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MS Miata clunk under hard braking

 
Old 03-14-2018, 08:25 PM
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Default MS Miata clunk under hard braking

So, the car is all stock except Toyo RA1s, and the car only gets driven for autocross. It's not mine, its my girlfriends fathers, but he doesn't drive it so it lives at my house with my girlfriend and I, and its her car to race.
For some time now, under hard braking, I get a clunk from what sounds like the front pass side area. One good knock. Now, I haven't had the car in the air, but hand test on the wheels shows no play any direction, visible sway bar bushings and end links look good, etc.
I don't have a ton of time with so many things going on, so I am hoping to generate a few ideas here of what to look for when I CAN get it in the air or even just take a minute to look at it.
So what are common or suspect things to check out?

My normal autocross/hillclimb car is a Porsche 944 Turbo S, so I only drive this when mine is down... Which has been a lot lately!

Thanks in advance!
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Old 03-14-2018, 08:52 PM
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Alignment cam bolts are slipping
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Old 03-14-2018, 08:55 PM
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Only miata specific clunk I've got that threw me for a loop is the bumper skin/fender brace that lives in the front wheel well fwd of the tires. I had one missing a nut and it would clunk while turning. That took a good minute to track down.

Also, could be an engine mount. The miata mounts shear in a way that's hard to spot because there's a steel tub hiding a bunch of the mount.
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Old 03-15-2018, 08:09 AM
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Sounds like loose camber bolts. Take it to any alignment shop and have them tightened. Need to really crank on them.
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Old 03-15-2018, 04:11 PM
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I've had that camber bolt issue a good number of times on my 944, and I'm pretty sure that's not it. It's not while turning, which is where I always hear it on my 944. It's really only under hard, usually straight, braking, and it feels more solid than that... Ill look anyways when I can, but I strongly think the issue is elsewhere. I appreciate the ideas though!
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Old 03-15-2018, 04:22 PM
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Almost definitely front control arm bolts... either the alignment bolts, or the upper control arm long bolt. I searched for that clunk under hard straight line braking for a long time until one day I overtightened all of the front control arm bolts at the track and the clunk disappeared.
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Old 03-15-2018, 04:24 PM
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I'll give it a whirl What's the worst that could happen!
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Old 03-15-2018, 04:59 PM
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My money is on failing lower ball joint.
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Old 03-15-2018, 06:52 PM
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Cracked sway bar mount.
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Old 03-16-2018, 05:29 PM
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Originally Posted by rleete View Post
Cracked sway bar mount.
Is that a common issue?
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Old 03-16-2018, 05:36 PM
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Originally Posted by rleete View Post
Cracked sway bar mount.
ill try to get the front in the air and inspect all of the above soon
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Old 03-16-2018, 05:42 PM
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Originally Posted by Pdx-944 View Post
Is that a common issue?
Enough so that I made the comment. It's not unheard of.
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Old 03-16-2018, 08:51 PM
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People just replace pads when brakes are worn.
Very few people actually take the pad retaining hardware off and clean (or replace) and lube them with copper grease.
Said retainers distort and/or get soft over time with all that heat and fatigue and whatnot and fail to, umm, retain the pads.
So they move, and they knock when you hit the brakes.

Just sayin'
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Old 03-17-2018, 07:31 PM
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K-mount bolts.

Get it on a hoist, and rattlegun them up tight. One will move more than the others.
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Old 03-19-2018, 10:36 PM
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Originally Posted by Pdx-944 View Post
ill try to get the front in the air and inspect all of the above soon
Would the test be to remove the swaybar and try heavy braking?
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Old 03-20-2018, 03:37 PM
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Most of the usual clunking suspects have been mentioned. Also look at your exhaust and see if there is sufficient play in the muffler to have it hit the frame, usually happens with lateral forces being applied. The rubber hangers tend to age and stretch allowing for the exhaust to move laterally, generally solved with polyurethane hangers and/or a small hose clamp on the rear muffler hanger piece.
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Old 03-27-2018, 01:09 PM
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So I jacked it up in the air on Saturday because I could hear the noise while pulling it out of the garage. I could occasionally hear a single knock both up in the air and on the ground when I turned the wheel full lock to the left, just before lock (not the sound of hitting full lock). Or if I quickly depress the brakes in reverse or in a forward gear sometimes at very low speeds even. But no matter what I did I could not find anything loose or with play or that looked out of the ordinary - tie rods, sway bar, control arm bushings, ball joints, strut mounts, strut bushings - all looked and felt good.

So Sunday we autocrossed the car and could hear the noise the whole time. At one point I tried to track it down and it sounded like it was coming directly in the lower middle of the engine bay, towards the rear of the engine, and I could actually hear it creaking / clunking / clicking (tough to describe, but the sound is more of a clunk tone, while the behavior of the sound was more of a creak) as we sat in the parking lot and she slowly turned the wheel back and forth The noise occurred while turning the wheel either direction. I say it sounded like a creak because it sounded like you would imagine if something we're repeatedly slipping in a bushing.
It seems to be something related to the steering rack. Though I cannot see from underneath without pulling the tray, and have not had a chance to do that yet. I can only see one mount for the steering rack from above on the passenger side, and it looks fine and has no movement while she is turning the wheel, even while the noise was occurring.

I will try to get video of the noise at some point. This reminds me of those commercials... "What sound did it make?"
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Old 03-27-2018, 02:02 PM
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Did you try to re tighten the alignment bolts? They don't need to be loose to make noise.
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Old 03-27-2018, 02:11 PM
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Try greasing the universal joint in the steering shaft.
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Old 03-27-2018, 04:18 PM
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Ive had this happen on 2 NAs. Everything was tight, checked a few times, and both cars were fixed by replacing the control arm bushings. They were worn enough to slide closer to the subframe, and under braking only the rubber would smoosh until the arm contacted the subframe making a click noise. Drove me insane for a few months on my 90.
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