TAB AND CARRIER RETURN CORD TENSION ADJUSTMENT ISSUES
The bolts that fasten the CR drum in position on the axle are how you adjust the cord tension. Loosening the two bolts, which are spaced ninety degrees apart around the hub, should allow for the rotation of the drum to pull on the cord until it reaches the proper tension. Then the bolts are tightened to lock the hub onto the axle.
The last times I did this, after struggling to get the drum to rotate on the axle, the bolts didn't hold the position so that the cord worked its way to be too loose. I removed the bolts, cleaned their threads and put a bit of lacquer thinner to loosen any sludge in the threaded holes on the hub. That might give them a bit more tension on the axle, but it is not certain that this will work.
CONSIDERING A PARTS SWAP
I do have the donor Selectric typewriter that I bought, which has a very nice assembly with a CR drum that rotates freely. I am considering swapping this for the current assembly on the 1053 to be able to more easily turn and tighten the drum to hold cord tension.
The assembly is a large bracket with the axle rotating in a bearing set in the middle portion of the bracket. The end of the axle has a nylon cam that connects the mainspring to the axle to power the forward (tab and space) movement of the carrier. The axle has its flattened section on the far end, where the tab drum will slide on and be locked into place with a single setscrew onto the flat surface.
The major hassle in making this swap is that I will need to readjust the positioning of the tab drum for the proper position, engagement and backlash into the gears on the operational shaft. I am reviewing the procedures and assessing my access to the area to accomplish these adjustments without incurring more dramatic disassembly of the typewriter.