Trying to help a friend get his OD installed. He's located a driveshaft from a '71 1800E, but doesn't know if it's the correct smaller diameter - this is going in a 66 122 with smaller diameter diff flange. Anybody know if the 71 is the smaller shaft and flange diameter?

On the other hand, when he bought the OD it came with the later, larger diameter driveshaft - Is it possible to use the short front half (larger diameter flange and shaft) mated with his original smaller diameter rear section?

Danny, see the above picture. Unfortunately the "J" flange I had in the photo was not the correct one. The 71 had a 2" shaft and 3.75" (or more) diameter flange (vs. the 1.75" shaft and 3.5" flange of the stock setup

It can be surprisingly difficult to get the right collection of parts together to shove a J-type into a 122.

The 71 shaft is 2" and the flange is too big to mate up with the 66's stock differential flange. You *can* use the short front half of the 71 driveshaft with your M41J (I'm assuming it's a J as those were stock in the 71's). The length is right, but the rear half is too short and the large diameter flange won't mate up to the diff. He'll need to take the stock 71 rear shaft and have it lengthened and then get a the larger diameter rear differential flange from the donor car. Swapping the flange is not too difficult.

Alternatively, he'll need to get the special small-diameter J-output flange and a short 1.75" front driveshaft. Either way, he's probably in it for at least another $100.00

Does your friend have access to the entire 71E? I'm looking for a whole rear axle..

I'm giving it up to the group in case someone else wants it:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=280388350979&viewitem=&sspagename=STRK%3AMEWAX%3AIT

As best I can tell this is not what we need. The price is right. No rear end, Nathan, just the shaft.

J had found an OD that he was assured had the smaller driveshaft, and yet when it showed up, it came with one of these larger units.

If someone can use it, great. This looks like what we already have.

Yeah, I got two of the large shaft sections, I figured the extra steel would be useful if and when I upgrade to the 2" shaft. JohnMC had issues with high torque engine wrecking the u-joints in his hotrod 544 and eventually upgraded to the 140/1800-sized driveshaft (which solved his problems) and I may do the same.

I'd recommend skipping the guesswork and calling Don Thibault at P1800.com.
You or he could also post a "wanted" here on the BB - that's how I got my short shaft.

I called Don and explained my problem. He came up with exactly the part I needed (small output flange for an M41J) and shipped it to me promptly. The price was decent and service was great. Have your friend call Don, and I'd guess he could come up with the correct flange and short shaft and get the job done quickly.

FYI - I paid $50.00 for each part, but I got the short shaft from Pierre up in Canada and the flange from Don.