A Syncro owner had this complaint after driving a long distance and parking:
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When I went to go drive it 30 minutes later there was a massive vibration, so much that I am not comfortable driving.
Most violent at ~5 mph, diminishes as I speed up, but still feels like I will do damage continuing to drive it.
Vehicle Speed-related, not engine speed (shift to neutral, vibration remains)
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Spicer-type driveshaft rebuilding is a very simple and common maintenance job. When I moved from a VW shop to a Mercedes specialist in the early 80’s, I’d never built one, but I did several just in the first month. And they all came out fine without need of further work because my new boss showed my how to get it right.
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It’s not uncommon to receive the first notice in the manner you did, I’ve experienced that exact sequence more than once myself. One or more of the bearings was very close to developing enough slop to announce itself; it was just barely OK when you began the last drive, by the time you arrived it had loosened a bit more, but while spinning the needles were kept in their cups by the strong centrifugal force and the shaft overall stayed on center. Once parked, if the loose needles end up on bottom, they may stay in place, but eventually they will be parked on top, or roll over the top slowly enough that they start falling out. Once more than two are lost, that cup will have plenty of slop and the next time it’s driven it will shake like crazy. And things fall apart from there. That’s how you get such a sudden-seeming failure after a long drive where everything was fine at the start.
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For the factory Giubo-jointed Syncro shaft, the spider is quite common, easy to find all over the place:
NAPA #813
Neapco #1-0321
Precision #2500070
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Specs (so you can check in the store; you did bring your digital caliper didn’t you?). There are only two important dimensions:
Cup OD: 27mm (1.063″)
Cross LOA assembled: 69.5-70mm (2.736-2.756″)
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If your replacement spiders have threaded holes for zerks, make sure to get 1/8″ MPT brass pipe plugs to close them, they won’t likely be usable in this installation.
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I find the main defect in new assemblies like these isn’t the parts, they’re as good as they ever were (really, there’s very little to one of these), it’s that like most pre-lubed assemblies they were way pinche with the lube. You’ll have each cup off in your hand anyway, so add a small finger-full of moly to each before they go back together, you can’t overdo it because any excess will easily squeeze out.
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This is a light press-fit job, meaning a vise can often be used but a press is always preferable for the controlled smoothness. Using a mallet and drifts, as I have seen suggested by the uninitiated, is ok for removal of the old bits because they’re junk, but don’t dare to strike your new bearing cups, they are very brittle sintered metal and will happily shatter with little abuse. Steady, even pressure, applied evenly around the perimeter, not in the center, you’ll cave the cup in. A pipe or flat-ended drift nearly the cup OD should be used for pressing below the yoke eye surface.
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Parts quality is what hobbyists blame when they botch the job. This is a job whose success depends more than 95% on care of assembly. Not much skill, just care, and if you do it at all well, a previously-balanced DS will emerge most of the time just as well-balanced. Screw it up and you may never get it balanced without doing the whole job over.
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A key detail is to take care to press each cup in only until its clip just pops into the groove. Go too deep and that joint will run off center and imbalanced. It’s hard to get a cup to back out, and past certain points late in the assembly it’s impossible without ruining the cup seal. So press the cup in, and just short of clearing the groove, insert the clip and then slowly press the cup home by pressing on the clip. Usually, once the cup has slid in that far it has cleaned the bore and will move further with little pressure, so there is normally little enough pressure that the clip will audibly click into the groove as soon as it can fit.
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Only after testing, on a balancing lathe or the road, would any cups be pressed in further to admit a shim, and that’s rarely needed. As I said, taking a previously-balanced DS, replacing only the spiders and indexing every other part to its mate including the trans and diff flanges, and it will usually be at or very close to good balance, close enough that small weights can be added to get it dialed in.
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Some driveshafts like the Syncro’s, some BMW’s and others commonly use a Giubo joint (joo-bow) as a vibration damper. These have no anticipated wear life or service interval, in normal use they will last the vehicle’s service life and more. So inspect the existing one for obvious damage, the most common is swelling from oil or grease contamination, apart from that there’s essentially nothing to wear. They don’t crack apart because the entire thing is under constant compression. Surface cracks are to expected in heavy rubber parts and don’t necessarily indicate separation, disassembly would be required to judge whether the rubber is cracking thru or only on the surface. About the worst that happens is one of the molded-in bushings loses adhesion, usually due to contamination rot.
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I won’t get into the poor-man’s balancing process today; hopefully you won’t even need it.