Early Chevelles have a stiffening rib running across the body, under the floor, just aft of the front U-joint. As we'd lost 1/4 inch of clearance between that rib and the driveshaft when we upgraded to the 3.5-inch unit, the additional 1/8 inch of the front balancing weight protruded, and the weight was nicking the rib when the powertrain moved after the car hit a bump. I took the shaft back to Inland to have the weight moved. I was ready for a longer road test. Long story, short: the darn vibration was still there. Was I ready to give in? Nope.
Transmission TraumaThat we'd been on this job for nearly six months and had either repaired or replaced everything from the transmission yoke back without solving the vibration started me thinking transmission; maybe it had a bad output shaft bearing.
We pulled the Malibu's ZF and I took it to ZR51 Performance in Cave Creek, Arizona, outside of Phoenix, which is approved by ZF Industries to do overhauls on '89-96 Corvette six-speeds.
Upon removal and cleaning of the transmission's five bearings, ZR51 Performance's owner, Bill Boudreau, did not find a problem. Though it wasn't necessary, I had Boudreau install a new set of genuine ZF Industries bearings (PN 1052BRGK) and a seal kit (PN 1052RBK) we ordered from one of the better sources for ZF six-speed parts, Rockland Standard Gear.
A week later, with the transmission back in car, we took a road test. The vibration was still there. Rats.
The Right AngleMost driveline vibrations are either one excitation per revolution, typically coming from imbalance or run out, or two excitations per revolution, which is usually caused by a problem with universal joint angles.
I began to wonder about the car's universal joint angles. Gary and I found that the car's rear upper control arms were not Chevrolet items. They were stamped "PONT" which I figured was an abbreviation for Pontiac.
Not having a set of stock Chevy arms as a standard and figuring these Pontiac arms could be of a different length, which would change the rear U-joint angle, I ordered a new set of reproduction Chevrolet arms (PN AU64RP) from Year One. I had them reinforced by Global West Suspension, painted them with Eastwood's Chassis Black paint (PN 10025Z), and installed them. The U-joint angle was unchanged. Several months later, I found out by checking the angles on a bone-stock early Chevelle at Auto Craft, a shop in Rialto, California, that specializes in restorations, the rear U-joint angle on my Malibu, 2.8 degrees, was nearly the same as the OE 3.0 degrees I measured at Auto Craft.
Thanks to the generosity of the Autocraft guys in letting me crawl around on their floor for a while measuring the driveshaft angles of their Chevelle with a Dana AngleMaster II, I found the vibration was not being caused by a driveline angle problem.
Well, it was nice to know what wasn't the problem, but that's really all I had at this point: a lot of potential causes that were not causing the trouble.
I'm going to keep beatin' on this problem until it's fixed because I believe persistence always pays off. Next month, in Part Two, you'll find out whether it pays off or not.