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Trouble Shooting Loud Bang when suspension loads/unloads

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#1
white_turbo

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So my car has been suffering from some audible banging noise in the rear when the car's suspension loads/unloads in quick transitions.  I know the first suspect is the sway bar and endlinks, but I have already checked those and they all look/feel fine.  Things I have done to isolate the issue: 

 

1) Sway bar endlinks replaced

2) Shock upper mounts replaced 

3) Checked bushings in control arms (seems fine)

 

I pulled this video from youtube so this owner had the exact same noise as me, but I am not sure if he/she has figured out what it is.  Anyone else has experienced the same issue?  Everything is stock except for cat-back (I initially thought the exhaust is moving enough to hit the chassis. It seems solid however, but is hard to simulate the g-force that the car sees by hand).  

 

Also worth noting, I don't get the noise on the streets, but only when autoxing/track in places where the car transitions left/right very quickly.  Thanks!

https://youtu.be/Cj_sgm4Dy8g

 

 

Only aftermarket parts on the car are: 

1) Shocks (noise happened when OEM shocks were still on)

2) Rear sway bar/endlinks (noise happened when OEM bar and links were on)

3) 5Zigen catback (noise came after this but only after quite a while.....possible that it is moving around under huge G, but I can't move it by hand enough to really tell)


Edited by white_turbo, 23 August 2018 - 02:33 PM.


#2
droptopp

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I’d lean towards bushings. Assuming the noise was there previously which caused you to start swapping things out.

Can you isolate if front or rear ? Go pro outside on back could help.
GTX3582R built and tuned by STM, AMS 4.1, Omega billet crank, Alpha Cams, STM DP, MP, 4 STM Titanium custom exhaust, STM Race FMIC 22x18x4.5, full 3" piping, ID 2000, Sheptrans OneK drop gears, DS axles, E85, Advan GT 10/12 285/315 R888 / MT ET 18x10/12 TE37 Saga MT ET SS 275/245.
Heartbreaker Mustang 1186 E70 low boost. Dynojet 1350 +/- 60-130 3.5 seconds. 100-150 3.4 seconds.

#3
white_turbo

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I’d lean towards bushings. Assuming the noise was there previously which caused you to start swapping things out.

Can you isolate if front or rear ? Go pro outside on back could help.

 

The noise was there before I swap things out. Pretty certain that it is coming from the rear too.  With regards to GoPro, I assume you are suggesting using it to see if anything moves like they shouldn't? 



#4
7racer

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thats kind weird.

are you stock?


In7anity!!


#5
droptopp

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Do you know if the noise if coming from the front or back of the car ? If not put the go pro in the front or back and see if you can isolate to start narrowing things.
GTX3582R built and tuned by STM, AMS 4.1, Omega billet crank, Alpha Cams, STM DP, MP, 4 STM Titanium custom exhaust, STM Race FMIC 22x18x4.5, full 3" piping, ID 2000, Sheptrans OneK drop gears, DS axles, E85, Advan GT 10/12 285/315 R888 / MT ET 18x10/12 TE37 Saga MT ET SS 275/245.
Heartbreaker Mustang 1186 E70 low boost. Dynojet 1350 +/- 60-130 3.5 seconds. 100-150 3.4 seconds.

#6
white_turbo

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thats kind weird.

are you stock?

 

Stock in terms of power and drivetrain. It started when my stock suspension was still on though.  It didn't go away with the new shocks, so that is ruled out.



#7
7racer

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Stock in terms of power and drivetrain. It started when my stock suspension was still on though.  It didn't go away with the new shocks, so that is ruled out.

 

aftermarket control arms?


In7anity!!


#8
white_turbo

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aftermarket control arms?

 

No stock arms.  The only thing on the car that is not OEM are: 

 

1) Shocks (ruled this out because noise started before I swapped the OEM ones out)

2) Rear sway bar (also ruled this out because noise started before I swapped the OEM one out)

3) Rear bar endlinks (also ruled out because noise before I swapped the OEM one out thinking it was possibly the links)

4) 5Zigen Catback (this one is tricky...I can't get shake the exhaust enough by hand to move it around, but the g-force may actually move it enough to hit the chassis) 



#9
white_turbo

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UPDATE:

 

I decided to check the nuts and bolts on the rear suspension arms again.  The two bolts that went through the control arm bushings were slightly loose (not a whole lot, but I was able to tighten them up with not much effort), so I torque them back to OEM spec. 

 

While I was at it, I went on to check all the rear subframe bolts also, they were tight to OEM specs, except for one that holds the transmission tot he subframe.  It was at least a few turns loose.  I tighten it back to OEM spec + a couple more ft/lbs.  

 

Unclear to me how this bolt got loose, and is not something one would expect it to come loose if the transmission has never been off the car.  I hope this resolves the noise I was getting in transitions.   I will know next week and will report back. 

 

I suggest everyone to check the two nuts that attach the transmission and rear subframe once in a while now. 


Edited by white_turbo, 26 August 2018 - 04:09 PM.

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#10
white_turbo

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UPDATE: 

 

This seems to solve the issue I have with the noise.  I have only done one autox event after this check, and I don't think I heard the noise anymore.  A few more events will confirm this more. 

 

 

 

Here is what I did (a repeat of the post above, but in a little more detail):

 

I rechecked all the rear subframe and rear suspension bolts again (this time properly with a torque wrench according to factory torque specs instead of the "hand-tight" check), and here are what I found.  Perhaps a combination of these, but one is particularly alarming.

 

1) All rear suspension arm bolts (they were all pretty tight, except for the two inner upper control arm bolts which were ever so slightly loose but not by much).  I re-torqued those to 61 ft-lb.  For the rest of the links (3 of them in the rear on each side), I checked those and they were at the factory spec 65 ft-lb

2) For the rear subframe, there a total of 10 bolts to check (you need to remove all three under trays at the back to access these:

- 6 to the chassis at 81 ft-lbs (these were still in spec)

- 2 to the transmission insulator at 68 ft-lbs (unfortunately, the exhaust is in the way of one of them, so I opted to check one and unless that one was loose, I skip the other one.  They were still in spec)

- 2 at the back of the subframe where the transmission has two studs that go through the subframe with nuts tighten to them at 81 ft-lbs.  One of the nut was a loose by a few turns for some odd reason and I suspect that was allow the transmission to swing side-to-side when the suspension unloads.  If you still have the OEM exhaust, it may be in the way for you to reach them.  A deep 17mm (maybe 19mm I forgot) socket/5-6 inch extension/torque wrench is needed for me.

 

I would suggest for those of you who drive your car in autox a lot, you may eventually hear this and I would check those two bolts at the back of the subframe that goes to the transmission. 


Edited by white_turbo, 16 September 2018 - 05:51 PM.

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#11
thehelix112

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Excellent! I have heard a thunk sometimes on track when changing direction.

Appreciate the pointer!

Dave

#12
white_turbo

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Update

I swapped out all four transmission mounts and subframe stoppers and the noise is still there. Next up, put stock cat back back on and maybe new exhaust hangers. At this point, I really have no idea where the noise is coming from. Car drives absolutely fine other than the noise.




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