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Old 04-09-2014, 07:08 AM   #1
Neptune15
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Rear banging sound. *solved*

I recently replaced my rear subframe, installed H&R coilovers, SPC camber arms and CFM toe arms. Currently there is no sway bar installed. All parts are brand new, and the shocks worked very well when I compressed them by hand.

I've been getting this loud banging sound over sharp bumps in the road. Over semi-flat surfaces the car rides and handles very well, but once the severity of a crack reaches a certain depth, this happens:

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Old 04-09-2014, 07:32 AM   #2
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Open up your trunk and make sure nobody is in it.

Sorry, couldn't resist.
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Old 04-09-2014, 08:20 AM   #3
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Moved to "Brakes, Suspension & Chassis"

Can't add much myself beyond the obvious checking of tightness & assembly. Users of those links & arms may comment - solid joints aren't going to be quiet like rubber bushes. Did you use urethane bushes in the rear arms?
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Old 04-09-2014, 09:49 AM   #4
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Quote:
Originally Posted by onlycodered View Post
Open up your trunk and make sure nobody is in it.
I'll double check.

Quote:
Originally Posted by sailor View Post
Moved to "Brakes, Suspension & Chassis"

Can't add much myself beyond the obvious checking of tightness & assembly. Users of those links & arms may comment - solid joints aren't going to be quiet like rubber bushes. Did you use urethane bushes in the rear arms?
I'll check the torque and look everything over tonight. The only bushings that are not rubber are the CFM toe arms, which have spherical bearings.

As I was sitting in the back seat, it sounded like the noise was coming from underneath, across the rear LCA/spring portions. Like I said I'll double check it again today. Maybe the spring isn't seated correctly.
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Old 04-09-2014, 10:11 AM   #5
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Those toe arms could definitely be the culprit. Spherical bearings are going to be much louder than the stock ones. Do you still have the stock arms that those replaced? Might be worth swapping those back in to see if that solves the problem.
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Old 04-10-2014, 07:08 AM   #6
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Found the problem. Bumpstops were too log. Makes me wonder if H&R designed these shocks to NOT use the bumpstops?
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Old 04-10-2014, 08:12 AM   #7
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No bump stops on the rear shocks, only at the end of the lower rear arms.

Front uses bump stops on the struts...

Was yours done differently somehow?
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Old 04-10-2014, 08:31 AM   #8
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Quote:
Originally Posted by sailor View Post
No bump stops on the rear shocks, only at the end of the lower rear arms.

Front uses bump stops on the struts...

Was yours done differently somehow?
My kit never came with any specific instructions (or I missed it.. I'll double check).

I looked it up online and never had a definite answer. I had it completely backwards according to your information: no front bumpstops, but rear shock bumpstops. I thought the struts had an internal bumpstop design, but I could be mistaken. I recall the front bumpstops not even fitting on the shaft properly.
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Old 04-10-2014, 09:08 AM   #9
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No instructions makes it harder, matching what you find on disassembly can help figure things out.

Front bump stops fitted to the rear would likely be loose on the shaft, struts have a much larger shaft as a general rule (more forces applied to them, not just vertical ones).

Bit of work to do now, need to get those off the rear shocks & onto the front struts.

Did you H&R's just include front struts & springs? re-used top mounts & bushings?
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Old 04-10-2014, 09:27 AM   #10
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Quote:
Originally Posted by sailor View Post
No instructions makes it harder, matching what you find on disassembly can help figure things out.

Front bump stops fitted to the rear would likely be loose on the shaft, struts have a much larger shaft as a general rule (more forces applied to them, not just vertical ones).

Bit of work to do now, need to get those off the rear shocks & onto the front struts.

Did you H&R's just include front struts & springs? re-used top mounts & bushings?
I am royally confused now.

This is how I understand it.

A stock focus of my vintage (07) would have 3 pairs of bumpstops total. One pair on the front struts, one pair on the rear shocks, and one pair on the rear LCAs. They are made of foam, except the ones on the LCA which are rubber.

So I get my coilover kit. They come with the struts and springs for the front, and rear shocks and springs/perch for the rear. The instructions appear to be general, and say "re-use your OE strut mount/fasteners" or something along those lines.

I'm taking apart the front struts. I try to fit the bumpstop+tophat, and even with a loose spring, I can't squeeze the bumpstop down enough to fit the top nut. It just wasn't going on. I check the internet, and according to other applications (couldn't find any decent information for our cars) H&R actually uses Bilstein struts, which incorporate an internal bumpstop; you don't need any extra bottoming-out protection in the front.

The rears, I just assumed, re-used the shock bumpstop. It fit perfectly, so I thought no reason not to use them... that is until I drove it, and here we are.

I never put the fronts on the back or back on the front. As it stands now my car rides amazing, so I think I'll stay on this set-up until I blow a shock, which may be very soon if I've misjudged something
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