Hello everyone, I have an issue with my 4l80e that I cannot find anywhere else, and would like some advice from people who know more about these transmissions than I do.

Vehicle: 1992 GMC G3500HD, 5.7. Vandura converted to 4x4... Van has only ~28k original miles on it. Yes 28k.

I have been driving it for the last 5k miles, problem-free. About 3k miles ago I had the fluid drained/replaced, NOT flushed. Fluid that came out looked good. Filter replaced at the same time. No problems.

Last week I hop in and the van takes off really slowly. Not sure what it is but eventually deduce that it's not going into first gear. If I select '1' the van will not move, just free revs as if in neutral. If I select '2' it seems to drive completely in second, never shifting at all. If I select 'D' the van drives in 2nd/3th only but will shift normally between those two gears. If I select 'OD' I get 2nd, 3rd, and 4th all functioning normally. Speedo works normally.

So I figure it's solenoids, take it to AAMCO and they come to a similar conclusion, telling me I have no 1st or 2nd gear. It's hard for me to tell exactly what the trans is doing while driving, so I figure they're right about 2nd even though it seemed to me that 2nd worked. Change the solenoids, which they insist were bad, but this has no effect. I am in ~$450 at this point. Their next step is a full rebuild at ~2600 +tax, citing the problem as 'something mechanical/internal' that cannot be deduced without tearing it apart.

Thoughts? Advice on what to ask them? To me it doesn't seem like two solenoids and two gears would fail at the same time. Maybe it's a $2600 chunk of crud somewhere, idk. Thanks for any help anyone can give.

 

http://www.atraonline.com/manuals/ge.../tetdv-c3h.htm

for starters, check it unplugged. You should be able to hear the A and B solenoids click when you ground their pins (assuming you provide +12v to C).

if no clicking, check the resistance, especially between A and C. Should be the same as between B and C. Neither should be open circuit.

if all check out, then plug the connector back in, and connect a light or meter that shows the voltage at A while the van is running. A should be 0 volts when in first gear. C should be 12 V. If the voltage is wrong, then look for a solution upstream.

This should be able to cut the problem in thirds and let you know if the problem is before the transmission, in the solonoids and their wires or somewhere else in the valve body. I you get the clicking and the voltage at A is right, then it's something in the trans.

I'm definitely not an expert on these, so I could be wrong and there may be more accurate advice out there. Although, I did just design and build a full function controller for my 4l80e.

 

kewilso3 did you ever come to a solution for this? I had a gmt800 Silverado turbo 5.3/4l80e and mine is doing this except 1st 2nd does the “free rev” and doesn’t move (will slightly then stops roughly) this seems to be triggered by doing wot pulls in the truck. Currently having it tuned and this issue has came back, will go away when going back and forth in the driveway it eventually snaps out of it. I wonder if the torque converter locking during the pulls causes some sort of limp mode or something. Had a trans shop look at it and of course it went away once they got it but it did act up from the start and they said they never seen anything like it… hoping it doesn’t need a rebuild because it’s got maybe 15k miles on it. Had to redone before throwing it into the truck.