Weird noises on engine breaking

[Matthew Jeschke]

When I have a decent speed going and engine brake in 3rd or below I get a weird noise. The transmission temperature is around 170F, fluid level is good, fluid smells and looks good as well.

I can accelerate with no problems, only does it when say I'm going 80MPH and let off gas in 3rd gear. Kind of feels like should be slowing truck down more than it is.

 

[exp500]

What was the thrust bearing clearance on your new motor? I tend to think flex plate before torque converter. Look into planetary clearance/wear too. See about updating your description.

 

[OR VietVet]

Can you describe the noise? What engine?

Friend of mine with a 2000 Yukon had a weird rattle/vibe noise on decel and could even duplicate when sitting in Park. I traced it to a bad EGR valve. Replaced and problem solved. He did not mention any engine break problems though but he may also not even know what that is. The noise was easily found with my stethoscope. The noise was constant and not intermittent.

 

[Matthew Jeschke]

It is really hard to describe the noise. It does seem to be coming from the bellhousing area though.

Engine is a custom 6.0L I built. Should easily be making 400+ hp and 400+ lbft torque. I suspect I did something to transmission hammering on motor to tune it but hope not.

I may try and get a recording of it. Doesn't do it under idle at all. The transmission is at approx 170f.

I can feel it happening. Seems like a rotating slippage of some kind. My passenger didn't seem to notice though.

I think the thrust bearing clearance in the engine was 15 thousands or something like that if memory serves me right.

I like the EGR theory as is easy to check... and for some odd reason I am rich on one engine bank and lean on the other... However bank 1 wo EGR is lean while bank 2 is rich.

Separate problem but perhaps related.

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[Matthew Jeschke]

Pulled off EGR valve and cleaned it. I can blow on open port and air leaks out around the valve. Not sure if that means it's warn out?

I'll have to listen to it with a stethescope but I don't know exactly what activates the valve... maybe I just connect and disconnect the electrical connector and see if I can hear it?

 

[OR VietVet]

When my friend would rev the engine and when he then released the gas pedal the vibe noise happened then. I could hear it near the EGR Valve and could feel it when I put my hand on it and was very loud with the stethoscope. May not even be related to what you are experiencing but it was fresh in my mind from 3 days ago when he had the noise.

It was a warm day around here and he said the problem happened with his a/c on but I could hear it the same whether the a/c was on or off.

 

[exp500]

With your thrust bearing clearance that tight, no worries on cracked flex plate usually. Above .060 -.080 its a time thing.

 

[Matthew Jeschke]

When my friend would rev the engine and when he then released the gas pedal the vibe noise happened then. I could hear it near the EGR Valve and could feel it when I put my hand on it and was very loud with the stethoscope. May not even be related to what you are experiencing but it was fresh in my mind from 3 days ago when he had the noise.

It was a warm day around here and he said the problem happened with his a/c on but I could hear it the same whether the a/c was on or off.

I just ordered egr block off plate so I can test wo EGR at all. Looked at new ones and they are $$$$

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[OR VietVet]

That may not be your problem but if you were going to do the block off plate anyway, well what the hell.

 

[Matthew Jeschke]

That may not be your problem but if you were going to do the block off plate anyway, well what the hell.

It is no worries $13. I think will be easier to tune knowing I am not fighting an old EGR valve.

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