Author Topic: M42 Vibrating (Read 4387 times)

Bammer · « **on:** February 24, 2012, 02:28:48 PM »

First post.

I own a ’91 318iS.

Love the car. Bought it for fun and fuel economy. Only had it 6 years or so --- but I’ve already put almost 170k miles (200k total) on her. Rims, suspension, brakes, driver’s seat . . . all up-graded. No wrecks, mostly original paint, regular service, never been apart.

A few weeks back, getting off the freeway, coming down from ~70 MPH, I noticed a shake. Light, almost like a tingle, high-frequency, but felt not so much heard --- kinda like driving on a grooved road surface. Went away as I stopped, but came back again at city-traffic speeds. Got so intense that at one point, all the junk in the door pouches was buzzing from it.

Next morning, I started the car, half expecting it to've cleared up --- no. And then, driving on the freeway? . . . . whole car groaned/vibrated/moo’d. It was awful.

And scary.

I’ve been driving e30s for almost 20 years, owned 5 --- all 4-cylinders . . . either M42s or S14s . . . never felt or heard of anything like this.

Took it to the Mechanic, explained the issue, they drove it, experienced the issue. Pulled the trans --- found a damaged pilot bearing. Swapped out the original open 4.10 diff, put in a used 3.91 LSD. Looked at drive shaft, half-shafts, CSB . . . nothing amiss.

Got the car back, but . . . not fixed. Buzzes so bad at 3k/5th on the freeway, car feels like a gigantic electric razor. Un-effing-believable.

Never the smoothest car, always been a bit 'buzzy' . . . but nothing like this. Apart from some odd buzzes over the years --- gave no warning. (And I did have the car smog-tested just before.)

The only recent issues have been the hydraulic tensioner (replaced ~1k mi, ago) and some racket from the exhaust --- light rattle at start-up . . . cat + silencer are original.

Any suggestions, insights, conspiracy theories to share? Car's a Keeper, always cherished, so . . . .

RVK

colin86325 · « **Reply #1 on:** February 24, 2012, 03:36:20 PM »

Possible damaged motor mount? Or cracked motor mount tab on the subframe?

Wrench · « **Reply #2 on:** February 24, 2012, 09:12:20 PM »

Check the motor mounts. All kinds of harmonic vibrations can be felt through a bad motor mount.

d.hitchcock · « **Reply #3 on:** February 24, 2012, 11:31:34 PM »

It sure sounds like a driveshaft issue.

A bad wheel bearing perhaps?

Wrench · « **Reply #4 on:** February 25, 2012, 08:03:42 AM »

Check the rubber flex disk at the front of the drive shaft as well as the carrier bearing in the middle. Look for cracks in the rubber on both. I just replaced one of these yesterday on a 1974 2002 turbo. It made the whole car vibrate.

Bammer · « **Reply #5 on:** February 25, 2012, 09:46:56 AM »

Motor (and trans) mounts? . . . looked OK . . . but we'll check for a 'cracked tab'

Drive shaft? . . . my M3's had a drive shaft service, as I recall --- the whole thing came out, got re-built/re-balanced. I asked about this --- 'looked fine' --- but I'll follow-up.

Wheel bearings/dragging brakes-bad caliper/tweaked half-shaft-bad diff? At one point, we had the car up on the lift, all put together, engine running . . . Mechanic put his hand up against the bell housing . . . could feel the engine shaking, like crazy --- even at idle/low power. Thought it might be the clutch had lost a chunk, was causing it. But the clutch looked fine.

Understand, this motor rarely sees the other side of 4k --- there's just no power up there. I bought the thing as a 'hooptie' --- not a racer, but I take good care of her --- she's spotless, garaged, serviced, etc. Always start off slow, warm 'er up, then hum along. Even at 200k, only uses a qt of Redline 20/50 every 3k mi. (I expect to put a million miles on 'er!)

So all of this trouble feels a bit odd.

Monday, I want to start from the top --- visual checks, etc. Then? Fuel/spark/ignition --- basics. Then? Compression/leak-down. Then? Guibo/harmonic balancer/dual-mass flywheel/obstructed exhaust?/??? --- we'll pull the effing motor, if we have to.

Mechanic is flummoxed, now --- and fired-up. (Big Racer, so he's not about to let my little sh!t-box antique get the best of him!) I'll let everyone know how things turn out.

R

DesktopDave · « **Reply #6 on:** February 25, 2012, 10:07:29 AM »

There's no power up top? Mine only has power above 3K RPM or so. Might it be a cylinder cutting out or bad cam sensor? Check the coils by swapping the harness around. The coils all come apart on the e30. I've seen several cars with a single bad coil (which takes the associated coil driver transistor with it), though none of them vibrated like yours does.

Did you do a stomp test?

If this is happening on your mech's lift, it'd have to be a motor/clutch/transmission issue. You eliminated the rest of the power train. I'd suspect the dual-mass clutch/shift fork or TOB personally, but your mech thinks they're OK. Maybe the transmission input bearing? He didn't pull the transmission, did he? I'd be tempted to go there first. I'd be tempted to swap in an M20 clutch or lightened flywheel & change all the seals while I was at it. That's a very popular mod, I'll bet it improves economy and off the line acceleration. IMHO I'd use an M40 or M42 non-A/C flywheel. They're smaller & lighter but unfortunately far rarer. The M42 doesn't make enough torque to be a problem. Valeo offers a BMW kit as well, but that's about $600 from what I've seen.

keflaman · « **Reply #7 on:** February 25, 2012, 10:03:42 PM »

Slap another set of tires/rims on it and see what happens. I know you said the mechanic felt vibrations while on the lift, but I think tires are worth investigating as well.

enildeR · « **Reply #8 on:** March 02, 2012, 12:54:16 PM »

Was there a conclusion on this? Was it a bad motor mount or something else? Mine was doing the same thing. Although, it did not get worse for a while. It didn't get really bad until I made a very hard stop on the freeway because of stopped traffic. The hard stop pushed the motor, and as a consequence finally broke the motor mount tab. (It was previously only bent.) FYI, if it is a bad motor mount, you can pickup a front subframe from any other e30. They're all the same (I didn't know if they differed between motors, as some cars are like that).

...And if that is the case, and you do land up replacing the subframe, do yourself a favor and buy this reinforcement kit.
http://www.turnermotorsport.com/p-4079-e30-front-subframe-reinforcement-kit.aspx

enildeR · « **Reply #9 on:** March 02, 2012, 12:56:06 PM »

Oh. Welcome to the board, too! Just noticed that these were your first two posts. I used to live in Tustin. Man, I really miss Newport!