Hi Dan,
With the tape frame in the storage position, the tapes should be just under tension. If the are not, pull the tapes up from the frame end and NOT the rear tape clamp bar as this would adjust the 'start' position also. Black and Brown tapes sound like Ampex stock and they should be hurled away as soon as possible as it is impossible to get a good adjustment(what we call good!) with that formulation.
Best,
Martin