Ultimate Diesel Builder's Guide - - Contents - Text/pho­tog­ra­phy: Chris Tobin

Street and race trans­mis­sion mods

The in­creas­ing pop­u­lar­ity of GM'S Du­ra­max pow­er­plant backed by an Al­li­son au­to­matic has prompted a diesel sub­cul­ture of D-max en­thu­si­asts. You can find good, used trucks for a de­cent price these days, and with min­i­mal mod­i­fi­ca­tions to an LBZ you can make an easy 400500 horse­power. Un­for­tu­nately, as is the case with most diesel trucks, the trans­mis­sion be­comes the weak link in the chain. But there are sev­eral op­tions to up­grade your Al­li­son to han­dle any horse­power or torque in­creases you can throw at it and keep the truck re­li­able.

The stock Al­li­son au­to­matic trans­mis­sion that backs the vast ma­jor­ity of Du­ra­max-pow­ered Chevro­let and GMC trucks on the road to­day is a great-per­form­ing five- or six-speed trans­mis­sion. When the Al­li­son trans­mis­sion is used with a stock or mildly mod­i­fied Du­ra­max en­gine, it will han­dle most mods—pro­vided it’s not abused or poorly main­tained.

As with any au­to­matic trans­mis­sion, if you over­heat it, over­load it or don't prop­erly main­tain it and al­low it to run low on fluid or with old dirty and burnt fluid, it will not last long no mat­ter what power level you’re at. Heat is the pri­mary en­emy of any au­to­matic and slip­ping un­der high power will cause a lot of heat buildup in the trans­mis­sion.

For GM own­ers who have stepped up the per­for­mance of their Du­ra­max engines to near 500 horse­power, a per­for­mance re­build to keep the Al­li­son re­li­able is the smart choice. And there are sev­eral lev­els of up­grades, de­pend­ing on us­age.

We stopped by Diesel Tech­nol­ogy Source (DTS) in Mon­roe, Ge­or­gia, to find out what con­sti­tutes the proper up­grades for a street-driven Al­li­son. David Brown­ing of DTS rec­om­mended his Street build for trucks mak­ing up to 800 horse­power. For trucks mak­ing more than 800 horse-

power, he sug­gests their Race build, which is avail­able with bil­let in­put and out­put shafts for up to 1,000-horse­power builds. And for trucks with more than 1,000 horse­power to the rear wheels, DTS of­fers a Full Bil­let Race Al­li­son trans­mis­sion build that adds a bil­let in­ter­me­di­ate shaft, planet and hub for the ul­ti­mate in strength.

Brown­ing said the good news is that the fac­tory shafts in­side the Al­li­son trans­mis­sions are larger and stronger than the fac­tory shafts found in other trans­mis­sions, al­low­ing the stock shafts to be used with trucks mak­ing up to 800 horse­power in the DTS Street Al­li­son. Brown­ing also feels that mov­ing up to the bil­let shafts is not nec­es­sary un­til trucks reach or ex­ceed

the 800-horse­power thresh­old for the Al­li­son trans­mis­sion, and even then he starts with just a bil­let in­put and out­put. He rec­om­mends the full bil­let treat­ment only for trucks mak­ing more than 1,000 horse­power.

All of the DTS Al­li­son trans­mis­sion builds use Diesel Per­for­mance Con­vert­ers (DPC) triple-disc bil­let torque con­vert­ers to han­dle the task of cou­pling the Du­ra­max en­gine to the Al­li­son trans­mis­sion. Since it falls on the torque con­verter to pass the en­gine's out­put to the trans­mis­sion and ul­ti­mately to the wheels to drive the truck, it’s vi­tally im­por­tant that the torque con­verter be up to the chal­lenge.

The DPC triple-disc torque con­vert­ers used by DTS in their trans­mis­sions fea­ture a bil­let front cover to pre­vent bal­loon­ing or de­flec­tion that’s com­mon with stamped-steel cov­ers like the fac­tory uses. In­ter­nally, they use Tor­ring­ton bear­ings rather than bush­ings for smooth op­er­a­tion as well as larger clutches with mul­ti­ple discs for more hold­ing power when locked than the sin­gle fac­tory clutch. The sta­tor is also op­ti­mized for bet­ter flow than stock and they’re even avail­able with a bil­let alu­minum sta­tor for the ul­ti­mate strength.

The DTS crew also uses their in-house ma­chine shop to mod­ify in­ter­nal trans­mis­sion com­po­nents to hold ad­di­tional clutches for bet­ter hold­ing power in each of the clutch packs. Tak­ing pre­ci­sion mea­sure­ments and ma­chin­ing com­po­nents as nec­es­sary al­lows Brown­ing to com­pen­sate for any cast­ing-shift or ma­chin­ing vari­a­tions from the fac­tory to make sure that each trans­mis­sion they build is in­di­vid­u­ally op­ti­mized rather than just drop­ping a kit into it that may or may not meet their strin­gent tol­er­ances for per­for­mance.

DTS pro­vides their cus­tomers the choice of build­ing the trans­mis­sion with ei­ther Raybestos or Alto clutches. The Street builds use ad­di­tional clutches and steels in the C1, C2, C3 and C4 clutch packs, while the Race builds use

the same amount in the stout C1 pack and one ad­di­tional clutch and steel in the C2, C3 and C4 clutch packs to hold more power with­out slip­ping. The C5 clutch pack is very ro­bust from the fac­tory and re­tains the orig­i­nal clutch count. The Street build comes in at $4,500 crated and shipped and the Full Bil­let Race build will set you back about $7,000.

With all of DTS' trans­mis­sion builds, the crew com­pletely tears down the trans­mis­sion, re­mov­ing ev­ery nut, bolt and piece of hard­ware be­fore thor­oughly clean­ing the case and all of the hard­ware. Af­ter ev­ery­thing comes out of the in­dus­trial parts washer, the trans­mis­sion case sec­tions are painted in DTS blue be­fore re­assem­bly be­gins. Brown­ing feels that paint­ing the

case sec­tions be­fore assem­bly gives his trans­mis­sion re­builds a more pro­fes­sional look rather than paint­ing over ev­ery­thing in­clud­ing the hard­ware as some shops do.

The pho­tos in­cluded here high­light the com­po­nents that go into an Al­li­son per­for­mance up­grade. If you’re crank­ing up the power on your D-max, a per­for­mance trans­mis­sion will put the power to the ground safely and re­li­ably. UDBG

6 David Brown­ing loads the first set of clutches and steels into the Al­li­son case to be­gin the build.

1 The trans­mis­sion is com­pletely stripped down be­fore it’s cleaned, painted and re­assem­bled. DTS mounts the case to an en­gine stand to se­cure it while work­ing on it and to al­low it to be ro­tated into what­ever po­si­tion is needed.

2 The fac­tory C3 clutch pack (on the right) shows burn­ing and heat dam­age from slip­ping. DTS re­places them with Raybestos GPZ clutch discs adding two ex­tra discs for more power han­dling ca­pa­bil­ity.

5 DTS re­places the fac­tory C1 clutch pack's six dou­ble-side clutches with a to­tal of 14 sin­gle-sided Raybestos GPZ clutch discs to pro­vide more heat-sink­ing sur­face area and more clutch sur­face area to give a more pos­i­tive en­gage­ment with less slip­page...

4 The C2 clutch pack on the right is the orig­i­nal and looks to be in de­cent shape but the high-per­for­mance pack on the left uses an ad­di­tional clutch and bet­ter ma­te­rial to hold more power with­out slip­ping and over­heat­ing the clutch pack.

3 The orig­i­nal C4 clutch pack is also show­ing signs of dam­age and will also be re­placed by Raybestos GPZ clutch discs. Us­ing a shorter ap­ply pis­ton al­lows DTS to use one ad­di­tional clutch in the pack.

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