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Discussion Starter #1
I get these bright ideas every once in a while, and my latest one is to possibly install a 700 R4 overdrive trans in my stock '71 GTO presently with a TH400. I'm running a 3.55 posi which I like a lot. Just trying to cut down the rpm's when cruising 50-55 mph. I'm sure others have done this. Are you happy with the results?? Would you do it again?? Much work involved?? Parts needed other then the transmission itself?? Thank you.
 

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A stock 700 R4 won't hold up long to a strong Pontiac, however it's possible to build one that will - for a price of course. Fitting one will almost certainly require modifying the transmission tunnel in the car to get some additional room because all the OD transmissions are larger and/or longer. You're right, folks have done it. I talked to some transmission vendors on the Power Tour in 2013, and they all recommended starting with a 4L80E. That transmission shares the same bones as a TH400 including the 1st three gear ratios, plus a .75:1 overdrive. I'm still running a TH400 in my car, but if I were to go to an OD transmission (and I'd like to "someday") I'd go with a 4L80E.

Bear
 

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I have a 2004R bolted to my basically stock 400
The tranny has a Probuilt kit installed, and is built to manage 500hp.

At 60 mph its turning around 2200rpm
At 80 mph it’s turning around 2800rpm

3:55 rear.

I purchased the car as is, so I can’t give you much more info than that - however I will say that the 2004R is, I have been told, a stronger unit than the 700R4.


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Discussion Starter #4
I have a 2004R bolted to my basically stock 400
The tranny has a Probuilt kit installed, and is built to manage 500hp.

At 60 mph its turning around 2200rpm
At 80 mph it’s turning around 2800rpm

3:55 rear.

I purchased the car as is, so I can’t give you much more info than that - however I will say that the 2004R is, I have been told, a stronger unit than the 700R4.


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Thanks for both responses. I do appreciate your time and effort. My car is a body off frame resto that happened about 8-10 years ago. Still looks great. I have absolutely zero desire to alter the transmission tunnel to accommodate the 700R4 transmission. I'm not going to butcher this car. So soberjoe, I know you bought the car as is, but would you happen to know if the 2004R transmission fit right in without altering any of the body metal/tunnel?? Thank you.
 

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The 200R4 physically should be a direct bolt in with no floor mods. That's why people use them. However, they DO need to be built up to handle the power levels of even a stock Pontiac, and they DO have to have their throttle cable adjustment perfectly set in order to not burn up. As Bear said, the 'best' solution is the bulletproof 4L80E...which is not a cheap unit and may require some small mods to fit.
 

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The 2004R that is in my GTO has a ProBuilt kit in it rated to 550hp

Yes -I am told that it was a direct bolt in. The bell housing matches the pattern on the 400 and the transmission mount holes are located in the same spot - no need to move the cross member.

My understanding is that ProBuilt have shuttered their business, which is unfortunate because their kits appear to be bullet proof. I am not gentle with my Goat, and while she is running a pretty tired, basically stock 400 and likely only throwing around 320hp I run her hard, manually up and down shifting all the time.

I am sure that there are other very reputable transmission builders out there that can set up a 2004R for you.

As always, YMMV


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