The measurement is known as “seal to center” and is the distance between the case of the transmission next to the rear seal and the centerline of the pinion yoke. When ordering a driveshaft you must complete the following form. Email this completed form to email@example.com, or fax the form, front and back, to 480.393.4180. How to measure the driveshaft and determine your rear universal joint size is demonstrated on the form. For late model Mustangs, a second page is provided to determine your rear flange size. Turnaround time, once your form is submitted, is 24 to 48 hours to build along with the amount of time require to reach your location via FedEx Ground (1 to 5 days).