JB Conversions 16-1200 HD Standard Length SYE Kit for the NP231 - Manual (Page 7)

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11) Verify the length of your mode fork shift rod as shown (Fig.11). If
your shift rod measures 10.2", it will need to be cut down to a length
of 9.380". This is typical to 1988 and 1989 model YJ's.
FIG: 11
12) Install the main shaft assembly and mode fork into the case as
shown (Fig.12). The mode fork rod should be well lubricated before
performing this step. The lubricated rod should slide down through the
range fork easily. Install the spring you removed in step 6.
FIG: 12