We do not have a 85 service manual in the tech section but in the
86 manual in section 3B4-21 (page 260), it shows a breakdown of the steering wheel and tell you how to service and take it apart and out.
From what I read, it does not seem like you "split" the upper from the lower housing, it looks like you have to take the whole thing off after you remove the steering wheel. Use the link and read through the manual, if you still have questions we can help you out.