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Originally Posted by 88JRFAN
I swapped to th400 in mine and it came with the brace arm that you show Larry. I've been contemplating how to mount it with the torque mount. Reading your comment's make me think to just take plate off. Then mount bar. Would make more sense. I really don't want to break tranny case. Thanks, Daren
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The support rod from the tcase to the trans bell is a good idea and I will eventually do that too once I find a support rod to modify to fit my contraption. The bracket from the tcase to the frame is a horrible design which has been a topic of many threads here in the 4x4 section and it seems everybody has and opinion.
Members Zoomand75, BeamN7, and I work in the class 5 through 8 truck manufacturing industry where one of our retired colleagues is also a retired service engineer from GM. In his years of service at GM he worked with GMC Truck and Bus after graduating GMI sometime in the 1960’s. Back in 2010 when I was doing this NV4500 swap the topic of supporting the tcase kept coming up over and over which I asked Winston his thoughts. Winston is an old guy with an engineering degree that can make any short story long where he told me all about the tcase adapter issues on 1969-1972 Chevrolet and GMC trucks that used the 205 to frame brackets and did not allow the tcase to rotate with the rolling torque of the engine resulting in broken adapters. He told the story like it was yesterday then said DO NOT use a frame to tcase mount and if you have an old truck with the bracket remove it. Much of his experience was supporting the Trans-Alaska Pipeline construction contractors where GM trucks were used to their fullest. The duty cycles those trucks saw on the job may not appear in a personal use truck for decades.
Yes, there have been tons of stories where members here claim to have a 43 year old truck with the tcase frame bracket and never broke a single adapter or broken bellhousing on a TH350 that they know of. Great for them, but the propensity of an adapter or auto trans bellhousing failure is much greater with the frame bracket. As he mentioned, tcase adapter failures on manual trans trucks happened often anyway even after the frame bracket is removed. That is one of the reasons GM was so happy to move to the SAE 6 bolt round adapter in 1985. The old skinny adapter used on the figure 8 205 tcase is just the weak link in the driveline but the tcase to frame bracket makes it far worse.
Back to the support/torque rod, the reason it is a good design is it supports the cantilevered weight of front output side of the tcase but the entire assembly is still supported to follow the engine/transmission assembly torque roll. This is the reason GM ditched the frame bracket in favor of a torque rod after 1972 although not all trucks got a torque rod. Which got them and which didn’t is still a mystery.
Funny modern story somewhat related to this concept. Our company used a long oil fill tube that was attached from the valve cover to the radiator support which is bolted to the frame at the other end. With the torque rotation of the engine, the oil fill tube adapter in the valve cover broke on thousands of our trucks because the entire assembly was not rotating together which allowed it to pull itself apart as the powertrain moved around during normal operation. That is exactly what happens when you tie the tcase to the frame and not allow it to rotate with the torque roll of the engine/trans assembly.