Braces the overhanging transfer case on 2001-2007 Allison 1000 4x4 Duramax trucks so the transmission adapter housing stops cracking.
If you own a 2001-2007 classic-body Chevrolet Silverado or GMC Sierra 2500HD or 3500 4x4 with the Duramax and the Allison 1000, you have probably read about cracked rear adapter housings: an ATF drip at the joint between the transmission and the transfer case, found on a truck that tows or launches hard. This is PPE part number 129020107, the brace PPE builds for exactly those trucks. It ties the top of the transfer case back to the Allison rear housing so the casting is no longer the only thing holding up the case.
On the 4x4 versions of these trucks the transfer case bolts directly to the back of the Allison through an aluminum rear adapter housing. Nothing else supports the transfer case, so its weight hangs off that flange like a diving board. Driveline vibration, wheel hop, a worn front or rear U-joint, and repeated heavy launches flex the joint, and over time the thin sections of the housing crack. The PPE brace is a 304 stainless assembly with two 7/8 inch support tubes and a stainless plate. It picks up two factory bolt locations on top of the transfer case and four on the Allison rear housing, which turns a cantilevered joint into a triangulated one and spreads the load forward into the transmission case.
If the housing has already cracked, the brace will not seal it. The housing has to be replaced, which means pulling the transfer case, and the brace should go on as part of that repair so the new casting does not see the same load.
Degrease the joint, drive the truck, and look again. A leak that starts at the adapter housing rather than the pan, the filter or a cooler line fitting points to the casting or its seals. Check fluid level hot and the right way first; our Allison 1000 fluid and filter service guide covers the correct check temperature and the TES 668 fluid change. If the truck is also throwing codes or dropping into a fixed gear, read the Allison 1000 limp mode guide before assuming the leak is your only problem. Also check every U-joint, because a brace does not cure the vibration that cracked the housing.
PPE lists 129020107 for 2001-2007 GM 4x4 trucks with the Allison transmission, which in the Silverado and Sierra HD means the LB7, LLY and LBZ Duramax classic body. Be careful with 2007: the 2007.5 new-body trucks with the LMM use a separate PPE brace (129020710), and 2011 and later trucks use another (129021115). It does not fit 2WD trucks, since there is no transfer case to support. If you are unsure which body you have, send us the year and VIN before ordering. Browse the rest of our Allison 1000 parts for these trucks.
PPE's instructions say the brace can go on with the transmission in or out of the truck. Remove the two factory bolts on top of the transfer case and the four Allison rear housing bolts, set the brace in place, and reinstall the factory bolts. Torque the transfer case bolts to 36 ft-lb and the Allison rear housing bolts (M10 x 1.5 x 40) to 38 ft-lb, and do not over-torque into the aluminum. Clean the threads and check that the brace sits flat before final torque. If your crossmember or transmission mount is rotted, fix that first, since a sagging mount puts the same twisting load on the joint. Top up with an Allison-approved fluid such as Castrol TranSynd 668 if you lost any fluid at the housing.
While the truck is up, it is a good time to do the pan and filter service in our Allison 1000 service guide; trucks running the deep pan can use our deep pan filter and gasket kit.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Only if it is the 2007 classic-body truck (LBZ Duramax, carried-over body style). The 2007.5 new-body LMM trucks take a different PPE brace, 129020710. Send us your VIN if you are not sure which one you have.
No. PPE states it can be installed with the transmission in or out of the vehicle. It uses two factory transfer case bolts and four Allison rear housing bolts, torqued to 36 ft-lb and 38 ft-lb.
No. A cracked housing has to be replaced. Install the brace during that repair so the new housing is supported from day one.
No. The brace supports the transfer case, so it only applies to 4x4 trucks.
It is cheap insurance on any 4x4 that tows, runs larger tires or sees rough roads, because replacing a cracked adapter housing means removing the transfer case and buying a new casting.
