Ultimate Diesel Builder's Guide - - Contents -

Mag­i­cally Con­vert­ing the Al­li­son 5-speed to a 6-speed

To most gen­eral au­to­mo­tive en­thu­si­asts the au­to­matic trans­mis­sion is some­what of a mys­tery, with gears, clutches, plan­e­tary sets and maze-like valve bod­ies some­how work­ing to­gether to get the power from our diesel en­gines to the ground. For many of us, an au­to­matic trans­mis­sion is quite sim­ply a magic box that some­how moves the power from the en­gine to the wheels and as long as it's work­ing prop­erly we don't gen­er­ally worry about it. Of course, most diesel en­thu­si­asts know that a stock trans­mis­sion won't han­dle much more power than stock and we'll need to turn to one of the many premier trans­mis­sion builders to up­grade the in­ter­nals to han­dle the power our mod­i­fied diesels can dish out. We know that the clutches, shafts and torque con­vert­ers are the key ar­eas that need im­prove­ment, but most of us couldn't disas­sem­ble and re­build an au­to­matic trans­mis­sion on our own.

The Al­li­son trans­mis­sion is known to be a smooth-shift­ing trans­mis­sion that is re­li­able at stock power lev­els and ro­bust when fully built to han­dle tons of power. The Al­li­son 1000 trans­mis­sions used in LB7 and LLY trucks from 2001-2005 were 5-speed units that of­fered a .71 ra­tio for the over­drive 5th gear, while LBZ ver­sions of the truck re­ceived a 6-speed ver­sion of the same Al­li­son 1000 that de­liv­ered a dou­ble over­drive with .71 in 5th and .61 over­drive in 6th gear. The ex­tra over­drive pro­vided a cruis­ing rpm at 75 mph about 325 rpm lower than the 5th gear over­drive of the 5-speed Al­li­son. Lower revs gen­er­ally means less fuel be­ing burned and higher mpg, along with less noise and re­duced wear on the en­gine.

Ob­vi­ously, early-model Chevro­let and GMC Du­ra­max truck own­ers would like the new 6-speed ver­sion of the Al­li­son trans­mis­sion in their trucks but they didn’t want to buy a new truck or new trans­mis­sion to get it. That is where the magic of the Al­li­son trans­mis­sion and the team at Sun­coast Per­for­mance comes into play. In some magical way, the in-

ter­nal clutches, shafts and plan­e­tary gearsets in the new 6-speed Al­li­son were still the same as the 5-speed; only the TCM and the valve body were dif­fer­ent to ap­ply the clutches dif­fer­ently and come up with a dou­ble-over­driven 6th gear. But a snag that pre­vented peo­ple from sim­ply swap­ping the newer TCM and valve body into their trans­mis­sion was that the newer trucks used a dif­fer­ent com­mu­ni­ca­tion pro­to­col so the new parts would not talk to the old truck.

Sun­coast and their en­gi­neers came to the res­cue and de­vel­oped a mod­i­fied valve body and TCM that would lit­er­ally bolt and plug in place of the ex­ist­ing TCM and valve body and talk to the truck prop­erly to op­er­ate the Al­li­son in 6-speed mode. Some­how these trans­mis­sion wizards mag­i­cally trans­formed the 5-speed Al­li­son into a 6-speed with­out re­mov­ing the trans­mis­sion from the truck or touch­ing any of the clutches or gearsets. With the Sun­coast TCM and valve body in­stalled, the truck will op­er­ate the same as it al­ways has in gears 1-5, but then it will shift into the dou­ble-over­drive .61 6th gear.

While the in­stal­la­tion is pretty sim­ple, it does re­quire you to re­move and re­place the TCM un­der the hood as well as drain the trans­mis­sion and re­move and re­place the valve body, which can be a messy task that may not be well suited to the faint-of-heart. Most gear­heads will be ca­pa­ble of per­form­ing the up­grade on their own if they choose to do so. Just be care­ful and prac­tice safe shop tech­niques while you are work­ing on and un­der your truck.

We took our 2001 Chevro­let Sil­ver­ado desert race project truck up to RLC Mo­tor­sports in Cookeville, Tenn., where shop owner Michael Dal­ton per­formed the in­stal­la­tion with a lit­tle help from Drew Richards on a few oc­ca­sions where an ex­tra set of hands was needed. To make it eas­ier for us to shoot the pho­tos and doc­u­ment the process, the in­stal­la­tion was done on one of the shop’s two-post lifts so that we had full ac­cess to the trans­mis­sion pan and valve body once the pan was re­moved. The in­stal­la­tion re­ally is pretty sim­ple and started with dis­con­nect­ing the truck’s bat­ter­ies be­fore the old TCM was re­moved and re­placed with the Sun­coast unit. Then the truck was lifted and the fluid was drained from the PPE cast-alu­minum pan be­fore the pan was re­moved to ac­cess the valve body. A trick to know which valve body bolts need to be re­moved is to look at the new one and see which bolts are miss­ing, then re­move those bolts from the trans­mis­sion.

Af­ter the old valve body was re­moved from the trans­mis­sion, Dal­ton trans­ferred the man­ual se­lec­tor valve and pin over to the new valve body and in­stalled the valve body in the Al­li­son trans­mis­sion, be­ing sure to torque the bolts to 100 inch-pounds as spec­i­fied. Then he in­stalled a new fil­ter along with a Sun­coast Fil­ter Loc and re­in­stalled the pan. We also opted to in­stall a new Al­li­son spin-on fil­ter and Mer­chant Au­to­mo­tive fil­ter guard, which had to be mod­i­fied slightly to work with the PPE cast-alu­minum pan. Once every­thing be­low was but­toned up, he low­ered the truck and filled the trans­mis­sion with about 2 gal­lons of Sun­coast full syn­thetic D-type ATF. Then he fired the truck up, checked for leaks, and topped off the level be­fore tak­ing it out on a test drive. Be sure to re­turn your old valve body and TCM to Sun­coast for the core charge re­fund. De­spite our typ­i­cal pho­tog­ra­phy slow­downs, Dal­ton com­pleted the in­stal­la­tion in about three hours.

Driv­ing the truck felt com­pletely nor­mal un­til you got out onto the open high­way and the truck lit­er­ally shifted into an­other gear! We have 37-inch Goodyear Wran­gler MT/R tires in­stalled, and af­ter we swapped the orig­i­nal 3.73 gears for 4.56 gears we no­ticed that the rpm climbed pretty sig­nif­i­cantly while cruis­ing along on the free­way. Our fuel mileage dropped by al­most 2 mpg down to about 15.5. At 65 mph the Du­ra­max was spin­ning along at around 1,900 rpm, while 70 mph was about 2,000 rpm and 75 mph was about 2,200. With the truck in 6th gear, 65 mph saw the Du­ra­max spin­ning at about 1,600 rpm, 70 mph was about 1,750 and 75 mph was about 1,850, for a re­duc­tion of around 300 rpm across the board. When we mea­sured fuel con­sump­tion we also found that we gained back the 2 mpg we lost with the gear change, so we now have bet­ter ac­cel­er­a­tion while

turn­ing about the same rpm as we did be­fore our gear change. With the same gear­ing we would have had sim­i­lar re­sults with a sim­i­lar de­crease in rpm and a sim­i­lar in­crease in mpg.

Com­ing in at just over $2,000, the Sun­coast Per­for­mance 5- to 6-speed con­ver­sion is not the cheap­est up­grade, but cruis­ing along the high­way at about 300 rpm less is some­what magical. It may not be for every­one, but we were happy that we made the swap in our truck and can now grab an ex­tra gear on the high­way. If you are look­ing for more mpg, lower rpm and would like an­other gear in your Al­li­son, the ma­gi­cians at Sun­coast have just the setup for you. Just be sure to tell them that your friends at Ul­ti­mate Diesel Builder’s Guide mag­a­zine sent you. UDBG

10 Next, Dal­ton drains the trans­mis­sion be­fore re­mov­ing the pan to ac­cess the valve body in­side.

11 When Dal­ton low­ered the pan the fil­ter dropped down with it, mak­ing us happy that we chose to use the Sun­Coast Fil­ter Loc on the new fil­ter when we put it back to­gether.

12 No­tice that the fil­ter seal (see ar­row) is still lodged in the trans­mis­sion case. Be sure to re­move it be­fore in­stalling the new fil­ter and seal.

8/9 Af­ter seat­ing the new TCM in the cover and se­cur­ing the clips the cover is slid into po­si­tion, mak­ing sure that the tabs at the bot­tom en­gage the slots in the fan shroud. Then the cover is bolted into po­si­tion to com­plete this part of the...

7 The con­nec­tors in the truck plug right into the new Sun­coast Per­for­mance TCM just like fac­tory, be­cause it is a fac­tory TCM that they re­coded to work with the truck and con­trol the Al­li­son as a 6-speed.

1/2 Af­ter dis­con­nect­ing the bat­ter­ies, Michael Dal­ton loosens both bolts se­cur­ing the TCM to the fan shroud and then lifts it out of the slots se­cur­ing the bot­tom of the TCM cover.

6 Dal­ton lu­bri­cates the con­nec­tors, seals and con­tacts with di­elec­tric grease to en­sure a good con­nec­tion that'll last for years—es­pe­cially con­sid­er­ing our predilec­tion to get the truck dirty.

4 Then he un­plugs each of the har­nesses to re­move the TCM from the truck.

5 Look­ing at the TCMS side by side, they are vir­tu­ally iden­ti­cal—ex­cept of course for the mud and dirt stuck to our old one.

3 Lay­ing the cover over, he un­clips the tabs hold­ing the TCM in the cover.

The Sun­coast 5- to 6-speed Al­li­son con­ver­sion kit sim­ply comes with the new valve body and TCM. We opted to re­place both the in­ter­nal and spin-on Al­li­son fil­ters and add a Sun­coast Fil­ter Loc to hold the in­ter­nal fil­ter se­curely in place. We also...

16/17 The man­ual se­lec­tor valve and pin must be re­moved from the old valve body and in­stalled in the new valve body; be sure not to lose the pin while han­dling the valve body or trans­fer­ring the parts.

15 Af­ter it is loose, he care­fully re­moves the valve body from the trans­mis­sion.

14 Us­ing the new valve body as a guide for which bolts to re­move, Dal­ton re­moves the bolts se­cur­ing the valve body to the trans­mis­sion.

13 With the pan and fil­ter out of the way, Dal­ton dis­con­nects the so­le­noids and trans­mis­sion con­nec­tors from the har­ness and re­moves the clips se­cur­ing the har­ness to the valve body, then moves the har­ness out of the way.

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