th200c to th400 swap

[1985Diablo]

OK I have read everything on this forum re: this swap.

This is going into my 1985 Caballero. SBC 305, 7.5 posi rear (factory)

I already have an "ice man" cross member in the car. The reason for the 400 is that the 200c is tosted, and I got the 400 cheap.

As I understand it all I need to do is shorten the drive shaft by 3/4", hook up the kickdown switch and vacume line, and its in. The mounting location is the same for both.

Did I miss anything?

 

[84GP455]

I'm not sure about the transmission mount but you're probably going to have to change that also. The hardest part is going to be wiring up the kickdown switch, first check your gas pedal bracket and see if there is a square opening with a little screw hole next to it, this is where the switch is mounted. Most of the earlier brackets had this mounting spot for the Th400 kickdown switch i'm not sure about the later years, if not you could get one at the junkyard out of an older "B" body car say 73-77 and it will bolt right in. I had to replace my 84 gas pedal and bracket with an older one from a "B" body it fits perfect. Then you have to run the wires to the fuse block and to the switch itself. Good luck!

 

[Blake442]

Don't forget you need a new crossmember for the TH400.

 

[1985Diablo]

Don't think so, just a different mount. They both mount at 27" so the cross member will be fine.

 

[Blake442]

Are you confusing transmissions?

The THM200 and the TH250/TH350 use the same crossmember.

The 200-4R and TH-400 use the same crossmember.

 

[1985Diablo]

My bad, the cross member needs to be moved back. 200c mounts at 22 1/4.

Now I have conflicting information on the drive shaft. if you have the 8.5 rear you need to shorten it, if you have the 7.5 (and I do) you don't?

 

[RegalBegal]

You have to shorten the shaft 3/4" regardless of which rear you have. Simply put, the TH400 with a short tail is 3/4" longer than a TH200.

Maybe this will help.

 

[1985Diablo]

Thanks for all the help, now to the next question. I have a 1988 T/A roller 305 (1 pc rear seal) in the car. What flexplate do I need to mate the TH400?

 

[84GP455]

Thanks for all the help, now to the next question. I have a 1988 T/A roller 305 (1 pc rear seal) in the car. What flexplate do I need to mate the TH400?

Any Pontiac V8 flexplate should work i believe

 

[1985Diablo]

You could be right, on the other hand, the 88 ta 305 is a chevy engine, so will the flex plate from a th200c work on a TH400?