Stainless brace that ties the transfer case to the Allison 1000 case on 2001-2007 LB7, LLY and LBZ Duramax 4x4s to stop cracked tail housings.
Searching for a transfer case brace usually starts one of two ways. Either a buddy with an LB7 or LLY truck had his Allison rear housing crack and you want to avoid the same bill, or you are already under your own 2001-2007 Silverado or Sierra HD looking at a wet transfer case and a new housing on order. This stainless brace is built for both situations on classic-body 4x4 trucks with the 6.6L Duramax (LB7, LLY and LBZ) and the Allison 1000.
GM mounted the transfer case on these trucks straight off the tail of the Allison, through a cast aluminum rear adapter housing, with no separate hanger or mount. The transmission mount on the crossmember holds the assembly up, but the transfer case itself is supported only by that bolted flange. Torque reaction from a diesel, a heavy trailer tongue pitching the truck, and every vibration that runs up the driveshafts bend that flange a tiny amount each time. A casting does not like being bent over and over, and the classic result is a crack in the housing that starts as a seep. This brace adds a second load path: two 7/8 inch 304 stainless tubes joined to a thick stainless plate tie the top of the transfer case forward to the transmission, so the weight is carried by the main case instead of pivoting on the adapter flange.
A brace is preventive. On a housing that has already split, it only belongs on the truck after the housing is replaced.
Make sure the leak is really the housing. Clean the area, run the truck to temperature and look for where the wet trail begins. A loose pan, a weeping filter or a leaking cooler connection can all wet the same area; if your 2006-2007 LBZ cooler lines are crusty, our braided cooler line kit for the LBZ and LMM may be the real fix. If you feel vibration, find it first: the Allison 1000 converter shudder guide helps separate a lockup shudder from a driveline problem. Check fluid hot, as described in our Allison 1000 service guide.
This brace fits 2001-2007 classic-body Chevrolet Silverado and GMC Sierra 2500HD and 3500 4x4 trucks with the 6.6L Duramax LB7, LLY or LBZ and the Allison 1000 automatic. The 2007.5 new-body trucks with the LMM use a different brace design, so a 2007 truck must be the classic body for this part to fit. It is not for 2WD trucks. If your truck has been converted, has an aftermarket transfer case or you are unsure of the body style, send us your year and VIN and we will confirm before it ships. See the full range of Allison 1000 parts.
It is a bolt-on job from underneath with ordinary hand tools and no cutting or drilling. The brace uses existing bolt locations on top of the transfer case and on the Allison rear housing. Clean each threaded hole before reinstalling the bolts, start every bolt by hand so nothing is cross-threaded into aluminum, and torque in stages to the values in the instructions supplied with the brace rather than guessing; these bolts go into soft castings. If you are replacing a cracked housing, the transfer case is already off, so install the new housing, rehang the case, then fit the brace before the driveshafts go back in. Refill with an Allison-approved fluid such as TranSynd 668 and check the level hot. A fresh filter and pan gasket kit is worth doing while the truck is in the air.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
The LB7, LLY and LBZ in 2001-2007 classic-body Silverado and Sierra 2500HD and 3500 4x4 trucks with the Allison 1000. The 2007.5-2010 LMM new-body trucks need a different brace.
Yes. It bolts on from underneath using existing bolt locations, with no drilling or cutting.
The housing itself, its gaskets and seals, and any worn U-joints that caused the vibration. Refill with Allison-approved fluid and check the level hot afterward.
Only if the leak was caused by movement at a joint that is still sound. If the casting is cracked, it has to be replaced; the brace keeps the new one from cracking.
No. It supports the transfer case, which only 4x4 trucks have.
