When building a high performance 4L60E transmission the first question usually ask is, "what type shift improvement kit should I use?". At Trutech Performance Transmissions our ASE Master
Technicians backed by years of transmission repair experience and training researched this issue. We have studied the operation of this transmission and determined what modifications will
actually improve shift performance and give a long service life. In most shift improvement kits on the market two areas are commonly targeted for modification. These being accumulators and
the separator plate. Understanding the operation of the automatic transmission we knew that modification to these parts would create a firmer quicker shift feel but would do very little to
improve the operation or increase durability of the transmission. We will attempt to unravel some of the mystery of shift calibration in this guide.
n the automatic transmission an accumulator's function does as it's name implies, it accumulates or absorbs fluid in a clutch apply circuit and normally uses a spring loaded piston to
cushion the apply of a clutch or band. Without an accumulator in the apply fluid circuit, the rapid buildup of fluid pressure would cause the clutch or band to apply very quickly and create
a harsh or "bang" shift. The separator plate has small orifices that regulate the rate of apply fluid into the apply circuit. This orifice diameter has a direct effect on shift timing of the
apply components. The larger the orifice the more fluid that will pass creating a quicker apply. It is easy to undertsand how modifing these two areas can change shift feel. At Trutech we
looked beyond shift "feel" to determine what modifications would improve transmission performance and durability. Issues we have found with drilling holes too large in the separator plate
is that it creates a shift overlap of apply components at certain RPM ranges. Shift overlap occurs when two apply components are applied at the same time. Shift overlap greatly decreases
the apply component life because the components work against each other. Blocking or modifing fluid passages in the accumulators also have an adverse affect, the rapid apply of the friction
component causes a jolting effect on both the apply components and the hard parts inside the transmission. If severe enough this jolting can cause broken internal parts.
The traditional 700R4 1-2 accumulator piston and spring setup was redigned by the factory in 1994 in the 4L60E transmissions. This was done because the accumulator spring normally broke or
caused damage to the separator plate. The redesign by switching piston and spring positions was an inexpensive solution to the problem. The Trutech Shift Module contains two options in the
4L60E kits for 1-2 shift feel. The first option: We include performance inner and outer accumulator springs to slightly speed up the rate of apply to the friction components. This option
the springs are installed as the factory designed and gives a nice crisp performance shift feel. The second option: for a very firm shift we have you convert the 1-2 accumulator piston
back to the pre-1994 setup and we supply a performance rated accumulator spring and a heavy duty plate to use between the spring and the separator plate to protect it from damage. The
700R4 kit uses this same set up with a different rated spring. We provide performance springs for the 3rd accumulator in the servo and 3-4 accumulator but we do not recommend any modification
that will make the accumulators inoperative. Our Modules contain new accumulator pistons to restore hydraulic intregrity to your transmission. The pistons are common wear areas that allow
fluid bypass. The later model 1-2 "plastic" accumulator piston is replaced with the more durable aluminum version. In our Performance Shift Module we upgraded with two pinless dual seal
At Trutech we were interested in improving the holding ability of the apply components. In an automatic transmission the diameter of the servos determine in a large part how well a band
will hold. As with any hydraulic component the larger the apply area the more efficient the component. In other words, larger servos mean better band holding efficiency. On the other hand,
in the 4L60E the servo size plays a large part in shift timing. The larger billet "super servos" are recommended for "racing applications only" by the manufacturer. These "super servos"
depend a large part on the servo return spring to release the band when changing to the 3rd gear range. Racing applications are operated at wide open throttle and rarely downshift, these
racing transmissions benefit from the larger servos. The 4L60 type transmission hydraulic design does not exhaust an apply circuit once applied as it shifts through all forward gear ranges.
The servo diameter and servo return spring determine timing of band release in the 2-3 shift when the 3rd accumulator circuit is filled. Modifications to the circuit apply orfices in the
separator plate are good modifications if done conservatively, large orifice sizes in the plate should be limited to race applications where down shifting and low RPM operation are not factors.
Racing transmissions have a certain amount of "shift overlap" at lower RPM ranges. Racing recommended servos and "shift kits" should not be used in street driven transmissions because this
lower RPM overlap will cause early transmission failure. Our shift module has a performance servo combination that works and provides excellent band holding ability in a street driven
transmissions. The increase in servo size also has an effect on shift feel. Our servo combination provides a firm crisp shift. There is a direct relation between the 1-2 accumulator,
accumulator valve and the 2nd servo. We have included a performance accumulator valve in our more comprehesive Performance Shift Modules. This valve is a must when using the larger
servos in transmissions with V6 engines. This valve can be purchased separately.
We also provide a performance calibrated separator plate with gaskets. This plate has a performance factory shift calibration. Because a common failure in the 4L60E and 700R4 transmission
is the 3-4 clutch the apply circuit orifice can be modified, allowing fluid into the apply circuit at an increased rate. To prevent shift timing issues in the 2-3 or 3-2 shift we use a
metered check valve for the 3rd accumulator circuit. Removal of the valve body will be required and the use of an inch pound torque wrench will be needed for reassembly.
The forward sprag clutch is an important part of moving the vehicle in the forward gear ranges. It holds in 1st, 2nd and 3rd gear ranges but overruns in 4th gear. This sprag overruns in
coast or deceleration conditions. In a high performance application under heavy torque conditions this sprag can fail. The help prevent failure the overrun clutch can be applied in manual
gear ranges assisting the sprag and preventing overrun condition. The factory calibration does not allow apply of the overrun clutch in manual 1st or 2nd gear when the shifter is in D3
range. We have included a heavy duty 2-3 shift valve that will allow apply of overrun clutch in all three gear ranges while the shifter is in the D3 range. Apply of the overrun clutch
will also allow engine braking. The heavy duty 2-3 shift valve is only included in the more comprehesive 4L60E kits but can be purchased separately.
The transmission line pressure is increased with the addition of a large diameter boost valve and heavier pressure regulator valve spring. Increased line pressure will provide higher
pressures for better apply component holding capability. We do not recommend any changes to the EPC solenoid calibration.
With the Trutech Shift Modules we took a completely different approach to transmission performance than that of other manufacture's shift improvement kits. We do not claim to correct
problems caused by wear. The only correction for a wear related issue is part replacement or the part must be remanufactured back to factory specification. Our Shift Module works with
the factory engineered design. The parts provided in this Shift Module are of the highest quality. No special tools are required and installation can be preformed with the transmission
in the vehicle.
Because every application is different, performance requirements are also different. We undersatnd this and offer custom shift modules to meet your specific needs. Call for quotes and
I have all sprags and assemblies listed in my online store. No purchase is required.
No purchase is required.
Our contact information
Call 1-800-762-9846 Inside USA
1-334-577-4400 Outside USA
Thank you for choosing Trutech Performance Transmission.