Ok, so Chamba asked for the pictures and how I did the triple wiper conversion, so here is how it was done. Again, huge thanks to Jetranger for all his help on this!
First you need an extra set of wiper linkages so you can cut out the middle arm and assembly and add that to the original linkages. Here is what the original linkage looks like.
All of the rods work on a ball and socket type of joint where they attach to the motor and the wipers. The motor and the left end are both single ball joints and the one in the middle is a double ball joint to relay to the next wiper. To convert to triple wipers you need another double ball joint assembly to relay to the left end wiper. Here is what the middle assembly joint looks like up close.
The linkage arms are shaped like a c channel and to join them back together, I just cut some 3/16" plate about 5" long and just wide enough to fit into the c channel and then welded it to one arm and then used small c-clamps to hold the other side into the other half of the arm until I could adjust the length and angle of the ball joint arm back to the same as you see in the photo above. I didn't take a picture of that part of the process but here is a pic of the finished arm after adjusting the length and welding the joining plate to the two halves of the arms. You can't see the other side, but it was welded on the other side as well.
The spacing of the holes for the wiper hubs was pretty simple. Jetranger had sent me some measurements that he had gotten from an Aussie with a BJ42LX with factory triple wipers and they were strangely spaced in my opinion. I ended up just laying my wiper arms with wipers on them down on the windshield frame and coming up with my own spacing that was evenly spaced from wiper to wiper. He later told me that was what he ended up doing as well.
I drew a centerline through the old wiper arm holes and then played around with the spacing so that the arm closest to the wiper motor didn't hit the winshield frame in the down position and the one at the other end didn't hit the other windshield frame upright when in the up position and then cut the distance in half to get the center wiper arm hole location. I then just drilled 1/2" holes through the frame and made new reinforcement plates to go on the backside to support the wiper hub assemblies and to keep them from rotating in the windshield frame. There are two nubs on the wiper hub housings that lock into these reinforcing plates and so you will have to get the holespacing right for them to sit flush. Here is a pic of the plates that I made.
I don't know why the factory made the notches around the center hole because there is nothing that corresponds to that notching on the housing, so I left that out on my plates. I made my plates out of some .093" thick cold rolled steel that I had in my shop. I then tacked them on 4 sides with the welder to hold them in place. I then cut some slices off of some 1/2" rod to fill the factory wiper holes and welded them in place from the back side and body filled the front side later when prepping for paint. You can just see the plug welded in in the upper pic of the finished linkage arm if you look closely.
Now to the most critical part of the whole conversion to triple wipers. The motor arm. The motor arm rotates in a circle and this circle must be shortened to get the proper linear travel of the triple wipers. The original wipers have approx. a 120 degree sweep and the triple wipers need only a 90 degree sweep. It took me a little while with my caliper to measure what the difference in linear travel equates to with a reduction in the radius of the motor arm, but I figured it out and it comes out to a shortening of the arm by .100" of an inch to get a reduction of .200" of linear travel. There is a dogleg in the motor arm for offset and that is where I cut mine for the shortening process and then just clamped in place .100" shorter and welded it back together. Here is a photo of the motor arm after welding it back together.
You can see that in my picture I have the overall length of my motor arm written on there as 1.700" reduced to 1.600" overall length. Your overall length of the motor arm may be shorter or longer, but the main point is that you reduce the length by .100"
Here is a pic of the finished product. These wipers are supposed to be 12" and when I installed them they ended up being 12.5" so they are a little too long and the one on the left is touching the windshield gasket. They will be replaced with the correct length here soon.
Well that is how I did it and hopefully I explained it simply enough so anyone can do it because it really wasn't that difficult, just time consuming.
Enjoy!
Don