I just had my trans rebuilt 2 summers ago:
The mrs drives it to and from work daily..(25 miles round trip)
Now heres whats going on....

This is on my 1999 Montecarlo Z-34 with a 3.8...

Its been working flawless....
The mrs came home today and said theres now no reverse..But drive works perfectly fine...
So I went out there checked the fluid...Its full and still looks like new..
I started the car, Put it into reverse....and nothing...Switched it to drive and it went into gear just fine....Switched back to reverse ,nothing, so I give it some revs...and suddenly it goes into reverse...I switch it several times from reverse to drive and it operates normally..engageing everytime.

Is there some electronic solenoid, pressure switch or something that would cause this issue?....
Its certainly not in the linkage.

I checked the common problem post that mike (chibi) posted a while back...But nothing matches the issue im haveing....with this transmission...
Hope someones has the answer...Thats a quick and simple fix...Considering I just spent a boatload of cash on struts and cartridges!

 

This isn't good. I believe you are going to need another rebuild/tranny. However, you can check your neutral safety switch (it's under the master cylinder on the tranny). Make sure the NSS is good... But if it took revving the engine to get it to engage that's an internal problem IMHO. It's possible it's the Torque Converter Clutch solenoid, but I doubt it.

 

Could it be the reverse servo seal worn out?its a common problem on the 4t60 transmissions

 

Just found the receipt for my trans warranty.. l had it rebuilt on 5-11-2011
12 month 12000 miles...(im past the 12 months but not the mileage)
Gonna call the trans shop in the am and get his opinion...

Its strange that it drives forward perfectly normal.(just did a test drive)
However: I once again tried reverse...nothing..til i gave it minimal revs..(1000 rpms)
and now...once again its acting like it never had a poblem going into reverse.....It seems to repeat the same same results....

Checked the system with a scanner....No codes..of any kind...system checks clear, even tried shifting it in and out of reverse....(which works)
and still nothing....shows up on a scanner.

The mrs did just tell me..That first thing in the morning..it works normally(going into reverse)
The only time it seems to act up is once it gets up to normal operating temp....

 

The real question is;
Wheres it located? inside or outside the trans?

Will it show up on a scanner? or is there some other test I can do?
To check it?

(theres no external leaks)

 

Apparently...

No one has an answer as to what the problem is....
So looks like im gonna have to take it in....
If it turns out i have to spend a ton of cash on it...
I just may end up scrappn it out....
Since im on disability ... Money around here is always an issue...
Thanks anyway EV1

 

The seals are inside the transmission, it needs to be taken apart and rebuilt or get a used transmission. Thought I was clear when I said it was an internal problem in my first post. Sorry to be the bearer of bad news.

 

netural safety switch (external near the brake pedal, might be loose), vacuum modulator switch (external as well, mounted right on the case of the transmission itself), those two can both cause you to loose Reverse momentarily.

 

that's an internal problem sadly if it is the servo seal