[Greyfox]

So, I was just getting started in the process of replacing the two guilbos and center bearing on the drive shaft since that is the only thing I can come up with causing the vibration I get intermittently.

I'm up under the car scoping out the exhaust and everything I need to take loose. I reach up and start feeling the nuts on the flange and get a shock. One of the nuts is only about half way on the stud. No where near being where it should be to hold the exhaust flanges together. Surprised I have not had an exhaust issue like a leak.

I've never nor any mechanic have had the exhaust off the car and I've owned it since 33k.

I picked up a set of brass nuts but all the studs are completely rusted up so I've put off continuing till I get 4 new bolts / studs.

[Efthreeoh]

I hate to tell you this, but you may be in for a world of hurt (well not that bad). So recently I've done a bunch of driveline work, which means anything to do with the driveshaft requires pulling the exhaust. I've taken my exhaust off several times over the past 11 years, but I have a lift, air tools, and various impact guns, all which makes exhaust work quite easy. But the last removal of the exhaust just two months ago, finally left the exhaust studs unusable and in need of replacement.

That's the trouble. With all the tools I have, I could not get the old studs out of the exhaust manifold. The general technique is to cut the studs flush with the face of the exhaust manifold flange, then hammer them out of the flange. With my car... no dice. I tried everything, I use Kroil as my rust penetrating oil (it's industrial strength), no help. I used my air hammer on them... nope. I used a 3 lb. sledge... zilch. Keep in mind the manifold has the cats (with a lot of mileage on them) in it and the O2 sensors, so you can't hammer on it too much.

So that means drilling the studs out, and that was problematic. I used industrial drills bits (technically they are called "drills") meant for drilling hardened steel and a very strong drill (technically its called a "drill motor"). The biggest hole I could drill in the hardened stainless steel flange was 3/8ths. 3/8ths is close to 10MM, but the BMW studs (new parts) are 10MM with knurl, so you need a bit larger than a 10MM hole. Anyway, it's very difficult to drill this steel and difficult to perfectly on center of the old, cut-off, stud. To drill them you need a center punch (a machine shop tool) to mark the face of the stud so the drill doesn't spin off center. You need to start with a smaller diameter drill like 3/16ths or 1/4. And remember the smaller the diameter the slower speed you need to drill. The correct speed is when the drilling "chips" comes out as a spiral of metal.

So I ended up using stainless steel bolts (at first) thinking they'd not rust up for the next removal. But it was a bad decision. Any stainless steel bolts you can get at a good hardware store are Grade 5 at best (i.e. not hardened) and can break eventually. So use hardened Grade 8 steel bolts. If you get the hole drilled to 3/8ths you need a 3/8 by 1.5 or 1.75 inch bolt. 1.5 inch length works fine if you use pinch nuts (i.e. no lock washer).

I wanted to get in the details so to have you understand the difficulty I ran into, and I'm no noob when it comes to DIY'ing. I did all that work standing on my feet. If you are on your back and the car on stands, it will be far more difficult. It might be wise for you to take the car to an independent exhaust shop and have them replace the studs for you.

Good luck with it.

[Efthreeoh]

Now, on the vibration....

I ended up installing a rebuilt driveshaft. I have a vibration in the driveline I eventually traced to my driveshaft (I already replaced the bearing once). I doubt it is the guibos. They runout play for the u-joints is minuscule and not really measurable. My driveshaft had 325,000 miles on it, so I figured it was time for a replacement.

My 2 cents on that.

[Greyfox]

Yep, I do wish I had a lift. But I'm not crazy enough to do this work on jack stands. I have cribbings built that puts 21" of lift under each wheel.

I'll probably use a nut splitter to get the existing nuts off the studs. Or a cut off wheel on the flexi shaft of my Dremel. If that does not work serious amount of heat with a torch works wonders. I may just have to leave the existing studs, clean them up, run a dye down them to true up damaged threads.

I've been debating on buying a front axle, front & rear drive shaft, and rear axle. Still debating and probably won't make a final decision till I get the drive shaft out.

Reason I'm replacing the guibos is because any amount of vibration will have weakened where the rubber and steel grommets are.

PS.... just found this trick also.... An old steam fitters trick. Heat and candle wax. Heat the bolt and push a candle against the bolt an threads. If you got the bolt hot enough it will draw the wax into the thread.