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95 Z26 3.1 4 speed auto with 169K miles , engine had a rythmic loud banging when not in gear and revved to 1500-2000 rpm.  It is regular at about 1 second intervals, hard enough to rock the engine forward.  Does not occur in when in gear going down the road.  Listening, it seems to be coming from the back part of the engine.  Tranny has been downshifting hard, but not every tme, took it to shop and fluid and pan did not have any debris.  Any thoughts?

Mounts? Does the engine rock when in gear with the gas and brake on?

(601beretta @ Nov. 02 2007,19:41)QUOTE95 Z26 3.1 4 speed auto with 169K miles , engine had a rythmic loud banging when not in gear and revved to 1500-2000 rpm.  It is regular at about 1 second intervals, hard enough to rock the engine forward.  Does not occur in when in gear going down the road.  Listening, it seems to be coming from the back part of the engine.  Tranny has been downshifting hard, but not every tme, took it to shop and fluid and pan did not have any debris.  Any thoughts?
Did you take it to a transmission shop or just your mechanic?
A friend's son has a 95 base that needs the 4T60E rebuilt. It was making knocking sounds in park and neutral, but was fine in gear. The interval of the sound you talk about was less than one second though.

I told him that's what I thought and an acquaintance who does trannies for a living validated it.

I talked to my friend on Halloween  and mentioned to him to ask what the specific problem was for my own benefit. I 'll relay that info to you when I hear back, if your problem still exists.

I did take it to a transmission shop.  I revved the engine so they could hear the noise.  They said they never heard anything like that.  It sound like what your friend has, so please let me know what he found out.  Sometimes, it also make a similar noise maybe up to 6 times when the engine is started cold and then it stops.