Having the same issue, 78 280 and the shaft has never been removed. 2nd owner bought it with 18k miles. Open end is just going to round them off. Replacing the diff with a R200. Need some advice from the Forum... Thanks in advance

Get a good small box end on a nut then turn the driveshaft by sticking a long screwdriver through the u-joint yoke.  The wrench will jam against the body and break the nut loose as you turn the driveshaft.  There are fine details to that description but that's the basic method I used to use.

Having the same issue, 78 280 and the shaft has never been removed. 2nd owner bought it with 18k miles. Open end is just going to round them off. Replacing the diff with a R200. Need some advice from the Forum... Thanks in advance

 

Thought about doing that, just thought there was something I was missing. Truly a poor design. I guess I should be happy there are “D” Heads on the opposite side. I’ll put some kroil on them and give it a shot. Thanks Zed

 

I just went through this over the summer take off the sway bar first it gives you just a little more room. Then you have to slip a wrench up there. Lock the drive shaft so it doesn’t spin and make sure your actually turning the wrench the correct direction since you will be facing the opposite way most likely. I almost gave up multiple times


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That was the direction I was heading. Sway bar was coming out eventually. Rebuilding the rear suspension with the diff swap. There just has to have been a better design. Appreciate the help... 

You could also try applying some heat with a Map gas torch and cooling it quickly with a penetrant  like WD-40, then repeat before using the wrench.

It's been a long time since I last did this job.  Obviously, a box-end wrench is preferable to an open-end.  You might consider buying an appropriate-length, decent-quality box end and then modifying it to fit.  For this job, I think you should be able to get away with grinding the thickness of the box down by at least 50% in thickness.  You can probably also get away with taking at least a millimeter off the outside diameter of the box.  Hopefully, you'll be able to take it down to the point where you can get it to slip over the nut.  You might also need to put a bend or two into the shaft to get the right approach angle.  Try not to put too much heat into the end of the wrench while you're grinding away.  You want to preserve the temper of the steel as much as possible.

I used the approach ZH mentioned, get the car up in the air so you have plenty of room, e brake off, get an open end wrench on the back nut, position the wrench so it will jam as you turn the drive shaft, should be able to get about 1/4 turn, maybe less, but once it breaks free, hopefully it will come of quickly. If not just reposition and repeat.

1 hour ago, Dave WM said:

I used the approach ZH mentioned, get the car up in the air so you have plenty of room, e brake off, get an open end wrench on the back nut, position the wrench so it will jam as you turn the drive shaft, should be able to get about 1/4 turn, maybe less, but once it breaks free, hopefully it will come of quickly. If not just reposition and repeat.

Reverse the above mentioned procedure to tighten the nuts. Works well for the half shafts also.

Went ahead and removed the sway bar. That helped a lot to gain access. Followed the technique you guys suggested and a little help from Kroil and the shaft is out. 42 years of tight, sounded like they were snapping in two when they broke loose. Quick question, The car is on skates while I’ve been working on it. After removing the diff, Can the vehicle be moved around on skates without putting back the front support. I have Stands under the chassis just to be safe. The front transverse link from what I see doesn’t have any support without it. Trying to do as much cleanup on the suspension as I go.

im late to this, but my trick is that i get a good open end on the shaft, then i used a bar between the ujoint to spin the shaft an break the nut.