"87 Chevy Won't Go Forward

[Deydad]

"87 Chevy w/ 700 R4 transmission lost all forward gears today. Was going over a high-rise bridge and once I got to the other side, I couldn't move. It still backs like a champ.

 

Trans fluid is at the full mark.

 

What else can I check ?

 

What else might be wrong?

 

No problems up to now.

[Deydad]

Turns out it was the modulator valve on the side of the transmission. Pulled the vacuum line off and had forward gears. Put it back on, and it still works. Can get a replacement at the local parts store pretty cheap.