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Old 04-09-2021, 04:05 PM
66sprint6 66sprint6 is offline
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Default Trans swap

When we got our LeMans in December, we expected to see a TH350 behind the engine. It's not the original engine, and the seller advertised having the 350 behind this 400 motor. So we were under the car a little while ago and took a look at the tranny pan. 14 bolts. Damn. Back to the 2 speed. I've got 2 tranny's in my garage. A TH350 and a 200R4. Do they share the same 1st gear ratio? I'm not concerned about overdrive at this point but do want the optimal gear off the line.

  #2  
Old 04-09-2021, 05:41 PM
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Sirrotica Sirrotica is online now
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2.52, T 350
2.78, 200 4R
3.06, 700r4, same as a 4L60E
2.52, T 400
2.52, 4L80E

5 most commonly used transmission in GM muscle cars. The T 400 and the 4L80E are originally designed to sustain the most torque, without being damaged right from GM engineering.

Your current transmission is a 1.64 first gear, so even going to a T 400 or a T 350 is a huge jump from the 1.64 ST 300. I've done the swap multiple times to a T 400 and it's like driving a different car with the deeper first gear, plus adding a second gear.

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Last edited by Sirrotica; 04-09-2021 at 05:48 PM.
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Old 04-10-2021, 07:30 AM
chrisp chrisp is offline
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Go for the 350T lower 1st. gear & direct bolt in with no changes .

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Old 04-10-2021, 11:58 PM
gtospieg gtospieg is offline
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The 200 has a lower 1st gear(2.78 vs 2.52) and is a bolt in if it's a BOP trans...and it's got OD. The 700's 1st gear(3.06) I feel is too low unless you're running a really high rear gear like 2.56....my thoughts

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Old 04-11-2021, 08:49 AM
Chief of the 60's Chief of the 60's is offline
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Quote:
Originally Posted by Sirrotica View Post
2.52, T 350
2.78, 200 4R
3.06, 700r4, same as a 4L60E
2.52, T 400
2.52, 4L80E

5 most commonly used transmission in GM muscle cars. The T 400 and the 4L80E are originally designed to sustain the most torque, without being damaged right from GM engineering.

Your current transmission is a 1.64 first gear, so even going to a T 400 or a T 350 is a huge jump from the 1.64 ST 300. I've done the swap multiple times to a T 400 and it's like driving a different car with the deeper first gear, plus adding a second gear.
You forgot to mention that the 200 is the weakest tranny of all those you listed.

OP..... Are you saying you bought the car thinking it had a 3 speed and you just realized it was a 2 speed?

  #6  
Old 04-11-2021, 11:25 AM
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Quote:
Originally Posted by Chief of the 60's View Post
You forgot to mention that the 200 is the weakest tranny of all those you listed.

OP..... Are you saying you bought the car thinking it had a 3 speed and you just realized it was a 2 speed?
Nothing 3 grand can't cure. I didn't forget it, I didn't want to be the cause of the thread being shut down, so I list the best option for strength, and the option I have personally swapped many times for the OEM ST 300 2 speed.

There were many B body cars that came with 389, 400, 421, 428 and 455 engines, had a 2.56, or a 2.78 axle, that would smoke the tires as long as you kept your foot in it, with a OEM stock 2.52 low, T 400.

Making a decision to put a 200 trans in without spending a small fortune on the build, to go from a 2.52 ratio to a 2.78 ratio in first gear is going to come down the the use of the car, and the owners wallet.

A T 400 would require a shift kit, possibly an inexpensive torque convertor and shortened drive shaft. Depending upon the year of the car it might need to have two holes drilled in the frame to move the crossmember rearward. I've done the swap easily in a day working on my back, and shortening my own driveshafts, because I can weld.

Back in the day I did the swap for under $100 using the undesirable B body long tailshaft transmissions, that at the time were a dime a dozen. By swapping in a T 350 torque convertor you gain some stall speed on a budget for a street car. You can pound on that T 400 for years with a shift kit and under 450 HP in front of it reliably. The rear axle then becomes the weak link, not the transmission.

The OP needs to be diligent, and do his own research to find what works for him. Reading some swap stories online from sources like Hot Rod magazine is what I'm referring to, asking on this forum isn't unbiased research.

I have laid out the T 400 swap that I have done half a dozen times on my own cars, and customer cars. IMO, the best bang for the buck. OP needs to weigh out what his criteria is, and what his budget is.

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1984 Grand Prix

100% Pontiacs in my driveway!!! What's in your driveway?

If you don't take some of the RACETRACK home with you, Ya got cheated

  #7  
Old 04-11-2021, 11:42 AM
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Definitely use the TH350 for now. Straightforward. Keeps you from going down the rabbit hole until you're ready. If or when you start thinking about running 3.42-3.73 gears, you'll like what the 200-4R offers. With a 3.55, the deeper first acts the car behaves like one with 3.90s, and the OD will act like a 2.4-ish final drive. Not quite as straightforward.

Quote:
Originally Posted by Chief of the 60's View Post
... 200 is the weakest ...
Every. Single. Time.

  #8  
Old 04-12-2021, 01:38 PM
66sprint6 66sprint6 is offline
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Yeah, we’ll probably drop the 350 in.
To answer Chief’s question, yes we did believe that it was a three speed auto, based upon the sellers’s description. No big deal, though. Either way, it wasn’t going to be the permanent transmission. I’ll take this opportunity to either beef up and rebuild the 200r4, or do the wholesale change of switching to a modern overdrive.
The car needs a crapload of other stuff, so that’s why we’re doing the band-aid solution now. This is just to get it driving better than the 2 speed. We’ve got the car running properly and everything, but when we took it around the block the limitations of the 2 speed really showed.

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