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Discussion Starter · #1 · (Edited)
I drive my car relatively calmly but I discovered a while back that I'm now financially ready to take care.
Whenever I do brake and gas at the same time, there's a heart wrenching grinding noise. It sounds like two metal pieces grinding together. I tried it today to see if the issue was still there and it seems the grinding noise doesn't come in until about 1300rpm. Considering idle is between 650-900 depending on the car temperature, that's not much at all. What's this issue? It's in the back of the car, so at least I know it's not the transmission or engine :D
 

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Would you be able to record a video of this sound?
 

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Discussion Starter · #3 ·
Would you be able to record a video of this sound?
yeah I just made one at http://youtu.be/wZc9L6mqpNY

I couldn't earlier because I was busy. Not sure if it's because I was in my garage but that's the worst it's ever sounded. The noises when off the parking brake and rolling off the disc brakes are normal for my car. What worried me was the grinding noise and then how it didn't stop ticking until my car moved forward a bit (it moved forward because I don't let off the disc brakes until the car is off and parking brake is up)
 

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Check your subframe.

I don't know why your car is dropping down in the back when you're accelerating and not moving...I don't think mine does that...so that itself makes me think subframe. Check your engine mounts and trans mounts too...as your engine would be freer to 'rock' and that's the only thing I can think of as moving when your car isn't. So, I think the issue 'starts' there...and then is attenuating some issue you have in the rear. Could be you've played around with your car and used alternate springs...or your shock is blown...but that grinding sound...that could be the trunk floor or shock towers in rear ripping apart. Look under your car with real good flashlight. They'll be something you can see. Search "subframe" to learn more about what I'm talking about. Inspect well first before driving again. It could just be messed up shocks, since they're also part of lifting up and down in the rear. (Also, careful by thinking things like "that's normal for my car" also--since normal for your car is normal for all our cars...you're isn't 'special' in that regard. If it's always made a sound no other e46 makes, it's not normal...it's an issue you should identify.)
 

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Check your subframe.

I don't know why your car is dropping down in the back when you're accelerating and not moving...I don't think mine does that...so that itself makes me think subframe. Check your engine mounts and trans mounts too...as your engine would be freer to 'rock' and that's the only thing I can think of as moving when your car isn't. So, I think the issue 'starts' there...and then is attenuating some issue you have in the rear. Could be you've played around with your car and used alternate springs...or your shock is blown...but that grinding sound...that could be the trunk floor or shock towers in rear ripping apart. Look under your car with real good flashlight. They'll be something you can see. Search "subframe" to learn more about what I'm talking about. Inspect well first before driving again. It could just be messed up shocks, since they're also part of lifting up and down in the rear. (Also, careful by thinking things like "that's normal for my car" also--since normal for your car is normal for all our cars...you're isn't 'special' in that regard. If it's always made a sound no other e46 makes, it's not normal...it's an issue you should identify.)
 

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Discussion Starter · #6 ·
Check your subframe.

I don't know why your car is dropping down in the back when you're accelerating and not moving...I don't think mine does that...so that itself makes me think subframe. Check your engine mounts and trans mounts too...as your engine would be freer to 'rock' and that's the only thing I can think of as moving when your car isn't. So, I think the issue 'starts' there...and then is attenuating some issue you have in the rear. Could be you've played around with your car and used alternate springs...or your shock is blown...but that grinding sound...that could be the trunk floor or shock towers in rear ripping apart. Look under your car with real good flashlight. They'll be something you can see. Search "subframe" to learn more about what I'm talking about. Inspect well first before driving again. It could just be messed up shocks, since they're also part of lifting up and down in the rear. (Also, careful by thinking things like "that's normal for my car" also--since normal for your car is normal for all our cars...you're isn't 'special' in that regard. If it's always made a sound no other e46 makes, it's not normal...it's an issue you should identify.)

Well luckily for me I had my car inspected by BMW a week after I bought it and it was confirmed that mine doesn't have a subframe issue (few!). As for engine rocking, isn't that something I could check while in neutral or drive? I can rev my engine in neutral and park without any problems (park on accident, neutral once for giggles).

As for the spring setup, I have no idea. How can I tell if they're shot? I've only had this car for 3 months or so, the first 3 weeks I didn't drive it because I was told the bushings were bad and I didn't want to harm the car more than I had to. Since then, that issue has been fixed. I had two or three replaced.

As for the lowering, I was told by my mechanic that this is normal for automatic BMW's, and is partially confirmed here on E36's (http://www.bimmerforums.com/forum/s...-E36-318i-Suspension-shifts-when-put-in-drive)

And when I say normal for my car, I mean in my experience. I haven't been in or driven a "well maintained" E46. I've seen other E46's, but have only ridden in one other, which vibrated when the revs were above 1500rpm or so. Very unpleasant ride. My girlfriends dad owns an E46 M3 and is taking me to a car event, so perhaps I can drive an E46 while I'm there for mechanical comparisons.

Do you think this issue could be linked to a very light clunk noise I hear from the back when coming to a stop? It's extremely audibly low so I couldn't pick it up on a mic but it only happens when I decelerate slowly. If I'm in manual override (+/- mode) and stop in 2nd it usually isn't heard.
 

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I'd remove the trunk lining and have a look at things around the shock towers. And, if you haven't inspected for subframe issue yourself, I'd do that. I had mine inspected also...a year later I found a crack...so perhaps in inspection they missed the beginning of a crack.

Only other thing I can think is that it's a trans. issue, because seemingly you're enjoying your steptronic...as you should be able to...

Anyway, usually when sounds sound that bad, their source is visible. Get a friend with a hose about 5' long to use as a stethoscope and isolate the source. I use a 1" diameter flexible electrical conduit. It's thick and sturdy, so you can easily get it to the center of the car while holding one end against your ear. When you find the location, you'll know better what's up.

hth
 

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Discussion Starter · #8 ·
I'd remove the trunk lining and have a look at things around the shock towers. And, if you haven't inspected for subframe issue yourself, I'd do that. I had mine inspected also...a year later I found a crack...so perhaps in inspection they missed the beginning of a crack.

Only other thing I can think is that it's a trans. issue, because seemingly you're enjoying your steptronic...as you should be able to...

Anyway, usually when sounds sound that bad, their source is visible. Get a friend with a hose about 5' long to use as a stethoscope and isolate the source. I use a 1" diameter flexible electrical conduit. It's thick and sturdy, so you can easily get it to the center of the car while holding one end against your ear. When you find the location, you'll know better what's up.

hth
I appreciate the response, I'm sorry I haven't been on in a while. I did self inspect for subframe issue and it looked really good under there. As for finding the source with a hose, I'd rather not force my car to make the noise if I really don't have to. To be honest, I'm so paranoid now that I think I'll just take it to BMW (if BMW is over $100 to look at it I'll go up). Fingers crossed it's not something crazy expensive. I've already put a lot in
 

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Discussion Starter · #9 ·
Just thought I'd update this. I went to a 3rd party mechanic that works on German cars, perfect yelp reviews (as in all 5/5). They said they'd check it out for $135 (BMW was $250). I got to the mechanic and showed him the very same video posted here, and he said it was my brakes (which are warped in the back and cheap in the front). I knew that wasn't the issue, but another mechanic took my car for a test drive and heard nothing odd. I know there's an issue, but if they said they heard nothing, I assume any present issue isn't something I should worry about. So that's that! :D
 

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...I know there's an issue, but if they said they heard nothing, I assume any present issue isn't something I should worry about. So that's that! :D
And this is why most of us DIY. It seems both mechanics didn't find the source of the problem but were happy to take your money. You will go broke having mechanics trying to fix your 15-year old car.

Buy a pair of ramps, and a good work light and get your face under the car and check EVERYTHING out. Pull off the wheels and inspect the brakes and bearings. You know there's a problem, and to ignore it is asking for disaster.
 

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Okay, so I missed before that you were accelerating and braking. I thought you were in neutral revving the engine and it was dropping down in back...but now I see my confusion. You wrote 'when you do brake and gas' at the same time in your post and I didn't quite understand that. Now I do. Stop doing that, especially if it's to get off the line quickly. That grinding noise was your car telling you to stop doing that. It might have been the abs kicking in too. Anyway, your car is old...treat her nicely!

I'm sorry I glossed over that before...it's just out of my experience to rev and engine in gear and brake at the same time. I thought you were revving it in neutral...though I noticed you did try to start it in first (Check your neutral safely switch...you need to have one on the car. A buddy in a shop almost got run over because someone installed a remote starter, removed the neutral safely switch, and gave him the key fob, which accidentally started the car and pinned him against a brick wall. Make sure you tell anyone who works on your car about that.)
 

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Okay, so I missed before that you were accelerating and braking. I thought you were in neutral revving the engine and it was dropping down in back...but now I see my confusion. You wrote 'when you do brake and gas' at the same time in your post and I didn't quite understand that. Now I do. Stop doing that, especially if it's to get off the line quickly. That grinding noise was your car telling you to stop doing that. It might have been the abs kicking in too. Anyway, your car is old...treat her nicely!

I'm sorry I glossed over that before...it's just out of my experience to rev and engine in gear and brake at the same time. I thought you were revving it in neutral...though I noticed you did try to start it in first (Check your neutral safely switch...you need to have one on the car. A buddy in a shop almost got run over because someone installed a remote starter, removed the neutral safely switch, and gave him the key fob, which accidentally started the car and pinned him against a brick wall. Make sure you tell anyone who works on your car about that.)
Pretty sure OP's car is an automatic.
 

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In the video you get in the car, foot on brake, put in drive, foot still on brake, and now push the gas pedal...

Correct me if I'm wrong but you're burning your torque converter up, no? Pretty sure that's your grinding noise.
 

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In the video you get in the car, foot on brake, put in drive, foot still on brake, and now push the gas pedal...

Correct me if I'm wrong but you're burning your torque converter up, no? Pretty sure that's your grinding noise.
No, that won't burn it up the TC prematurely. Though I wouldn't do that repeatedly! :eeps:

I heard two distinct noises in the video, one sounded like rocks in a can and the other like a grinding noise. OP needs to fully inspect the rear suspension, brakes, drive train, etc., for signs of problems. Barring that, maybe have someone (who knows what they're doing) put the car on a rack and duplicate the problem.
 

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You shouldn't be able to start a car at all in anything other than neutral or park. Unless he'd disengaged his safety switch.

I think his abs may have engaged owing to his brakes beginning to slip...or just the groan from them slipping against his revving.

OP, your car is faster than most, not all. You don't need to launch it.
 

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Ok. Just hooked up my Bose.

That sound is either the torque converter or the parking brake. I'll almost put money on both. The parking brake on the e46 uses a separate drum brake. That what that sound is right at the end when you let off the gas. The rear end is still squatted, so there's a brake involved there... Parking brake/ebrake. The other is torque converter.

If it's not, it'll be something in the drivetrain off the transmission. Only thing that makes sense for that type of sound is commonly the TC. Otherwise, it's the diff... And neither are good.

Edit 2: when you put it in park, always let off the ebrake and let it settle. Then apply the ebrake and let off the brake pedal. It sounds exactly like my '76 stingray. I know you're gonna say different worlds, but not really. The stingray is of the same suspension and drivetrain setup. It will make almost exactly those noises.

Are there any other times you hear these noises other than the circumstances in the video? Also, if you've been taught to EVER do brake and gas at the same time with an automatic transmission, please go backhand whoever taught you that. It's extremely bad.
 

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Discussion Starter · #17 ·
Ok. Just hooked up my Bose.

That sound is either the torque converter or the parking brake. I'll almost put money on both. The parking brake on the e46 uses a separate drum brake. That what that sound is right at the end when you let off the gas. The rear end is still squatted, so there's a brake involved there... Parking brake/ebrake. The other is torque converter.

If it's not, it'll be something in the drivetrain off the transmission. Only thing that makes sense for that type of sound is commonly the TC. Otherwise, it's the diff... And neither are good.

Edit 2: when you put it in park, always let off the ebrake and let it settle. Then apply the ebrake and let off the brake pedal. It sounds exactly like my '76 stingray. I know you're gonna say different worlds, but not really. The stingray is of the same suspension and drivetrain setup. It will make almost exactly those noises.

Are there any other times you hear these noises other than the circumstances in the video? Also, if you've been taught to EVER do brake and gas at the same time with an automatic transmission, please go backhand whoever taught you that. It's extremely bad.
I'm sorry for the late reply. I think the parking brake's only issue is that noise it makes when the ebrake is on and I let go off of the street brakes. If it was the Torque converter, wouldn't the noise have to come from the front of the car where the transmission is?. Also, so how I stop my car is I come to a stop on street brakes, shift to park, raise ebrake, turn off the car, and then let off the street brakes. Then when I start my car, I put my foot on the street brakes, turn on the car, lower the ebrake, and then shift and go on my way. I was told this was the best way to help my transmission last since it reduces the strain on park (??) by my driving instructor when I got my permit. So which is it? Park then let off street brakes and then engage ebrake OR park then put up ebrake and let off street brakes?

Also, since the diff is back there where the noise originates, how can the diff fail? isn't it simply a series of edged gears? Don't make fun of me if that's wrong >.< I'm learning cars as fast as I can.

No, I don't here these noises in any other occasion. I do hear a quiet "thunk" when I come to a stop when decelerating slowly. Brakes make a noise when I crawl very slowly

Who taught me brake and gas in automatics? YouTube and Topgear! :D This is the first car I've driven that was older than 6 years. I watch video's on other cars and they do it, but I get there cars are newer and because I watch videos about performance cars, they adjust or whatever for launch control and stuff. Don't worry, I don't do it after the first time I tried it. After that and paying for my bushings, I drive my car very gently.
 

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Discussion Starter · #18 ·
And this is why most of us DIY. It seems both mechanics didn't find the source of the problem but were happy to take your money. You will go broke having mechanics trying to fix your 15-year old car.

Buy a pair of ramps, and a good work light and get your face under the car and check EVERYTHING out. Pull off the wheels and inspect the brakes and bearings. You know there's a problem, and to ignore it is asking for disaster.
Thank you for your reply. I did forget to mention the mechanics chose to not charge me anything for looking at it. And what do you mean a pair of ramps? I can't imagine what is capable of holding up my car and can lift it. Can you recommend me a product? I'll be pulling off the wheels and brakes because I bought new rear brake discs and pads that are very nice quality (my fronts are even more responsible for noises when stopping :p) and will be installing them myself (will look here for a DIY).

And yeah you're right, it's just easy to ignore a problem that only comes around on rare circumstances, but I know it's all connected and everything should be considered.

Anything I should look for when my wheels are off? Or should I look at other forums for what symptoms to look for? Mainly thinking of suspension, and I don't know what to look for in drive terrain. I'm not that in depth with car knowledge, I only really get numbers. And as you said, yes, my car is an automatic. :) Haven't had the privilege to be offered the opportunity to learn stick.
 

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Discussion Starter · #19 ·
You shouldn't be able to start a car at all in anything other than neutral or park. Unless he'd disengaged his safety switch.

I think his abs may have engaged owing to his brakes beginning to slip...or just the groan from them slipping against his revving.

OP, your car is faster than most, not all. You don't need to launch it.
So referring to your first post, my car is an automatic. My car did the lowering when I shifted from park to drive, and I built revs in drive by holding on the street brakes, not the ebrake or with any clutch magic :p. But yeah I only discovered this issue when I first bought the car because I was being a bit of an idiot and just over excited. After I got my bushings, I've been driving her very nicely :).

And what's a neutral safety switch? I doubt mine was removed, the previous owner was obviously not car savvy and the miles (and owner which BMW accidentally gave me) suggest the car was driven calmly. I believe on modern cars it's a little tab near the shifter, right?

I did notice the wheel to slip, and I do feel it's partially due to my rear brakes, which are also warped and they look old old old. The noise is just so loud that in the garage I couldn't pinpoint the source, and while driving you can only tell it's in the back. Perhaps my brake rotor and pad replacement will fix the problem? I want to believe it's my brakes, since it only happens when they're engaged, but I know when I let go of the brakes, other parts can move freely as well, possibly parts that are grinding against each other are free to move apart from each other. I guess I should make another thread once I do my brake replacement
 
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