1992 735i, Automatic transmission, output shaft seal replacement


Note: This is for a 1992 735i, details vary for different models.

There aren't any real surprises to doing the job. You'll have to remove the muffler, heat shield, & unbolt the front of the driveshaft & swing it out of the way & temporarily support it. I did all of the work with the car up on 4 jack stands. Support the rear of the transmission with a floorjack & a large block of wood on the pan of the tranny, it really isn't all that much weight to worry about stressing the pan. I bent a temporary support out of flat bar stock & bolted it to the chassis to support the pan of the transmission while I removed the rear tranny crossmember to get to it, which you'll have to do anyway to get to the front driveshaft flange. If re-using the same driveshaft, mark the yoke flange & driveshaft flange at one of the bolt holes to make sure it goes back together with the same orientation so you don't end up with any imbalance issues. To get the yoke off, there is a stamped sheet metal retainer to keep the output shaft nut from backing off & it should fall out on its own or pry out with a screwdriver. Bentley says to buy a new one, I flattened it with a hammer & reused the old one, I think they're only a dollar at the dealer. The output shaft nut takes a 1-3/16" or 30 mm thinwall socket. I had to turn down a socket on a lathe to make it thin enough to fit in the recess. I turned it down to 1.5" o.d., for about 1/4" back from the end & that was enough. You could grind it down on a grinder if you don't have access to a lathe. Don't get an impact wrench socket because they're really thick & it would take all day to grind it down & you need carbide tooling to turn it in a lathe. Slide the yoke out, have a drip pan handy as it will drain a pint or so of tranny fluid. The old seal prys out with a screwdriver. Clean the recess well & put some Permatex "Ultra Copper" oil resistant RTV on the outer brim of the new seal & gently tap it in evenly all the way around with a small hammer & block of wood. Clean the splines of the output shaft & inner splines of the yoke. Some recommend putting Loctite #242 on the splines to keep them snug but I didn't learn that until long after I finished the job. Grease the inner lip of the new seal, polish the o.d. of the yoke & grease the seal region lightly & slide it on. Put some of the Permatex sealer on the flange surface of the flange nut & around the end of the splines since the splines are a leak path for the fluid. I used Loctite #271 on the threads since it was only finger tight when I removed mine. The torque spec is 74 ft-lb. I torqued mine much higher, like 100 ft-lb since it was loose before. Replace the nut retainer & it's ready to go. Inspect the rubber rear tranny mounts closely. You may as well replace them with new ones, they're only $9 or so at J.A.C., Zygmunts, etc. The seal replacement should only add another 1/2 hour or 45 minutes if you're already doing a driveshaft job, otherwise plan on at least 1/2 a day for removing the exhaust & driveshaft & getting it all put back together again.

gale, 92 735i

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