THM 700R4 - 4L60 Transmission Remember when the THM 700R4, now more commonly know as the 4L60/E, transmission was introduced in the early eighties. The 700 transmission drove the industry crazy with broken pump vane rings, burned 2-4 bands, premature 3-4 clutch failure, sprag failures, planet failures, etc. I'm sure you remember the first few high performance transmissions? During the mid to late eighties, many performance and durability products had been developed so that the 700 could be successfully repaired in average vehicles as well as for high performance street strip vehicles.
I will discuss some of the principal areas for high performance modifications. Although there will be discussion on hydraulic controls, the various high performance, after market valve body kits, work very well whether it's for furnishing very short and firm tire chirping shifts in an IROC-Z , or ferocious shifts in a drag strip 11.52 et runner. Valve body kits offer convenience, since most are packaged with parts and data to modify main line pressure, shift scheduling, shift feel and firmness, detent downshifts etc. The parts and technical information also coordinate with the separator plate orifice sizes, 2-4 servo pistons, accumulators etc. For all installations, we suggest that you follow the instructions carefully. Write down every step that you perform. This way, if a calibration change is needed, you will at least have a reference point.
Okay, let's build this 700 to be a winner! You, the transmission, and whomever the customer is will be a winner too!
I will discuss some of the principal areas for high performance modifications. Although there will be discussion on hydraulic controls, the various high performance, after market valve body kits, work very well whether it's for furnishing very short and firm tire chirping shifts in an IROC-Z , or ferocious shifts in a drag strip 11.52 et runner. Valve body kits offer convenience, since most are packaged with parts and data to modify main line pressure, shift scheduling, shift feel and firmness, detent downshifts etc. The parts and technical information also coordinate with the separator plate orifice sizes, 2-4 servo pistons, accumulators etc. For all installations, we suggest that you follow the instructions carefully. Write down every step that you perform. This way, if a calibration change is needed, you will at least have a reference point.
Okay, let's build this 700 to be a winner! You, the transmission, and whomever the customer is will be a winner too!
Intermediate Servo Piston
This servo piston technical information has been around for years but since it's really important for high performance usage, let's quickly review it. Look at the casting number stamped into the second servo piston. There are three different size second servo pistons identified by the last three digits of the casting number which are 553, 554, and 093. Corvettes came with the 093 piston. For short, firm, but fairly comfortable shifts for street use start off with the 553 piston. For street and strip use or for big blocks and high-rev small blocks, or for tire chirping shifts to show off, use the Corvette 093 piston. For brutal, tire peeling shifts, a billet servo setup is available, however, use this setup with caution: The maximum throttle 1-2 shift will be really firm which can cause the sun shell to fail from overload. Never use the 554 piston in a performance application: You can burn up the 2-4 band over the weekend.
Accumulator Valve
Located in the valve body, there are six known different size accumulator valves used in the 700. There is a letter code stamped into the end of the valve bushing. Letter codes A and N will provide the firmest shift while letter M provides excellent overall operation in passenger vehicles, trucks, and some low geared sports cars. Letters K, F, B should not be used in performance or heavy duty applications. Once you have chosen the right accumulator valve for your application, you are going to need the spring specifications. For the A and N valves, begin with a two pound, six ounce, spring at ta reference height of .073". For code M, start with a three pound spring at the same reference height. These specifications will help you to coordinate with the accumulator piston trim spring(s), second orifice feed, and the servo piston you're installing.
Main Line Pressure & Boost Systems *(really important!)*
Most valve body kits will contain a heavier tension spring for the pressure regulator valve, to increase pressure. For the boost systems, begin by checking the size of the intermediate boost valve by measuring the long, smaller land. If it measures below .297", you very likely will not achieve a short, firm, tire chirping manual 1-2 shift. The . 297 inch valve and bushing is available from GM or your parts distributor under part number 8648959. Now check the land opposite the stem end of the TV boost valve. Don't use a size less than .422 inch. The .433 inch valve is suitable for street and strip cars, trucks, Vettes, and IROC's. For big blocks or highly modified small blocks, use the .471 inch boost valve. The .422 inch boost valve and bushing is available under part number 8634941, the .471 inch setup is 9634940.
IMPORTANT TECH NOTE: On most high-rev applications, an upshift to second can occur even though the selector is in manual one. Installing the #8648959 .297 inch setup will keep the unit in first with the selector in manual one right up to floating the valves, however, at moderately higher speed, the unit will go into first if the selector is pulled into manual one after an upshift to second or third gear.
Be careful and thoughtfull here. Given the right road conditions, this can cause loss of vehicle control. Be sure to caution your customer! Having him or her sign a waiver or disclaimer ont he repair order might be a good idea. Installing a heavier pressure regulator valve spring only and ignoring these two boost systems could lead to sup standard performacne and many hours of rework so why not Fix It Right The First Time!
IMPORTANT TECH NOTE: On most high-rev applications, an upshift to second can occur even though the selector is in manual one. Installing the #8648959 .297 inch setup will keep the unit in first with the selector in manual one right up to floating the valves, however, at moderately higher speed, the unit will go into first if the selector is pulled into manual one after an upshift to second or third gear.
Be careful and thoughtfull here. Given the right road conditions, this can cause loss of vehicle control. Be sure to caution your customer! Having him or her sign a waiver or disclaimer ont he repair order might be a good idea. Installing a heavier pressure regulator valve spring only and ignoring these two boost systems could lead to sup standard performacne and many hours of rework so why not Fix It Right The First Time!
3-4 Clutch Pack
High performance, heavy duty and even light duty 700's have been known to experience premature 3-4 clutch failure or distress. This durability concern can be easily and effectively prevented by utilizing several options after confirming that the pressure rise control system is functioning properly. Check it with a gauge!
One option is to install standard thickness high capacity or high energy friction plates readily available from your parts distributor. These friction plates use use a special composition of friction paper for heavy duty and performance applications. Another option is to install thinner friction and steel plates-which are available through the aftermarket-allowing you to install as many as eight or nine friction's. When the eight or nine friction pack applies, the energy of the apply is distributed over more surface area therefore the clutch pack is able to hold much more torque load as opposed to the original capacity. In addition to increasing the torque holding power it also adds much more resiliency and an accumulative value to the clutch pack.
With an eight or nine friction pack installed, you can increase the third feed orifice to as much as .180 inch without experiencing a cut loose-providing that the pressure rise control system and everything else in the unit is functioning properly. If the third feed is between .093 inch - .110 inch and you desire additional high throttle firmness, remove the 2-4 servo assembly, and replace the original band release spring with a stock THM 400 intermediate band spring number 8623489.
When using the eight or nine clutch pack, we suggest using the red friction plates with either the dull or Kolene steel plates. If you purchase these plates separately instead of in kit form, ask your distributor for the four page instruction sheet which contains valuable technical information as well as stack-up procedures.
One option is to install standard thickness high capacity or high energy friction plates readily available from your parts distributor. These friction plates use use a special composition of friction paper for heavy duty and performance applications. Another option is to install thinner friction and steel plates-which are available through the aftermarket-allowing you to install as many as eight or nine friction's. When the eight or nine friction pack applies, the energy of the apply is distributed over more surface area therefore the clutch pack is able to hold much more torque load as opposed to the original capacity. In addition to increasing the torque holding power it also adds much more resiliency and an accumulative value to the clutch pack.
With an eight or nine friction pack installed, you can increase the third feed orifice to as much as .180 inch without experiencing a cut loose-providing that the pressure rise control system and everything else in the unit is functioning properly. If the third feed is between .093 inch - .110 inch and you desire additional high throttle firmness, remove the 2-4 servo assembly, and replace the original band release spring with a stock THM 400 intermediate band spring number 8623489.
When using the eight or nine clutch pack, we suggest using the red friction plates with either the dull or Kolene steel plates. If you purchase these plates separately instead of in kit form, ask your distributor for the four page instruction sheet which contains valuable technical information as well as stack-up procedures.
Odds And Ends
When building this unit for really heavy duty or high performance application, we suggest installing the heavy duty low-reverse planet with the deflector shield and matching output gear support. Always replace the sprag assembly on any 700 that has over 30,00 miles on it. using medium grit emery paper, hand sand the input sprag races. This unit needs a near perfect pump to maintain enough pressure and volume at high revs. your parts distributor can furnish you a high-rev pump ring kit with priming spring that reduces high-rev slide flutter and can handle up to 8,000 rpm. There are also relined 2-4 bands available with the red high performance paper. With this band, on manual high throttle 1-2 you'll spin the tires for sure! Finally, if the unit doesn't shift at the right time and/or doesn't shift firm enough, check and confirm that the main line pressure rise system is functioning properly before you start changing springs, servos, orifice sized and so on. If you don't check pressure rise...you'll be on a witch hunt for many hours. Fix It Right The First Time, so you and the transmission can both be winners!
Numbers and Measurements from ATRA's
-GEARS Magazine May 1997
-GEARS Magazine May 1997
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