As for the driveline vibration, we mentioned that the rear gears were unlikely culprits. However, there's a good chance your vibration is coming from the driveshaft, either because it is out of balance, or because one or more of the universal joints is faulty. Pull the shaft and check the U-joints for play and to make sure their retaining clips are intact and secure. If the U-joints are in good shape, have the shaft checked by a driveline shop on a spin-balancing rig. The shop should be able to balance the shaft with minimal effort so long as it isn't somehow damaged or bent. Note that Ford Racing offers a complete aluminum driveshaft for Fox Mustangs that comes complete with universal joints and yokes at an extremely reasonable cost that may be a better choice than investing in your stock shaft, should it prove faulty.
If the driveshaft checks out OK, check the runout of the rear axle shafts at the wheel mounting flanges. This can be accomplished with a simple dial indicator using a clamp-on or magnetic mounting base. You should find virtually no runout on either shaft. Any significant runout detected on the face of the wheel mounting flange is probably a good indication that you should replace the shaft. Have the axle shop verify your findings before ordering new shafts. While you're at it, make sure the axle bearings, transmission mount, and rear-control-arm bushings are in good shape.
Z Real Thing?I have had my '69 Z/28 for over 30 years. Lots of fun and lots of combos. Now that I am considering selling it, the first thing people ask is "Is it the DZ 302?" The guy I got the car from (the second owner and a personal friend) worked at a speed shop and had the 302 engine "balanced and blueprinted," which naturally included having the block align-honed and decked. Therein lies the problem.
Now that I realize how valuable my car is with all the original parts, I find myself looking at an engine block with no visible numbers. I had never even noticed that the numbers were not there until I was looking at the stored block in my garage recently and realized that they would have been machined off during the decking process. I know this is the original engine because I have had it apart many times and have verified all of the parts, but how can I prove that this is indeed the engine that originally came in my car? What do other people do when having an engine decked? Can the numbers be raised? I'm getting kinda tired of being asked, "Is it a real Z/28?"Wendell E. SmithSpokane, WA
As you've found, the '69 Z/28 is not only one of the most desirable cars of the first musclecar era, it's also one of the more difficult to authenticate. This is largely due to the relative lack of factory distinctions that designate a Z from other more common Camaro models. Of course, the 302 small-block was unique to first-generation Z/28s, but unfortunately, since it was based on a fairly common production block (the 327, and later, 350), there are no factory casting marks to separate an original 302 block from much more common engines. For the '69 model run, which actually included nearly 16 months of production, there were three block casting numbers used for '69 302s, including the "010," which many Chevy guys will recognize as a super-common 350 casting.
You do have one hope, however. Although you didn't mention when your car was produced, or at which assembly plant, some '69 engines had the VIN stamped in another location in addition to the front of the passenger-side deck. Look on the driver-side of the block at the rear, near the oil filter adapter, and find the flat surface that faces outward, parallel to the bellhousing mating-surface at the point where the dowel pins are located. There you may find the original VIN stamped into the block, but not the other codes that would have been stamped in the deck.