It's ironic, but the guibo -- also called a "flex disc" -- isn't really built to withstand a whole hell of a lot of flexing. It's built to withstand short-duration flexing, like when the car hits a bump and the engine rocks on its mounts. But it's not a universal joint. It's not designed to run in a flexed position. It's designed so that the back of the guibo should be perfectly parallel -- and flush -- with the front of the driveshaft flange. If it's not parallel -- if, say, the back of the transmission is too low so the bottom-most ear on the flange is too far from the guibo and the top-most ear is bending the guibo toward the engine -- that wubba-wubba-wubba on the guibo will be happening 6000 times a second at 3000 rpm in 4th gear, and will tear the guibo apart in a few thousand miles.

When these cars left the factory with the shorter four-speed trani, it's not that the driveshaft and guibo were laser-aligned. They weren't. And, even in their prime, using OEM German parts, 2002s were certainly known to go through guibos. However, the 5-speed is longer than the 4-speed, there are not stock mounting points for the 5-seed, the cars are now 40 years old and things sag, many people say OEM German rubber isn't what it used to be, and many aftermarket guibos are crap. These things all exacerbate the problem. The U-shaped bracket comes closest to giving you stock mounting points because at least it bolts to the stock mounting points, but 1) Tom Jones says that the U-shaped bracket puts the trani slightly too low and that the original design had a kink at the support bushing to kick it up slightly, and 2) even if it's at the right height, the back of the trani can still be off substantially left-to-right.

If you search the FAQ for "5-speed guibo alignment," you'll find dozens of posts. They all tell you to install the 5-speed, install whatever rear bracket you're using, bolt the guibo to the back of the transmission, install the driveshaft at the rear, loosely attach the center support bearing, do NOT bolt the guibo to the driveshaft, and then put the trani in neutral, lie beneath the car, slowly spin the driveshaft, and look at how the transmission flange's ears touch the face of the guibo. If all ears touch simultaneously, it's aligned, you're done, tighten up the guibo and CSB, go beat on it. But if, say, the top ear is pushing the guibo forward but the bottom ear is not touching, it means that the bottom ear has to come closer. You can do that by raising the back of the transmission higher with washers under the rear support bushing, or by lowering the driveshaft by putting washers beneath the CSB's attachment points. Similarly if there's a gap on the right ear, you can loosen the bracket and shove the back of the transmission to the right, or slide the center support bearing to the left.

FAQer Marshall Lytle explains this all particularly well. ALL that matters, Marshall says, is getting the guibo and driveshaft parallel. Transmission centered in the tunnel? It just doesn't matter. Back of the shift platform centered in the gearshift hole? It just doesn't matter. Center support bearing has to have slots cut in it and slid all the way to one side and dropped down by half an inch? It just doesn't matter. The driveshaft has TWO UNIVERSAL JOINTS in it, Marshall says. Let them do their work so the guibo -- ahem, the "flex disc" -- doesn't flex.

I completely agree with Marshall. And I'm reminded of Bill Murray in Meatballs shouting "IT JUST... DOESN'T MATTER!"

And yet, for some reason, my '72tii is mocking me, and has vexing guibo alignment issues.

In order to get the guibo/flange aligned left-to-right, I had to push the back of the trani very far to the left. That wasn't enough, so I had to cut a slot in one side of the center support bearing, elongate the hole the other side, and mount the CSB so far to the right that the left side of the CSB is barely grabbed by the nut and the body of the CSB is hitting the body of the car,(see pic). It's almost as if the engine is cocked to the left. I loosed the engine mounts and tried to shove the engine to the right, but there's not any real adjustment in those mounts, short of removing them and elongating the mounting holes. I thought I had the eureka moment when I discovered that the driver's side engine mount was installed backwards, but since the front-to-back dimension is identical when measured back-to-front, turning it around the correct way made no difference.

Then, with the guibo close to aligned left-to-right, it was still too low, with a gap at the bottom-most flange ear (see pic). I put one of the fat 0.16" washers (the one that's meant to go on top of the support bushing) underneath the bushing, between it and the U-shaped bracket. That helped, but it wasn't enough. I put a second washer under there, which nearly closed the guibo/flange gap, but when I looked in the engine compartment, raising the back of the transmission tipped the engine forward enough to cause the fan to hit the radiator. My car has a triple-core radiator that has caused me clearance problems even before the 5-speed went in.

I went back to using a single 0.16" washer between the U-shaped bracket and the bushing and tried instead to lower the center support bearing. I used one standard 1/4-20 washer per side. Not enough. I tried two. Not enough. Three. Closer, but still not enough. And that that point, the nuts on those funny T-bolts holding up the CSB were not biting onto a lot of threads.

So... I need longer T-bolts. The stock ones are listed in realoem as "M8-18 square-headed bolt," part number 23711130250. Now, I'm usually quite adept at finding generic sources for metric hardware, but this one has me stumped. I've measured the base of the T-bolt -- the part that slides in the groove -- and the base of the bolt is 0.31", the groove in the body is about 0.34". The nearest thing I can find are T-slot bolts made for holding things in slot-based machinist jigs. McMaster-Carr has an "M6 T-slot bolt" 25mm long that fits into an "M6 slot." You have to look at the T-slot nuts in the McMaster catalog to see the size of an "M6 slot." It's 8mm, which is 0.312". Might fit. But, sheesh, the bolts are nearly $15 apiece. And the CSB is held on by13mm nuts, which usually means M8, not M6. A detail, but enough to give me pause in ordering longer T-slot bolts that might not work.

I looked further for a BMW alternative for a longer bolt. Right there in realoem it lists another "square-headed bolt," this one M8x21, part number 26111205004, used on later 2002s that have the heat shield over the guibo, and on larger cars up through E24s. And more like $5 a bolt.

I've ordered two of these. When they come, I'll install them and see if they're long enough to let me put a fourth washer beneath the CSB. I'll also loosen the differential again and smack it forward, since every time I lower the CSB, the driveshaft flange pulls slightly away from the guibo.

There may well be something with the engine alignment I'm not seeing. But I'm close enough to be able to drive it around that I can smell it. Besides, even if the engine is cocked slightly, it JUST... DOESN'T... MATTER...