4l60 Problem

[NT5N]

My G20 van (305 TBI) has a tranny problem that developes after the engine warms up. After the van has been sitting for a while and cools down, i can start it up and drive it for a few blocks(until it warms up) then all of a sudden it looses all drive functions (r,d,dr,). I just bought the van recently (64,000 actual miles) but it was in well maintained shape. I changed the rear end out from 4.92 to a 4.88 and drove it to another city(125 miles away) and returned a couple days later at about 75 mph ,all interstate, non-stop. When i stopped the first time at traffic signal the tranny slipped badly in D so I downshifted to d1 and manage to make it home just a few blocks away. The next morning I drove it for 5 minutes or so(everything seemed normal) and the same thing happened but this time it had zero drive ability in any selected range. I was told by a friend that this tranny is computer controlled and that the problem lies within something electrical.
Any ideas and advice will be welcomed as i am at a complete loss on where to begin my checking. Thanks

[MagicRat]

You did not give the year of the van, so we do not know for sure if its computer controlled. If it is a 4LE60 trans it is computer controlled. If its a THM700 R4, its not computer controlled.

However, a partially clogged transmission fluid filter will produce they symptoms you experience, whether the trans is computer controlled or not.
I would suggest dropping the pan and changing the fluid and filter. Clean the pan and install a transmission magnet into the inside of the pan. Most transmissions include a magnet when new, to trap metallic debris but often mechanics just throw them away when they service a transmission.

[NT5N]

Originally Posted by MagicRat

You did not give the year of the van, so we do not know for sure if its computer controlled. If it is a 4LE60 trans it is computer controlled. If its a THM700 R4, its not computer controlled.

However, a partially clogged transmission fluid filter will produce they symptoms you experience, whether the trans is computer controlled or not.
I would suggest dropping the pan and changing the fluid and filter. Clean the pan and install a transmission magnet into the inside of the pan. Most transmissions include a magnet when new, to trap metallic debris but often mechanics just throw them away when they service a transmission.

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Thanks MR...It's a '92 Chevyvan and I did find out that it's a 4L60-E.
I dropped the pan and the filter was clogged alright. The bad part was it was clogged with ground up brass and steel parts...some as big as 1" square. I'm talking a half cupful of grindings. So, I guess it off to the re-build joint. (My ole' 70 YO brain/body is not up to that chore.)
Thanks again for the reply.
Capt Jim (ret)

[RNRea]

For fun you can take the cupful of grindings to the shop and tell them "I need a new one of these."