trans. swap

I got a 1984 firebird. it has a 700r4 in it now but I want to put in a th350. is there anything I am going to need to change? I have the torque arm bracket but is the driveshaft going to need to be cut or do I need a longer shaft? please help!!

Why do you want to put a TH350 in it??

The belhousings are going to be totally different. The th350 is designed to bolt up to a 90* motor (your 2.8 is a 60* motor).



And welcome to the forums!

first off, the th350 is a stronger tranny. and who the h3ll said it has a v-6 in it. the car has a 305 that is built as much as one can be. thats why I want the stronger tranny.
first off, the th350 is a stronger tranny. and who the h3ll

Ah, brain fart.. Sorry about that. I just saw 700r4, and for some reason thought of the 2.8.

first off, the th350 is a stronger tranny. and who the h3ll said it has a v-6 in it. the car has a 305 that is built as much as one can be. thats why I want the stronger tranny.
first off, the th350 is a stronger tranny. and who the h3ll

Stock the TH350 is stronger, but the 700R4's can be made as strong as any built TH350. That said, I think you might need a different crossmember/trans mount and possibly a modified driveshaft. I'm not real sure because I've never done the swap...never made sense to me. I have a 700R4 in my car living behind a 425+ HP, 420+ ft/lbsTQ 350. Now thw 700R4 is built and built quite stout, but it is the original trans that was in my '85 IROC (just has new guts). It'll smoke em hitting first & second and chirp em hitting 3rd. (even breaks loose at 40 when I nail it)

yo morley. sorry to thread-jack but damn, your car sounds mean.. whats in her?

what came on most 2.8 is the 200r4. without the overdrive I am actually making the car have more take off. the trasn crossmember and mount will be OK, but I just ain't to sure about the drive shaft. your IROC sounds sweet. I have an older 305 that is punched .060 over, has clean burn heads, rough idle lunati cam, headers, intake and carb. it is pushing about 300 hp. is there anyone out there who has done this swap?

700r4 > thm350

He thought you had a v-6 because you said firebird, not T/A. Most people with a v-8 know to say "trans am".

With the OD feature, you can gear the axle to have more off the line. With a 350 trans (3rd = 1.0) your looking at way less top speed if you are gearing it for a launch, compared to the 700r4 (4th = 0.7 "ish").

GM made so many different variations of BOTH of these transmissions, saying one is stronger or better than the other is subject to each ones intended application. Would you rather have a 700r4 out of a corvette, or a TH350 out of a pickup truck.

Unless you have a 700r4 that came out of a camaro/firebird, dont bother because camaro/firebird trans have a specific case built to support a torque arm mount. What are you going to do with the torque arm, hold it in your hand?

sorry i cant offer much help with the swap but I also will tell you that I would also recommend you keep the 700R4. It will be much easier to get the 700R4 to handle the power than it is to make a TH350 work (buying/fabbing a new driveshaft, balancing it, getting correct shifter location, crossmember, etc.).

I cant remember the first gear ratio of the th350 but the 700R4 has one of the lowest first gears of any auto tranny (3.06), which is best for off the line speed.

you also keep the benefit of overdrive.

all you really need to handle ~300-370hp is a transgo shift kit and better servos.

if you need more power handling you'll also want to add a line pressure boost valve, kevlar band, and beefier reaction shell.

switching to a tranny without overdrive is not going to get you a better take off. it's all in the gearing.

yo morley. sorry to thread-jack but damn, your car sounds mean.. whats in her?
Les' see... 350 4 bolt mains, Trickflow heads (pushing 10:1 CR), Lunati Voodoo cam, Accel TPI bigmouth base (port matched), SLP siamesed runners, ported and port matched, Ported & siamesed plenum, 52mm throttlebody (my own overbore & hand made blades along with needle bearings on the shaft), SLP stainless headers & Y pipe, High flow cat, Thrush 3" cat back, LS1 injectors, adjustable regulator, Converted from 870 ECM to 165, my own custom tune, K&N filters..yada, yada, yada and my 700R4 rebuilt using the B&M performance rebuild kit (replaces more parts than an overhaul does).

As stated above the 700R4 just can't be beat for a steep 1st gear, and with the overdrive you can run some pretty steep rear gears too.

Might want to register at thirdgen.org (TGO) and ask them. There are lots of people over there that have done TH350 & TH400 swaps.

hotrod_chevyz, you don't have a clue. the tail shaft on the 700r4 is removable, as long as I have the tail shaft it doesn't matter. as for putting a th350 in it, I have the kit from hurst to hold the torque arm. :disappoin
700r4 > thm350

He thought you had a v-6 because you said firebird, not T/A. Most people with a v-8 know to say "trans am".

With the OD feature, you can gear the axle to have more off the line. With a 350 trans (3rd = 1.0) your looking at way less top speed if you are gearing it for a launch, compared to the 700r4 (4th = 0.7 "ish").

GM made so many different variations of BOTH of these transmissions, saying one is stronger or better than the other is subject to each ones intended application. Would you rather have a 700r4 out of a corvette, or a TH350 out of a pickup truck.

Unless you have a 700r4 that came out of a camaro/firebird, dont bother because camaro/firebird trans have a specific case built to support a torque arm mount. What are you going to do with the torque arm, hold it in your hand?

hotrod_chevyz, you don't have a clue.

This coming from a guy saying a th350 has better take off. All your going to do is headache over getting it installed only to find out it will be slower on launch and top speed, and both can easily handle the likes of a 305 engine.

i looked it up.... the TH350 has a 2.52 first gear which will definitely keep you slower off the line compared to a 3.06 first gear....

...unless you have a very powerful engine (>450hp), very large rear gears (>4.10), have a very high stall converter (>2800rpm), or very skinny/crappy tires... in which case you might want the th350 first gear instead to keep the engine from overpowering your launches, causing wheelspin.

i looked and cant find any info about 700R4 to TH350 swap info for third gens....most people are swapping the other way in different cars (for good reason).

at any rate here is some info i found... http://www.oldengine.org/unfaq/leadfoot/th350in.htm
by the looks of it, i believe you'll need a different crossmember and torque arm mount.

All your going to do is headache over getting it installed only to find out it will be slower on launch and top speed, and both can easily handle the likes of a 305 engine.

hotrod is right about that. slower take off, lower top speed, not the easiest swap.

I have a 1982 T/A setup 350/350 and my biggest regret IS the TH350. Its not slow but it could be much faster with AOD trans. The way mine sits now if i was to put a 1/4 mile oriented rear gear my top speed would be what, 110-120 MPH.

Its better to concern over the pathetic axles third gens have than a weak trans. And even then you have to be pushing +375 HP to have a reason to worry about anything breaking because your engine has some balls .

B&M makes a conversion kit to do this exact swap.

The swap is a simple. Everything should line up pretty much. you need the 350 filler tube and the torque converter. Other thing you will need is a free manifold vac and a long metal line to run to the very back of the transmission. The difference in length is about 1/2 inch. Mine has a 700r4 driveshaft that goes 350 after the front u-joint. No probs. Here is where it ends up.
http://i2.photobucket.com/albums/y18/hotrod_chevyz/1982%20Pontiac%20Trans%20AM/sheetmetalshifterholecover.jpg

It started out as a 4 speed std, then converted it to a th350/v8, and im building up a low mile pontiac 400/400 for it next. If it ever has a SBC again it will be with a 700r4. That way i can gear the axle to something worth having.

rob roy03: Good luck whatever you do with it.