can you tell us about the tranny? did you just put it together? Did you buy it used? who put it together? This is a simple problem but we need a solid place to tell you to start looking. Depending on the year of the case............................ you probably have reverse flowing in the wrong hole were the early model rear pump was, making for no reverse when a transbrake vb is used, transbrakes all use the latemodel cases with reverse feed hole near the bottom not the top. When using a 62-64ish case you need to plug the origonal hole and drill it in the latemodel spot. I could fax you pic if needed.
Keith