I am hoping to install the TH-400 I have into my '67. Could someone measure the length of their driveshaft from say u-joint to u-joint and post for me? I don't have the crossmember yet or trans ready to go in, so I wasn't sure of this dimension. I know it is shorter than the current driveshaft I have for the ST-300. Any help is much appreciated. Thanks.

I am not sure if all FGF's use the same driveshafts from year to year. Here is the information from the 1969 Pontiac service manual for Firebirds:

Turbo 400 (M40) - 49.30"

3 and 4 speed manual, 2 speed automatic, Turbo 350 (M38) and 3 speed HD manual - 49.96"

All driveshafts are 2.75" diameter.

The manual does not show how to measure the length.

Hope this helps.

Tom

There are long and short TH-400's. The driveshaft dimensions for them are drastically different. I've never tried to put a long tailshaft TH-400 in a FGF, but I assume it can be done.

You might need a different (longer?) speedometer cable.

I have always gotten whatever car I'm working on put together (as far as I can, anyway), tried the driveshaft I have, and measured how much it needs to be shortened. (So far, all my driveshafts have been too long.)

Take the driveshaft to a shop, tell them how much you need cut out, and they can do it. You might as well have new u-joints put in it at the same time.

It will also need to be balanced.

Good luck!

Wayne.

I was wondering, are the output splines the same on an ST-300 and a TH-400?

I think they are not. As far as I know, the yoke needs changed to do that swap.

All driveshaft lengths are posted in the AMA specs. Click on the link at the bottom to find the page for your year.

(it doesn't say how to measure there either, but you could use your current shaft as a guide. i think it's from center to center of the ujoint yokes... center of where the ujoint caps go...)

Any good driveshaft shop can get new transmission yokes for you.

Tom

Thanks for the replies. I didn't mention that I was buying a used driveshaft from another member and he has a few that were different lengths. I was just trying to make sure the right one was shipped out. I measured my current one (ST-300) and it was roughly 50" from u-joint center to center. I wanted to keep this driveshaft in tact for later when I can install the 4 speed I have for another car.