I had barely pulled up in the driveway when my daughter started stepping down from the old Discovery 4×4. She was putting one foot on the ground at the moment my foot was coming off the brake pedal, prompting the Disco to lurch two or three centimetres back down the slope before settling.
Caught on the hop, as it were, she said: “Doesn’t the handbrake work?” “Perfectly,” I replied, “That little move came from normal slack in the driveline. Don’t worry, the old girl is well anchored to terra firma now.”
My grandson got the subject back on the agenda that afternoon by querying my ‘driveline-slack’ explanation. It was news to him as a car driver.
I explained that all drivelines have ‘slack’ because it’s essential to the function of gears and splines that they run with minimal, predetermined clearance or ‘lash’ between mating components to prevent seizing or excessive wear.
It’s invisible in normal use – unless the vehicle has a transmission-mounted handbrake (like many trucks and old-school 4x4s). I think the young fella was still pretty much with me as we knelt beside his car, identifying the handbrake cables leading back to the drums that directly lock the wheels with the handbrake on.
I sensed I was starting to lose him, though, by the time I coaxed him to wriggle under the Disco with me to view the transmission-mounted handbrake drum, positioned well upstream along the driveline from the back wheels.
The subject was still on my mind that night as I sat down with the latest issue of Unique Cars which included a Morley update about coming to grips with an example of Henry’s finest, the 1924 Model T Ford that he inherited from his late father-in-law.
The transmission-brake issue is more crucial with the remarkable Model T where the brake pedal operates on a drum that actually lives inside the T’s epicyclic gearbox. It’s not about your car rolling back a smidgen before settling when the handbrake is applied – it’s about your brake-pedal having no effect at all in the event of a driveline failure.
Whether it’s a universal joint that lets go, or an axle, or more likely, collapsing ancient thrust washers in the diff, you and your Tin Lizzie are potentially left rolling freely along the road with no anchors at all apart from the minimally effective handbrake.
The fact that the handbrake is restricted pretty much to a park-brake role is confirmed when you see that its cast-iron shoes that bear against a steel drum have no linings, no friction material at all.
Similarly, T owners who opted for the popular, Ford approved, Ruckstell two-speed rear axle lost braking altogether if they unexpectedly found a neutral between the diff’s ‘High’ and ‘Low’ positions.
It was an old KB5 model International tip-truck that I drove casually during my uni days that first brought transmission-mounted handbrakes to my attention. Dramatically …
An old contractor presided over a modest fleet, a pair of old KB5 Inters, that he kept in the backyard of a derelict house close to Melbourne Uni. If I had a free day coming up, I would catch up with him at his favourite pub and book myself in for a 7am start on the agreed day.
The two old Inters were in quite good nick for a pair of fairly ancient trucks, although the one I drove for my first couple of jobs was the pick of the pair. First time out in the backup KB5, I had no idea that its handbrake assembly was caked with a poultice of gear oil and dirt thanks to a worn gearbox oil seal.
Not only did that make the handbrake totally ineffective, it meant you had no clue if you inadvertently drove off with the handbrake on. And that’s what I did on the way back to the city after dumping a load of rubble…
Suddenly a headlight-flashing, horn-tooting RACV ute overtook me rapidly before forcing me into the kerb. The guy was out and running toward me with fire-extinguisher in hand before I finished rolling to a stop…
While an oil-soaked brake doesn’t do much in the brake department, it can generate enough heat to burst in to flames.
With no real harm done, the old KB5 and I both lived to fight another day, and I never used that handbrake again.