Fusspot or Crackpot?

As for me, I’d think removing the rear axle assembly of a road car, for the sole purpose of cleaning and painting would fall on the crackpot side of the line. Usually… Naturally, I can find self-justification as readily as the next fellow, so hold your judgment, please.

Since installing the 5-speed overdrive gearbox a few years ago, the Austin has had a persistent, annoying driveline vibration under load and especially when lifting the throttle at highway speeds. The driveshaft had new U joints installed and was balanced after being shortened to accommodate the new gearbox, and that’s when the minor annoyance began. I had a second shop rebalance the shaft, but it made no difference. Many other projects intervened, plus working on the Brit Stop last winter, so I just kept this problem in the back of my mind. I knew I’d have to expand my car knowledge into a new area.

The underlining problem was there to see every time I got under the car; the driveshaft was working through pretty extreme angles – the tranny and differential were not even close to being in alignment. As you’ve seen yourself, the driveshaft is seldom a straight line between the tranny tailstock and the differential pinion. Assuming a one-piece driveshaft, the U-joints at either end have a small amount of angularity. 2 degrees down at the forward end and two degree up at the diff are considered near ideal. On the Austin, in this one instance, the word ‘small’ didn’t apply.

The way these situations are corrected sounds easy; just tilt the tranny down and the axle up until they have a smaller degree of vertical misalignment. In reality, it isn’t so easy.

Tilting the powertrain down offers only small relief. A couple of degrees is probably the limit before new problems are created, such as engine components fouling the firewall, oil accumulating at the back of the cylinder heads and the gearshift lever fouling the tunnel, for starters. More common is rotating the rear axle pumpkin on its spring perches to aim it upwards. Readily available (I learned) tapered shims are stocked at the speed shops catering to Off Highway Vehicles and for guys who harbor a strange desire get up into their pickup cabs via ladders.
With car enthusiasts, there may be a fine line separating those two characterizations and the separation may shift with circumstances. Boy, I hope so!

Before getting into all that, I wanted to start off with all new spring-to-frame bushings and spring-to-axle rubber perch pads. This is a miserable job working underneath an old car – a veritable shower of undercoating crumbles and metal filings (the bushings don’t come out without a fight). I finally gave up and removed the whole axle assembly to make life easier. Naturally, I wasn’t going to reinstall it looking fifty years old crappy, so why not clean and paint while convenient?

The skilled part of this job is quite interesting and we’ll save that for next month.

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