The warning on the bellhousing of the Hydra-Matic states "This housing must remain with this engine." The GMC Maintenance Manual states "The flywheel front and rear housings comprise a matched set which must remain with engine on which originally installed."

The reason for this is that the engine and front/rear flywheel housings are all machined to match.

When was the last time you used a dial indicator to check a late model automatic for center when installing it? Any race builder will tell you that you have to get the transmission input shaft exactly in line with the crankshaft centerline to avoid excess wear and pressure on the tranny case. Most broken tranny cases in racing can be traced back to poor assembly resulting in heavy stress on the case.

You SHOULD keep the flywheel housings with the correct engine but if you can't you should at least use the dial indicator to make sure the crankshaft and tranny input drive are in line. Is it critical on a daily driver? Probably not.

Hope this helps.

Robert
Sonora, CA

"I always win." Working mainly alone I do not let my trucks win a war. Maybe a battle here and there but never the war.

Robert
55.1 GMC 450 COE
51ish GMC Suburban