94 Z71 will not go into overdrive

[georgewe4]

I rerally hope to find some help here. I have found in the past that you all have been a wealth of knowledge and it has been very much appreciated.
My 94 Z71 has just developed the problem of not going into overdrive. All other gears shift just fine with no problems, just no overdive. The fluid is at the correct level. No slippage at all in the first three gears. The truck has the 350 with the factory tow package. I am ASSUMING it has the 700 transmission. I would change the fluid and filter if I thought this would help, but I have never had any luck doing that when I have had problems with transmissions before. The tranny also is not making any unusual noises, no leaks either. Thanks for any advice in Advance.
George

 

[HI85WH1]

George... 94 is the second year of the 4L60E (ELectronic version of the 700R4)
beyond that, I'm of no help... sorry.

How many miles?

 

[chris718]

2nd and 4th gear are basically initiated by the rear planet overdriving the front section ,in other words second gear is first overdiven and fourth is 3rd overdriven.this should rule out a planetary or mechanical problem.the band is used to initiate both ratios,but the servo uses 2 different pistons to apply the band.looking at the 4th piston may show a problem although it is highly unlikely.i would recommend the use of a scan tool to see if the computer is commanding a 4th gear shift and go from there.in 4th gear output rpm will be faster than input rpm when reading the scan tool.

 

[georgewe4]

Thanks

I will check the area to see who I trust to run a scan, as I have no scan tool. I did have one other thought though. The evening before this happened I did try out the 4 wheel drive to see if it worked. Everything worked just fine, I didn't go off road or anything, I just wanted to make sure it was operating. Overdrive did work right after that. Im not sure if overdrive works in 4 wheel or not, or if something may have happened by trying out the 4 wheel and it didn't show up until 100 miles later.
Thanks again
George