Normal driving it is fine shift at about 35 mph but put down the accelerator to the floor and it won't shift into 4th all the rest of the gears are fine/. 1987 Camaro 355 built.

 

This is the "Normal" operation of the THM700-R4 Transmission.

This can be changed with modifications to the Valve-Body (Throttle-Valve Sleeve and 3-4 Shift Valve-Train).
But require improvements made to the 2-4 Band, and the 3-4 Clutch-Pack...
or the Transmission will Burn the mentioned Band and Clutch-Pack.

 

The talent here is amazing. So the reason they designed it to not shift to od at wot is because it would burn out the clutches. I have a upgraded steels and clutches, shift kit, 2800-3000 stall. So if that's what is needed, how do I get it to shift to over drive. I have a 411 Ford 9in with 30 inch tires , so it's around 140 in 3rd at 6500.

 

What model-year is the Transmission?
What year Core is the Valve-Body?
And which "Shift-Kit" or Aftermarket Parts, have been installed?

 

More or less, yes.

-The Throttle-Valve System needs an overhaul.
-The Separator-Plate Orificing needs an overhaul... actually much of the hydraulics need an overhaul.
-More TV Pressure and Line-Pressure are needed.
-A "Corvette" or larger Aftermarket 2-4 Servo is needed with a pristine Drum and Band.
-The 3-4 Clutch-Pack needs to be updated to newer standards.
-And then a bunch of minutia.

 

See the WOT 3-4 shift sticky at the top of this forum. Dana added to that thread with additional information on making the 2/4 band live.

RBob.