2007.5-2010 Chevy Duramax LMM Transmission Rebuild Parts

The Allison 1000 in the 2007.5-2010 LMM Silverado

One transmission came behind the LMM in these pickups: the double-overdrive six-speed Allison 1000, which gained its sixth gear and driver-selectable shifting for the 2006 model year. Gearing runs 3.094, 1.809, 1.406, 1.00, 0.711 and 0.614 with a 4.48 reverse, and the input torque rating climbs through the run, from 660 lb-ft on 2008-2009 trucks to 765 lb-ft from 2010. It takes Dexron-VI with a TF920 sump filter and a TF950 spin-on, serviced at 50,000 miles in normal duty or 25,000 in severe service. Tow/Haul, Tap-Up/Tap-Down manual mode, auto grade braking and shift stabilization are all factory features, and HD trucks got a heavy-duty auxiliary transmission oil cooler as standard equipment. The 6.0L gas Silverado used a Hydra-Matic 6L90 instead, so gas-truck transmission parts are not interchangeable.

What fails and why

Start under the truck. The factory cooler lines leak at the crimp where the hose meets the hardline, sometimes under 25,000 miles, and hoses that have aged next to the exhaust make it worse. You see red ATF misted across the frame and crossmember, then overheating and flaring shifts. Add power and the stock torque converter is the first casualty: the thin stator cracks, the soft front cover balloons, and the debris that comes off it contaminates the fluid and takes the rest of the unit with it. Slipping in the C3 gears and a drop into limp mode, locked in third gear, shows up with added power or heavy towing, and ECM tuning without matching TCM tuning will limp an Allison quickly. On high-mileage units, valve body valves seize or their bores wear, pump gears lose efficiency and babbitt bushings wear out, which reads as sloppier shifts than new, quick downshifts under load and delayed engagement. At extreme power the C2 hub and the P2 planetary snout break on hard third-to-fourth upshifts, and the pre-2011 input shaft is good for roughly 600 hp.

Stock replacement vs. upgrade

If the truck is stock and towing inside its ratings, replace like for like: correct fluid, both filters, new cooler lines when they weep, and OEM Allison solenoids. The practical ceiling for a stock LBZ or LMM-era unit is about 430-450 rwhp and 850-900 lb-ft, so if you are past that, the order that works is TCM tuning first, then a billet-cover multi-disc converter, then the valve body, then a built unit. Inside, the proven parts are a billet C2 hub, a billet P2 planetary, a PTO cover that feeds oil to the C3 clutches, hardened pump gears and bronze bushings. Deep pans, sump and spin-on filters and fluid service kits cover the maintenance end. Keep in mind that adaptive shift logic can hide degradation until something lets go, and heavy towers commonly report servicing fluid far more often than the factory schedule asks for.

What we carry

This page is the hard-parts side of the Allison. PPE supplies most of it: billet input, intermediate and output shafts, a billet C-2 clutch hub, Stage 5 and Stage 6G transmission kits, C5 clutch kits, valve body recalibration and pressure calibration kits, a low-profile aluminum pan, a performance transmission mount, bar-and-plate coolers, and a transfer case brace and gasket. Merchant Automotive covers the service side with deep pans and filter-lock kits, converter housing reseal and bolt seal sets, pass-through connector seals and a left-hand dipstick tube. Mishimoto brings direct-fit and universal transmission fluid coolers, including one with a fan and a radiator-plus-cooler bundle, and XDP adds a flex plate bolt kit and a direct-fit oil cooler. ATS Diesel Performance, BD Diesel and Fleece Performance Engineering are on this page as well, alongside Allison PTO cover gaskets, Dorman converter bolts and an ACDelco transfer case output shaft seal for the small stuff. The Duramax section has the rest of the 6.6L parts when the transmission is not the only thing on the list.

Fitment notes

These pages cover the GMT900 body only. The LMM arrived mid-2007, so a 2007 Silverado HD "Classic" is the older body with the LBZ and does not always share parts. Plenty of Allison hard parts carry across 2001-2019, but the six-speed valve bodies and shift kits are listed separately from 2011-up units, and the shift kit is a 2006-2008 part. Built transmissions are built as 2WD or 4WD units, not one part number for both. Internal filter depth changes with a deep sump, so order the filter that matches the pan you are running. Nothing from 2011 forward is a safe assumption here, because that is the LML with a different pump and emissions system. Check the fitment box on the product page or call the shop with your VIN.

Frequently asked questions

What fluid and filters does my LMM Allison take?

Dexron-VI, with a TF920 sump filter and a TF950 spin-on. The factory interval is 50,000 miles for normal use and 25,000 for severe service. If you install a deep pan, move to the deeper internal filter that matches it, because standard and deep sumps take different filter depths.

Do I need transmission tuning before I add engine power?

Yes. ECM tuning without matching TCM tuning is the quickest way to put an Allison into limp mode, where it locks in third gear. TCM tuning is the first step in the upgrade order, ahead of a converter or a valve body, and it is part of any built-transmission install.

Can I fix the stock unit instead of buying a built transmission?

Often, yes. A unit slipping only in the C3 gears, or shifting sloppy from valve body wear, can be addressed with the billet hubs, PTO cover oil feed, hardened pump gears and bronze bushings on this page. Once the converter stator or front cover has come apart and pushed debris through the fluid, you are into a full teardown and a built unit usually makes more sense.

Not sure what fits? Call the shop at the number in the header, or use the fitment checker on any product page. We install everything we sell.