700R4 VS 200R4

[Tom Carter]

Hello all, 

I have been thinking about replacing the th400 with an over drive type transmission. Of course with that I plan on changing to 3:55 rear gears. I haven't heard enough research to make any kind of a decision so I was looking for input. The engine is a 350 with about 400 hp.  I have talked a little at different shows and keep hearing different information. Because I have the th400 I was hoping not to modify the dive shaft. I was hoping to keep the th400 and drive shaft I am currently using. Is the 700r4 about the same size and the th400. I have heard the 200r4 is about the same size as the th350. That could be wishful thinking. If modifying the drive shaft is necessary I will probably just find a different one to modify. Is the 200r4 easier to install than the 700r4 or they about the same. Which unit is a better and easier to repair.  I have done nothing to get this going other than ask people there opinion. Also what are the thoughts on the 3:55 gears. I do drive on the high way a lot so I don't want go to crazy. 4 1/2 hours down 81 to get to Carlisle Pa. As always appreciate the help and input.

[Scott S.]

Hi Thomas,

The th400 has a 32 spline output shaft whereas the th350, 200r4, and 700r4 all have 27 splines.... so you'll have to change the transmission end of your driveshaft no matter which one you choose.

The 200r4, which is the one I went with, is pretty much a bolt in, excepting for moving the cross member back. (350 cid/th350) and trimming the balance weight at the transmission end.

The th400 cross member is different and the transmission is a couple inches longer, so you will have to find/build a new driveshaft. I've also read that there's minor clearance issues using the th400.

Personally, I like the 200r4 for the wider gear ratios (0.67 to 1 overdrive and 2.67 to 1 first gear) for highway driving. But if you choose the 200r4, make sure you get it rebuilt with heavy duty internals..... 400 hp is a lot for the original "off the shelf" units where as the th400 could take that kind of hp.

 

As for the rear gears, 3.55 should make a nice street/highway combination.... Montelishi originally had 2.73's, which are really nice on the open road, but a little lagging at the stoplight. I eventually went to the 3.42's. Still a little slow at the light, but I've pulled around 20 mpg on the highway with them.

There are a few threads here that discuss who likes which better, I'm sure more will weigh in eventually.

 Good Luck with your swap, 

Scott.

[Scott S.]

Sorry, I listed clearance issues with the th400, should have been 700r4..... As well as the 700r4 can take more hp. 

 

[ouch]

Curious to know which way you went. I have whole new drive line going in this summer. I bought a 200-4r worked for 700hp (California Performance Transmission). Gear Venders and a th400 though would be very nice too.