I have an LQ9 6 liter engine and a 4l60e transmission installed in a 1956 post car. I purchased the combo from a wrecking yard out of a 2006 Silverado truck. The engine has sat a while as I installed corvette suspension front and rear, I never tested the engine and transmission on a stand. The engine mamagement system is fromn Howell.
As the transnsmissio sat it leaked so I dropped the pan and reworked the computer plug on the passenger side of the transmission. I don't think I screwed up anything when I did the repair but now the transmission does not turn the wheels in reverse. (I never tested it before) What is the most likely reason for this transmission have a reverse problem. Could it have sonething to do with it sitting fror a couple of years? Or do I just have to pull it and rebuild the unit?

 

I see that you started a new thread.
First make sure your linkage is working and that the trans goes into Park.
(You confirmed this in your previous thread, but since a 100+ people may read this thread, I like to keep my posts complete.)

There is nothing related to the solenoids, wiring harness, PCM or anything electrical that would affect reverse. Just the manual shift valve activates reverse.
The most likely problem is that one of the teflon rings inside the reverse drum is damaged. With such a new transmission, it might not even need a rebuild (although that is always a good idea.) Only the pump needs to be removed to replace these teflon rings. Replacing these rings is best done with special tools; don't recommend trying it yourself.

I regularly see 4L60E on Craigslist with "No reverse", but they are generally much older than yours. An honest trans shop should be able to tell if you need a complete rebuild after pulling the pump.

Just two more things I would check before pulling the trans out...
I would put the rear wheels up and let the engine and trans reach full temperature with the shifter in Drive. Then check the fluid level (engine running) and try Reverse again. The teflon rings may have dried out and might start sealing better again.
Very unlikely, but you never know with a junk yard trans. Last (just before pulling the trans), drain the fluid and drop the pan and filter. Take out the Boost valve which is held with a C-clip in the pump. It can be accessed through an opening in the case on the passenger side. Make sure it is assembled correctly as the reverse fluid goes through this area. (Just thinking that someone at the junkyard might have cannibalized it.)

It is possible there is a leak/problem inside the reverse drum, but usually it is these teflon rings.

 

When I worked on the leak problem, I think it was leaking through the pins on the electrical connection,I need to replace the harness in the transmission. For now iI used some rtv to seal it. Will the rtv get loose and screw up some of the valving? I wasn't completely sure that I was installing the boost valve and the clip completely right. Does the valve have to be clocked a certain way or just so the filter can be installed?
As for the linkage I've been moving the linkage from under the car by hand, so it's not a linkage problem. While under the car I noticed that the electrical switch that surrounds the shif lever doesn't have any wires running to the computer. Does this seem right? How does the computer know what gear I'm in?

 

The boost valve needs to be installed as shown in the picture below. The left-most part is the pressure control valve which "usually" does not come out when you change the boost valve, but if it does, stick it back up with vaseline.

I don't understand your Q about "clocked a certain way". It needs to be installed as in my pic. If unsure, PM me and we can set up a time to talk by phone.



I would personally never use RTV within the trans, but I know an expert suggested this to you; just be careful.

While it is best for the PCM to know when the trans is in reverse, this is not necessary for Reverse to work. Even if you remove the trans connector, reverse will still work.

 

I jacked up the car and ran it through several heat cycles and engine rpm's, whatever was sticking seems to have worked itself loose and the trans now works well. I haven't tried wot shifts yet because of a slight brake issue but I'm happy at the moment. Thanks for your help.

 

Glad to hear that you have reverse again; my suggestion was a bit of a guess, but I try to cover all possibilities.
Sure beat pulling the trans to rebuild it. At least for now.