R4 can go with a complete valve body replacement right out of the box, TCI also offers kits for the later model guys that require modifications to the valve body plate and valves. The Transcat kit comes with excellent instructions, drill bits, and related hardware to enhance the stock valve body pattern to a higher performance application. When matched with a performance boost valve, the transmission is able to stand up and deliver when the performance enthusiast wants to pour on the power.
Matching the best combination
Unless you are building your car from scratch, most people don’t consider the transmission unit until it blows, or they are having some sort of a problem. Many mistakes are made in the improper selection of components to fix the problem and keep the problems away. While it sounds really cool to brag about a large stall converter with a jumbo servo and trick shift kit, it isn’t always all needed or desired in every application. Jumbo servos and shift kits with boost valves will generate aggressive shifting patterns that may not be suited to your better half. If you spill your coffee in the seat every time the trans hits 2nd gear, you might regret your selection in application. Stall converters do wonders to increase acceleration, but they generate more heat, require an additional or larger cooler, and will also cause the car to feel loose and sluggish in normal rush hour bumper-to-bumper traffic. A stock L98 1989 Corvette would benefit very little from such aggressive mods.
However, matching the right mod to your application will pay major dividends at the finish line and save money you won’t be spending with the shop for common ordinary failures. While parts like the five-pinion planetary sets, Beast Sunshell and performance clutch set won’t change the personality of your Corvette, they will ensure long life and plenty of opportunity to use the performance enhancers on your wish list. These heavy-duty internal parts should be standard order in any Corvette rebuild.
Getting Down to Business
Our 4L60E adventure began with our highly modified C4 Corvette. One moment we were zipping down the road, and the next found us coasting to the side with no warning. While complete replacement transmissions are available from TCI, we decided to jump right in and rebuild our existing unit.
With the transmission drained, out of the car and on the bench, it was simply a matter of diving in to see what we would find. We pulled the converter, then the pan and removed the TCC solenoids. This gave us access to pull the pump bolts and slide it out. Our stock 13-vane pump cracked, causing the pieces to wedge in the housing and snap one corner of the torque converter cleanly off. With the pump dead, nothing else was happening behind it.
We called TCI and explored our options. Since this 4L60E was basically stock and had come out of a 2001 Silverado, there was plenty we could do to get it up to the challenge and repair our problem. Whether a Corvette 700R4, 4L60E series, or Silverado overdrive, they share many of the same internals and all the applications are the same for rebuilding and modifying. Once behind the pump, it is like a massive 3-D jigsaw puzzle. Armed with only basic hand tools, a high-quality pair of snap ring pliers and a borrowed clutch compressor tool, we started lifting each component out and inspecting them, placing them in series on our work bench. At this point, all components are held in place by snap rings or sequence of installation. We pulled each assembly until reaching the reverse piston housing at the very rear.
On the valve body side, we pulled the fasteners and slid the valve body clear of the transmission housing using an 8mm and 10mm socket. It is very important to pay attention to the check balls that will fall out during this procedure. There are seven balls on the valve body side and one additional one on the transmission housing side that can be accessed when the valve body plate is removed. Our Transcat shift kit had easy-to-follow instructions and drill bits needed to modify the valve body plate and swap out the valves and springs. In fact, it was priceless during reassembly, thanks to the clear description of the location of the check balls and which bolts go where in the valve body housing. Mixing up the bolts can result in an instant failure, and we don’t want to go there.
We opted for the five planetary gear set and Beast Sunshell to beef up the internals. The clutch kit came complete with all the friction material and band to do the job right. The trick to replacing the clutches is to re-stack them with the replacements (metal, fiber, metal, fiber) exactly as the stock unit came out or in all cases to the same thickness as what was stock. This will work with most applications where some more custom applications may require additional clutch packs to get the desired result. The gasket and seal kit came with new O-ring seals for the reverse input and forward clutch housing. This can be a tricky task when doing the rebuild at home. We were able to fashion a simple slip tool using the skin of a 12-ounce cola can. This allowed us to lubricate the seal and slide the pistons in place without disrupting the orientation of the seal or damaging it while trying to stuff it in the housing. Sometimes, backyard engineering late on a Saturday afternoon is required after the shops have closed for the weekend. The seal and gasket rebuild kit really comes with everything you could imagine to do the job. It includes complete replacement springs and even the check balls in the event you lose one during disassembly. We also cured the pump failure problem once and for all with the new 10-vane billet rotor pump from TCI.
With the internals built and valve body in place, the job wraps up quickly with the replacement of the servo. Our transmission wasn’t originally a Corvette model, and it didn’t have the heavy-duty servo. The great thing about the servo is it can be changed in the car. It yields itself a bit to experimentation to determine how aggressive you want your Corvette to shift. The Transcat kit comes with replacement springs to trick out a stock servo, while the Jumbo kit comes with everything to go extreme, including a trick new outer cover to properly seat to the piston.
We opted for a TCI StreetFighter torque converter for our application. Right now our Corvette is putting out 400hp, and the StreetFighter is tough and balanced to our application. The folks at TCI were very careful to exam our cam specifications and modifications to create the best possible match.
Reinstalling the transmission is a textbook event. There is nothing special except for taking very careful notice not to bind or press the torque converter in the wrong way. A misaligned torque converter will result in instant pump failure as previously mentioned. Your torque converter kit will come with specifications to measure against the area between the converter and bellhousing to guarantee it is properly seated. Our application required 11/16 inches to verify the torque converter is seated in the pump.
With the transmission reinstalled, we made a few other changes. Although space was at an absolute premium, we managed to add an additional cooler to the system. Our installation was topped off with nothing other than TCI brand Max Shift fluid. This fluid has been proven to run up to 30 degrees cooler than conventional fluid and provides superior lubrication during extreme duty. It is also a light-greenish color, which is not what you expect when you pull the stick on your automatic transmission.
Unlike rebuilding an engine, there is very little you can do to “test” the transmission before installing it in the car. With fingers crossed and a deep breath, we fired it off on the jackstands and slowly moved it through the gears, allowing the fluid to travel through the entire system. Once on the ground, we headed out on the road to test it. With all systems go, we’re now ready for plenty of extreme duty with confidence that we have the right parts for our application.