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Old 08-20-2014, 09:51 PM   #1
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Default Sunfire low speed clunk.

Hello everyone.

So I have a '98 Sunfire with 2.4 Twin Cam. 173K miles. Automatic.

The car has developed a clunk. You are sitting at a light in D with your foot on the brake... when you go, it accelerates a little bit then clunks pretty hard and then accelerates and drives fine. Slowing down, it will occasionally do a much lighter clunk when the car has slowed down to about 10 mph, right before you stop completely. Clunk seems to come from front passenger side.

It clunks regardless of steering angle or throttle application and only clunks in D.

So, I'm fairly sure its not the engine mounts... when it clunks, it rocks the drivetrain, but only after the initial drivetrain twist that occurs when you start off. Plus I visually inspected the mounts.

I am also fairly certain its not a trans fluid issue, as it clunks AFTER the car has started moving. My experiences with low tranny fluid usually result in the trans losing power when under power going around turns, when the fluid sloshes away from the pickup.

I don't think its the brakes sticking as I tried slowing down using the parking brake and downshifting to slow to a crawl... when I step on the gas, it still clunks.

Its not the struts, as they have been recently replaced. It does not feel like a broken swap bar link.

I was thinking ball joints, but I've never seen ball joints cause this kind of noise.

So I worry that its an internal transmission problem. Next change I get I figured I would replace the filter and top off the fluid... though its hard to do without a dipstick.

What could I be overlooking? What could be causing this?

BKNJ
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Old 08-20-2014, 11:00 PM   #2
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Check the front axle shaft nut goin through the center of the hubs. Seen a few work loose or left loose.
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Old 08-21-2014, 11:10 AM   #3
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Is this clunk happening during a shift?

More often than not, clunks are caused by excessive engine movement, due to mounts.....loose brake pads in calipers....broken stabilzer links and in some cases, stabilizer bars....hangers on exhausts.....CV joint on acceleration....
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Old 08-21-2014, 10:15 PM   #4
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Quote:
Originally Posted by chevy82 View Post
Check the front axle shaft nut goin through the center of the hubs. Seen a few work loose or left loose.
Will check this... but I don't think this would make a noise as nasty as the clunk I have.

BKNJ
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Old 08-21-2014, 10:27 PM   #5
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Quote:
Originally Posted by Tech II View Post
Is this clunk happening during a shift?

More often than not, clunks are caused by excessive engine movement, due to mounts.....loose brake pads in calipers....broken stabilzer links and in some cases, stabilizer bars....hangers on exhausts.....CV joint on acceleration....
That'* the thing that'* driving my nuts, the sound does not not correspond to a shift or suspension, steering or acceleration rate change. It usually happens about a quarter second after starting off... but sometimes its later, sometimes it doesn't happen at all. Usually happens between take off (7~10ish mph) and the first shift (15mph abouts).

I have experiences with a lot of the "usual" sounds... broken stablizer bars/links, CV pops, brake pad/caliper noises, exhaust noises, engine mounts loose... this don't sound like any of them.

I thought I might have a caliper hanging up... as the clunk, when it happens, actually makes the car lurch a bit... but even stopping the car with the handbrake results in the clunk on acceleration.

BKNJ
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Old 08-22-2014, 10:02 AM   #6
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As Mike would say, "You Tube is your friend."

When I would have problems with a sound, squeak , rattle, etc., I would call TAC at GM, and while talking to the guy, I would email a short video I would take of the "concern" to him.......usually helped more than trying to explain it....

Last edited by Tech II; 08-22-2014 at 10:04 AM.
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Old 08-22-2014, 09:00 PM   #7
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Quote:
Originally Posted by Tech II View Post
As Mike would say, "You Tube is your friend."

When I would have problems with a sound, squeak , rattle, etc., I would call TAC at GM, and while talking to the guy, I would email a short video I would take of the "concern" to him.......usually helped more than trying to explain it....
Been on YouTube... nothing like it has been posted.

Hopefully Sunday will give me the opportunity to jack the car up and give it a good vetting.

BKNJ
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Old 08-22-2014, 10:58 PM   #8
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I think he was meaning, shoot a video of it doing it, then post it to Youtube so others can see/hear the issue.
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Old 08-24-2014, 04:28 PM   #9
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I think he was meaning, shoot a video of it doing it, then post it to Youtube so others can see/hear the issue.
Honestly, I don't think I could capture the clunk that well while driving.

So I just got out from the car... I can't duplicate the clunk with the wheels in the air, and poking around with a lever, nothing seems loose.

Looking at the passenger side output shaft, I can see a small bit of silver wear... so I imagine the shaft is moving a bit... not sure this is normal, but this is not visible on the other side. Shaking the CV around, it didn't move any more than expected.

The sway bar bushings has some rust, indicating some wear... but I was unable to make them move much... I doubt the clunk is coming from there.

I did find some info on another site which mentioned that the output shaft support being worn causing a clunk... but I was not able to find any more about the support, such as where to get one and how to swap it out. Considering that there is a bit of silver wear protruding on the CV, I thought this might be the culprit. Any thoughts?

BKNJ
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Old 08-25-2014, 10:28 PM   #10
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If your able to duplicate the problem in the drive way. Get a second set of eyes and ears to help.
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