Lots of prior discussions on this and related issues. Go to the bottom of this page and see the Search Forum box. Enter “driveshaft” and or try other key words and threads from a bunch of different postings comes up. Click on the number in the upper right hand corner of a thread that looks interesting and you will be taken to that thread.
I think Ken/kid442 may have driveshafts
Also, here’s a post I did on the 6163skylark forum which is also a great source of info for our cars.
If the spring is the only problem that may work. The other big problem that is experienced is that the “ball” that is on the splined section and the bushing/insert that is on the rear section of the shaft that contains the spring also wear out. The ball is a machined in part of the front splined part of the rear shaft and is not replaceable, it is replaceable on the big GM 2 pc shafts of the era and a rebuild it is still available, but it won’t work on the F85/Skylark shafts. I was able to pick up a “good” used shaft and “good” used parts to repair a shaft, both of which we will use but I opted for a new shaft on mine. Also, there is a shop in TX that has a fix. I posted this on the jetfireforum a little while ago.
Since I have changed the trans in the car to a TH200 3spd auto with a sliding rear yoke, vs the Roto5’s fixed rear yoke, I have decided to go with a new driveshaft with modern components including a modern center support bearing and carrier that doesn’t simply float in the bracket. It’s larger in size but I flipped the support bracket upside down and rotated it 180 degrees and everything fits great with superior and easily replaceable modern components-basically Bronco II. Much more robust Cardan joint.
I did talk to Craig at Driveshaft Specialists in TX 210-342-6622 and he is familiar with the original shaft and the CV joint problem. He said they machine out the existing ball making it replaceable and make both sides of the yoke compatible with the “big” GM 2 pc driveshaft CV rebuild kit which is still available and uses a larger replaceable ball and bushing, all of which comes in the rebuild kit. Not cheap to do but a good solution if you want to keep the original shaft and don’t have good parts.