So yesterday my 700r4 failed on me and im looking at a rebuild now.(700 wouldnt shift past 1st)

I talked to one of the guys that helped set up my engine, and he recommended me a turbo 350 transmission, but he said the driveshaft would have to be cut (im guessing id have to get it balanced too?)and hed rebuild the turbo 350 with a shiftkit and bushing kit for 750 installed.

but what exactly am i getting into with this swap? and does that price sound reasonable?

Ive been doing some research, so far what i have is a bunch of cons.

Cons
Poor gas milage
Requires custom fit
Custom driveshaft
Custom crossmember
will loose my 2500 stall that was on my 700r4
Speedometer wont work? I have an 89 Firebird im not exactly sure if my speedometer is electronic or mechanical but im leaning towards electronic?


Pros?

What are the pros of going through with this swap?

Is it worth getting this done? What gains will i see from doing this swap if any?

My motor is completely rebuilt (Vortec 355) but i never got to the transmission so im guessing thats why it went out on me. My car is a daily driver but i dont care much if it wastes more gas...otherwise id buy me a prius.

I need all the advice i can get so please post a reply and help me make a decision.

I have a th350 installed
I never had to change the drive shaft
I just bought the b and m kit from jegs (or summit )
that lets you install the torque arm


The main difference between the 2 transmissions is the overdrive.
your rear end gear becomes extremely important if your going to use it on the highway with a th350

If it is a street car I would run 273 gears in the rear with a th350 and save money
If your running something like 411 gears you want the 700r4 or you hate your car on the highway

In town or at an autocross or drag strip you won't see a big difference between them.

Really you didnt have to switch the driveshaft? i was under the impression that was a must.

Do you have a link to the kit?

I have stock gears right now 2.73s i believe, but i did plan on switching over to 3.73s should i forget about doing that now? lol

http://www.summitracing.com/parts/BMM-30299/

I would stay with 273 with a th350
I have 340 something in mine and I don't like it on the highway

I used the stock driveshaft in my 82 z28 and it works fine

damn i think the driveshafts change since mine is an 89, summit says it requires an 82 driveshaft, guess u got lucky.

Thanks for the link man.

an old iron drive shaft is a cheap thing in a junkyard
cheaper than making one

If your planning on ever going to different gears I would go with the overdrive now.

Which driveshaft you can use depends on whether you have a long or a short tail TH350.

i have had both th350 and 700r4 in my '82 over the
years,th350 had advantages and disadvantages Vs the
700r4;
th350(+),
-nice ratio spread
-lighter than 700r4
-speed parts reddily avalible
-near bolt in to an '82(my tranny was from an '80z28)
(-)s,
-no OD
-older '60s design generates a lot of" trash"in the pan
-fixed displacement pump not as efficient at "cruize"
conditions,generates more heat
swapped in the th350 in 1993,took it out 2yrs later
when i decided to reactivate the A/C and didn't want
the compressor running at 3500+rpm at highway
cruise speed-put in a 700r4 from an'85 caprice,did
put in a shift kit
700r4(+)s,
-4 gears
-almost a bolt in using '83-later parts
-more modern better wearing design
-varible displacement pump more efficient,tranny runs
cooler at cruise
700r4(-)s,
-3.06 1st gear a bit deep for my 3.42 axle and torque
heavy engine(though i like this under certain conditions
)
-big 1st to 2nd ratio jump.
-clutz shifting every one in a while.
did not really notice a big change in fuel economy with
the OD but it did get my engine (and AC compressor)
speeds down
The '85 caprice 700r4 has been very reliable and tough
over the last 15+years i have had it in the car,and when
i had it apart last year to muck out after a torque
converter blow up(aftermarket"stall"converter) it was
still in very good shape.
You should try to fix your 700r4 before considering a
swap-might only have a broken governor gear or other
minor problem...

Yeah i wish it was the governor gear, i took it out and the thing was flawless, looked brand new.

How does the high rpm affect the compressor?

This is the transmission thats gonna go in, im assuming its a short tail?
It is much smaller than a 700r4.

Before the transmission goes in is there anything i should make sure is done while the tranny is outside?

What about my speedo am i going to need a converter or something similiar?

i just put a th350 in my 82 and i didnt need anything besides the kit for the torque arm and a new kickdown cable. first drive today!! i thought it drove nice on the highway. my rpms r odd though but i believe its just the gage cause it wasnt loud or anything. all in all it bolted right up no problem. i should say it had the th250 not a 700r4 so ur situation might be different. i should also mention im having trouble with the shifter linkage lining up so i have to be careful and pay attention to what gear im in