Strange Driveline Noise

[TNM42]

Hey Guys & Gals,

I'm a long-time lurker, but new member to M42 Club.  I recently purchased my first e30 and love the car. It's a 1991 318is, mostly stock but a little rough around the edges.

I am working on bringing the car back to great condition, a little bit at a time.

My question involves an odd noise coming from under the car.  The best way I can describe the sound is to say that it sounds like an amplified version of a baseball card in the spokes of a bicycle wheel and seems to come from somewhere between my shifter and the passenger seat.

The sound is not constant, but rather begins to rattle when I have taken a hard/fast right turn, after I brake firmly, or when reversing. The speed of the sound seems to be positively correlated to my forward speed and occurs whether I am in gear or not.

The exhaust was completely shot when I got the car, and the CAT rattled like crazy when I hit it with my hand. The only local BMW mechanic I could find told me that he thought that was the cause of the sound. Today, I took the car to a local muffler shop and had a new cat, resonator, and muffler welded on.

As I left the shop the car seemed to be fixed, but after taking it out for a drive the sound started to occur again under the same circumstances as before. However, it is now harder to make it happen and it doesn't continue to do it for as long as it did before having the exhaust put on.

So it seems that the new exhaust has helped the situation, but not cured it. It honestly sounds like something ticking against my driveshaft, but when the car was on the lift today I took a good look under it and couldn't see anything hitting it.
Any ideas as to what it could be?

Kurt

[DesktopDave]

My guess is a rear bearing or the parking brake is out of adjustment.  Does the brake grip both rear wheels equally?  If not, that might be your trouble.

If it was constant in accel or decel I'd suspect the driveshaft, but since it varies with both speed and side loading, I'd guess it's isolated to one side.  I have a similar problem with mine, I'll post results when I get a chance to check it all out.

[e30Andym42]

This sounds a lot like what mine is experiencing.  Not guaranteeing it, but sure sounds like mine.

Mine happens when I take right turns, at varying speeds.

For years I've had this scary noise, and then I finally lifted the car and started banging around on some suspension components after being convinced it was suspension related.  Then it hit me.  The exhaust.  I had finally discovered the cause of the noise.  The muffler bracket was banging on the underside of the car.  I am still scratching my head on a solution, but you can check my "Help!" thread lol

http://m42club.com/forums/showthread.php?t=12541



To determine if you have my problem, take a piece of rubber hose or something to "pad" the part of the car where the muffler bracket may cantact the car in the driver's side rear wheel well.  It should be right around this loop thing:



Underside



I just shoved some rubber hose in that loop (as you can see in the second picture) and took it for a spin.  The noise was gone until the piece of rubber hose was pushed out of the way.

[TNM42]

Thanks a lot Dave and Andy.  I really appreciate your input, as well as the photos.

While I am home for the holiday this weekend, I will try to sneak in some garage time and get the car lifted so that I can check to see how the parking break holds and get a better look at that exhaust.

When the sound is at it's most severe, I can feel the thump through my seat. It's starting to really concern me.

I'll report back with what I find.

[DesktopDave]

I'd take a good look at the drive shaft too.  The guibo is fairly easy to inspect but the center support bearing is hidden above the heat shield and exhaust.  Those two items are right beside your seat, you will definitely feel problems as well as hear them.

I'd also advise checking the rear transmission mounts.  They're easy to check - on the rear of the transmission - just look for cracking.  I put a jack under the back end of the transmission and lift it slightly (1/2" or so) to see if they're still firm, not squishy or broken.  In a pinch you can use virtually any BMW manual transmission mount to replace them.  IIRC the e28 535i or e21 320i is a cheap OEM upgrade.

I've had e30s that both of them were severed...as in no connection of the tranny to the car.

[e30Andym42]

My support bearing went bad after I replaced the throwout bearing.  The rubber was completely shot.  The center connection was banging on the exhaust shield.  So every rotation, there was a really bad banging noise.  I forgot the conditions that it made that noise worse, but it happened pretty much as long as I was moving.  If the noise isn't relative to the speed of the car, then this shouldn't be your problem.  However, it never hurts to look since it isn't too hard to get at.

[TNM42]

Thanks for all of the great tips, guys. Being new to e30s, it is super nice to have knowledgeable people so willing to help.

I was finally able to get the car on ramps and crawl under it this afternoon.  After removing the heat shield, it was immediately apparent that the center support bearing is completely shot; there isn't a single ball left in the bearing.

Tomorrow, I will be ordering a new CSB and a guibo (the current one isn't shot, but it certainly isn't in great shape either.)  Is there anything else I should go ahead and order and/or fix while I do these two items?  

Unfortunately it looks like i may have to drop the brand new exhaust that was just welded on a week or two ago in order to get the drive shaft out, so I'm hoping I can talk the exhaust man in to letting me use his lift to do the entire job.  This isn't the best time of year to be laying on concrete.