brake rod ?

[turmoline]

I understand that there is a difference in lengths of the rod that goes between the brake pedal and the master cylinder. 67-70 is one length and 71-72 is a different length. Does anybody know the lengths or the difference in lengths of the rods? I've got a 70 and am having a problem getting pressure to the rear disc brakes. I've got a disc to disc master cylinder w/ proportioning valve and am getting pressure to the fronts. I adjusted the rod that I have almost all the way out and kinda came to the conclusion that it might be the rod I dunno. Oh and I also have fluid to the rear calipers. Thanks.