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Discussion Starter #1
I have a '68 GTO
Removing a Turbo 400 to install a 2004r.
From what I've read the 2004r is about 11/16" shorten than 400, the easiest fix is to get a longer slip yoke.
Does any one know the slip yoke part number?
 

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I believe the slip yoke is the same as the TH-400? Try it to confirm. If so, measure your length and then get on line and look for one that length you want. Should be able to find what you need. I know there are different lengths for the TKO-500/600.

I don't know if this is any concern, but looking at the slip yokes for my TKO-600, they have the long & short ones, but in my thinking, the longer it sticks out the back of the transmission, the more up/down leverage that will be put on the back of the transmission as the suspension travels up and down. It could possibly damage the tailshaft, seal, bearings, etc. or prematurely wear out parts. No expert on this, but thinking about it will have me purchasing the shorter slip yoke and correct length driveshaft. More money spent on a new driveshaft, but maybe not in the long run.
 

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Discussion Starter #3
Thanks PJ, from reading the Turbo 400 SY is 32 spline and larger diameter, while the Turbo 350, 2004r, 700r4, long shaft Turbo 400 are 27 spline same diameter. From a 2009 Hot Rod Article the turbo driveshaft assembly is about 11/16"shorter, apparently the Turbo 350 drive shaft assembly is the correct length.
 

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John let me know your experience with that swap, if my t 400 wacks out I might head down same road thanks
 

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Thanks PJ, from reading the Turbo 400 SY is 32 spline and larger diameter, while the Turbo 350, 2004r, 700r4, long shaft Turbo 400 are 27 spline same diameter. From a 2009 Hot Rod Article the turbo driveshaft assembly is about 11/16"shorter, apparently the Turbo 350 drive shaft assembly is the correct length.
Here is a chart from off the web showing trans dimensions. Looks like the difference between TH-400 and 2004R is 1/2" being the TH-400 is longer. So technically, you need a driveshaft 1/2" longer. But look at the TH350 which came in the Lemans. The driveshaft is almost the same, 1/8" of a difference shorter - which is nothing. Automatic Trans Dimensions

The TH-400 is a bigger slip yoke with 32 splines versus 27 for the 2004R. The TH-350 appears to use the 27 spline slip yoke as well. Here are the dimensions for one: Powerglide/TH350 N3R Series U-Joint/Slip Yoke

So it would seem to me that a TH-350 driveshaft and slip yoke from a Lemans (possibly a Chevelle?) would be the answer.
 

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Discussion Starter #8
Everything I read agrees with your summary. I removed my driveshaft an measured it last night, driveshaft center to center is 55 3/8" which seems to be correct for my Turbo 400.
I measured the slip yoke center to end, 5 3/8" add 5/8", i'm going with a 6" 3R/1344 27 spline slip yoke.
I found a 6 1/8" at a place called Fort Wayne Cutch & Driveline or I could order a longer one and cut it.
 

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Everything I read agrees with your summary. I removed my driveshaft an measured it last night, driveshaft center to center is 55 3/8" which seems to be correct for my Turbo 400.
I measured the slip yoke center to end, 5 3/8" add 5/8", i'm going with a 6" 3R/1344 27 spline slip yoke.
I found a 6 1/8" at a place called Fort Wayne Cutch & Driveline or I could order a longer one and cut it.
I would think the 6" would work. The important measurement is the distance from the back of the tailshaft to the end of the machined end of the slip yoke. You do not want the slip yoke to bottom out. With the car on its wheels and weight on the suspension, you want 3/4" -1" of space. So insert the slip yoke and bottom it out, then pull it back the 3/4" - 1" and that should be where you want it.
 

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Discussion Starter #10
Thanks, I'll report back. I just can't believe the thousands of time this mod has been completed no one know whats needed.
 

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Thanks, I'll report back. I just can't believe the thousands of time this mod has been completed no one know whats needed.
Actually they do....on the PY forum. You'll have to use the search function buy plenty of guys there have done it and posted up threads with the whole operation and parts. Here's a few (first one deals with 2004R driveshaft stuff in the conversion.


There is also a thread here although it's a '67 GTO:

There is also good general info on BowTie overdrives which guys on PY have used:
Especially info on the all important TV cable setup.

Personally if I ever go overdrive and dump my TH400, I'll go 4L80E
These threads show installation and list parts.

Best of luck with your O/D conversion(y)
 

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Discussion Starter #12
I've seen all of those articles, most mention when swapping from Turbo 400 to 200-4r a longer drive shaft assembly is required and that a Turbo 350 driveshaft assembly is the correct length,it's obviously less expensive to get a longer yoke since the Turbo 400 doesn't fit the 200-4r, most state in one way or another needs to be 1/2" to 3/4" longer. Not one article or person states an exact measurement for the new yoke or mentions a part number. I could have missed it. Yes i could have purchased a used drive shaft from a 68-72 Lemans but they cost more than the slip yoke.I think I stumbled across the necessary yoke but don't want to put it in writing until i know its the correct part.
 

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Discussion Starter #13
Transmission swap has been side lined by this Covid thing and building a deck. I was able to find a driveshaft form a 2003 Silverado that seems to be correct or a little long, i can cut the slip yoke.
Now on to the wiring and TV cable.
 

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Discussion Starter #16
As stated earlier I found an entire driveshaft out of a 2003 silverado, the yoke fits in the transmission and the rear u-joint is the adapter u-joint need to go from the silverado yoke to the TH400 driveshaft.
 

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Discussion Starter #18 (Edited)
You'll also need to drill your flex plate for new converter bolt holes, the TH400 is about 10" hole to hole where the 2004r converter is about 9.5" hole to hole.
I'm going to make a disc that has an outside diameter of the crank where the flex plate aligns (the hole in the center of the flex plate) and a hole diameter of the boss on my converter that will align everything centered. Then I'll mark the converter hole locations using a transfer punch or transfer screws.
 

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Discussion Starter #19
I ordered a Summit Universal TV cable, can be cut to length, a trans cooler, dipstick.
As an FYI my 2004r came with a TSI 3000-3400 stall converter (hope its not too much) the converter hits the flex plate bolt heads, I need to put 0.100" washers between the converter mounts and flex plate. I asked TSI how come interference? TSI said converters are made for Chev or BOP and I must have a chev. the only way to know is shipping box is labeled BOP or Chev. you cant make this stuff up.
 
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