My, Tom Bell, experiences changing the center support bearing in my 2+2 last month (April 1997). We did it ourselves, and here's how. It took us about two hours.
(Pretty long post coming up. Read it all the way through before deciding what to do.)
The center (centre) support bearing serves as a junction between the forward part of the driveshaft from the transmission to it, and the rear driveshaft from it to the differential. The angle on these two shafts must be maintained in a very narrow range: the front shaft must be from zero to minus one degree,but not more than four degrees down, while the rear shaft must be at least one degree, but no more than four degrees down. If the center support bearing is worn out, it means that something has changed its location in relation to the bearing. This is usually the transmission mount, located on the transmission crossmember, which is mainly a formed rubber shock absorber. These mounts sag with age, and can be the direct cause for center support bearing failure. If you plan to replace the center support bearing, you should consider replacing the transmission mount as well. These parts are different for manual(11320-30P00) and automatic (11320-40P00) transmissions, but are easy to replace while you have the car up in the air.
You will need a good metric tool set, some anti-seize compound, replacement gaskets for at least one exhaust joint, a scraper, some penetrating oil, rags and such, a hammer and small cold chisel or punch, some lubricant (Vaselene, WD-40, etc.) for rubber parts, plus some good grease with Molybdenum Disulfide (spelling?) [MDS] in it for bearing surfaces, and a small wheel puller (you can rent them here in the US, but they're not expensive).
First, go on a crash diet so you can fit under the car. If this is not an option, then get some good jack stands that will lift the car at least 18" and a jack that will do the same. Remember the car weighs about 3,600 pounds, so don't choose a couple of chunks of 2 by 4. Jack up the car and put the jack stands in front near the ends of the frame rails (the boxy form under the car). Put the rear ones under the mounting point for the stabilizer bar so you have some room to work. First Steps:
Remove the small stiffener that bolts from frame rail to frame rail across the exhaust system (I think they're 14 mm bolts). The exhaust system is next. The catalytic converters (US spec models) are joined to the exhaust system by a pair of bolts on the lower outside of the exhaust flanges, and two nuts on bolts on the upper inside. Depending on the condition of the bolts, you may need to soak them and the nuts in penetrating oil for a while.
BEFORE YOU REMOVE THESE BOLTS AND NUTS, DECIDE ON HOW YOU WANT TO TAKE THE EXHAUST OFF. You can disconnect the 'h-pipe' (crossover and equalizer pipe) from the mufflers or take the whole thing off in one piece. The weight of the system is about 60 pounds, so it's more bulky than heavy, and if you have two people, I'd suggest you do it in one piece because it's easier and you won't need two sets of exhaust gaskets, which are somewhat prone to leakage....
The mufflers themselves are mounted by pins welded to them at three points: two under the rear bumper and one at the front of the muffler. These mounts are rubber grommets and are easy to get off without hurting anything. Take the one at the front out of its grommet on both sides first. Then, take ONE of the two under the rear bumper out on both sides, leaving one in place on both sides. You will use this as a pivot point later.
The muffler and the 'h-pipe' are secured to each other by a multi-purpose fitting which joins the two flanges together and then bolts to the frame. Remove the frame bolts from these fittings (I think they are 13mm) on both sides. You may need to soak these bolts in penetrating oil before they come out.
Next, remove the bolts and nuts (I think this was 17mm) from the 'h-pipe' and the catalytic converters - CAREFULLY. If you can't get a bolt out and it snaps off, then you have some other work to do. The nuts are up on the top inside, and they should come off with a little gentle coaxing ... Next, pull the 'h-pipe' back away from the cat's and let it down to the ground gently. The back of the system is still secured by the one remaining rubber grommet on each muffler - right?
You take one muffler and have your friend take the other: remove the remaining pin from its grommet and lower the mufflers to the ground. Then pull the whole assembly out from under the car so you can work on the rest.
Start with the heat shield above the catalytic converters: remove the nuts and bolts that attach it to the car (I think these are 10 mm). Remove it by wiggling it around the cat's until it's free. Next, put the parking brake on and loosen the four bolts that hold the rear section of the driveshaft onto the differential. Try one or two and then rotate the driveshaft to get to the others. MARK THE WAY THE DRIVESHAFT MATES TO THE DIFFERENTIAL FLANGE ON BOTH PARTS (matchmarking) FOR REASSEMBLY. If you don't get it aligned the same way going back in, it may vibrate some more... Next, remove three of the bolts and nuts from the differential flange and the driveshaft.
Next, unbolt the center (centre) bearing from the driveshaft tunnel (I think it was 15mm), taking care not to lose the two washers on the bolts. SUPPORT THE REAR OF THE DRIVESHAFT DURING THIS OPERATION. When the bolts are out, remove the last bolt from the differential flange, lower the rear driveshaft to the ground, and pull the front driveshaft out of the transmission - SLOWLY. The tranny should not leak, but it's possible, so have a rag ready to stem the flow and stuff it in the rear of the transmission.
Now that you have the driveshaft out of the car and ready to work on, take a short break for tea or some other soft drink (beer comes later). Inspect the center support bearing for cracks in the rubber (mine was cracked through almost halfway around!). Then, matchmark the flange joining the front and rear driveshafts so that they will align correctly when you put them back together. Loosen and remove the four bolts from the flange and pull the two sections apart. The nut holding the flange onto the front driveshaft is visible now. CAUTION: THE FRONT DRIVESHAFT IS SPLINED AND SO IS THE FLANGE ON IT. MATCHMARK THE FLANGE TO THE KEYWAY IN THE DRIVESHAFT SO YOU WILL PUT THEM BACK TOGETHER ALIGNED PROPERLY. IF YOU DON'T THEN THE DRIVESHAFT ASSEMBLY WILL BE OUT OF PHASE AND WILL VIBRATE BADLY.
Notice that the nut which holds the flange on is 'staked' - that is someone punched a part of it into the keyway so it wouldn't work loose. Take a hammer and the chisel and work the material out of the keyway so you can get the nut loose. [You should have a new nut and washer with the new bearing.] Loosen the nut, remove it and the little washer. Then, pull the flange off of the driveshaft (DON'T POUND IF OFF!!!! Use a wheel puller if it won't budge). The center support bearing will come off next, with some effort.
Take the new bearing and push it onto the shaft. Then, apply some MDS grease to the bearing surfaces which contact other parts, align the flange with the matchmarks and push it back on. Then lubricate the new washer and the bottom of the new nut which contacts the washer, and screw the new nut onto the shaft. Tighten the nut hand-tight.
The next step is critical. Align the rear driveshaft flange with the matchmarks on the front one and bolt it together loosely. Check that all of the knuckles on all of the u-joints line up. If they don't, then you need to reposition the front driveshaft flange on the splined shaft, so that they will. If they do, then unbolt the rear driveshaft, tighten the nut inside the front flange to 65 ft/lbs, and 'stake' it into the keyway on the shaft. Reassemble the front and rear driveshafts. You're halfway there! Take another tea break.
With help, slide the driveshaft back under the car. Remove the rag from the transmission (if you had to use one), and slide the splined shaft back into the transmission. Position the rear driveshaft flange onto the differential flange, and put a bolt into a hole to hold it in place while you align and tighten the center (centre) support bearing to the driveshaft tunnel. Try to get the alignment straight from the transmission back to the differential. Then, align the rear driveshaft flange and differential flange to the matchmarks, bolt up and tighten to 45 ft/lbs torque.
Finally, starting with the heat shield, reassemble all of the other parts in reverse order. Be sure to scrape off all of the old gaskets from both exhaust flanges on the 'h-pipe' and the catalytic converters. Use anti-seize on the gasket surfaces and the bolts/nuts for the exhaust system, and Vaselene or WD-40 on the rubber grommets for the mufflers.
If the vibration is still there, you may need to do some adjusting. The Service Manual tells you to rotate the rear driveshaft on the differential flange 90 degrees if there's still a vibration. If that doesn't work, rotate it 90 degrees again and try again, etc. You can do this without taking the exhaust system off, but you need to get the car in the air.....
My advice is to try something first: when you get the car up on jack stands, get in, start the car and run it up to the speed where you get the vibration. Then, when the car is reassembled, do the same thing and compare sensations. That way, if the vibes are still there, you can adjust the flanges until you sense the vibes are (hopefully) gone.
This procedure is really simple, and involves only basic mechanics. It should take about 15 to 20 minutes.
You will need metric sockets (12, 13 & 14 mm) and rachet, a floor jack (if you're doing this while the car is supported on jack stands), and a block of wood which fits on a jack.
Locate the transmission crossmember, which is at the rear of the transmission, just where the exhaust pipes begin to come together from the sides of the engine. It's secured to the floor of the car with six bolts.
Position the floor jack under the transmission so that you can still work on the crossmember, put the wood on it, and raise the jack to take the weight of the transmission partially off the transmission mount. NOTE: If you're doing this procedure on a hydraulic lift, you will need a different jack that is tall enough to reach the transmission. DON'T TRY to stack 2 by 4's on end on top of a floor jack: that's dangerous!
If your car is a manual transmission, there is a small cylinder counterweight attached to the transmission mount and to the exhaust pipes. If you have an automatic, you have a bracket instead. Remove the bolts or nuts that hold whichever you have onto the transmission mount.
Using a deep well socket, remove the two nuts that hold the transmission mount to the crossmember.
Loosen the six bolts that hold the crossmember to the floor of the car, and lower it slowly, wiggling it to get it around the exhaust system.
Remove the two bolts that hold the transmission mount to the transmission. Remove the mount and replace it with the new one and bolt it to the transmission at 45 ft lbs torque.
Lift the transmission slightly with the jack so that it's slightly higher than it was.
Replace the crossmember, and bolt it loosely into place with the six bolts.
Put the nuts on the two bolts that hold the mount to the crossmember and use the deep well socket and torque them to 45 ft lbs. Then, raise the transmission with the jack until the crossmember is touching the floor pan. Then tighten the six bolts holding the crossmember, torqued to 60 ft lbs.
Finally, bolt up the bracket or counterweight to the transmission mount.
Lower the jack SLOWLY and remove it.
End of Procedure.
Hope this helps you. I've been there - done that, and the vibes are still there.
'90 2+2 NA