I've seen a number of threads/posts asking about installing a TH400 into a C5, so I thought I'd share how it's done.

My car is a track only car. While it could certainly be driven on the street, not having an OD would suck.

There are two options for rear diffs, the C5 and the C6. I've done both, and I highly recommend using the base C6 diff from a manual trans car, as you can install any of the various gearsets available.

In either case, these is quite a bit of fabrication needed.

You have to remove the front bell of the 4L60 because you'll need that to bolt to the TT.
You have to cut the bell off the 400. Buy or make an adapter plate to go between the 400 and the stock 4L60 bell.

Take the tail shaft housing off the TH400.

Also, the 400 comes with a 32 spline output shaft. You need to replace that with a 27 spline shaft from a TH375.

You will use a standard TH400 converter of your choice, but you'll need the spacers between the converter drive plate and the feet of the converter.

There are several adapter plates needed as well. These can be sourced from RPM Transmission (I think) or sourced locally from a quality CNC capable machine shop.

You'll need to cut out part of the trans tunnel and reconfigure it to fit the bell of the trans, as this conversion moves the transmission forward a few inches depending on which diff you use.
If using the C5 diff, you'll need to have your torque tube shortened 3.5". If using a C6 diff, you'll need to shorten the torque tube 2".
Doing this will place the diff mounts in the correct location to use stock style mounts. I highly recommend the Hinson Diff mounts.

Another reason I recommend using a C6 diff is you'll have more room for routing the exhaust piping because the transmission is farther back due to the modified torque tube.

You will need to reconfigure how the E brake handle/cable works - if you intend to keep it. I removed it because I don't need it.
You will have to install an aftermarket shifter. There are many available, but you'll need one with a rear exiting cable.

Pictures to come...

 

 

 

 

Very nice work!! What were those welded areas on the tail shaft area of the transmission??

 

Good eye sir!

So a stock tail end of a TH400 has ribs to the flange area that the tail housing bolts to.

This has gussets welded into these ribs to strengthen the tail of the trans case, as it bolts directly to the diff that wants to twist the sucker off on every launch.

 

Nice work Pete....as always !!

At your power level....the th400 is the best option.

Your badass ride is gunna fly this year, can't wait to see the numbers it will put up...

 

Nice work Pete! Are you going to make to the track now

 

Thanks, but the questions is, Are you???

 

Great info Pete.

Can you do mine while I do yard work this spring ?

 

Very nice work you did. I did not know a TH400 could be used with the C5 and learned something new today.

 

I edited my original post as I forgot to mention a few things.

 

That is some serious engineering and fabrication! Props to you!!

 

Thanks! I can't take credit for all of the fabrication, as the original set up I have came from Yank Converter. They no longer make this conversion.

I do have access to a machine shop that can make all the adapter plates though. In fact, I used them to make the plate for my C6 diff when I switched from the C5 diff.

 

Question for you:

Even though the C6 Z06 differential is much stronger (larger ring gear, etc) than the regular differential, is your choice to use the regular C6 diff due to the limited availability of different ratios for the C6 Z06? AFAIK, the only ratio available for the C6 Z06 is the 3.42:1 ratio.

 

That's correct. As an NA car, I want as much gear as I can get. I went with 4.10s.

A power adder car would likely set up differently.

 

so how much would you say you have into parts and machining for this setup? a lot more work involved on adapters and bell housing than i would have guessed.

 

Most of what I have came as a package as I got it in trade from another guy.

That said, I'd think that all the adapters/plates could be had for about $1500. Then the trans tail shaft is under $100, plus whatever internals you want it built with.

Shortening the torque tube and propshaft is the big question. I have no idea how much a place would charge to do that.

Then getting a C6 diff and cradle stup is probably another $1500 or so.

 

Really would be nice if someone made the adapter plates in a kit. I think that is what really limits a lot of people from taking this on as a diy. Also is the output shaft a factory unit out of a th375? The one on your transmission looks a bit longer.

 

Yeh, It's an OEM TH375 output shaft.