In last month's issue, we followed Zip Products technician Keith Wilhelm as he assembled one of the company's heavy-duty Dana 36 differentials. This time around, we'll detail the process of installing the diff and matching cover in our '96 C4 project car. Although most elements of the job should fall well within the comfort zone of a competent mechanic, access to both a lift and a task-specific spring-compression tool is strongly recommended. Lacking all of the foregoing (especially the competence part), we outsourced the project to our Vette-savvy friends at AntiVenom in Seffner, Florida. Follow along now as we cover the highlights of the installation.
Break-in
Now that you've spent a few hours swapping in your new heavy-duty differential, you'll want to make sure you break it in properly. Failure to do so can leave you with a diff that whines, chatters, and otherwise impersonates your mother-in-law. Fortunately, Zip includes detailed break-in instructions with every unit it ships, so doing the job right is simply a matter of reading them and doing as you're told.
After filling the diff with fluid and traction additive (remember: no synthetics), take the car out on the road and check for noise. If none is present, continue to drive at a steady 45 to 65 mph for 30 miles, avoiding heavy acceleration and, if at all possible, stopping. Let the rear cool completely, then repeat the process. After three of these 30-mile driving cycles, the rear should be fully broken in. Have your rear alignment specs checked by a qualified tech (preferably one who's worked on Corvettes before), and you're ready to enjoy your new heavy-duty differential. As for us, we'll have driving impressions and drag-strip numbers for you in an upcoming issue.
 After raising the car on the...  After raising the car on the lift, AntiVenom tech Casey Willard begins the job by removing the rear wheels. |  Next to go is the spare-tire...  Next to go is the spare-tire carrier. We decided to leave ours off for good, since the spare itself had long since gone missing. Jettisoning the carrier not only saves weight, it also cleans up the appearance of the car's rear-underbody area. Just be sure to have your AAA card handy in the event of a flat. |  |
 Willard then removes the exhaust...  Willard then removes the exhaust system and hangers aft of the differential. This provides unfettered access to the car's rear suspension components. |  The next step involves decompressing...  The next step involves decompressing the rear monoleaf. Ideally, you'd use a purpose-built tool for this job, but since AV didn't have one (they're pricey, after all, and C4 suspension work isn't something the shop does every day), Willard was forced to improvise. Although this cobbled tie-down-strap arrangement worked fine in our case, it's not something you should attempt to duplicate at home. Translation: Use the right tool, or have a pro do it for you. |  With the spring compressed...  With the spring compressed by the tie-down strap, Willard loosens the castellated nut and bolt that hold it in place. This allows the spring to decompress, as shown here. |
 With that done, the bolts...  With that done, the bolts holding the spring in place can be removed, followed by the spring assembly itself. (In case you're wondering, the control arms were yanked just prior to this step. Your author was coping with a camera-battery failure at the time and didn't manage to snap a photo.) |  |  Willard then disconnects the...  Willard then disconnects the U-joints from both the driveshaft and the halfshafts. |