Occasional clunk on hard braking/acceleration (2012 Mazda5 6MT)

[d00df00d]

Recently got our 2012 Mazda5 back from having the clutch, RMS, and all 3 powertrain mounts replaced. A few days later, I had to brake pretty hard over a rather bumpy section of road and got a mighty clunk from the front left. Car seemed fine afterward, but then twice more on the drive – once while braking over bumps, and another time when hitting a bump while turning – I got a smaller but pretty sharp clunk from the same corner.

Since then, I occasionally get the same clunk, most of the time from the front DS but occasionally from the front PS. Only happens on sharp acceleration or braking, especially on uneven surfaces. Sounds like a rock hitting the underside. Once or twice, I had it clunk once under braking and then clunk again while setting off under mild acceleration, almost like something had clunked out of place under braking and then clunked back into place when the suspension loaded in the other direction.

Front control arm, strut, strut mount, and all bushings and ball joints on that corner have ~8k miles or less on them.

Any advice on what I should check? The mechanic and I are both stumped!

 

[ctechbob]

Sway bar bushings new as well?

 

[d00df00d]

Sway bar bushings new as well?

Good call. Yes.

 

[Soft Cars]

Engine mounts and transmission mounts instantly comes to mind when hearing the word "clunk."

 

[ctechbob]

I can't remember, does that front end use eccentric bolts to set part of the alignment or is it all done with the struts.

Reason I ask. The Miata's have a hard time with their front camber bolts and they need to be replaced every few alignments, and there's an updated part for them as well. They yield over time and don't hold their clamping force and you end up with a noise almost exactly like what you're describing.

 

[The Critic]

https://www.amazon.com/Steelman-ChassisEAR-Diagnostic-Transmitters-61082/dp/B0BLFHVHZF/ref=pd_lpo_sccl_2/134-7482470-2951944?pd_rd_w=D82KL&content-id=amzn1.sym.116f529c-aa4d-4763-b2b6-4d614ec7dc00&pf_rd_p=116f529c-aa4d-4763-b2b6-4d614ec7dc00&pf_rd_r=K5JJ3JQ0RPZBQFPWW91Z&pd_rd_wg=ckdXR&pd_rd_r=db52d64f-de5d-4ed4-aab2-51574af3b603&pd_rd_i=B0BLFHVHZF&th=1

 

[tcp71]

Upper strut mount bolts tight? I had one that had slightly loose bolts and in the right circumstances the bolts would shift in their holes and clunk from one side to the other. The bolts were tight enough that it only happened with just the right forces.

Lower control arm mounting bolts are another clunk point. The CX5 in my signature needed a ball joint that only came with a lower control arm. After I replaced it, I thought I had the bolts tight enough, but one was not and a clunk would happen if enough force was exerted. Cranked it down and the clunk disappeared.

Considering the amount of work, just performed, I would spend some time with a socket set and recheck the tightness of every bolt you can get to.

 

[d00df00d]

Engine mounts and transmission mounts instantly comes to mind when hearing the word "clunk."

Same. But they're all brand new!

I can't remember, does that front end use eccentric bolts to set part of the alignment or is it all done with the struts.

Reason I ask. The Miata's have a hard time with their front camber bolts and they need to be replaced every few alignments, and there's an updated part for them as well. They yield over time and don't hold their clamping force and you end up with a noise almost exactly like what you're describing.

Interesting. No adjustability up front except for tie rods. Might be worth checking the strut clamp hardware, though.

https://www.amazon.com/Steelman-ChassisEAR-Diagnostic-Transmitters-61082/dp/B0BLFHVHZF/ref=pd_lpo_sccl_2/134-7482470-2951944?pd_rd_w=D82KL&content-id=amzn1.sym.116f529c-aa4d-4763-b2b6-4d614ec7dc00&pf_rd_p=116f529c-aa4d-4763-b2b6-4d614ec7dc00&pf_rd_r=K5JJ3JQ0RPZBQFPWW91Z&pd_rd_wg=ckdXR&pd_rd_r=db52d64f-de5d-4ed4-aab2-51574af3b603&pd_rd_i=B0BLFHVHZF&th=1

Good call. Tempting!

Upper strut mount bolts tight? I had one that had slightly loose bolts and in the right circumstances the bolts would shift in their holes and clunk from one side to the other. The bolts were tight enough that it only happened with just the right forces.

Lower control arm mounting bolts are another clunk point. The CX5 in my signature needed a ball joint that only came with a lower control arm. After I replaced it, I thought I had the bolts tight enough, but one was not and a clunk would happen if enough force was exerted. Cranked it down and the clunk disappeared.

Considering the amount of work, just performed, I would spend some time with a socket set and recheck the tightness of every bolt you can get to.

Will check the upper strut mount bolts.

Everything below that, the mechanic swears he tightened the heck out of...

 

[Soft Cars]

Have someone watch the engine while you power brake the car. Excessive engine movement while rowing through the gears is the dead giveaway. Being that it's front wheel drive is even harder on the mounts due to the torque direction while accelerating.

 

[IndyIan]

Have someone watch the engine while you power brake the car. Excessive engine movement while rowing through the gears is the dead giveaway. Being that it's front wheel drive is even harder on the mounts due to the torque direction while accelerating.

Also try this with the the parking brake on so the front wheels can move freely.

 

[Jetronic]

Lower wishbone mounts have likely been undone, aswell as the steering knuckles (to remove the subframe). Pretty standard to do when replacing a clutch in transverse setup. check those are all tight. Could be one of the mounts aswell, but I'd expect more vibrations from those rather than only clunks.

 

[tcp71]

Same. But they're all brand new!


Interesting. No adjustability up front except for tie rods. Might be worth checking the strut clamp hardware, though.


Good call. Tempting!


Will check the upper strut mount bolts.

Everything below that, the mechanic swears he tightened the heck out of...

I thought so too, but ended up using a cheater bar to get it tight enough not to clunk. It was the rear bolt on the lower control arm. Had to muscle the hell out of that one.

 

[PimTac]

Were the replacement mounts OEM?

 

[d00df00d]

Were the replacement mounts OEM?

Yep. All Genuine Mazda.

 

[The Critic]

Everything below that, the mechanic swears he tightened the heck out of...

 

[d00df00d]

404 lie not found

The mechanic literally said he air gunned all the fasteners down there.

 

[The Critic]

404 lie not found

The mechanic literally said he air gunned all the fasteners down there.

I'll just say that 3/8" air impacts are a lot weaker than some may expect - wouldn't surprise me if something is undertightened. My "powerful" 3/8" air impact, even with 150 psi, won't tighten brake caliper bolts to spec if I use any swivel socket.

 

[Overfill]

I was going to say that this clunk story sounds like my clunk story. A lower brake caliper bolt worked itself loose. brake caliper was biting, rotating, and clunking into brake dust cover.

 

[14Accent]

Long shot, but If I'm not mistaken your Mazda5 uses the same front caliper setup as a like-year 3? TOTAL left field suggestion, but it's possible that the caliper bushings (guide pin bushings) are worn, allowing the caliper to rock ever so slightly?

Also: upper strut mount bolts have been mentioned, but I didn't see anyone mention the actual strut ROD nut. The one in the center of the mount. Check that as well.

 

[Armkb]

I was going to say that this clunk story sounds like my clunk story. A lower brake caliper bolt worked itself loose. brake caliper was biting, rotating, and clunking into brake dust cover.

^^^^^This