This last summer I replaced the original u-joints in the syncro prop. shaft. The previous owner had removed the shaft for the summer, but told me there was some drive line vibrations. There are a lots of tales of woe and intrigue on the net about prop. shaft vibrations, causes and cures, so I decided to have a go at fixing mine. First thing was to replace u-joints. Stock VW joints are expensive, so I used the same replacement joints as Herman did on his syncro project (Precision brand, part #813). The bronze bushings that the yoke assembly and shaft fits into at the guibo end of the shaft seemed ok, the shaft fit in snugly. I just re-greased that, installed the new joints (blanking off the grease nipple fitting holes – I couldn’t get a nipple to fit in the tight spot, you’ll see what I mean if you ever do this job), and then painted the shaft. I re-installed the shaft and still had drive line vibrations at around 50-60 kph. I tried the trick of loosening the front differential mounting bolts and driving the van to let the drive line “find its sweet spot”, but that did not work. I removed the prop. shaft and re-examined it, and noticed some play in one of the joints. I removed that play by installing a thicker circlip (new joints came with two sets of circlips, differing in thickness).
That seemed to have removed the play. I double checked the fit of the yoke shaft into the bronze bushing, was ok.
The next step is to make sure transmission output flange and front differential input shaft are aligned to specifications. They are supposed to be aligned longitudinally, but each flange can be pointing down slightly, 4 degrees or so. I have made a laser alignment tool and I need to get under van and do the deed. One thing that has slowed me down is my suspicion that my viscous coupling is weak, but that’s a story for another blog entry.
Meanwhile have a look at the old u-joints. Notice the pounded marks on one of the bearing surfaces! (apologies for the blurry pic).