BluExpress

Chevy express 6.0 v8

4L80e transmission



My issue; slight random vibration under very light throttle acceleration

Give it more gas it goes away, or let off the throttle it goes away.

If you feather the throttle while accelerating while it’s vibrating, it goes away and drives smooth.



It’s very random 9/10 times it drives perfect.



I’ve replaced motor mounts & transmission mount, all new front end components, brand new drive shaft, all shocks and recently idle air control valve and throttle position sensor



All that helped tremendously.



But the random vibration while under light acceleration is still there. It’s very random and will randomly happen at any given speed.



Zero engine codes



Any ideas ?

hanky

Could we be looking at an intermittent misfire ? These don't always throw codes if the conditions required to set a code are not met.

Where do you feel the vibration more, steering wheel, driver's seat, front, rear? The more info you can provide would help to isolate the area and some possible causes.

BluExpress

I feel the vibration more towards the front. I would say more on the foot throttle than the steering wheel.

also something I’ve noticed when the vibration is happening
I feel like the engine rpm are off. Best I can describe it is, imagine driving a stick shift car and being in the 3rd gear instead of 2nd and giving it gas.
This was the reason I changed out the idle air control and throttle position sensor and cleaned out the throttle body.

a few months ago, I replaced all spark plugs and cables.

originally I thought it was the drive shaft, I replaced it with a brand new one and it helped a lot. But the dang on vibration is still there. At times it goes days with zero issues. Then all of the sudden. It appears.
It tends to show its face more when I’m going 65-80mph but it’s randomly happened at all speeds above 30mph

Triaged

Sounds like it might be torque converter clutch chatter or shutter. Modern transmissions don't have just on/off for the TCC but can feather it on. When is the last time the transmission fluid was changed? What fluid was put in? The bolt bosses were welded on the torque converter and make a hard spot where the TCC rides which can cause this. Sometimes a fluid change and/or additive can help for a while.

I'd start by changing the fluid with GM stuff then might think of adding some shutter fix if it's still there.

https://www.amazon.com/Lubegard-19610-Tranny-Instant-Shudder/dp/B0002JMLQU/
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Edit: do you have a scan tool? See if you can display the TCC percentage.

mountainmanjoe

Please post complete information. ie. years, miles
Thanks.

BluExpress

2004 chevy express 6.0 v8
340,000 miles
transmission is less then a yr old. Engine is original.

Triaged

When you got the new transmission put in did you also get a new torque converter? Billet or rebuilt stock?

BluExpress

yes sir, it was a complete rebuild of the original transmission with a new torque converter my total was $3,700 for the rebuild.

It shifts and downshifts perfect.
feels like a race van with overhaul activated 😅

I’ve owned this van since new.

I’ve got a cheap scanner from harbour freight ZR15s but it doesn’t read the TCC

Triaged

Search here for ELM and the Torque App. I think lockup percent is one of the things you can display. If you can see that on a scanner then you can see if it coincides with the vibration.
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mountainmanjoe