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Suspension & Braking Forum by BimmerWorld
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Old 04-18-2013, 03:05 AM   #1
jeremy0000
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Knocking sound from rear when braking or hitting a bump

On my way home tonight I heard a knocking sound everytime I hit a bump in the road. I dismissed it for something loose in the back as the sound was kind of faint. As the drive went on the knock started getting louder and I started hearing it when I applied the brake as well. Within a couple of miles everytime I hit a bump the knock was so loud it felt like something was going to fall off, and I could also not only hear it while applying the brake pedal but could feel it in the pedal as well. By the time I got home when I applied the brake I would get two loud knocks coming from the right rear, and the car would come to a stop without any subsequent knocks solong as I kept my foot on the brake pedal. Releasing and reapplying resulted in two more knocks. I intend to jack it up and invesigate in the morning but I was hoping someone might have some insight as to what to look for. Thanks, it is a 2003 325iT.
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Old 04-18-2013, 03:16 AM   #2
Kar Laeda
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Got a brick in the trunk?
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Old 04-18-2013, 04:15 AM   #3
MJLavelle
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Check your rear shock mounts. They can fail, and cause some noise. Hopefully, they don't look like this:

Untitled by MJLavelle, on Flickr

Another possibility, which would be much worse, would be rear subframe damage. You can find plenty of info on here as to what you need to check.
B
It could also be a brake issue. Some things to look for would be any calipers that are loose, meaning the mounting bolts are not locked down, or a broken or missing caliper pin, which would be rare, but possible. You may have a caliper that is sticking, and not moving freely on the guide pins. One sure sign of this would be excessive heat on the sticking caliper after a short drive. Take the car out for a few mins, press the brakes a few times, and when you get back home, check and see if one side seems much hotter than the other. It could also be a parking brake issue, where the pads are rubbing all the time, because they need adjusted, or have rusted, and are rubbing all the time. That would also be pretty rare.

Other issues could be a suspension issue, where something has come loose, like a sway bar. Another remote possibility would be a bad bushing, possibly your RTAB's, or the rear differential bushing.

The rear shock mount or a rear subframe issue is a more likely explanation, if the noise is as loud as you say it is. I hope I am wrong, but if it has to be anything, I hope it is the rear shock mount, since that is a fairly easy and cheap repair. But the list of possibilities is fairly long, so you have plenty of things to check.
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Old 04-18-2013, 08:47 AM   #4
dre8119
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Maybe differential mounts. Also check for cracks in the subframe, just to be on the safe side. Happened to me, but I was only hearing it on shifts.
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Old 04-18-2013, 12:01 PM   #5
jdstrickland
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Shock mounts, suspension mounts, differential mounts, exhaust system banging around.

Maybe you should put the car on jack stands and crawl under it to look around. There are lots of things that can make noise when going over a bump.

The first thing to do is look to see if the spare tire is secured in the trunk, and that there are no cans rolling around in the spare tire well.

Your question is sorta like, "Good morning you guys, what should I do first today?" Have you gone to the bathroom yet? Had breakfast? Where do we start?
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Old 04-18-2013, 12:14 PM   #6
jeremy0000
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Quote:
Originally Posted by jdstrickland View Post
Shock mounts, suspension mounts, differential mounts, exhaust system banging around.

Maybe you should put the car on jack stands and crawl under it to look around. There are lots of things that can make noise when going over a bump.

The first thing to do is look to see if the spare tire is secured in the trunk, and that there are no cans rolling around in the spare tire well.

Your question is sorta like, "Good morning you guys, what should I do first today?" Have you gone to the bathroom yet? Had breakfast? Where do we start?
I mentioned in my post that when I apply the brake pedal I can hear a knocking noise as well as FEEL it in the brake pedal. If my spare tire were moving around would I feel it in the brake pedal?
I also said that I intend to jack up my car and investigate.
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Old 04-18-2013, 12:43 PM   #7
jdstrickland
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I missed the part about feeling it in the pedal.

Put the car on jack stands and take the tires off to inspect the brakes. Look at the bushings where the suspension components are attached to the frame. The worn parts should be pretty obvious.
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Old 04-18-2013, 01:00 PM   #8
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Check any thing that might be loose in the trunk.
Factory jack, spare tire, wheel chock.

I once mistook the loose factory jacks for the busted RSMs and ordered them with reinforcement plates and all the hardware. I used them when I mounted my coils anyway. It might not be in your case.
But never hurts to check the RSMs. Remove the rotors and check the parking brake as well. May thats loose and hitting something within the hub.
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Old 04-18-2013, 10:33 PM   #9
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I am guessing this is my problem?

This is my first time working on suspension. Do I need any specialty tools?
I'll try searching the forum for threads.
Thanks again.
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Old 04-18-2013, 10:36 PM   #10
trj
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You might want to really check rsms if your bump stops look like that.
No speciality tools needed. Just 13mm and 18mm sockets, torque wrench.
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Old 04-18-2013, 10:42 PM   #11
Blueandwhite85
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Knocking sound from rear when braking or hitting a bump

Eagle eye LEDs?


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Old 04-18-2013, 10:43 PM   #12
jeremy0000
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Quote:
Originally Posted by trj View Post
You might want to really check rsms if your bump stops look like that.
No speciality tools needed. Just 13mm and 18mm sockets, torque wrench.
Thanks! In addition to the rsm what else should I get? Bushings? Also should I go ahead and do the other side while I am at it?
Sorry I am pretty ignorant when it comes to suspension.
thanks again. Gonna try and get this done tonight.
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Old 04-18-2013, 10:54 PM   #13
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Yah do both sides. With suspension and brakes always do in pairs.

Check out the DIY's on rsms and rear shock installation. RTAB might be too much of a DIY if you are just starting to work on the car and don't have correct tools.

You might want to add z3 reinforcement plates is you are doing rsms.

I'd say check all the components of the suspension and change what you think is important and feasible.
If I had money I'd change every component but if I had money I'd buy a new car as well.
It's important to prioritize what you feel is important and what should and can be done while you change the bump stops.
In my case I changed the shocks, springs, rsms, washers, nuts and bolts. My shocks were leaking and I wanted to lower the car a little so I went with coil overs. My inside side of the tires were wearing out quickly so I did the RTAB with limiters as well. And since my rsms were old, I changed to new rsms and hardware.
I spent almost 6 hours as because of the Rtabs. If it were just shocks, it can be done in an hour both sides.
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Old 04-18-2013, 11:26 PM   #14
jeremy0000
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Quote:
Originally Posted by trj View Post
Yah do both sides. With suspension and brakes always do in pairs.

Check out the DIY's on rsms and rear shock installation. RTAB might be too much of a DIY if you are just starting to work on the car and don't have correct tools.

You might want to add z3 reinforcement plates is you are doing rsms.

I'd say check all the components of the suspension and change what you think is important and feasible.
If I had money I'd change every component but if I had money I'd buy a new car as well.
It's important to prioritize what you feel is important and what should and can be done while you change the bump stops.
In my case I changed the shocks, springs, rsms, washers, nuts and bolts. My shocks were leaking and I wanted to lower the car a little so I went with coil overs. My inside side of the tires were wearing out quickly so I did the RTAB with limiters as well. And since my rsms were old, I changed to new rsms and hardware.
I spent almost 6 hours as because of the Rtabs. If it were just shocks, it can be done in an hour both sides.
Cool, thanks so much for you help!!!! I will definitely do both sides. I am assuming the washers, nuts and bolts come as a kit with the rsms???

I will also look into the RTAB. I am clueless about suspension, and definitely an amateur but I have done a little work on my cars; brakes, alternator, water pump, fuel pump and filter, power steering pump, starter by way of removing the intake manifold, drive and idler pulleys and on my Ranger I have done the clutch twice, universal joints, just never suspension until now.
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Old 04-18-2013, 11:52 PM   #15
jeremy0000
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Quote:
Originally Posted by trj View Post
Yah do both sides. With suspension and brakes always do in pairs.

Check out the DIY's on rsms and rear shock installation. RTAB might be too much of a DIY if you are just starting to work on the car and don't have correct tools.

You might want to add z3 reinforcement plates is you are doing rsms.

I'd say check all the components of the suspension and change what you think is important and feasible.
If I had money I'd change every component but if I had money I'd buy a new car as well.
It's important to prioritize what you feel is important and what should and can be done while you change the bump stops.
In my case I changed the shocks, springs, rsms, washers, nuts and bolts. My shocks were leaking and I wanted to lower the car a little so I went with coil overs. My inside side of the tires were wearing out quickly so I did the RTAB with limiters as well. And since my rsms were old, I changed to new rsms and hardware.
I spent almost 6 hours as because of the Rtabs. If it were just shocks, it can be done in an hour both sides.
Would a worn RTAB cause the inside of the tire to wear out? I had a blow out about 6 months ago. Both rear tires were really worn on the inside and the outsides were still in good condition.
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Old 04-19-2013, 12:08 AM   #16
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Yes, if the insides of your rear tires wear out a lot compared to outsides it's most likely the Rtabs. This was the condition of my rear tire and shock. Sure enough my rsms were shot too. I did everything at once.

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And no the washers don't some out as a set. I can check if I have the part numbers for them.
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Old 04-19-2013, 01:26 AM   #17
jeremy0000
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Quote:
Originally Posted by trj View Post
Yah do both sides. With suspension and brakes always do in pairs.

Check out the DIY's on rsms and rear shock installation. RTAB might be too much of a DIY if you are just starting to work on the car and don't have correct tools.

You might want to add z3 reinforcement plates is you are doing rsms.

I'd say check all the components of the suspension and change what you think is important and feasible.
If I had money I'd change every component but if I had money I'd buy a new car as well.
It's important to prioritize what you feel is important and what should and can be done while you change the bump stops.
In my case I changed the shocks, springs, rsms, washers, nuts and bolts. My shocks were leaking and I wanted to lower the car a little so I went with coil overs. My inside side of the tires were wearing out quickly so I did the RTAB with limiters as well. And since my rsms were old, I changed to new rsms and hardware.
I spent almost 6 hours as because of the Rtabs. If it were just shocks, it can be done in an hour both sides.
Quote:
Originally Posted by trj View Post
Yes, if the insides of your rear tires wear out a lot compared to outsides it's most likely the Rtabs. This was the condition of my rear tire and shock. Sure enough my rsms were shot too. I did everything at once.

Attachment 501312

And no the washers don't some out as a set. I can check if I have the part numbers for them.
awesome, thanks.
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Old 04-19-2013, 03:47 AM   #18
MJLavelle
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Quote:
Originally Posted by jeremy0000 View Post
I am guessing this is my problem?

This is my first time working on suspension. Do I need any specialty tools?
I'll try searching the forum for threads.
Thanks again.
I think I pretty much covered the rear shock mounts in the first serious answer in this thread, so, you're welcome.
You may want to consider some new rear shocks as well. Also, you should consider something stronger than the OEM rear mount. There are lots of choices available. It really just depends on how much you want to spend.
If you choose to replace the RTAB's, then you will need to buy or rent a speciality tool, and it is not something you can get from your local Autozone. There are people with listings in the classifieds who rent out the tool.
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Old 04-19-2013, 11:06 AM   #19
jeremy0000
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Quote:
Originally Posted by MJLavelle View Post
I think I pretty much covered the rear shock mounts in the first serious answer in this thread, so, you're welcome.
You may want to consider some new rear shocks as well. Also, you should consider something stronger than the OEM rear mount. There are lots of choices available. It really just depends on how much you want to spend.
If you choose to replace the RTAB's, then you will need to buy or rent a speciality tool, and it is not something you can get from your local Autozone. There are people with listings in the classifieds who rent out the tool.
Yeah thanks indeed! I think I will replace the RTAB's. I dont really want to spend the money to rent the tool but I figure I will see the savings in my tires eventually and avoid another blowout.
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Old 04-20-2013, 07:44 PM   #20
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Your RSM and RTABs are probably not causing you as much trouble as your old shocks. You can see if the RSM is bad by removing the trunk liner; nothing in your picture suggests it is bad. However, since your bump stop is old enough to be literally cut in half, your shocks are probably completely toast as well. I'd start by replacing those.
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