Alright i did a search, couldnt really get a straight answer.

My car is a 1987 Firebird Formula. The original engine has been replaced with a 1970 355 thats built up. The original transmission and torque converter is still in place however, and is on its last leg.

I have 2 transmissions that i could swap in.
1) A built TH350 with some 700R4 internals, that was MADE to work with this engine as a combo. Aparently it shifts into 4th, has a good stall, and will work amazing with the engine. I REALLY WANT TO PUT THIS ONE IN.

2) A 700R4 pulled from a 1993 Astro EXT with a 4.3L. It has some kind of dampner bolted to the tailshaft, that basically makes it a direct bolt in for our torque arm cars. Not my first choice, but its the easiest choice.

However, my car currently has an electronic speed sensor, and electronic speedo. I also bought a 1989 GTA dash cluster, to replace mine, which has the 140mph speedo and 8k rpm tach which i really want to keep. All this is electronic.

SO, if i were to put in the TH350, where would i be able to find a speed sensor that matches my car, rear end, tires, etc, AND is electronic?..... Im sure someone sells them, so many people put in TH350s into the car. Im pretty sure this th350 has a mechanical speed sensor. If not, is there such a thing as a mechanical 140mph speedometer that has the later dash trim?

Any help appreciated.

 

I dont know about you or anyone else, but im going to say #1 is BS...

I say its just a reworked 700R4 or a 200-4R. I dont think its possible at all to convert a TH350 to a 4spd OD...



Calibrating the speedo is 'easy'

Check out the main pages tech articles. One of the writeups should give you all of the calcualtions and part numbers to identify and find the right speedo gears you will need.

 

Well dont worry about the BS part. I have the means to test it, and if something seems fishy or it doesnt shift into 4th, them im getting my money back. However, the 4th gear isnt actually a 4th OD per say like the 700R4, the guy described it as having some modification or addition of a clucth, and toying with the governer to trigger a shift. Sounds possible, im not all that knowing about auto trannies as you can tell, but we'll see.

Secondly, thanks for giving me the link. I havent looked at it yet, but id LIKE to do the conversion from mechanical to electronic AT the transmission rather than at the speedo.

 

Your looking at a th350C (same as i run)

Its basically a regular old th350 with the addition of a lockup torque converter like the 700r4 has.

Its still a 3spd tranny not 4! though the lockup will help slightly with fuel economy.


I would be leary of the tranny if hes asking alot of money for it. Dont let him fool you into thinking he modified the tranny for lockup, its a stock tranny just the way GM delivered it!


But if hes selling it cheap i would jump on it. Stock for stock the 350C is supposed to be slightly stronger than the regular 350 plus the addition of the lockup is better than a kick in the crotch. I would stay away from the 700r4 all together unless you plan on spending some money on it to build it up.

 

No its not a TH350C, it has nothing to do with the lockup. He sold me the car, and it hasnt disappointed me one bit, hes a honest hard working guy, so i have no reason to beleive he's lying. BUT im skeptical for the same reason you are. He said, flat out, the car shifts into 4th at 75mph and still chirps the tires. You can tell just by looking at the converter that its big and has a stall. The tranny is definately built, and the $500 is probably much less than what it cost to rebuild, but i have a hard time beleiving it has a 4th. A lockup will not chirp the tires when engaged.

In any case, im spending $100 to have it dyno-ed later this week, that will tell the story, in the mean time, does someone sell electronic sensor for the TH350?

Edit:
Holy crap, i just noticed youre in yellowknife???? Wow howd u get a thirdgen up there, and more importantly, how do u maintain it?

 

Im sorry, but i still dont think the guy has a 4spd TH350...


What do you mean how did i get a thirdgen up here?? I bought it from a guy that moved up here from BC and drove the car up.

Maintain it? Much like anyone else, regular maintenance with a few extras... lol


Im not sure what your thinking yellowknife is, but its not a little hut in the middle of the arctic next door to santa. Its a fair size little city with tons of cash to be made!

 

You know, i dont beleive its a 4spd either, thats why i want the dyno test. I spoke to the guy, i said either you say in the receipt when i pay up, that it has a 4th shift, OR give me the oppurtunity to have it tested. He said, if "as is" isnt good enough on the receipt then he'll sell it to someone else. He sounded pretty pissed, said, YOU TOLD ME YOU WERE BUYING IT, so i turned away other potential buyers. I said yea i did, and YOU TOLD ME IT HAD A 4th GEAR! So you know how that ended.

As for yellowknife, i didnt mean its a little hut, but obviously its not as easy to maintain an older car up north. When i was in BC/Alberta 3 summers ago, i only saw 1 thirdgen, and i was on the road quite a bit. In any case, i think you know what i mean, obviously you can get parts and stuff just like anyone else, but you gotta be very knowledgeable and willing to work on the car, cuz i doubt theres alot of other ppl in yellowknife that do. If its a booming city though, thats probably changing.