Vibration upon Coasting

matreyia

Major
Apr 19, 2017
1,732
Hey Everyone, I just developed a vibration when coasting from rear end. Tested in neutral and does it too. Applying brakes also has this sound. Basically anytime I decelerate in any manner it has this sound...see video to hear.

Anyone had this before? I changed guibo in case that was the cause but no luck. Transmission shifts fine and car works perfect when accelerating...only decelerating shows this noise.

I also checked brakes and shields and cleaned all wheels. I have the M Factory LSD.
Input appreciated.

VT
 

matreyia

Major
Apr 19, 2017
1,732
Do you know if you could possibly have defective bolts do you know manufacturer date of your lsd
What bolts are you speaking of? Wheel? Or differential?

All m3 bushings, diff was installed with brand new BMW bolts as per manual.
Installed new guibo and inspected center bearing support and universal joint and driveshaft to diff collar nut...all tight, normal play. When riding in the back...the helicopter sound did not seem to emit from center of back seat where the differential is located. I sounds like it is coming from left wheel. Only when coasting, or braking, or neutral does the helicopter come into play.

Transmission shifts flawlessly, fast, no issues when applying power...no matter how much. The only thing that is a problem is the helicopter sound when letting go of the gas pedal.

So I think that the wheel bearings need to be replaced...although I replaced them a little over three years ago. But...I have been working at an address with lots of pot holes and been on those roads for almost two years daily. Like...SHITTY potholes and rough surface with RR tracks too... for about 1.5 miles every day. Jarring surface... not acceptable for driving over 30 mph safely. And I did replace shocks with Koni Yellows on medium setting in front and firm setting in rear. Maybe this combination of things is the perfect storm for accelerated decrepitude of the rear wheel bearings.

Anywho, I am going to replace the stock brakes with M sport rear brakes and new rotors and steel lines this week. So new brakes, new rotors, new wheel bearings... and if it still sounds like a helicopter...well, then I guess I have to get a new differential. Damn... This time, I will try wavetrac instead of M Factory.
 

Jeffman

Captain
Jan 7, 2017
1,445
My money is on the rear diff, sorry to say. The sound is not present when accelerating, so what else could make such a sound? Plus Rob noted the diff has a recall.

How about hard braking? Do you get the sound under hard braking?
 

matreyia

Major
Apr 19, 2017
1,732
My money is on the rear diff, sorry to say. The sound is not present when accelerating, so what else could make such a sound? Plus Rob noted the diff has a recall.

How about hard braking? Do you get the sound under hard braking?
Didn't do hard braking test but normal braking does too. Only happens if speed is over 30mph. Jackstands test has no helicopter sound. Wheels must be under load. Could also be parking brake?

Also, sound emitting from wheels.
 
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matreyia

Major
Apr 19, 2017
1,732
My money is on the rear diff, sorry to say. The sound is not present when accelerating, so what else could make such a sound? Plus Rob noted the diff has a recall.

How about hard braking? Do you get the sound under hard braking?
M factory says my unit is not affected. Only 2015 and earlier. And the symptoms are catastrophic and car will bind up and unable to drive. And will make severe grinding at all speeds.
 

Jeffman

Captain
Jan 7, 2017
1,445
Hmmm...
Sounds like we need more data to diagnose the patient.
Maybe stick a GoPro or microphone under there in different spots and test again?
 

tisdrew

Corporal
Jun 27, 2017
170
I had a vibration from rear only on decel, ended up being a warped bolt going into the shock absorber pad for the rear strut. I had just recently taken out/put in the strut when the vibration started so it didn't happen over time. Not sure if this helps your situation.

 
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Reactions: matreyia

matreyia

Major
Apr 19, 2017
1,732
I had a vibration from rear only on decel, ended up being a warped bolt going into the shock absorber pad for the rear strut. I had just recently taken out/put in the strut when the vibration started so it didn't happen over time. Not sure if this helps your situation.

Good idea, I will check these parts too. Yeah, I was driving out of a drive way and it just suddenly happened.
Transmission, engine...ultra smooth shifting and power delivery... ONLY on deceleration does the noise, not even vibration, can't feel anything when helicopter sound happens...only hear it rear wheels.

And if RPM matches the speed of the car, then no noise, only if the wheels spin at different rate as RPM transmission does the noise rise. Also RPM of the noise coincides with the diameter of the wheel...that is to say, it matches the rate of wheel spin and not driveshaft or differential parts. If it were differential or driveshaft spin, I think it would have higher frequency due to the fact that those parts are smaller and have less distance to make full revolutions. Or I could just be full of ignorant shit and don't know what the hell I am talking about. Which is very possible.
 

matreyia

Major
Apr 19, 2017
1,732
I had a vibration from rear only on decel, ended up being a warped bolt going into the shock absorber pad for the rear strut. I had just recently taken out/put in the strut when the vibration started so it didn't happen over time. Not sure if this helps your situation.

Just ordered. Will go ahead and do these too. Now if new brakes, rotors, calipers, wheel bearings and lower shock mounts don't fix the noise, then it has to be the differential... I will also do a review after a few miles.

Screen Shot 2019-07-22 at 11.19.26 AM.png
 

matreyia

Major
Apr 19, 2017
1,732
I had a vibration from rear only on decel, ended up being a warped bolt going into the shock absorber pad for the rear strut. I had just recently taken out/put in the strut when the vibration started so it didn't happen over time. Not sure if this helps your situation.

OK, I can rule this out. Definitely NOT the lower shock mounts. Just installed Turner monoball mounts and car rides smoother (just a tiny bit) but the helicopter sound is still there in the back end. And each day of driving makes it louder and louder. Tomorrow (Friday July 25th) I will have all the wheel bearings delivered. And I will install new bearings on both rear wheels, new M Performance brake calipers and ECS M Performance two piece light rotors and steel lines.

So here is the details on ECS tuning's two piece rotors for stock 335i cars... the listed dimensions are:
336mm x 22mm
and the F30 M Performance retrofit kit for e93 caliper/rotor listed dimensions are:
350mm x 24mm

So when I measured them, the usable contact surface was:
Stock: 60mm
M Performance 65mm

So this works out to roughly 4-5% more area for the M Performance rotors. I suppose any increase is better than no increase. I will weigh them tomorrow after removing the old two piece rotors.

The caliper for F30 M Performance is 3.9x larger than the stock 335i caliper for the rear. I suppose better for heat dissipation.
 

Rob09msport

Major
Oct 28, 2017
1,928
Monroe CT
Center support bearing? Could you have had a diff bushing fail or bolt shear. Have you tried applying parking brake a little too see if it keeps happening ? That could rule out the parking brake .

If you have a diff lockdown remove and see if better if you don't try clamping a plate out something to lockdown diff and see if more noise transfers
 

matreyia

Major
Apr 19, 2017
1,732
Center support bearing? Could you have had a diff bushing fail or bolt shear. Have you tried applying parking brake a little too see if it keeps happening ? That could rule out the parking brake .

If you have a diff lockdown remove and see if better if you don't try clamping a plate out something to lockdown diff and see if more noise transfers
Not center bearing or driveshaft or guibo. All those are fairly new. And guibo is brand new. Differential is smooth and quiet. Noise is from wheel well areas. No vibration from any center location at all.

Parking brakes check out good. All bushings are newish upgraded m3 genuine. No leaks, again...if it were inside the diff...there would be much worse and constant noise and not only decelerating but especially accelerating.
 
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matreyia

Major
Apr 19, 2017
1,732
Ok update. I replaced the bearings, upgraded the rotors and brakes and no dice. While the axles were out I tested the play by holding on to the opposite ends and twisting opposing directions and found the axles had way too much play. So this could very well be the problem. I will order the mfactory axles and if that doesn't work then move to replace the diff.

I will post the particulars of the m performance brakes weights and stupidity of the install.
 
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