# TH400 to 200R4 conversion Question



## CTCarGuy (Nov 17, 2009)

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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## Thumpin455 (Feb 17, 2010)

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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## Rukee (Feb 8, 2007)

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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## 66tempestGT (Nov 28, 2009)

im pretty sure the 200 was used in the grand national. i think it will be fine.


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## Eric Animal (Oct 28, 2007)

I've been advised to use a L480e in my build....basically a TH400 with OD. Something about "programability" and "excessive HP/TQ arty: E


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## 66tempestGT (Nov 28, 2009)

Eric Animal said:


> I've been advised to use a L480e in my build....basically a TH400 with OD. Something about "programability" and "excessive HP/TQ arty: E


you think? :rofl::rofl:


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## geeteeohguy (Feb 2, 2008)

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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## Thumpin455 (Feb 17, 2010)

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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## Rukee (Feb 8, 2007)

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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## Thumpin455 (Feb 17, 2010)

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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## Rukee (Feb 8, 2007)

Thumpin455 said:


> But hey, what would I know?


Being a shop owner for more then 19 years, I'm in the same boat. :cheers


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## ppurfield001 (Jan 21, 2008)

Rukee said:


> 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.




I'm going to hijack this thread, so I apologize in advance. I want to be able to cruise in the teens on the highway and I'm looking to swap out my 4-speed manual Muncie for a new transmission with overdrive (Richmond five-speed has been suggested). Currently running with a ten-bolt rear with 3:55:1 gears and a pretty stock 400 CID with 335 horse. Any other suggestions to achieve my goal? Thanks.


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## geeteeohguy (Feb 2, 2008)

Gear Vendors makes a bolt-on overdrive for the Munice. Also, ther's a company that makes gearsets for muncie trannies that gives them an overdrive. The shift pattern gets changed, and you still have only 4 gears, but one of them is OD. Both of these would require no floorpan butchering. I've had great results in 4 speed GTO's with a 3.23 gear. With the amount of torque a Pontiac makes, you won't notice the difference off the line from the 3:55's, but the freeway cruise is much better..about 3k at 73-74 mph. Doug Nash also had a 5 speed, but I think mods are needed to the pan, as well.


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## Eric Animal (Oct 28, 2007)

ppurfield001 said:


> I'm going to hijack this thread, so I apologize in advance. I want to be able to cruise in the teens on the highway and I'm looking to swap out my 4-speed manual Muncie for a new transmission with overdrive (Richmond five-speed has been suggested). Currently running with a ten-bolt rear with 3:55:1 gears and a pretty stock 400 CID with 335 horse. Any other suggestions to achieve my goal? Thanks.


Paul, go toMedatronics Corporation's 5 Speed Home page!speak to Paul he has been building standard transmissions since we were kids. Yes over 30 years. tell him you are a friend of mine and you need a solid 5 speed for a GTO. He will steer you in the exact right direction and or supply what you need. He has also written and published a book. Tell him Eric Aull sent you....this goes for everyone else also...GOOD STUFF!!!:cheers


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## ppurfield001 (Jan 21, 2008)

Eric Animal said:


> Paul, go toMedatronics Corporation's 5 Speed Home page!speak to Paul he has been building standard transmissions since we were kids. Yes over 30 years. tell him you are a friend of mine and you need a solid 5 speed for a GTO. He will steer you in the exact right direction and or supply what you need. He has also written and published a book. Tell him Eric Aull sent you....this goes for everyone else also...GOOD STUFF!!!:cheers



I will try calling him today. Thanks for the lead. What type of transmission are you installing in your new goat, which sounds unbelievable, by the way? Regards.:cheers


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## Too Many Projects (Nov 15, 2008)

CTCarGuy said:


> 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.


If you are getting the trans from a reputable builder, don't they have a yoke to purchase with it for the conversion ? Maybe Thumpin' 455 can come up with a GM part number or specific application yoke that he has used in the past for you to get. If not, I would bolt the trans in place and measure from the center of the u-joint to center of the yoke travel in the trans. If you can't get the original driveshaft to work with those dim's, I would consider a new shaft and leave the original in the corner. The original shaft can be cut, shortened and rebalanced by a reputable shop with the proper equipment to do that, but it's never going back behind a TH 400 then....

I seriously considered a 200 for my 67 Camaro and wouldn't hesitate to use one that is built by a reputable aftermarket builder to handle 400 lbs. ft. of torque, but again, it HAS to be a high quality build to last. I'm a clutch in a muscle car guy and will, instead, convert my PG to a manual in time. For you, the overdrive will be sweet in a street cruiser on the highway...:cool


Uh, Eric.......what happened to the manual trans idea ??? If you put a slushbox in that car, I'm gonna sneak up there and swap in a 6 speed myself. That combination just SCREAMS for a 6 speed and 3.90's......:willy:


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## Eric Animal (Oct 28, 2007)

ppurfield001 said:


> I will try calling him today. Thanks for the lead. What type of transmission are you installing in your new goat, which sounds unbelievable, by the way? Regards.:cheers


I am going to use a 4 speed automatic....probably a L480e the electronic stuff scares me. I've been told that you can really tune the shift points, and firmness of shifts very easily. I think it is basically the same tranny that is in a Chevy Tahoe or Silverado 1500. Gotta look into it further. "All those little chunks of aluminum and pretty gears, springs,balls and servos sprayed on the pavement" sounds like an expensive improper choice to me....gotta get it right. Eric:willy:


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## injn37 (Nov 16, 2008)

I put a Tremac TKO 5 behind my 455 in the 65. Got it from Keisler Engineering. Fit pretty good with the stock floor. Just had to open up the floor a little in the front ( a 1" x 4" strip) and a 2" x 2" area on the pass side back. I just modified the porch for a slick fit. Cross member moved back to where the front holes in the bracket located into the back holes in the frame and drilled new back holes. Shifter locates correctly into the console. Done.
Haven't driven it yet as not done, but a friend has one in his 67 Chevelle, and and he swears by it, that it has changed his ride for the better by leaps and bounds, what ever a leap or a bound is!

If you need, I can try and take some pictures if you want

rich :cheers


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## Rukee (Feb 8, 2007)

injn37 said:


> I put a Tremac TKO 5 behind my 455 in the 65. Got it from Keisler Engineering. Fit pretty good with the stock floor. Just had to open up the floor a little in the front ( a 1" x 4" strip) and a 2" x 2" area on the pass side back. I just modified the porch for a slick fit. Cross member moved back to where the front holes in the bracket located into the back holes in the frame and drilled new back holes. Shifter locates correctly into the console. Done.
> Haven't driven it yet as not done, but a friend has one in his 67 Chevelle, and and he swears by it, that it has changed his ride for the better by leaps and bounds, what ever a leap or a bound is!
> 
> If you need, I can try and take some pictures if you want
> ...


I'd love to see some pictures, and to have a 5 speed in mine! :cheers


Were you able to keep the HURST shifter?


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## Too Many Projects (Nov 15, 2008)

Rukee said:


> Were you able to keep the HURST shifter?


Hurst makes shifters for them but, obviously, the 4 speed shifter won't convert to a 5 speed...
RICHMOND 5-SPEED SHIFTER


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## injn37 (Nov 16, 2008)

I'll try and get some pict's tonight when I am working on it. As for the shifter, it came with a round shaft shifter just like the Hurst, bit it sais 'TKO' on the shaft. I think the bolt pattern is the same though, I will check.

rich


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