swat518

iTrader: (5)

Finally, the long winter past and I started my 1st track day in Apr. Unfortunately, I had to stop after the 1st session, my car had a really weird and super loud bang noise, I have been trying to find out the issue, but no luck. I want to post a help thread and see if anyone would have an idea.

Background
Last year I hit the wall @ Watkins Glenn due to coolant residue from the last session, it made me side way couple times but eventually from fun to cry... the car hit the wall parallelly, result in front suspension damage and body damage on the entire driver side. but no visual damage on the rear suspension.

The symptoms
I believe the noise came from the rear. The noise sounds like using a metal hammer to hit metal, very loud. It only came on once per turn, I did test runs in autox & track, this is what I noticed
- Autox: Happened during slalom, every time come out of a left turn and steer for the next right turn. I felt it affects the mobility of the car a little bit.
- Track: Every time after coming out of a left turn, happened at corner exit/enter the straight. I didn't feel it affect car mobility.
- Neighborhood: Not a street-legal car, drove about 15-20 mph in my neighborhood, left turn or slalom - no noise.

What I have done
- Visual check: All rear bushings have normal wear
- Visual check: All suspension connections are firm and no sign of movement marks.
- Quaife LSD: I spoke to Quaife about my story, the technician stated Quaife diff either works or catastrophically failed, so it's not diff. Diff cover & fluid replaced, color looks ok, no metal pieced found in the fluid or diff case.
- Wheel bearing: I spoke to SKF, they don't believe this is a bearing issue.
- Replaced driver side Axle
- Disconnected sway bar
- Asked couple of technicians from different shops, no clue...

coletrickle74

iTrader: (1)

You said you only did visuals? Jack it up and check the suspension properly. Did the check the diff fluid for shavings or pieces? It can't be that many things

swat518

iTrader: (5)

When replaced axle, I checked cracks on the driver side. and later checked the passengerside, everything looks fine.

I replaced diff cover, fluid color looks ok, no metal piece in the fluid.

dkmura

iTrader: (64)

Good info in your first post, but it would help to get more details from your first track session. First, which racetrack were you at? Where were you on the track when you first heard this loud noise? Was it under braking? on corner exit? Or during sustained g-force cornering in a long radius turn? Your memory usually holds clues that will help the engineering part of your mind sort though the likely possibilities.

swat518

iTrader: (5)

Thanks for the response!

Actually before that accident, it had the same bang noise but only happened at NJMP lightning after left-hand turn 4 (finished exit) and initial turn-in for right-hand turn 5, I believe I noticed that sound in 2017. I did track days in NJMP thunderbolt, Watkins Glen, Palmer, Shenandoah, Englishtown NJ, noise never happened at these tracks or I didn't hear it. The accident happened last year at Watkins Glen, last turn before long straight, it hit the concrete wall, see pic.

Front repair done on the driver side:
- used knuckle & new wheel bearing
- compression rod & spl solid bushing

I tested it last month at Englishtown raceway NJ. the noise did NOT happen before turn in (not S turn) nor during the turn, it happened when I unwind the steering wheel after every left turn, pretty much straighten the steering wheel with foot on gas (I was on gas after apex, so just to clarify the noise wasn't happen when I step on gas).

dkmura

iTrader: (64)

Offda- that is some heavy damage! But your description offers a few clues- since the loud noise happened after completing a left-hand turn, something must be shifting or moving b/c of the loading onto the right side tires/suspension. That it happens with power on is another clue. Could it be diff or suspension related? Perhaps. Depending on the quality of the sound, it could be some component hitting the unibody with a mighty twack!

The only way to narrow it down is painstaking detective/engineering work. Think of it as mechanical forensics work. You'll need to spend more time than you already have inspecting the RR side. Personally, I'd pull the RR shock to make sure the rebound setting is working up to spec. I'd examine all the rotating/dynamic diff/axle components AND the nearby unibody areas for any sign of M2M contact. The search for new clues has to be extensive at that corner before you decide on whether your original hypothesis is correct or not.

swat518

iTrader: (5)

Thanks dkmura!

Here was my thinking process
1. RL alxe - it had slight movement from wheel bearing to diff. my original thought this make sense to create the noise, but not it.
2. Quaife LSD - As Quaife customer service explained, this shouldn't be it. But one thing I am confused is, when rear wheels both in the air, car in neutral, turn one wheel very slowly, the other wheel turns the same direction (not always happen, something the other one doesn't turn), if speed up a little bit, the other one stops. My Mini installed Quafie as well, I turn one wheel w/ no matter speed, the other wheel turns the same direction. My friend has a spare 350Z Quaife LSD, turn one flange, the other side turns the same direction. Could be the diff?
3. Wheel bearing - based on SKF customer service and my checks with turning the wheel and cross-shaking the wheel, they feel ok
4. KW v3 shocks and springs - shock mounting points or spring perch have no sign of movement.
5. Subframe bushing - visually checked, no sign of movement
6. All metal suspension parts - visually checked, no sign of movement.

I will recheck the rear suspension. Since the noise started before the accident, my guess is the accident accelerated the deterioration on RR, even though the hit is on RL?

dkmura

iTrader: (64)

I don't know much about the quaife, except that it needs both tires to be on the ground to function properly. I still wonder if there's a possibility that your right rear shock is not rebounding properly after being heavily compressed coming off a turn. Looking at the mounting points or spring perches may not show a worn or sticking damper.

swat518

iTrader: (5)

That makes sense, I will check this weekend and let you know. Thank you!

DmanG281

iTrader: (3)

Have you checked the torque on the front two differential bolts? I had a thumping noise on right hand turns just before I had a left rear lock up that caused a spin a Sebring. Upon dissassembly I found one of the two diff bolts had backed out and was causing the differential to flex around the bushing. This caused the left rear axle to hit the subframe under load, when the diff moved laterally. When it unloaded it would bang back up against the subframe. My GoPro picked the banging noise up.

swat518

iTrader: (5)

I removed the diff to replace the cover, and check if any metal debris. I remember I torqued everything to the spec, but I will surely double check. It's a good idea to use gopro, where did you mount it?

--> checked today, all 3 bolts torqued as to the spec

260DET

Jack it up on a hoist, start from one end and work your way to the other checking everything as you go. Wobble things around, use a bar to lever against structural items and so on. And use a bright light.

swat518

iTrader: (5)

I focused on RR suspension, what I found
- rebound to full stiff on kw v3. I jacked rear mid link on both side then release the jack, I felt RR shock dropped a little faster than RL. I don't understand how bad rebound can cause the 'bang' noise?
- checked the spring, noticed there are 3 cuts towards to the diff, not sure where that came from. see pic
- removed perch, some evidence made me think the spring perch might be moved under the load? see pic


circle the cuts

should the perch rubber pad like this?

not a good angle, the tab circled was bent downward

there is sign of metal contact that circled in blue, but shouldn't be the noise from.

swat518

iTrader: (5)

I put it on two jack stands, did several times as exactly what you mentioned, still cannot figure out...

dkmura

iTrader: (64)

When checking shocks, I take them off the car and manually see how they're compressing (bounce setting) and extending (rebound) via their full range. It sounds like you checked the rears on the car, but even then, you spotted some differences. Your upper spring adjuster shows a lot of wear and signs the spring is loading and unloading without much dampening control. How long have these KWs been on the car? Have they ever been rebuilt?

swat518

iTrader: (5)

I bought them new from another member a while back, put them on 2 years ago, had probably 10-15 track days (no street life) and I am aggressive in the corner. the top of the extended reservoir is greasy on both rear ones. never rebuilt yet. I usually have rebound setting around 9-11 clicks from the soft. but I was stupid to keep 2 clicks from the soft for rebound while 12 clicks for the compression, cause I turned the rebound opposite way... that last for about 2-3 track days.

I am not an Engineer, I cannot understand why worn shock can cause that bang noise?

dkmura

iTrader: (64)

I'm no engineer either, but if you stay in motorsports for long enough, you begin to think like one. If your shocks are badly worn, the springs will have little control in either the compressed state (bump) or extended (rebound) phase of cornering. That could allow the spring to be free of much control (hence the worn top of the KW spring perch).That in turn will cause some thumping around the rear section of the Z FM chassis. It's uncontrolled motion that is also degrading your handling.

You say these KWs were purchased about two years ago with no history behind them and have run them multiple times since then; including in one crash. That's ample reason to get them sent back to the factory and rebuilt. It's a common problem with novice racers and the decline is so progressive it may not be noticeable.

swat518

iTrader: (5)

That make sense.
I sent a long email to KW customer service to give their advice, also requested to rebuild them. will update once hear back from them about my story.

swat518

iTrader: (5)

Heard back from KW, the worn coilovers can cause this 'bang' noise, but no explanation why. Quote from the expert "The v3’s are not intended for any track use which is why you are hearing that noise. The rebuild would fix the issue but tracking the car with those coilovers will just cause any interval valving to fail and cause the issue again." SO...

Can anyone recommend some shocks/coilovers brands for dedicate trackday use?

dkmura

iTrader: (64)

OK, so one mystery (and the reason for this thread) is solved. Now you need competition damper recommendations? Do some research on this board and you'll find several recommendations. Everything from uber-expensive Moutons or Penskes, to older Koni 2812s (like I use) or others. It depends on what class you're running, rulesets and other factors. It's not an easy, pat answer.