Loud Clunk When Let Off Accelerator

[SmokeShow]

Not sure whats going on but I'm getting a loud metallic clunk when I let off the accelerator pedal. It is most noticeable at lower speeds but I think that's mostly because everything else is quieter when going slower so I can just hear it better then. It does not sound like heavy metal objects banging together. Sounds kind of hollow to me. Sound seems to be coming more from the front of the trans/back of engine area rather than back of trans area. It does not feel bound up and then suddenly lets go creating the bang. It is not dependent on gear, speed or RPM. The trans still shifts the same as it always has. It still seems to be holding the power - can't tell of any TC slip and no CELs thrown. I can't feel the bang in any way - floorboard, seat, pedal, steering wheel. Its just a loud clank.

As soon as I let off of the throttle, it does it.


Any thoughts on what it could be? Cracked flywheel? Something bad in the convertor? it's always sounded kinda like a dual disk clutch at idle. Its an ATS 5-star convertor. Ujoint? Transfer Case?

 

[duramaxzak]

Bad motor mount?

 

[SmokeShow]

Hmm, could be. I'll try to check that out too. It's usually the driver's side that fails isn't it?

 

[Mike L.]

Sounds more like geartrain. Maybe loose converter bolts.

 

[WolfLMM]

Grease up the slip yoke?

 

[WolfLMM]

Also check the cross member to frame bolts.

 

[c20elephant]

Grease up the slip yoke?

Sounds more like geartrain. Maybe loose converter bolts.

...quit driving with both feet, worked for me to some degree along with a few other changes I did that made the clunk go away on mine about 8 months ago and has not returned......

 

[SmokeShow]

Grease up the slip yoke?

I've had that but that does it on take off after it binds up a little bit while slowing down and coming to a stop. Then on take off, it releases the bind. My clunking issue is different.

 

[SmokeShow]

...quit driving with both feet, worked for me to some degree along with a few other changes I did that made the clunk go away on mine about 8 months ago and has not returned......

No two-footed driving here.

Although, I did do a really small (probably less than 1000rpm but for sure less than 1500rpm) 4wd boosted launch about a month ago and it was some time after that this issue started. That was the only two-footed driving I've done recently and I couldn't tell you when the last time was before that.

 

[SmokeShow]

FWIW, I did do a spin-on filter change and fluid top off maybe 1500mi ago. IDT it's the transmission internals causing the issue but just wanted to add all the detail I can think of.

 

[SmokeShow]

Also check the cross member to frame bolts.

That's a possibility and the trans mount too. I'll check those and the engine mounts.


What's a reasonable way to check the engine mounts? Have someone rev it while I watch them? Or hook a hoist to the engine and jack it up to see if the mounts are separated?

 

[NC-smokinlmm]

Rev it up in drive with your foot on the brake and watch the mounts to see if they move.

 

[Dan@PPE]

Rev it up in drive with your foot on the brake and watch the mounts to see if they move.

Then do the same test in reverse to check the other mount.

 

[Pure Diesel]

Exhaust pipe hitting cross member.

 

[KyleC4]

almost sounds to me like excessive end play in drivetrain.

 

[Mike L.]

Not a mount.

 

[RPM Motorsports]

My guess is a converter bolt backed out. Sounds like a metallic rattle on decel, or clunk if a few are loose and converter is moving slightly.

 

[mechman3]

My guess would be ujoints.

 

[SmokeShow]

What's the torque spec on the converter bolts? Does it matter that its an ATS 5 Star converter?

 

[Chevy1925]

What's the torque spec on the converter bolts? Does it matter that its an ATS 5 Star converter?

they must be red loctited just so ya know.

check the bolts. if those check out, look at the crossmember bolts for the trans and the t-bar crossmember rubber bushing mounts at the frame