Panther Cars are Cool--

Driveline stuff.

One of the challenges of buying a used car is figuring out what is normal for that car- how it’s supposed to feel and sound. For example: is that noise, clunk, or whine an indicator of a problem, or is it just what the car does. And if it is a problem, how serious is it? Do I need to fix it ASAP, or can I put it off?

My ex-police Crown Victoria had this slight driveline shudder at really low speeds, like when you’re creeping along in traffic. Take your foot off the brake and the car kinda jerks along. Give it some gas, and it’s as if you released a trans brake: the car takes off with a neck-jerking snap. Funny thing is that it doesn’t do this all the time, and it only does it when the engine is warm.

There are a number of things that could cause this to happen; my first reaction was that the trans is bad. I bought a factory service manual, and one of the diagnostic charts suggested that a vibration like this could be the result of bad U-joints. Cool, I hadn’t considered at all. Curious, I spent a couple dozen minutes hanging from the steering wheel with my head under the car with it idling in gear. Imagine my shock as I discovered a substantial wobble in the driveshaft. It was bent, but there are no signs of dents or damage- I had checked that before. Who knows how that happened- it may have been balanced sometime in the past because there was a stack of weights welded on either end. Maybe the heat from the welder warped it. With the car on or lift, I put a dial indicator on the driveshaft in a couple different locations and the readings indicated just over .060” runout. The service manual had no specifications, but searches on the internet warned against driveshaft runout of more than .010”. A really cool thing about these cars is that millions of them have been made so far, and therefore, there are thousands in the junkyards. It took me about 10 minutes to find a good propshaft from a junked taxi, and I was out the door for less than $35.00. Not a bad price for a 4-inch aluminum driveshaft, huh? While I was at it, I grabbed a rear lower control arm from another taxi in the yard to replace the one on the passenger side than had a dent in it from what looked like some off-road adventure in it’s past life.

Neither of those parts totally solved the problem, but the shudder is greatly diminished. That’s cool with me, I like the challenge of figuring out the cause and chipping away at all the little problems.