Upon disassembly, the transmission is thoroughly cleaned, and the caserepainted. This and most of the other major components (e.g., the frontpump and valvebody) will be reused because, as a rule, they just don'twear out.
When horsepower figures are up and consistent shifting performance is therequirement, it's impossible to beat Ford's tough and dependable C6three-speed automatic transmission. Some folks choose to beef up the C4small-block Cruise-O-Matic for their high-performance transmissionneeds. And while the C4 is a terrific transmission, no amount ofhardening will get it to stand up to the punishment a C6 can endure.
Toget the skinny on all of the latest in C6 performance and durabilityenhancements, we're venturing out to California PerformanceTransmissions (CPT) in Huntington Beach, California. The driving forcebehind CPT is none other than the respected racer, Art Carr. Art is oneof the elder statesmen of our industry and hobby. Art has been workingon automatic transmissions since 1953, and he's been in businessrepairing and modifying them since 1960.
The C6 core is completelydisassembled. Components that will be used again, such as the case,front pump housing, sun gear shell, and valvebody, are cleaned andcarefully inspected. Everything is rebuilt using all new soft parts,such as clutches, bands, and seals. The valvebody gets some secretmodifications for shift improvement and durability. Hard parts, such asnew rings, clips, and bushings, are replaced.
When we make improvementsto the valvebody, we are not only improving shift quality, but we extendtransmission life. In firming up the shift, we reduce clutch and bandslippage, which reduces unnecessary friction material in the fluid thatcauses excessive wear at the seals and hard parts.
When CPT builds a new transmission, improved durability is paramount.The list of durability improvements includes the C6 ring gear housingand rear planetary gear assembly, which are specially modified to acceptnew inner-and-outer bearings. The stock arrangement used only brassthrust washers and bushings. Reduced internal operating friction andimproved longevity is the result of this modification.
Here, we compare the stock brass thrust washer used to support the rearplanetary gearset to the new needle bearing replacement. The pointershows the separation between the upper-and-lower halves of the lowprofile bearing. This greatly reduces internal friction and instability. | 
The new bearing is installed on the back of the rear planetary gearsetafter being generously lubricated. Once in place, these bearings reducefriction along with heat generation and parasitic power loss. The bonushere is less wasted power. | 
Transmission assembly begins here. The case is stood on end and loadedfrom the top. Here, the rear planetary gearset and sprag are installedfirst. |
The stock C6 clutch pack contains four clutch frictions. A CPT C6rebuild includes five Raybestos clutch frictions for improvedengagement. To accommodate the additional clutch friction, the pressureplate must be machined down to create the additional space required.
The new CPT clutch pack has five Raybestos frictions instead of thestock four-disc setup. This improvement amounts to a big increase inholding power. The rings at left show how the parts are installed in analternating fashion. | 
This photo shows the specially machined clutch pack pressure plate usedby CPT next to the stock component. The reduced thickness of themodified part makes room for the extra clutch friction set. | 
The CPT five-clutch pack is loaded into the sun gear shell. Notice thelubrication holes in the side of the shell added by CPT. This is a nicerefinement for C6 performance automatics. |
For a street performance transmission, the stock ratio sun gear shell isemployed. However, for racing applications, the ratios can be modifiedto give us the advantage. The clutch band surface on the stock shell hasno lubrication holes. CPT adds four or five holes to improve lubricationand prolong band service life. Several measures are taken to strengthenthe transmission in the all-important area of the one-two upshift.
CPT pays close attention to the intermediate clutch band. Besides havingimproved lubrication to the band, an improved replacement band is alsoused. This band differs from the stock component in two ways. First, thereplacement intermediate band has a smooth inner surface rather than thechanneled pattern found on the stock band. Second, the new component iswider by a full 20 percent. Both of these elements add up to a moreusable surface area. When these two factors are combined, it's easy tosee why this part contributes to improved holding quality in secondgear.
When the band is installed, CPT likes to set the adjustment a pinchtight because this firms upshifts and prevents premature wear. Whilewe're on the subject of second gear durability, another CPT modificationcomes to mind. A billet servo arm and cover are used in the CPT buildprocess to increase the force of second gear application.
The sun gear shell is loaded into the case. With the shell in position,we're moving on to installation of the intermediate band (second gear). | 
This comparison photo shows the solid surface on the inside of thereplacement band, as well as the extra width of this extra-heavy-dutypart. | 
This photo shows the billet servo cover and piston compared to the stockpieces, which is shown without the piston. The important difference issimple--the billet replacement has a larger volume of fluid capacity thanthe stock servo for a more forceful second gear engagement. |