milo30

I never really gave this much thought as I thought the tunnel would be the same on either but I saw another thread and not wanting to hijack it I started this one.

I am building a BB for my 78. I have a 4sp in it right now but am wanting to swap it out to an automatic. I'm tired of shifting and my wife wants to drive it too and she is too short to work the clutch all the way. I planned on using a th400 or 700r4 in it and thought it was going to be pretty straight forward. Now it seems that the tunnel may have to be altered for a 400 to fit because of the modulator. I wanted the 400 over the 350 mainly because of the strength of the unit. How much is involved in working the tunnel to make one fit. Are there any other transmission options that I can look at that will fit in the tunnel?

Gordonm

Put in the 4 speed automatic. you will be much happier. Either the 700R4 or the 200R4. The turbo 400 is a dinosaur and takes a lot of HP to drive it. The 4 speed autos will fit.

jnb5101

there is a relatively small hump in the side of tunnel on the pass side about where the radio is in auto cars. it would be an easy fix to cut the tunnel to clear the trans,and then repair the glass. don't let this small problem interfere with your change. i hate to say it, but that is probably going to be one of the easier "humps" in the road.

SHAKERATTLEROLL

The Turbo 400 is a good unit as it is very strong. As well as suggested the 700R4 or the 200R4 if built right. But it also depends on what gear you now have in the differential and what kind of power your big block is going to be putting out. Also if the car is just going to be used for messing about around town or more highway use.

S&S_ShovelHead

Does the weld in crossmember need to be modified to use a t400 or 2004r/700r4?

Father N Son

sent you a message.

c69vete

The crossmember does not have to be cut for the 700R4 but it will make the install easier. There have been several threads here about how the crossmember has been madified to be a bolt in.
A search for 700R4 will pull up hours of reading, details and pictures. You will like the 4 speed O/D swap.

my72vette454

I did a 4l80e swap in place of my 4 speed several years ago. I made my cross member removable. The only modification I had to do to the tunnel was cut a hole on the driver side for the electric plug to go into the trans, I had to find a place for the wiring to enter the interior anyway so I brought the wiring in there. Other than that the trans fit in the tunnel, its tight but it fit. Mine is an early 90's with the cooler lines up front. I am running 3.08 gears and with the overdrive it's sweet to run down the freeway with.