The parking brake on the old C models was a pulley looking sheave & wedge assy in the bellhousing. They didn't work to well even when brand new- stopped working altogether once worn. There is an adjustment inside the bellhousing at the wedge assy- just wouldn't count on an adjustment being the culprit.
Replacing the wedge assy is quite an undertaking- you have to work from under the truck, up through a hole in the bellhousing- doable but tricky & time consuming.
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