HKanada182

Well I'm sure there are a few guys on here scratching their heads, so let me explain what I've got here.
About a year ago I picked up a 1972 Chevrolet K20 4x4 3/4ton Pickup truck. I know, I know, I'm in the oldsmobile forums, please don't throw me out Under the hood is a 455 olds, a TH350 transmission, and an NP205 transfer case. Once I was starting the clean up the engine and transmission, I notice a crack from one side of the transmission housing to the other. After digging a little bit, I came to find out my olds is putting out too much torque for the TH350 that was originally in there. I am looking at putting a manual transmission back into it and wondering what my options are. I am looking at a SM465 Muncie, (this was what was originally in there) or if you guys have any other transmissions you have opinions on would help me out a lot. Also would be nice to know if it would bolt right up to the 455, and the NP205 transfer case without having to relocate mounts, cross members and hopefully leave all my drive shaft lengths the same.
I know this might be a long shot but any help and info is greatly appreciated. Thanks in advanced.
HK

joe_padavano

Well, your first problem is that Olds motors that came from the factory in front of automatic transmissions usually did not get the crank drilled for a pilot bearing for the manual trans. You will either need to have your current crank machined or use a conversion bearing. Folks here have had mixed results with the conversion bearings.

As for adapting the trans to a BOP engine, you'll need a correct bellhousing. The SM465 uses the larger truck-style bearing retainer, so it won't fit a normal BOP bellhousing from a car. There are BOP truck bellhousings, which were used behind Olds 350 diesel engines in Chevy/GMC trucks, but these are EXTREMELY rare (I've only ever seen one and like an idiot I did not buy it then). You can have a car bellhousing machined to fit the truck bearing retainer, but the pivot ball for the clutch fork is usually too close to the hole, so you will likely need to go to a hydraulic throwout bearing. In any case, the transfer case will likely move, so you're stuck moving the crossmember and changing driveshaft lengths.

If the crack is in the bellhousing area, the easiest, cheapest thing for you to do is to get a Superbell bellhousing. These are designed for drag racing. You cut off the old bellhousing from the TH350 case. The Superbell attaches with the front pump mounting bolts.

Kennybill

Just another option, maybe. Speedway has an adaptor bop to Chevrolet. Maybe u can find a turbo 400 4wheel drive trans.

joe_padavano

If the OP wants a stronger AT (as opposed to the manual trans he asked about), just get a BOP TH400 and the output shaft for a 4x4 TH400. Install this output shaft in the BOP case and no adapter needed. Many of these adapters are of questionable strength, given that they only pick up four of the six trans to bellhousing bolts. Of course you don't want to use an adapter on a manual trans bellhousing.

Of course, the TH400 option also moves the transfer case back, so new front and back driveshafts are required. The only option that doesn't require this is the Superbell on the TH350, which is why I suggested that.