Which trans? SPID & Build Sheet Each Use Different Codes

[Jahloha]

My truck is a 1970 C20 350

I am trying to plan out my project and trying to learn the pros and cons of my transmission, but only thing is that my SPID has code M49 which would be either for the TH350 or TH400...but my Build Sheet has code M38 which is only the TH350.

Is this normal?

I am building a dd and do not believe I have the skills to conduct a tranny swap, so I am wanting to pin point which trans I have, in order to read what all you have to say about the pros and cons of it. Or what I need to do in order to make whichever trans it is, a better dd (mpg).

Thanks for all your help with this.

[Bigdav160]

What you say is correct about the RPO codes. TH400 would have been a M40 on the build sheet.

The TH350 is a fine transmission for all but the highest or torque/horsepower small block engines. It will also holdup to a very mild big block.

[Jahloha]

Originally Posted by Bigdav160

What you say is correct about the RPO codes. TH400 would have been a M40 on the build sheet.

The TH350 is a fine transmission for all but the highest or torque/horsepower small block engines. It will also holdup to a very mild big block.

Digdav:

So I should go off the build sheet code? (I will also get under tonight to verify by using the pan bolt pattern).

Also, I have read all about the 700r4 being the trans for daily driving, but I dont feel quite ready for that sort of swap. So in the mean time, outside of rebuilding the trans, what other components things should I do, to make the th350 achieve its best mpg?

[WIDESIDE72]

Imo, buy a B&M shift improver kit, and when you have the pan off for the install, put in a new filter and fluid. Im not aware of much else you cna really do to one still in the truck.

[Jahloha]

Originally Posted by WIDESIDE72

Imo, buy a B&M shift improver kit, and when you have the pan off for the install, put in a new filter and fluid. Im not aware of much else you cna really do to one still in the truck.

WestSide:

I plan on pulling the engine and trans next week...so options are open.

I made a contact with bud who's grandpa does trans rebuilds. The guy is nearly 70 and been working on old Chevys for forever. If I do end up going through him, what is a list of items he should do or I should ask him to do? To help this trans be the best it can for my daily driving.

[WIDESIDE72]

Originally Posted by Jahloha

WestSide:

I plan on pulling the engine and trans next week...so options are open.

I made a contact with bud who's grandpa does trans rebuilds. The guy is nearly 70 and been working on old Chevys for forever. If I do end up going through him, what is a list of items he should do or I should ask him to do? To help this trans be the best it can for my daily driving.

What type of driving do you plan for the truck? If a lot of highway driving is planned, now is the time to go with an overdrive. I have swapped a 700r4 into three 71/72 trucks. I also heled my brother install a 200 4r into a 72 in the early 90's. i really liked the dact that it dodnt have the low first fear like the 700r4. I also have a 200 4r in a 79 malibu. It lived behind a 500hp 383 til thecam went bad and ruined the engine. Its still in the car behind a milder 355. The cost of putting one in now is not that much higher than rebuilding your existing trans, other than the core needed. Your friends grand dad could surely help out there. Its really a straight forward swap. Youll need to slide the trans crossmember back and drill new holes. The driveshaft out of da mid 80's truck originally equipped with a 700r4 will bolt in. (Use one out of a swb if yours is a swb and likewise for lwb.) the tv cable bracket is available from several sources depending on what carb you run. the lower rpms will benefit you both with better mileage and extended engine life.

[Jahloha]

Originally Posted by WIDESIDE72

What type of driving do you plan for the truck? If a lot of highway driving is planned, now is the time to go with an overdrive. I have swapped a 700r4 into three 71/72 trucks. I also heled my brother install a 200 4r into a 72 in the early 90's. i really liked the dact that it dodnt have the low first fear like the 700r4. I also have a 200 4r in a 79 malibu. It lived behind a 500hp 383 til thecam went bad and ruined the engine. Its still in the car behind a milder 355. The cost of putting one in now is not that much higher than rebuilding your existing trans, other than the core needed. Your friends grand dad could surely help out there. Its really a straight forward swap. Youll need to slide the trans crossmember back and drill new holes. The driveshaft out of da mid 80's truck originally equipped with a 700r4 will bolt in. (Use one out of a swb if yours is a swb and likewise for lwb.) the tv cable bracket is available from several sources depending on what carb you run. the lower rpms will benefit you both with better mileage and extended engine life.

WestSide:

It will be a DD with a daily highway round trip of 20 miles, average about 320 miles every 15 days or so. The occasional 700 mile trip to SoCal and the occasional tow of a trailer.

Should I look for a rebuilt? Just looked online in my area and saw rebuilts for 600 and another from an early 90s burb for 75.

I am new to all this, but am trying to steepen my learning curve. So thanks for the help and input.

[Lattimer]

swapping a trans is actually pretty easy. If you can take yours out and put it back, you can do the swap just as easy with some reading on this board.

[Jahloha]

FYI...I will also be running larger tires, probably 285/70/17 at the most. Will this tire size affect my choice of trans?

[Keith Seymore]

Go by the build sheet; that's the document that drives the initial build. The SPID sheet reports what happened after the fact.

Also - you should be aware that there are "Merchandised Options" and "Non Merchandised Options".

Merchandised Options are what the consumer/dealer selects when he says "I want an automatic", or "I want a manual trans". That selects the "family" of options, so to speak.

The Non-Merchandised option selects the specific transmission within that family based on all the other design considerations (model/series, engine, rear axle, GVW, etc).

K

[Jahloha]

Originally Posted by Keith Seymore

Go by the build sheet; that's the document that drives the initial build. The SPID sheet reports what happened after the fact.

Also - you should be aware that there are "Merchandised Options" and "Non Merchandised Options".

Merchandised Options are what the consumer/dealer selects when he says "I want an automatic", or "I want a manual trans". That selects the "family" of options, so to speak.

The Non-Merchandised option selects the specific transmission within that family based on all the other design considerations (model/series, engine, rear axle, GVW, etc).

K

K:

Awesome insight on the merchandised and non-merchandised items. I never knew that, but it makes a lot of sense.