Help Diagnosing Rear end vibration

[Gabs]

Hey guys,

As of late I'm having a loud hum and vibration, enough to rattle things in my center console. I'm quite convinced its within the drive line.

Things I've noticed are, the Hum/vibration begins at 80km/h and up, before that speed it doesn't seem present. When turning right the hum stops until going straight again. When turning left the hum does not go away.

Today I had a chance to open the differential, the fluid was quite dirty though I found no shavings. I removed the back plate and and inspected for damage. The ring gear looks factory fresh still, and very minimal wear on the axle gears.

Ive reassembled the backplate and mount with new gaskets (plate,sensor etc), and In the morning will fill with new fluid and check for the hum.

My fluid level was fine before i removed the back plate, so I'm quite doubt full that fresh fluid will help this hum.

My best guess would be an axle bearing or wheel bearing, what are you guys thoughts?

[romkasponka]

Check your wheels...

[nicknikolovski]

Possibly a wheel bearing. Try shifting the weight of the vehicle. Road test the vehicle similar to how race cars warm up they're tyres. The pitch of the noise should go up & then down, up & down. Not constant. Check the amount of backlash in the tailshaft and also the axles. Also check over your rear components and see if anything is rubbing on the wheels or tyres (the noise would proberbly happen all the time). Good luck.

[DesktopDave]

I'd suspect a left rear wheel bearing or half-shaft also.

While you're down there, check the center support bearing, along with the transmission mounts.  They usually last 150k miles or so.  On a 20-year-old car they've likely never been replaced.  They can cause all sorts of odd noises.

[Gabs]

Sorry guys, Work has been more then hectic lately.
Something I neglected to mention in my original post, the vibration began after taking a 500km Trip (250 There, 250 Back). At an average speed of about 140 km/h.

My original thought was the differential, because the plugs are both practically seized in. I had not checked for level, ever on this car (1.2 Years of Ownership). Also it leaked from the bottom of the diff plate. So I figured I ran it dry and ruined the axle gears or something. Anyway I digress.

Tonight after work, I tried what nicknikolovski suggested. When jolting my wheel to the left the vibration goes away for that split second of weight transfer. When to the right the vibration is unaffected.

Leaving me to think a wheel bearing is begging for replacement. Question would be which side? Taking into account my suspension is quite soft and worn, when moving my steering wheel to the left in quick motion, the weight of the vehicle would be shifted to the right side of the vehicle, correct? Assuming I have that correct, the problem would most likely be a right side issue?

A thought just crossed my mind, last weekend I finally had a chance to install my new cross drilled rotors and some fresh new pads. Though oddly my front passenger side has a odd kind of a cling clang of a loose bolt type of sound when I go over bumps. Ive thoroughly checked and rechecked for loose bolts, bad pad springs, loose mounting brackets, slide bolts are all thread locked. I cannot figure out where this sound it coming from but its quite unnerving. Could this be the possibly sound of a bad front right wheel bearing?

[DesktopDave]

The level of oil in your diff isn't critical.  It has enough oil below  the level of the seal to provide a fail-safe.  I'd bet it's OK.

Vibration is difficult to track down.  Worn bushings can cause it, worn bearings as well.  The front bearings rarely go bad, the rear ones more frequently.  So I'd suspect those more.  Test the bearings in long sweeping turns.  The car's weight shifts less dramatically, but you should be able to determine a side that's louder.  After you've narrowed that down, load the bearings front/rear with braking (front) and acceleration (rear) tests.  You can also use the parking brake at higher speeds to load the rear bearings (just don't lock it up).

Clunking could be the fit of the front pads too - some just don't fit, the pads are slightly too small or the carrier slides are worn.  Some hard high-performance racing pads clatter away, that's the way they are.  How are the slide bushings in the caliper?  They have to be really tight..was it difficult to get the caliper posts back in?  Did you lube them with high-temp lithium grease?  Does the rattle go away if you're using the brakes?  Or is it constant?  Did the rotor fit perfectly on the hub, or was it difficult to install?

[Gabs]

Hmm good to know dave, ill worry less about my differential but yes I was in the differential a few weeks ago, and it looked factory fresh.

As per the vibration/hum, when I turn left the vibration goes away, though when turning right or moving in a straight line the vibration persists. Im not quite sure what you mean by load the bearings, I would assume your meaning put load on them to help diagnose which bearing it is making noise?

The carrier slides seemed to fit well with the new pads, though I suppose there could be some play, ill investigate this weekend. Though I'm not sure I have racing pads, they are street pads labeled as "High Performance". I cant say I tightened the slide bushings with any extreme force, I thread locked them and put them in tight enough so they wont be going anywhere. Ill give them a better tightening this weekend. No difficulty installing the posts back in. I did not lube them. I'm not sure if it goes away while braking, ill check tonight after work and report back. ill note again the rattle is only while going over bumps. I had no Issue with the rotors, they fit the hub like a glove. Though I did have to drill the heads off 2/4 retaining bolts, both on the right side.

[DesktopDave]

Yep, that's what I meant.  The varying dynamic load on each wheel as you 'push' the chassis really can help narrow down the source.  Clunking or rattling in the suspension is difficult to chase down at times.  Have you tested the ball joints too?  They should have no discernible play.

I have also had trouble in the past with the lug bolts, believe it or not.  The wheel fits very tightly on the hub in BMWs, a little grease or dirt can make it sticky.  If you don't follow the recommended x-pattern to re-tighten, the wheel can mate solidly but have a bolt or two come loose later on.  I go twice around with a torque wrench now, haven't had the problem since.

Those rotor hex bolts are unnecessary IMHO.  Just another annoyance.  If the car had studs they wouldn't need them.

[DesktopDave]

Just to clear things up, I meant the rubber isolation bushings inside the caliper ears...they erode over time and then can squirm a bit on the mounting pins.  Maybe give the big caliper carrier/hub bolts a twist too.

You can also also check for front bearing play by grabbing the offending passenger side wheel & trying to wiggle it back & forth.  There should be no play in that either.

Believe it or not, I have a similar problem with my car.  I have a slightly worn tie-rod that's not bad enough to replace yet.  It makes for a bit of vibration.  That's not the problem though...from what I've been able to guess, it's a bad bearing in the steering column itself.  Not the u-joint, not the slide joint, but the steering tube.  Not fun nor easy to replace.  I just live with it.  I will post pics when it comes out though...

[Gabs]

Looks like this issue is slightly irrelevant now. I present to you with a broken, 318iS loving heart, my bent up 318iS. A dear jumped out at me at 100km/h on the highway on my way home from work, I hit half of it. The damage would appear to be minor for a dear hit, though pay close attention to the ripple in the 4th picture (top left). Anyone know if this is a main structural support? Will a body shop even touch such damage? I know that they wont touch sub frames anymore, welding wise. So I'm thinking they wouldn't touch that.







While the m42 is still undamaged, This is a heart breaker. Fender, Hood, Headlight assembly, Fan, Shroud, Kidney Nose, Passenger grill, Radiator, Radiator hoses, and most likely a quite few other things as well all need replacement. Assuming the damage to that front support is repairable. sssiigggghhhhhh

[harvey2]

I was following this thread because I've got a vibration too, then I come across these pictures and its like being punched in the gut.  I really feel your pain, man.

[Gabs]

Yes harvey, its quite unfortunate. The poor car is sitting in my backyard with the entire front end stripped naked, Plus about 1/4 Inch of snow on it. Managed to body slam my hood flat enough to protect the engine bay, to some degree. Currently I'm catching up on bills, though within a month or two I plan to have a portable carport & 20 000BTU heater all setup in my backyard.

Suffice to say this wasn't how I expected to start the 318's rebuild, but regardless the fact that its repairable after hitting a large male deer at 100km/h, makes me think life wanted me to rebuild it, instead of drive the poor thing through another harsh Canadian winter.

I figure since winter here in Canada will last until the end April, I might as well rebuild the majority of the car, my intention is to race this car around the track next summer. So I will likely be upgrading to race worthy parts.  

As per you vibration, I'm 98% sure I narrowed my vibration down to one of the two rear wheel bearings. So let us try and narrow yours down.

Is the vibration constant?
Have you tried a weight transfer test? (Mentioned above)
Does it go away while turning a certain direction?
Have you check drive shaft play?
Have you checked your half shafts? (Rear Axle shafts)
Have you Checked you Guibo Disc? (Drive shaft Flex disc)
Middle drive shaft bearing?
tires and rims balanced & Undamaged?
Transmission mounts?

I think starting your diagnosis with those question, will lead you in the correct direction. Big thanks Dave for helping with the diagnosis, and the brake rattle. While I never had a chance to go look at the brakes again, I'm sure ill get it sorted out this winter.

[Gabs]

Well since I still have one devoted follower I decided I'd post a few pictures from the weekend after the accident. The beginning of the tear down, unfortunately I stopped taking pictures the weekend after, when I did the full tear down.

Looks pretty cool without the hood, I must admit.


Look at that 1/4 of the kidney nose survived, found it pinched between some of the broken rad mount pieces




Draining what little was left in the Rad


And The moment I decided it was repairable, after removing that fender, to find a perfect undamaged unibody.




May I also brag quickly, the BMW Strip Oil cap and spark plug cover were painted by yours truly. A man who had never really painted anything before I highly recommend Krylons "Fusion" line up of rattle cans. Unbelievable quality, that paint will stick evenly to literally ANY surface, sanded or not. I also paint my old alternator with it with little sanding done, very nice looking finish, though never got around to rebuilding the old alt haha.

[DesktopDave]

Sorry to hear about the deer strike.  Glad to hear you're OK.  I feel your pain, but the car is replaceable.  We have millions of deer here too, surprisingly dangerous for such a cute & furry critter.  Occasionally someone gets killed by an injured deer!

You have a few alternatives...none of them especially fun.  You could attempt to bend it back into shape. Might need a hydraulic ram or a come-along, but even a hammer and an anvil of some type will do a surprising amount of good.  I'm figuring the really tough part will be the alignment of the hood though.

If the rest of the car is pretty straight I'd be tempted to fix it right though...get an angle grinder, Eastwood epoxy panel adhesive (or a Harbor Freight welder) and some thin scrap steel (cut it out of the bent bits).  Cut the entire upper front box from a parts car, maybe the donor that gives the hood & passenger panel (salvage yards will be very helpful for this).  Cut the bent support out, glue in some scrap steel shims to support the repair & glue the new one on.  Epoxy is shockingly strong, but you'll need the right temperature for it to cure.

Your facia panel/bumper/driving lights all look really good, there's a little good news, eh?

[Gabs]

Well I guess not everyone can find fun in bending their car back together, I found it to be a fun new challenge.

Armed with a "scissor" type car jack, a nice 4ft long piece of 2x4, 2 mid and long size pry bars, and various hand tools. I was able to do some straightening. Though I still don't plan on driving this car just yet.
 
The problem Dave, is that the salvage yards in this city rarely come across e30 bmws. The only one I know of in this city, they wont let you take parts from, they want to sell the car as is. And I'm not about to drop $1500 on a parts car.

I may see if any welding shops around the city can reinforce it and/or repair it.

Although the hood is slightly misaligned at the moment, it does now fully close and properly seat in the roller grooves. The hood is pretty mangled but I've bent is close to straight, only for the purpose of knowing if I have aligned everything properly. Looking into a aftermarket hood, maybe santa will bring it