85ss swapping 2004r for a th400

[blackmagic85]

After about 2 transmissions within a month going out (my original and the junkyard one) the trans is 2004r by the way. Ive decided to change to a th 400 since the junkyard is out of 2004r's My question is what all will i have to do in terms of the driveshaft and kickdown? Surely somebody has done this swap any help at all would be extremely appreciated

1985 monte carlo ss 305 l69
2004r trans
3.73 posi rear end

 

[Blake442]

Why not just get the 200-4R rebuilt? It's not that expensive. With all the time and effort you'll have into swapping another junkyard trans into your car that is a complete gamble as to if it will last, you could've just had the proper trans rebuilt with a warranty.

If you do go through with the swap, prepare for your 305 to become even slower, because TH-400's require more effort to spin.

The TH-400 will sit right on your current crossmember, but your driveshaft will have to be shortened 1/2" to 3/4", measure for yourself to be sure. You'll also need to change the slip yoke on the end of the driveshaft for one that fits the TH-400.

You'll need a kickdown switch and wiring also. There is a place to mount it right above the gas pedal where the factory had the a/c cutoff switch in some cars. I got my switch and wiring out of a '72 Riviera. Some cars had them mounted above the pedal, some had them mounted on the throttle linkage under the hood, so be aware when you're looking in the yards.

You'll also need to modify the ends of your transmisson cooler lines to fit the TH-400.

Take it from somebody who also has 3.73's and swapped from a 200-4R to a TH-400... Get your 200-4R rebuilt.

 

[pontiacgp]

the 400 takes up to 40 hp to run it...

 

[78 Green Lemans]

If you really want a 3spd i would just swap your cross member and put in a th350. You wont need to change your drive shaft that way and about the only mod needed woul be bend the cooler lines a little. Your car should already have the mounting point for the th350 crossmember so it basically a bolt in, requires alot less power to run and will still take quite a bit of abuse . It also has a lower 1st and second gear ratio.
The th400 usually came stock with a very low stall converter as well, not usually a good thing.

 

[blackmagic85]

Appreciate the help guys. Just got the trans today it looks real clean guy said he was going to install it in his daughters car but went with something else instead. Said it was rebuilt 15yrs ago and has just been sitting and from the outside it looks legitimate. Going to install it tomorrow already have the 32spline yoke but the guy said something about needing some kind of adapting u joints if my driveshaft is metric and the yoke is standard its a year 69 model trans by the way so im pretty sure ill have to go standard with the u joint for the yoke and have the part that connects to my driveshaft as metric just not entirely sure which size. Ill let everyone know how it goes and also will surely be bitching about the dogish acceleration but hey i just need to go from point a to b for a month or two so this will do while i rebuild the 200 4r (in the army and always have to go places at random so needed a trans stat) anyways thanks again

 

[blackmagic85]

So worked on the car again today. No good news to come of that. The guys at oreillys didnt know what i was talking about when i said i needed a 1350/1344 conversion u-joint, the torque converter i got for the transmission has the bolt hole spaced to far apart to fit my flexplate. The rear seal i got for the transmission is actually to small. Two of the trans pan bolts stripped when i went to remove them and here i sit.

 

[dogsht]

You won't be bitching about the power lossor slight et drop as much as the rpms with the 3.73s on the highway and the extra fuel she will consume. If in time budget allows and or for other readers http://www.extremeautomatics.com has 200.4Rs warranted good to 10.9 ET with no exchange required on special for $1,200.

Try it now.

 

[pontiacgp]

dog..that link isn't working...

 

[dogsht]

OK try it now.