TLDR;
I attempted to install rear trailing arm pivot shafts into new bushings over the weekend and it was a disaster. First go split the bushing. Second go with bushing from alternate vendor went in by hand. I assume if it went in that easy, something is not right.

DETAIL
I started with new shafts from Restoration Design, as they seemed closest to original design (i.e., hollow). I also used their Prekom brand bushings as I was told it was the original durometer and being supplied to Porsche, Rebel Racing and Elephant Racing.

The trailing arm bushing split the top lip from the base on the first attempt to install a pivot shaft. Per conventional wisdom, I thoroughly lubricated them with dish soap, used a shop press, and had a helper.

I didn’t want to mix bushings with different specs, so I pull out all the Prekom. They seemed pretty brittle and broke apart in most cases.

Note: The dimensions (mm) of the bushing are quite different. Left to right in photos.
WDG ID: 28, Height 54
Prekom ID: 26, Height 47
Original ID: 28.5, Height 55

I wish I had measured the OD of the new pivot shaft, but didn't think to do it before installing them.

Click to view attachment
Click to view attachment

I tried again to install, this time with the same pivot shaft but using WDG bushing which I had on hand and are very close to the same dimensions of the originals. In this case I was able to install the pivot shaft into the bushings by hand. I assume it should not be that easy.

They did appear to set up a bit after leaving them overnight, but I am able to rotate the link bearing by hand with some moderate effort. Nut torqued, but not installed on car.

So now I am left to decide if I leave it as is, or pull the pivot shaft and bushing and start over with another combination.

Yes - they are a pain to install when you have the proper preload or squish between the ID and OD.

I successfully used restoration design bushings but did tear one due to not enough lube and trying to press it too fast. I ordered a 2nd set and had no issue once the lesson was learned about how fast to press them in. And you can never have too much lube. I prefer glycerin over dish soap.

You are absolutely correct they should not install by hand.

We make bushings and shafts that are the same dimensions as the OEM. I do know with ours it it a tight tolerance, and is not a hand fit. It can however be tapped into place with lubrication.

Hi Mike. The second set of bushings that I used, where I was able to install the shaft by hand, were from 914Rubber. Marked WDG.

Perhaps the pivot shafts from Restoration Design are not stock OD. Though if they were smaller, I wouldn't have thought my first install try would have ended like it did.

That shaft shouldn't rotate easily. It should be tighter than socks on a Rooster. Your suspension depends upon the drop arm not rotating unless a lot of torque is applied. At least you didn't install those urethane POS bushings.

Hi Dennis. I have a good pair of oem pivot shafts you could borrow if you want to try them on for size.

I know early 914rubber bushings were a loose fit. I purchased 2 sets from the initial group buy. They might have changed things in later production runs.

"Socks on a rooster"

How does one can establish what the dimensions and tolerance of the original could have been?

Were these ever available separately, uninstalled, so they could be measured and reversed engineered as such?

Thanks for the kind offer Andy. The car is in MO, so it would be tough to fit at the moment. I did measure the originals I removed. They were about 28.2mm OD. Wish I had measured the RD ones before install. I guess I'll get another chance when I take them back out.

I haven’t tried all the options but Elephant racing is the closest to stock that I’ve used.

You pay through the nose but well worth it.