Hello all,

I need some help, I have a 72 Vista with a 350 and I am swapping to a built 455. I would like to put a 200R4 in it when I do the swap and I already have the tranny. Question is, the 200R4 is 28 1/4 in long and the 375-THM is like 35 or so inches. I assume I may need to move the cross member or at the least get the drive shaft lengthened. Has anyone done this swap that can assist?

thanks!

 

The reason the original transmission is so long is that it keeps the driveshaft short enough that vibration is not a problem.

You may need a larger diameter shaft to solve the problem--and there is not enough room for a much of a shaft size increase..

Before you get very far with this project, you must evaluate your driveshaft options.

You'll need to find the minimum clearance around your original shaft. To do that:

• measure the distance between the axle bump-stop and frame
• disconnect the driveshaft at the rear axle
• raise the rear of the driveshaft by the measured amount

If the closest spot is on top, you'll need to calculate how much closer the clearance will be with the shorter transmission.

Call one of the national driveshaft shops and discuss your options. I used Denny's. They will ask you current shaft diameter, horsepower, driveshaft rpm, and new driveshaft length.

Calculate driveshaft rpm based on tire diameter, rear axle ratio, and top speed.

Good luck and keep us posted.

 

Vistas use the long tail version of the TH375/TH400. The trans mount doesn't change, just the length of the tailhousing. The 200-4R will use the same crossmember location. Unfortunately, the 200-4R is the same overall length as a short tail TH350, so even shorter than a short tail TH400. Make sure your driveshaft is very well balanced.