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Questions on this Transmission. Being that the 3153B is a Truck 5 speed would this be a good alternative to using an NV4500 ? Will a 235/261 bellhousing /clutch assembly work with this Transmission ? Are these transmissions fully synchronized ? What is the OD on these ?

Hy TUTS 59, the information I found said that transmission was used in Chev and GM trucks, so I would assume it will bolt to their bellhousings, it is synchronized in all gears but first, the overdrive ratio is 0.79, hope that helps.

I'm trying to find the information on the input shaft. I have seen pictures of a splined shaft with no provision for a pilot bearing. Dose this sound right? Would there be multiple input shaft designs?

I'm taking a different approach with the big GMC 3 ton that's going to be an upcoming project. I'll stick with the SM420 main biox, and add a 3 speed Brownie in the same place where the center driveline carrier bearing is located currently. That setup, along with the vacuum shift 2 speed rear axle, will give me 24 forward speeds- - - - -and six in reverse! That should keep the 270 engine humming along in its happy place RPM no matter what the terrain happens to be! Plus- - - -it's been a long time since I've had two shifters and an axle splitter valve to play with!
Jerry

I know I'm bouncing a lot of ideas around and trying to play with the numbers. I really want to be able to keep the 235/261 happy in it's power band. I'm not afraid to push the engine on up to 2800- 3000 RPM, I just don't want to keep it there. I'm looking at the ratios of various transmissions, some overdrive and some direct, The Clark 282 is a 5speed direct drive, the difference is that it's a close ratio. Using a close ratio gear box would allow the engine to stay in it's power band and not drop so much between gears. I just don't know if the 235/261 would have enough HP to keep up with an overdrive without down gearing, especially under load.

Being as "Thor" is a 1.5 ton flat bed and I use it as such, I'm leaning more towards the close ratio Clark. While this transmission is not an overdrive, it combined with the now 4.88 rear gear and 34" tires should get me be close to the sweet spot in the power band. I don't have any ideals of flying down the interstate at 70 MP, I would just like to do 60-65 on occasion.

Your thoughts are appreciated.

https://garage.wiki/clark/transmissions/282v-close-ratio.html

There's an old saying on the NASCAR circuit- - - - -"Horsepower is to brag about- - - -torque wins races!" The same is true for load pulling. Getting the engine into it's favorite torque band and keeping it there as much as possible is the key to moving a heavy load efficiently. That's why the old Detroit diesels needed so many gears- - - -we only had a torque band of 400 RPM to work with (1750-2150) and the bottom half of that was pretty weak. Fortunately, a stovebolt engine has a much wider sweet spot on torque.

The HP rating of a 235 or a 261 is achieved somewhwere north of 3K RPM, and back when these old engines worked for a living, they stayed up there pretty much all day every day. Keep the rod bearing clearance narrow and the oil pressure good, and they will run all day at wide open throttle. I think I'd opt for the OD top gear instead of a close ratio box, and use the full RPM range of the engine, instead of artificially limiting it to low and midrange speed by shifting, instead of letting the engine rev. A 261 with more torque was GM's answer to moving a heavy load more efficiently- - - -and that option is just as good today as it was 70 years ago. The engines I've got on the drawing board with 3/8" extra stroke should do even better.
Jerry

Jerry, I live and learn from the advice of others. Looking at the numbers the current SM420 puts the engine RPM at 2850 or so at 60 MPH. An overdrive would drop that RPM to about 2300 at 60 MPH. As you said the 235 and 261 power band is 3000 RPM +. The 2nd gear on an SM420 is 3.57, and the 3rd is 1.70, that's a large step to over come. With the Clark 282, 2nd is 4.09, and 3rd is 2.17 add the 4th gear at 1.17 and the engine stays in it's power band longer.

I don't question your logic or numbers. I have a "93 K1500 with an NV4500, 4.11 gears and a 350. Heavily loaded, say a medium sized tractor and an equipment trailer and 5th gear is unusable, even on flat level ground. Just thinking that a 1.5 ton truck with 4.88 (now) rear gear and a 235 would be struggle even harder. Wouldn't the close ratio be beneficial here?

OD is usually a "no load- - - -get on down the road" gear for keeping up with traffic while running empty on the way to the hauling job. Once the truck is earning its pay, stay out of OD unless you've got a Brownie with an OD position so you can split every main box gear three times.
We also called shifting a Detroit-powered rig "rowing it with the shift lever!"

LOL!
Jerry

I've seen a few posts recently about you looking for an NV4500, so why not? I was looking into using one a while back and wanting to keep the mechanical speedometer. D*dge '94-'97 NV4500 had a mechanical speedometer drive. It might be possible to use the output shaft and tail housing, or adapt the input? (I ended up using a 5LM60 5-speed and attach a motor to the back of the mechanical speedometer.)
Link to a speedometer parts site: https://torqueking.com/category/speedometer-parts-1994-1997-dodge-nv4500/#y=758

Hotrod, do you already have the Brownie? Every once in a while I think about adding one to my two ton. Which model brownie do you recommend?