My thoughts/experience on the Rubber vs Plastic type.

Just replaced my Steering Coupler / Rag Joint today.
I've had the truck 15+ years and drive it often/daily. Haul material in it when needed, tow our vintage trailer on trips, etc.
I replaced the coupler that was in it somewhere around 7-9 years ago when I had the steering box rebuilt.
The rubber type that was in it was getting a bit ragged/soft/floppy but was still in one piece not tearing of falling apart.
Replaced it with the type that is more of a hard plastic material not the rubber type that was in it. IIRC the harder plastic type was claimed to be stiffer to minimize play.

The steering was feeling a little looser lately making me wonder if the rebuilt box was not holding up well, but there was also an occasional clunking noise in the steering column when hitting some bumps.
Looked under the hood to make sure the steering box was not loose, mounting point of the box to the frame cracked (had that happen on a Suburban with PS).
The coupler was cracked into several pieces with a few small chunks missing. No wonder the steering was starting to feel as sloppy as a 13-year-olds room.
I replaced it with the rubber type. It seems like the hard plastic type, when they go they GO!

This is what it looked like after I used some baling/rebar wire to hold it together to get home. It actually even tightened it up a little.

This is after it was pulled out of the truck.

 

Wow! Things could've gotten sketchy real fast.
I've only ever used the rubber type and the 2 failures I've had were mostly caused by the column bearing failure. The lateral stretch/stress was no bueno. The last one to fail had me scratching my head a bit as I noticed an odd vibration coming from the front end. Oddly, I didn't feel it in the steering wheel at all and only noticed it on a particular stretch of road. Actually had decided that it was the front shocks. Eventually figured out that 1 bolt had completely tore out of the rag joint. Have since modified the column to accept a sealed bearing and have vowed to give it a peek anytime my head's under the hood.

 

I had been aware of some members dissatisfaction with the harder “plastic” replacement steering couplers, so I went with a genuine Ford one when mine needed replacement. For the 1966 trucks, there were two possible replacements, depending on the production number. You can search on it in the archives, but you can tell which is which by the diameter of the larger of the two pins on the coupler. 66 model year, other years are different. Be sure the grounding /bonding strap between the two sections is present, or add your own as the OP has apparently done on his.

 

Hi Steve.
I did add that grounding strap to the plastic one but honestly can't remember it's purpose. Thought it might have to do with the horn, but the new one does not appear to have one and the horn still works.

AZSCAWPION, I put the sealed bearing on the bottom of my column when I had the box rebuilt by Blue Top.

 

Ted, I think it is a redundant ground, it won’t hurt. I’d bought an original ford part that had the metal bonding strap, but I have heard many don’t.