FastKat

iTrader: (10)

The title sums it up - my 4L80E from a 2003 Express van makes a hissing sound when it's running and in gear. It makes it in both drive and reverse. When you put it in neutral, the hissing sound goes away.

I noticed it after driving for about 200 miles on the highway.

On a side note, I think my first gear is a little noisy too. It sort of whines like reverse in a manual transmission. I'm not sure if that's related or not.

Any thoughts?

FastKat

iTrader: (10)

Everybody's stumped? I was thinking maybe it has something to do with the trans fluid filter. Maybe the filter came loose and sucked itself to the bottom of the pan? I had some dents on the pan that I pounded out - maybe something else is going on down there?

Monte4ever

iTrader: (2)

My guess is the trans needs to be rebuilt.

maddoglou454

Probably converter, but in some cases , the filter is clogged up replace filter and you're good to go. It's worth a shot.

FastKat

iTrader: (10)

Thanks guys. It might be my imagination, but I hear the hissing sound when the trans is hot. I will try dropping the pan and putting in a new filter.

Is there any other way to isolate it or isolate it to a converter??? I have HP Tuners so I can command the trans, etc.

maddoglou454

Change the filter if it still does it,it is definitely the converter. Do not exceed more than 10% line pressure over factory tune.

gtxracer

iTrader: (1)

Bump - having the same issue. New converter, fresh fluid, fresh filter on a pre-96 80e. Only does this when it’s hot - any ideas?

MaroonMonsterLS1

Did you really just revive a 7 year old thread?
Try the recommendations posted above...then if that gets you nowhere...start your own thread with detail

gtxracer

iTrader: (1)

Gee thanks, how helpful.

MaroonMonsterLS1

Have you tried any of the recommendations above?
They are good recommendations so try them first