Bruce Banner

iTrader: (2)

I recently experienced a terrible vibration when I step down on the clutch and brake very firmly.
The shop that looked at my car told me I needed rotors, they said they were warped.

I was driving and I thought about it today. It seems to ONLY happen when I depress the clutch and do firm braking to stop.

So to test this, I drove it today and got it up to 40mph and some hard stopping but I put it in neutral and did not step down on the clutch. Did this 3 times, no vibration.

There should be no correlation between a clutch and the brake. If my rotor really was warped, wouldn't it still vibrate when I brake hard in neutral?

I also experienced this the other day when I parked up an incline, I put it in first gear gave it gas then quickly stepped down on the clutch and brake to prevent from going to far and I had a terrible vibration. I quickly put it in neutral and it stopped.

pohljm

not the rotors

NetGnome

Motor mount?

justnspace

iTrader: (1)

you've recently done clutch work.
did you replace the flywheel?

Bruce Banner

iTrader: (2)

Yup new fly, they said all mounts were good. I had this issue before the clutch job

justnspace

iTrader: (1)

^i was discussing clutches, and pressure plates and flywheels yesterday with StreetKA over on the CL side.
something struck out to me.

he said: " refinishing/turning flywheel is not really recommended, you'll get drive line vibrations"

but you replaced yours.
Hmmmm.

Bruce Banner

iTrader: (2)

Yup, I bought a new OEM Luk fly.
The shaking doesn't happen all the time, just when I depress the clutch and apply firm braking.

I also noticed this odd behavior: Holding down the brake at a stop, sometimes if I depress the clutch the brake pedal will sink a little bit. Dunno if that is normal.

Bruce Banner

iTrader: (2)

I now know how to make the violent shuddering occur.
When I brake over bumpy roads, the car begins to shudder violently, like it's falling apart.

I found this thread on another forum, where people are experiencing the same issue. No real answer over there.
Does anyone here have an idea?

I just had new ball joints put in, the mechs that looked at it, said everything looked ok.

http://www.bimmerfest.com/forums/showthread.php?t=81465

04WDPSeDaN

iTrader: (1)

go on the highway get your brakes fairly warmed up, do about 75 and press them moderately hard. If you feel a shake, shimmy in your seat or steering wheel or pedals your rotors are warped. forget about pressing the clutch in or anything just put your foot on the brake and let me know what happens. And to confirm anything else, do 75 and put it in neutral and then press on the brakes. Last test... do this once more but slowly pressing on the clutch without brakes see if you feel vibrations. This is the only way to eliminate issues

Bruce Banner

iTrader: (2)

I have done drives with the brakes warmed up at 50-60mph on long roads and hard braking, with the car in neutral no clutch. I don't experience any shuddering.
I will try what you suggest though.

Like that thread from the bmw site, my experience with the shuddering is the same as their situations. One guy was saying he would experience the shuddering pulling up on his driveway and I have experienced that. Ive pulled up to park, clutch down and brake to stop and I got crazy shuddering. Other times I'm going 45mph slowing down to enter a turn, the road is bumpy I brake firmly and the shudder kicks in. I have a slightly bumpy road at the corner where I live, every time I enter that lane and I brake firmly in neutral going over the bumps the car shudders. The shuddering is very violent, literally feels like the car is falling apart and I feel vibration at the brake pedal.

It's happening at pretty low speeds. That BMW thread was suggesting like ABS sensor, control arms.
The previous owner had the control arms and suspension replaced last yr. I recently had both the front lower ball joints replaced. Replacing those did resolve another "dok" sound I would hear backing up.

When I back out while turning I do hear another"dok" kinda sound coming from the front. It's not the same sound as before the new ball joints. Its lower in tone
I've asked techs to look at my mounts, bushings to see if anything is wrong. They all say its ok. I don't think anyone's tried to take the calipers off to look.

connork53

iTrader: (1)

what happens when you do clutch + brake without shifting same result?

Bruce Banner

iTrader: (2)

When I first experienced it, I was probably in 5th gear. I left it in 5th, then clutch +brake and it did shudder.
Seems like the clutching isn't related, which makes sense cause now I can replicate it by braking firmly in neutral over bumpy roads.
It's a pretty scary feeling, really feels like the whole car is falling apart and affects my stopping ability.

pohljm

sounds like your ABS is pulsing to me.

Bruce Banner

iTrader: (2)

ABS sensor was one of the suspected culprits in that bmw forum.