questions
 

Just got some questions maybe someone with experience can help me answer. iv never really worked on a car unless you count changing oil and air filters, but im good with a wrench.

i got a 75 chevy stair body, with np203, th350, 454, 3/4 rear and dana 40 in the front.

my question is since i got the cab off to primer and paint. iv decided i dont need a 454, but rather a 383 i got in the shop from my dad.

-will the 383 bolt to the th350 tranny, or do i need an additional adapter plate.

- is there a way of servicing the transfer case, or transmission while i have the body off and am able to work on them with ease? is it worth rebuilding either one. i.e. buying new bearings etc...

-how can i calculate my gearing in the rear diff? which spline do i count and what is the equation i can use. the truck sits on a 8inch lift with 33's

- the 454 i was told, was old and worn. i dont know its its been rebuilt before, but is it worth rebuilding? how can i tell?

thanks guys! sorry if the questions are a bit vague, iv been trying to do my research to learn as much as possible as soon as possible.

Re: questions
 

Welcome!

While the body is off the frame, its a perfect time to freshen up the transmission and transfer case! Otherwise you'd be doing the same work from underneath. But opening up either one is not exactly for novices. If it were me, I'd take them out and bring them to a reputable transmission shop to be rebuilt. Then you can install with new mounts and such.

The engine is another matter. Do you know the condition of the 383? it might be a screamer, could be set up for a drag car or a nice truck engine, but I don't know. My personal opinion is that the 454, even stock, will give better daily driving in a lifted truck with big tires. If this engine is freshened up, it will drive very nice with good torque in a usable range. The small block may be fine as well, but it depends on the set-up. Each will use some gas in a lifted 4x4.

The 383 will bolt right up, but the torque converter may need to be changed based upon a more appropriate stall speed for the small block. The motor mounts are slightly different too, but I don't think thats an issue.

A quick way to check your gears if there is no tag on the axle or you don't trust is is to block up the front tires(so the truck won't move), lift one rear tire enought to turn it (if its got a limit-slip or locker, you'll have to lift both rear tires). Mark a spot on the tire with a refence point on the floor. Turn the pinion and/or driveshaft (truck in neutral) and count the revolutions it takes to turn the tire 360 degrees. 4 turns is probably 4.10:1, 3.75 turns is likely to be 3.73:1, 3.5 turns is likely 3.42:1, etc.

Re: questions
 

- or - if the axle is just sitting there you can pull the rear cover and count teeth.

# of teeth on the ring gear divided by # of teeth on the pinion is your gear ratio.

41 /10 = 4.10
41/ 11 = 3.73

etc.

K