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(Rebuilding the Syncro drive shaft)
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Reprint of post to Syncro
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From: "Jerry McCavitt" <mccavittj@m...>
Date: Sat Nov 18, 2000 5:17 pm
Subject: Rebuilding the unrebuildable (long)
Hello all,
I have just installed my newly rebuilt driveshaft (center) and would like to share the process with anyone interested.
First I ordered the parts: the "flex disc", is indeed a BMW part, kudos to Jon Magoun for tracking that one down. I got it from www.germanparts.com go to the BMW section and search "flex disc", purchase PN 26111106113, 4cyl 4spd 70-80 8-hole, it's $36.00 plus shipping. This is the mysterious rubber biscuit at the tranny end of the shaft (front diff end for the diesels). This allows some rotational play in the shaft to absorb sudden torque inputs. Interestingly, there is actually an axle built into the end of the shaft that the assembly twists upon. Examine yours carefully at the bearing ends of the "axle" for pitting or spalling, dress them with emery cloth or very fine sandpaper and lube well before re-assembly.
Then I located the elusive U-joints. Past postings have had clues, but here's the real deal: The Weasler PN in the archives (I don't have it here) is good, and the size is 27mm X 70mm. This breaks as a NEAPCO PN; 1-0321. I found them at BAUM HYDRAULICS in Omaha, NE.
Tel (402) 345-4122, ask for Dick. Grand total with shipping is $29.95 for two. Any good supply shop should be able to get them. These are an absolute direct replacement,made in Italy, no shims, and the come with new snap-rings, too. They are also equipped with grease fittings! Unfortunately, there is insufficient room inside the yokes to install the large, angled fitting that is supplied. You must find either a bolt that fits this hole to seal it, or use the lowest-profile grease fitting you can find. Either way, the joints must be disassembled to service them.
This lack of space is probably why VW didn't include serviceable joints in the first place. With these parts, any competent driveshaft shop or machine shop can put it together. For those wishing to do it themselves, read on.
Ideally, you use a hydraulic press to remove and install u-joints. Not having this luxury, here is the driveway-proven home method; Soak everything in your favorite loosening agent. Remove the snaprings. Use the following sockets, preferably Craftsman or Snap-on, 'cause your going to trash them; a 17mm and a 30mm. Place the 30mm open end up on the ground. Rest the yoke of the shaft on the socket, so that the end cap being driven OUT will go into the socket.
STEP 1: Use the 17mm on the opposite end as an anvil and drive (hammer) that end IN as far as it will go. This should result in the OUT end protruding about 10mm. Now flip the shaft 180 deg., positioning it over the 30mm socket again.
STEP 2: Drive out the opposite end cap by hammering (carefully) on the OTHER yoke, (not the protruding cap); the ends that are 90 deg. to the one you're removing. This should bring that cap out 10mm as well. The joint will now be loose in the yoke, but not coming out. Use a pin punch or med. screwdriver inserted past the joint and into the cap to drive it the rest of the way out. Repeat opposite side.The joint will now come out.
STEP 3: Do the same for the remaining yoke, but now hammering directly on the joint axle during the second step. Repeat for other end of shaft. Remove the flex-disc bolts with an 8mm allen socket, using a large screwdriver or floor jack handle through the yoke as leverage.
Reassembly is the reverse of these steps. Bolt new flex disc to it's yoke. Lube the "axle" shaft, and reinsert into driveshaft, (mind the o-ring!), and bolt assembly to the driveshaft.
STEP 4: Install new u-joints. CAUTION; grease needle bearings in end caps well, and work slowly, as the bearings tend to fall over into the cap just at the wrong moment. Greasing them well keeps them stuck in place.
STEP 5: Smooth out any distortions of the yoke holes with a Dremel drum sander or small file.STEP 6: Insert one new end cap into yoke as far as you can by hand. Install joint, carefully mating axle and end cap, double checking needle bearings.
STEP 7: Keeping the axle in the cap, drive the cap into the yoke until the snap-ring groove clears the cap.
STEP 8: Install that snap-ring. Flip yoke, and fit other end cap by hand. Slide joint into this cap to hold bearings in place. Drive cap carefully into yoke. Grease seal on cap must touch the body of the joint, and rotate freely. If it does not, or one snap-ring won't seat, you've dropped a bearing in the end cap, and must take it apart again to remedy. This happened to me twice doing the eight caps.
If required, sand and paint drive tube while dissasembled. I scraped off a layer of undercoating from one side of the tube, a possible source of vibration.
And the results.......
Well, I can tell the shaft is in the van, versus the feel of driving without it, very faint rumble @ 35, felt, not heard. Not bad. I do not know the original positioning of the shaft, so I just bolted it up where the holes lined up.
Something that we might look into is the joint angles.... specifically, the angle at one end of the shaft MUST match the other end, or a vibration will result. My 4-Runner has this problem from a suspension lift, it vibrates like a cheap motel bed at 60mph. Very annoying, and hell on the u-joints. If this is the source in some of our vans with incurable rumble, perhaps shimming the front tranny mounts or the rear mounts of the front diff would help. Something to think about.
Jerry McCavitt
'86 Syncro GL