TH400 to 200R4 conversion Question - Pontiac GTO Forum
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post #1 of 22 (permalink) Old 03-08-2010, 09:05 AM Thread Starter
 
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TH400 to 200R4 conversion Question

I am changing out my th400 in a 71 GTo for a built-up 200R4 so I have an overdrive for the Hot Rod Power Tour in June. I already have the transmission but there is a question on transmission yoke and drive shaft. The TH400 is 1" longer than the 200R4 and uses a 31 spline. I want to retain the original drive shaft and just replace the yoke (and u joints if needed)with a 27 spline yoke. The question is how long the shaft on the new yoke should be. I have not removed the original yoke to measure it yet. New yokes have a 3" or 6" shaft. I don't want to put in a too long or too short shaft! Can the shaft be cut and if so, what is the best method? Thanks.
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post #2 of 22 (permalink) Old 03-08-2010, 01:52 PM
 
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You need the yoke that will fit far enough into the transmission to fully seat on the rear bushing, if you dont it will leak and the tail shaft will have no support. On my 70 the 2004R and the Th400s are nearly the same length, so I just swap yokes, is your Th400 a short shaft or is it out of something other than an A or F body?
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post #3 of 22 (permalink) Old 03-08-2010, 03:53 PM
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The turbo 400 is ten times the tranny, I might have been inclined to swap out the rear gear before putting in that metric tranny.
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post #4 of 22 (permalink) Old 03-08-2010, 11:44 PM
 
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im pretty sure the 200 was used in the grand national. i think it will be fine.


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post #5 of 22 (permalink) Old 03-09-2010, 07:24 AM
 
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I've been advised to use a L480e in my build....basically a TH400 with OD. Something about "programability" and "excessive HP/TQ E
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post #6 of 22 (permalink) Old 03-09-2010, 09:05 AM
 
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Quote:
Originally Posted by Eric Animal View Post
I've been advised to use a L480e in my build....basically a TH400 with OD. Something about "programability" and "excessive HP/TQ E
you think?


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post #7 of 22 (permalink) Old 03-09-2010, 09:14 AM
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I'm with Rukee on this one. While the 200 has and does work, it is nowhere near the strength of a 400. I put a taller rear gear in my '67, and love it. No mods, and the car's a highway star....(just like the song)...............
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post #8 of 22 (permalink) Old 03-09-2010, 09:39 AM
 
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Is he drag racing it and asking it to take WOT rips through the gears multiple times when its driven, or is it more of a cruiser? No doubt the Th400 is stronger, but unless you are beating on it the 2004R lives behind 455s pretty well. I have built both of them and if I have lots of power I like to use, it gets a th400, if it makes longer trips on the highway often, its gets an overdrive. The 65 is getting the 2004R, but the Formula has a th400, but then again when you have around 700hp/700tq a th400 is the least you can do. I've broken just as many Th400s as 2004Rs behind my engines, its all how it is used.
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post #9 of 22 (permalink) Old 03-09-2010, 10:45 AM
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Even if he's not running WOT down the track every weekend, you don't want the tranny to fry the first time you do go WOT and let it rip through the gears.
They used the 200r4 behind the 231 buick engines and they would take them out.
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post #10 of 22 (permalink) Old 03-09-2010, 11:58 AM
 
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There has been one in my 70 for the last 7 years, it has a 455 that pushed a 4100lb car with 2.93 gears through the 1/4 in 13.50 and the 2004R was in it at the time. That takes quite a bit of grunt to achieve that with a stock stall. It was a stock one from a Cadillac that I replaced the seals and clutch packs in. Nothing special done to it. I did get it to slip a bit with the ethanol for fuel, it makes quite a bit more bottom end and mid range torque. Would I run one behind a 600hp engine? No, not really. Behind a 450hp engine? Sure no problem especially if it doesnt have highway gears. With some upgrades they will handle racing even in heavy cars, but there is no need if you just have a cruiser.

They are a little bit stronger than breaking the first time you go WOT. But hey, what would I know? I only build transmissions, engines, rear ends, and entire cars.. right? ASE master certs dont really mean much in the real world. You can hate on them though, I dont mind at all. No I am not trying to be mean about it, just sayin.

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