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Transmission Output Shaft Bushing. ...we replaced ours ('89 745) a few months ago, at appx. 115,000 miles. Why? I noticed that the output shaft was spraying a bit of oil onto the underside of the car... and my experience teaches me that such leaks only get worse, plus tailshaft play accelerates other wear.
Let me say that this is not necessarily bad or that you don't have an output bushing worn and a seal leak. You should try shaking the driveshaft radially at the transmission and see if there is any lateral movement...if you're unsure try shaking a known good one. Also, you can replace the seal yourself and leave the bushing alone...it will seal for awhile, perhaps a LONG while. Last point...when replacing seals like these, check the metal part that the seal rubs against...if there is a notch you can catch your fingernail on you probably need to replace the metal part too...a rear axle pinion flange is easy but a driveshaft yoke you have to replace a U-joint, etc. (some people think U-joints are easy.)
This is part of what I'd refer to as preventative maintenance. I was quoted a price of $300-$350 to replace the seal/bushing. Bought the parts for about $45 (seal/bushing/trans gasket) and performed this operation myself in about 3 hrs, including setup/replace/cleanup time. Pulling the housing is relatively straightforward once the tranny's supported and the cross member and mount are removed. I believe that there are six bolts to remove and the housing's in your hand. Have a new gasket on hand and make sure that both mating surfaces are completely clean with no trace of the old gasket. You don't want to have to do this job a second time because of leaks.
[Another tale:] The tail housing removal is really pretty simple. I just finished replacing a transmission in my '89 744 project car. The tail housing was cracked and we initially hoped to replace only the housing, but Volvo wanted $253 for it and the junkyard had an entire AW70 for $400. Anyway the Dexron is still in my hair from finishing up the job, so my experience is as fresh as it gets. What you're going to do is take out the bolts that connect the output flange to the driveshaft, support the tranny and remove the rear transmission mounting bracket. Four bolts hold the tail housing to the rest of the transmission case.
Start with the driveshaft bolts while the car is still on the ground. That way you can roll the car a little to get to all 4 bolts "easily". If you're driving up on ramps like I did, this won't work and you'll need a crow's-foot wrench (my 9/16" worked fine) to get to the ones on the top of the flange. A generous supply of profanity helped in my case... It's a good idea to mark the output flange and shaft flange so you can mate them up when the time comes to put it back together. Once the bolts are out, push the driveshaft toward the rear of the car and it will pop out of the flange. You can shove it up above the flange to get it out of the way. Raise the car up (jackstands, ramps whatever)if it's not already and drain the tranny fluid. Put the selector in Park and use a socket to remove the bolt in the center of the flange. This bolt holds the flange to the output shaft. Once it's out you can pull the flange out of the housing. Remove the 15mm nut in the middle of the transmission mount (rear end of transmission). Support the case with a floor jack, just enough to take the pressure off the tranny mount. You should see the mount bolt come up slightly. Then remove the four bolts that hold the mount to the chassis. The mount will come off, and the tail housing will be clearly visible. Four bolts (14mm I think) hold the housing to the main body of the tranny. The top and bottom bolts are different lengths, so note where they came from. With a little "gentle persuasion," the housing will come off. On my particular car, the PO slid it into a ditch and caught the end of the center mount bolt which cracked the housing. This also saved me the trouble of taking off the "L" mounting bracket. It won't have to come off if you just plan to replace the seal. The seal is easy to get to and "looks" like you could pry it out with a screwdriver, but I have never tried this. You're going to end up with a roughly 6x6x8 inch housing which you can work on at your leisure. Worst case is you'll have to have a shop press a new one in. (But hey, I'm just speculating at this point). Anybody else have any experience with this? Plan for about 2 hours under the car to get it out. If the gods of rusted bolts are on your side, it could be done in 45 minutes or so, I'd guess. Nothing is particularly difficult about the operation. Although I recently told someone to shoot me if I ever said it, "installation is the reverse of removal" (BOOM). The center flange bolt only holds the flange to the shaft; no pre-tensioning or any of that other technical stuff.
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