Dabney was driving his 1966 Rambler wagon while on an errand to the local home center. He was surprised to meet up with his old friend, the Doctor, at the checkout counter. It seems both of them had some home maintenance tasks to perform and had independently gone to the center. Anyway, they walked out to the parking lot together and the Doctor helped Dabney load some 2x4s into the Rambler's tailgate area.
As the Doctor was walking away toward his car he heard Dabney pulling out of his space in reverse. The Rambler was emitting a chattering sound as Dabney slowly backed out, but the sound went away as soon as the transmission was shifted into neutral. The Doctor instinctively knew there was something abnormal going on inside the Rambler's drivetrain.
"How long has that been going on?" quizzed the Doctor.
"Oh, it's done that since I first bought the car," answered Dabney, "but it's never gotten worse over the 10,000 miles or so I've driven. What do you think it is?"
"It could be anything, dear Boy, from a loose bracket to something inside of the transmission to a cracked case. Too tough to tell," said the Doctor.
"Do you think we could troubleshoot it?" asked Dabney.
"Sure, we could test it in varying conditions and at least pin down the symptoms to a few causes," said the Doctor.
They met up at Dabney's garage and unloaded the items he bought at the home center, and then the two proceeded to drive the Rambler in all sorts of conditions in an attempt to narrow the circumstances of the chattering. Sure enough, the car only chattered while in reverse, whether it moved slowly or fast, uphill or downhill. There were no other sounds or abnormalities present.
The put the car on the lift and inspected everything underneath, from exhaust brackets to engine and transmission mounts. They inspected the driveshaft and the transmission's output shaft bushing and found nothing to be concerned about.
That's when the Doctor said, "You know, Dabney, that Ramblers used Ford C4 transmissions back then. The Cruise-O-Matic, as it was known, was a pretty good piece of engineering and would last a long time, but if it got out of adjustment things could get bad pretty quickly. Let's go through the numbers and see if we can nail down the problem."
"What numbers, Doc?" asked Dabney.
"Well, first let's check the fluid for proper level. Then we'll disconnect the throttle linkage at the transmission and manually shift it into reverse. If it still chatters, we know it's not an adjustment problem. Then we'll hook up a pressure gauge and see if the control pressures are at spec. After that, if the problem still exists we'll have to take the transmission apart," said the Doctor.
Unfortunately, everything checked out fine, so the two of them spent the rest of the afternoon removing the transmission from the car. They drained the fluid, opened up the case and removed the inner components, checking for damage or wear. Other than the usual mileage wear on the clutches and bands, the transmission's components were clean and in very good condition.
"Well, Doc," said Dabney, "I figured we'd get this thing apart and find a bad clutch or loose band."
"So did I," said the Doctor. "I think before we make a decision to rebuild this transmission we should thoroughly clean the case in a tank of water and detergent. Back in the days of the C4 there were some cases that developed cracks and the tell-tale was severe chattering in reverse."
They cleaned the case and, after drying it out with air pressure, inspected it carefully. Sure enough, they found a crack near the tail housing mounting area.
"Well, now what do we do," asked Dabney.
"It's simple," replied the Doctor. "You buy a rebuilt C4. It would be more expensive to find a good, usable case and replace your components than it would to get a whole transmission. That's just the way these things go."