Loud thunk at idle after coming to a stop

[GMblood]

2000 ccsb 5.7 4l80e 4x4
Not sure if this is the right section to post this issue but i have no idea what it could be. I have only owned the truck for a few months now, its always done it. Been trying to figure it out but no luck. Every time I come to a stop and idle for a minute (red light) ill hear and feel a big thump like somebody softly rear ended me. I also have been getting a vibration from around 35-60mph I suspect driveshaft center bearing.

 

[shorepatrol]

Ac on ?

 

[jkeaton]

What is the idle doing when this happens? Help us narrow it down...do you hear anything or just feel it?

 

[BoxerPitMix]

I had something similar with my Yukon. When I would left off the brake after coming to a stop there would be a similar noise. Turned out the yoke was binding at the transmission. I pulled it out, greased and it went away for a while until I bought the nickel plated one. I've never heard of it being an issue on the trucks, though.

 

[Boyd McDuffy]

I have a 1990 1/2 ton Silverado. It has been doing that since I bought it brand new. Not all the time, but, often. I have always been told it's normal.

 

[redfishsc]

I had something similar with my Yukon. When I would left off the brake after coming to a stop there would be a similar noise. Turned out the yoke was binding at the transmission. I pulled it out, greased and it went away for a while until I bought the nickel plated one. I've never heard of it being an issue on the trucks, though.

This is most likely what's going on with your truck. It's not a sign of anything terrible, I'm not even entirely sure that it can even call the problem. I bet if you pay attention, you'll notice the problem happens more if you have let off the brakes just a tiny amount, which releases some of the tension that has the yoke bound up in the transmission,. My Suburban did this with a 4 L 60 e, but when I rebuilt the rear end, I cleaned up the pinion part of the yoke that fits up in the transmission a little bit with some 600 grit sandpaper, and it doesn't seem to do it anymore.

 

[Steve A]

Check the torque converter to flexplate bolts. Worked on a Jeep one time with similar symptoms, found the torque converter bolts had worked back and forth till they were almost cut through.

 

[GMblood]

Thanks for the replies,
The A/C is not on it alot louder than the compressor clutch. I can feel it throughout the cab when it happens. It doesnt happen all the time only, after ive been driving for a bit at high speed. I thought the same thing that maybe i was slightly letting off the brake and that was it but im pretty sure im solid on the pedal when it happens. I agree it could maybe be the torque converter. Im taking to a shop to see what they say about it ill let you guys know what i find.

 

[BubbaGump]

Check your transmission mount.

 

[Nathaniel2g]

Rear u-joint or severe backlash can cause this. Mine was so far gone you could get almost a quarter turn on the yoke before the wheel moved.