Bad noise on TC unlock

[ees]

So the nightmare that is my new to me suburban continues. I don't have any solid history on the truck since most things the seller said has turned out to be a lie. Suposedly the tranny has been overhauled in the not to distant past, but I don't believe it.

My problem is this. When traveling on level ground at a constant speed above 55 mph everything is great. At this point if you force a kick down by either extra load from a hill or extra pedal application a horrible noise comes from the transmission. The noise is very similar to a horribly bad wheel bearing. If you let off then reapply your foot it pulls fine.

My theory had been something with TC unlock. The local tranny shop agrees, but has never seen it before. Turns out I also had a bad battery. They felt there was a slim chance this might be the culprit. I doubt it, but it would be a nice change from my luck so far.

I am not yet in a position to test the theory as I am replacing all the fuel and brake lines right now since they are all rusted out.

Does anyone have any thoughts on what would cause this sort of noise? Oh yeah. If you drive with it in 3rd you have no problems at all which is what makes me think it is related to the TC lockup.

[john8662]

Just a thought, but I heard of a few broken flex plates that caused problems like this. You could take off the inspection cover and have a look. most times they crack either connecting to the engine or the bolts going to the torque convertor. Maybe some of the bolts on the convertor are loose? But its odd how you say it works in 3rd, but if I'm not mistaken the TC will lock in 3rd too above 45mph.

[ees]

Well to be honest I have only driven it a few times since I keep finding more things wrong with it. I have only test drove it once in 3rd and that was to get it home from the transmission shop. I did get over 55 mph, but I might have coasted down past the unlock point. It seemeds that the times it made noise it was under load during the unlock.

I hope in the next week and a half to have it buttoned back up and inspected so I can drive it some more and troubleshoot it.

What sort of quotes have you guys had for overhaul of a 4L80E transmission? This small transmission chain said $1600 with 2 year warrentee. My contacts at the dealer said this sounded more like a 4L60E quote.

[john8662]

That price is in the ballpark. The dealer always wants more for a tranny rebuild, but they are usually quality rebuilds. Another thing to check for are check engine codes or Diagnostic Trouble Codes (DTC's). Are you getting any codes that you are aware of?

[ees]

To be honest I have not gotten that far yet. The tranny shop that looked at it did not say there were any, but they also didn't say if they checked. Once I get the fuel lines back in it I will check that.

Thanks