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www.gmhightechperformance.com28 GMHIGH-TECHPERFORMANCE

By Rick JensenPhotography by the author

It is no secret that the computer-controlled4L60E transmission, found in F-, B-, and Y-body performance GMs, is just barely

strong enough to handle the stock LT1 andLS1 engines. GM has fixed many of theinherent problems in the new 4L65E, butthere are a ton of 60s floating around outthere. And we all know someone who, after ablower, nitrous, or a few more cubic inches,

had the stock tranny go south in a big way.Strangely enough, the 60’s reputation is to thepoint where many racers are actuallyswapping it out for alternate means oftransmitting power to the tires. The turboBuick’s TH200-4R is a popular choice with itscloser gear ratios, as is the dreadfullyinefficient TH400 3-speed. Even the 4L80Etrans has been considered by speed freakswho are just tired of the cracked sun shellsand wasted 3-4 clutches of the 4L60E.

But its factory weakness can, in mostcases, be overcome. Century Transmission,found in Richmond, Texas, has been buildingauto trannies for 19 years. Besides its solid200-4R upgrades, proprietor Mike Kurtz andhis team specialize in high-10-second-strong4L60E rebuilds. We showed up one day to seea customer’s tranny get built, and the folks atCentury were happy to show us the parts andtechniques needed to get this ill-reputed gear-changer to survive.

Only TheStrongSurvive

Building a 10-second-

capable Century

Automotive 4L60E

The completely disassembled tranny. Century Transmissions will turn your weak factory4L60E into a 10-second-capable Street/Strip unit for $1875, barring any worncomponents or bad electronics.

CenturyTrans usesa 13-vanepump(above) toreplacethe factory10-vaneunits frompre-19984L60Es. A Teflon slide seal replaces thesteel GM one. Also, a stronger pumpslide spring is used to keep trans fluidvolume high at higher rpm ranges.

NOVEMBER 2003 29www.gmhightechperformance.com

A strong trans needs strong internals. Here is the five-pinion Century Trans planetary onthe left compared to a four-pinion GM planetary on the right. Century uses the five-pinionplanetary to spread the load out on the carrier more, which makes it less likely to fail.

A close-up of the bands reveals thatCentury Trans’ is 3/8-inch wider, has athicker backstrap and anchor strut, andfeatures a reinforced anchor pin recesson the right, as compared to the GM uniton the left. The Century Trans band’sthicker anchor strut allows the pin to seatdeeper than the factory strut will allow,which keeps it from ripping out with thehigher line pressures of a performancetrans. The reinforcement around the holealso helps to keep the pin from beingripped out, and a better method ofattaching the strut with rivets is used onthe upgraded unit.

This shot shows an upgraded CenturyTrans Super Sun Shell on the left, a stocksun shell on the right. Century Trans hasfound that the thickness of the sun gearspline ring from GM can vary up to 30thousandths, and these sun shells cancrack behind even a totally stock motor!The Century shell is a GM part with ahardened sleeve used to prevent crackingaround the sun gear splines. Its sleeve hasto be custom-ground to each individualspline ring, then furnace brazed and blackoxide coated.

Century Trans modifies the factory lowreverse inner sprag race (left) by grindingit down to make clearance for therollerized Torrington bearing. Thishardened steel unit is so hard that it can’tbe turned by a lathe.

A durable Torrington roller bearing (left)replaces the flimsy plastic thrust washer(right) between the sun shell and the lowreverse race. This is a high thrust area,and this plastic piece is one of the firstitems to wear––if it does, the race grindsinto the sun shell.

Here is the stock apply servo for secondand fourth gear on the left, and a billetapply servo on the right. The billet unithas a larger apply area for a crisper bandapply and 40 percent more holdingpower over a stock servo.

Compare the factory band with theCentury Trans unit: there’s a Kevlarfriction lining as opposed to the factorytan paper lining. Notice the curvature ofthe stock band as well––do you see thatmating perfectly to a round drum?Neither does Century.


The TCC valve bleed orifice has been modified by installing an orifice cup plug in place ofthe two-piece OEM orifice. With the stock unit, the pin can sometimes fall through theseat, which will interfere with the lockup valve and possibly cause a non-lockupcondition.

When installing the low/reverse sprag,the inner race should rotate clockwise toseat it. Next, the snap ring is installed,and Dorris uses a long-handled flatscrewdriver to ensure that the ring isinstalled correctly. Finally, Ronnie usescompressed air to leak-check thereverse clutch operation.

A cast GM rotor ring is on the left, withCentury Trans’ stronger hardened ringon the right. The hardened unit meansless of a chance of the rotor vanebreaking.

Ronnie Dorris, the head transmissiontech at Century Automotive, begins theinstallation. After the factory ring geargoes in, the five-pinion low/reverseplanetary is lowered into place andconnects to the splines of the outputshaft.

A wave (or steel cushion) goes in first,then alternating GM turbolated (withholes) steel, Borg-Warner Heavy-DutyTan clutch five times until the last clutchis up against the center support.

An anti-rattle clip is installed, and Ronniepre-lubes the low/reverse sprag with amixture of Mercron-III trans fluid and JBgear oil treatment.

The input sprag, which is found inside theinput drum, is upgraded from 26segments to 29. This distributes the loadfrom all four forward gears more evenly.The 26-segment sprag can slip theraces, and when shifting to Third, thiscan cause a clutch-slipping effect.

The outputshaft isinstalled bysliding it upthrough theback of thetranny casebushing andusing a snapring by thefive-pinionplanetary toretain it.


Now, the factory issued sun gear isdropped in to mesh with the five-pinionplanetary.

The upgraded sun shell goes in next,followed by the GM hub assembly thatattaches to the front planetary ring gear.

The front planetary goes in now. CenturyTrans will oblige customers requesting afive-pinion front planetary, but the factoryfour-pinion unit hardly ever fails.

The third and fourth gear piston releasespring and retainer from Century (right)has a stronger set of springs for use withthe TransGo HD2 shift kit.

Here is a comparison of stock aluminum(left) versus steel bonded overrun, 3-4,and forward pistons. The aluminum cancrack in the 3-4 piston after shift kits (andthe corresponding increase in linepressure), which means that all pieces willhave to be replaced for reliability’s sake.

The torqueconverterclutch orificeon the inputshaft is set upfrom thefactory torestrict andslow down theTCC apply forgooddriveability. Ofcourse, youdon’t want thisfeature for a

performance car, as it results in moreslippage, more heat, and worse ETs.Dorris uses a flathead screwdriver and ahammer to twist and gently remove thisobstruction.

GM’s stock forward clutch springs andretainer are on the left, and the upgradedassembly is on the right. Century Transuses stiffer springs to keep the clutchpack disengaged so it won’t try toengage the clutches centrifugally at highrpm. The two-piece cage is for a latersteel bonded piston.

The reverse input drum piston ismodified by decreasing the orifice sizewith a restrictor for a quicker Reverseengagement. Some 4L60Es experiencea delayed Reverse engagement whenthe trans fluid is hot.

The sequence to assemble the forwardinput drum: steel, clutch, steel, clutch,pressure plate, seal, Torrington bearing,sprag assembly, wave, five steels andclutches in alternating order, thenpressure plate. A smaller snap ring holdsit all in place. Next in the input drumcomes the 3-4 clutches, known as theweakest link in the stock tranny. Thepressure plate goes in first, followed bynine Alto Red Eagle clutches and eightKoleen steels installed in alternatingorder. Compressed air is applied in thethree clutch feed holes to verify thatthere aren’t any leaks past the pistonsand to seat the clutch packs.


The anchor pin goes in, then from thetop you can lightly pry with a screwdriveruntil it seats in the band strut recess.When the pin is in correctly, it is about1/16-inch below flush on the case.

Here is the pump cover with a 13-vanepump and a bigger spring.

Once together, the clutch drumassemblies are dropped into place, andRonnie uses a Vise-Grip to lightly holdthe splines and rotate the unit back andforth to get all of the teeth on the clutchfrictions to line up with the grooves anddrop into place.

After the input sun gear is installed intothe tranny case, the reverse input drumis assembled next. The beveled plategoes in with the concave side down,then four sets of steels and clutches inthat order are held with a snap ring. Thisdrum is air-checked as well.

The stator side of the pump is machinedwith a carbide bit on a lathe. Two to fivethousandths come off the face of thestator to make sure that it is straight andflat. This will prevent any cross leaks.

The pump is placed onto the input shaft,then seven bolts with special O-rings toprevent trans fluid leaks are torqued to20 lb.-ft.

Then the pump is assembled. Once thefive pump bolts are snugged up, analignment tool comes into play. When thepump’s two sides are aligned perfectly,the bolts are tightened to 15-20 lb.-ft.The thrust washer is lubed up andplaced, and the O-ring follows.

The 2 5/8-inch Kevlar band is droppedinto place, and Ronnie uses a flatscrewdriver on the bottom side wherethe pump goes in to pry up onto thereverse input drum slightly. Once theband strut falls into the case, lightly tap itwith your hand to verify that it’s seated.

A factory470thousandthsaluminumboost valveis on the left,a TransGo500thousandthssteel HD2boost valveis on theright. Thehardenedsteel won’twear or sticklike thestock unit(this canreduce linepressureand burn upthe tranny).

The HD2’s bigger diameter will also givemore line pressure, and stiffer springshelp on that front too.


SOURCEMike Kurtz’s

Century Automotive & Transmission811 Plantation DriveRichmond, TX 77469

713/666-2616www.centurytransmission.com

The accumulators are installed next.Century Trans uses the originalaccumulators with custom-lengthspacers to make the shifts firmer. Thecheck ball is installed now.

The valve body is installed, 17 bolts aretightened down to 96 inch-pounds, andthe harness connections are made. ATransGo 4L60E HD2 shift kit is utilized.

If the transmission has over 50,000 milesor if it has been contaminated by afailure, Century will replace thesesolenoids. The two square ones are shiftsolenoids A and B. The two tall roundones are pulse width modulatedsolenoids: one controls the TCCengagement, and one controls the 3-2downshift for a gradual engagement.The big round one is the EPC. The platein the foreground is a sensor manifoldassembly that sends trans pressure,temperature, and gear selectionfeedback to the ECU.

Century Trans complements its 4L60Erebuilds with custom-built, computer-balanced torque converters. Theyfeature a custom anti-balloon billet frontcover and a custom billet clutch disc,lined with a high-carbon-composite-lining, with a surface area of 40 squareinches (the factory size is 22 inches). Acustom billet clutch disc prevents flexunder pressure, and heat-treated steelsplines are used. Internally, everything isfurnace-brazed and rollerized. These canbe had in stall speeds from 3000-6500,and retail for $860.

The feed holes to the 2,3, and 4 circuitsare enlarged to increase the fluid volumeto the band servo and 3rd clutch pack.This will make the shifts firmer. The casegasket is placed down, the shift plategoes on, and the valve body gasketgoes on top. If you’re doing this at home,always match the old gaskets to the newone––there are three different types forthe 4L60E. On the shift plate, two of theholes are tighter for alignment purposes.

Our servo piston is assembled andinstalled by placing the spring in first, thenpushing the servo assembly in andholding it with a snap ring. Ronnie thenrotates the output shaft so he can checkthe servo clearance.

With the EPC (or variable force motor inGM-speak), a 15 Torx can be used toincrease line pressure, but is usually notnecessary (or recommended) unlessdone by a professional with a linepressure gauge.

The rooster comb detent is installed withone bolt. After that, a new filter is installed,the pan goes on and you have got a4L60E that won’t cry behind a big-horsemotor. If you’re going with a stock-sized 12-inch converter, the trans will need between12 and 13 quarts of fluid to top it off.

Then the TCC harness goes back into place.

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