to recap… purchased ’86 syncro this last summer, prop shaft out because of vibrations, vc was assured to be ok. U joints on prop shaft looked suspect, but i installed and yes, vibrations at 50-60 kph. Also vc was weak, not passing the 2×4 test.
I replaced u joints on shaft (precision brand, #813, see earlier post), checked the fit of the shaft and bushings on guibo end (nice and tight), and popped shaft back in. Still vibrated at same speeds. Loosened front diff mounting bolts, drove around, no difference.
Removed shaft, examined u joints, one was loose so I replaced circlip with thicker one (u joints came with 2 sets of circlips). Checked bushings and shaft fit again.
Two days ago I put it back in, but before it was installed I did a quick check on vc by using the volvo method outlined on testing vc post. I got a value of 17 ft/lbs. Not much eh? Confirms vc is weak.
It would would be interesting if others would do this simple and quick test and post results, I bet there is a range of values.
Oh, and as well as putting prop shaft back in today, I replaced the dodgy Uniroyal Laredo tires the van came with with some Nokian Hakkapeliitta CS tires.
Road test: tires louder and firmer. Vibrations almost gone, A very slight vibe at 50-60 kph, but its very slight and not bothersome (that said, I will work to eliminate it).
Mud test: on the farm here there are ample spots to get stuck, and it has been raining pretty hard the last 2 weeks. Last week with prop shaft out and the Laredo tires on, I tried going up a curving, maybe 20% hill, grass and clay/mud. I never made it, even with rear diff lock on. Today, with much wetter conditions, I made it up no bother, and no diff lock.
i toodled around lumpy, uneven, sloping ground, grass over North Saanich clay. Didn’t get stuck, but the front wheels didn’t “feel” like they are doing much.
Conclusion: prop shaft vibes mainly due to “loose” u joints, either when they were old worn out units, or new ones, not installed with correct circlips. The “off road” performance I attribute mainly to the great tires. Perhaps the vc is allowing a little torque to get to the front, probably wishful thinking.