Front left clunk due to change from deceleration to acceleration

[JHZR2]

This is my 2008 ML320.

When I got it, I knew it needed shocks/struts, brake lines, etc. but the rest was pretty good.

I’ve replaced sway bar links that got rid of one rattle, and I did the struts, strut mounts, springs, and shocks.

Still, and perhaps getting worse, I get a clunk when I change from deceleration to acceleration.

For example, driving in a neighborhood, if I brake reasonably hard to a stop sign, then start going again, I get two clunks from the front left. It seems if I steer left it’s more likely to happen. If I decelerate gently, don’t use brakes, or turn right I don’t seem to get it at all.

Doing a hard left turn, like a k-turn can cause it to happen as well as the wheel is turned relatively hard left.

Every joint looks fine. Every boot clean, dry, no rips. I’ve tried jacking up to check for ball joint play and nothing. No play at all in the suspension that I can find. Aligned to spec.

So what can I do to test, and how do I diagnose this? LCA bushings all look fine. Could it be a transmission or engine mount? The transmission shifts smoothly, engine has no vibration at all.

How do I diagnose?

Thanks!

 

[Rand]

I had that once with loose caliper bracket bolts. Might want to check that everything is tight?

Did it always do it.. or after the work?

 

[RooflessVW]

Subframe loose?

 

[cptbarkey]

I havent worked on any Mercedes, but did a few BMWs. I agree a close look at engine or transmission mounts, logically it would be the weakest one or the one that prevents pivoting of the engine. Older Camry's had one right at the top of the engine that could cause that to happen.

 

[JHZR2]

I had that once with loose caliper bracket bolts. Might want to check that everything is tight?

Did it always do it.. or after the work?

It always did it. It seems to me that it has gotten a bit more noticeable after the struts?

I know it happened before that because I had another clunk that was a sway bar link. After I changed the link I still got this clunk from deceleration/acceleration.

It seems that something shifts to affect it too. So that points me towards something besides suspension…

 

[FZ1]

It always did it. It seems to me that it has gotten a bit more noticeable after the struts?

I know it happened before that because I had another clunk that was a sway bar link. After I changed the link I still got this clunk from deceleration/acceleration.

It seems that something shifts to affect it too. So that points me towards something besides suspension…

Bent axle?

 

[JHZR2]

Bent axle?

I mean, I guess? But wouldn’t it manifest in other ways, and always? If I decelerate gently and minimize braking, I get no clunk. Wouldn’t a bent axle always be an issue?

 

[FZ1]

I mean, I guess? But wouldn’t it manifest in other ways, and always? If I decelerate gently and minimize braking, I get no clunk. Wouldn’t a bent axle always be an issue?

I had the clunking with my Camry when turning left. The dealership told me it was a bent axle, replaced it, and the clunking stopped. Who knows, they may still be laughing at the dealership.

 

[Lubener]

Check for a broken motor mount.

 

[Jetronic]

Check for a broken motor mount.

broken or worn motor mount

 

[Egg_Head]

4Matic/AWD I presume, could be a bad CV axle?

 

[PontiacHO]

Diff case bushing-bearing worn causing excessive movement in the CV joint.

 

[Trav]

I would be looking at the CV joints especially the inner. What you describe is a common symptom of a bad tripod joint, boots do not to be leaking or torn for these joints to fail.

Edit: You may be able to get GKN joints only for about $100ea, you need to look around.

https://www.gknautomotive.com/en/Aftermarket/our-products/cv-joints/

 

[Astro14]

Take a good look at the front control arms, both upper and lower, as well as ball joints. Check subframe bushings.

If the car was old enough to need shocks and struts, there is a good chance that the control arm bushings are worn out as well.

 

[oil pan 4]

My Nissan leaf started doing that this year. Pretty sure it's a worn CV. I'm not worried about it.

 

[iCurious]

Grab onto the axle and shake it. Is it solid or is it clanking?

 

[Oliveoil2]

Grab onto the axle and shake it. Is it solid or is it clanking?

This^. You need a new half-shaft (left front axle). I might do the right side too.

 

[JHZR2]

Take a good look at the front control arms, both upper and lower, as well as ball joints. Check subframe bushings.

If the car was old enough to need shocks and struts, there is a good chance that the control arm bushings are worn out as well.

UCAs are new, LCAs don’t show any cracking or issues with the bushings that I can see. Ball joints are tight and pass the crowbar test 100%. I didn’t check receipts to see if/when they were done.

Grab onto the axle and shake it. Is it solid or is it clanking?

Ok thanks, this is a good objective test. Should the vehicle be on the ground, or wheel hanging?

Check for a broken motor mount.

I was definitely thinking this, since the drivetrain really needs to shift to create the noise. But none of the usual tests (that I believe I kmow) indicates anything. Smooth idle and fine shifting. Any recommendations on best ways to test?

 

[FZ1]

UCAs are new, LCAs don’t show any cracking or issues with the bushings that I can see. Ball joints are tight and pass the crowbar test 100%. I didn’t check receipts to see if/when they were done.


Ok thanks, this is a good objective test. Should the vehicle be on the ground, or wheel hanging?


I was definitely thinking this, since the drivetrain really needs to shift to create the noise. But none of the usual tests (that I believe I kmow) indicates anything. Smooth idle and fine shifting. Any recommendations on best ways to test?

Take it to the dealer. Let 'em diagnose it and give you an estimate.

 

[Lubener]

I was definitely thinking this, since the drivetrain really needs to shift to create the noise. But none of the usual tests (that I believe I kmow) indicates anything. Smooth idle and fine shifting. Any recommendations on best ways to test?

Have someone firmly press the brakes, goose the throttle in drive and reverse. See if the engine looks like it's going to jump out of its craddle.