My guess is you have at least two problems with the engine.

First of all, probably at least a bad transmission mount. Every 740 I've seen has a bad one by now. They aren't expensive, and other than the possibility of bolts getting stuck in the crossmember, the job is very straightforward. You'll want the car up in the air, either on jacks or good jack stands, and you'll need to support the trans while you remove the crossmember.

If it's like most of them, the mount will be split and it will probably fall apart before you get a chance to unbolt it. Replacing this helped a lot with vibration in my 88 740.

This isn't what your friends are hearing, though. Part of the noise is the cooling fan: it's big, it runs all the time, and it makes a pretty loud roar. But I bet you also have bad exhaust gaskets. These are on the right side of the engine, between the manifold and the head. Have a close look at the 8 nuts that hold on the exhaust manifold. If they're really scary, you could have problems replacing the gaskets. You want to avoid breaking off an exhaust stud.

You may see rusty edges of exhaust gaskets poking out around the 4 manifold ports- often the first and last one blow out first, for whatever reason. The gaskets are cheap, and you should replace the nuts with new copper nuts if you can. If some of the studs pull out complete, with the nut attached, that is ok too, as long as the aluminum threads in the head aren't damaged (usually they're fine). Before doing this job, you want to prepare for it by thoroughly soaking the nuts with PB Blaster or similar penetrating oil. You will get some smoke when the exhaust is hot, not to worry.

If you're not comfortable with the work, and it isn't really a "beginner" type of job, then I'd recommend having a shop do it. Still, spraying the manifold nuts ahead of time will make their job easier, and your bill smaller.

Good luck with it!
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::: Rob Bareiss, New London CT ::: 92 244 M47 212K ::: 90 745GL M47 275K ::: 90 745T AW71 213K ::: 90 745T Parts Car ::: 88 245DL SOLD! ::: 84 242DL Project ::: 70 VW Bus ::: 70 VW Pickup Project ::: 71 VW Notchback :::