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1965 Malibu Driveshaft - Bad Vibrations

The First Part Of One Chevy Fan's Quest For Smoothness

Chevrolets.We love 'em, right?

Well...not always; sometimes, they make us crazy, cost too much money, cause wives/girlfriends to leave, and even (sharp intake of breath) get us thinking about selling them.

My '65 Malibu is like that. Okay, my girlfriend didn't split on me, but it was no secret: she didn't care too much for "that ugly blue thing."

"Sweetheart, how can you say that about the 'Blue Bullet?'"
"Oh puh-lease. Bullet?! More like a slug-not even that, really, because slugs move. It doesn't."
Ouch. Tough crowd.

Of late, my Malibu has spent a lot of time in the garage. A while back, it developed a vibration I could feel through the seat-often a sign of a driveline or rear-wheel problem. By 70 mph, it blurred the rearview mirror and it excited parts of the car's structure to buzz like angry bees. This vibration limited speed to about 65, making my Malibu anything but a hot rod.

Strange vibrations and weird noises can be difficult problems for DIY enthusiasts to fix. My friend, Gary Peterson, and I chased my Malibu's vibration for a long time. We eventually solved it, but getting there was an ordeal.

The Chase Begins
First step: Rule out tire balance. I went to Tucker Tire Sales in Covina, California, and had the car's Goodyear Eagle F1 GSes balanced. A road test showed the vibration unchanged.

Next: Rule out rear brake rotors. For this, we needed the car in the air with the rear suspension at ride height. I use a Lincoln Automotive, 2-ton floor jack, because of its low pad height, 20-inch lift ability, and robust construction, as well as Lincoln jack stands. We set the front lower control arms on 2-ton stands and the rear axle housing on a couple of 6-ton stands.

We spun the rear wheels at 65 mph and felt the vibration. We did the same with the rear tires and brake rotors off, and the vibration was unchanged. We pulled the driveshaft and had its balance checked by Inland Empire Driveline Service in Ontario, California. Inland's Jeff Gilroy reported no problem.

Suspecting a bad bearing, we sent the rearend to Tom's Differentials, which replaced all the bearings and shipped it back. The car still vibrated. We sent the axle to Tom's, again-250 miles later-to check for bent axles, which can also cause vibration, and they sold me a second set of new bearings and new axles. Later, I found there was nothing wrong with the original axles. After having the rearend rebuilt twice, up on the Lincoln stands at 65 mph, the vibration persisted. Frustration and expense were building.

In an under-car inspection of anything that moves, my friend, Gary, noticed the front yoke was loose on the transmission output shaft splines. I set up my dial indicator, and sure enough, free-play measured .008 inch. I pulled the driveshaft and temporarily installed a new yoke from Clippinger Chevrolet in Covina, California. It moved only .0015 inch.

Measurement of the two yokes showed their spines had the same minor diameter, 1.310 inches, but different major diameters, 1.395 for the bad yoke and 1.376 for new unit. We learned the .019-inch difference is a common, but sometimes undetected, problem for those using transmissions with the 32-spline output, such as Turbo Hydramatic 400s, 4L80-Es, later Muncie four-speeds, the ZF S6-40, and some aftermarket manual transmissions. That much free-play will cause a driveline vibration, and I thought we might be on to the problem. Unfortunately, we'll never know for sure, because we couldn't test the original driveshaft with the tight yoke.

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