BLACKBOURN

REAR END BLUES

MICK MCCRUDDEN’S

expert advice in UniqueCars is a must-read for me. The specialist tips you get from an experienced front-line automotive engineer like Mick are great value. His ‘Diff Jockey’ article in the last issue was a good example. Who knew that grease can be a practical substitute for bearing blue when you’re checking the engagement of pinion and crown-wheel teeth? Makes sense once you know.

If I’m honest though, I’ve generally left finessing diffcentre set-ups to experts like Mick. I’ve swapped a few, mind – only modest skills are needed to pull a diff-centre from the banjo housing before bolting in a fresh unit.

One episode that did get me on intimate terms with diff set-up subtleties was during my troubled relationship with a classic 1929 Austin 7 Meteor. Forget shims and bearing-blue (or grease for that matter), the baby Austin had externally accessible adjusters in the axle-housings each side of the banjo-housing that enabled you to move the crownwheel assembly laterally, to either load up or back off its engagement with the rigidly supported pinion. The good book’s message was simple: If the diff whines under load, back it off a whisker. If it whines on the over-run, wind it in a bit. Actually the task of finding the sweet spot was far from being that simple – it involved numerous stops along the road where you wriggled under the little Austin, tools in hand, to have another suck-it-and-see go. Thankfully I got there in the end.

With electronic stability and traction-control systems now the norm in mainstream motoring, the once sexy limited-slip diffs and lockers have been pushed toward the margins; these days it’s mainly motorsport folk and serious 4x4 off-roaders who use them. Similarly the basic trick of welding diff spidergears, not that uncommon a while back, has been almost consigned to the dustbin of car-fettling history. It was an inexpensive DIY-way to consistently get the power down via both back wheels. It had its shortcomings though when used on the road – I recall mates upsetting servo operators by leaving black rubber tracks where they pulled U-turns around the pumps, and occasionally breaking half-shafts, and having to fight for steering response in some situations against the diff ’s efforts to push the car straight ahead.

My most memorable diffcentre swap came during a quick HR Holden trip from Melbourne to a Gold Coast wedding. Just before dawn on wedding-day Saturday, not far south of Maclean on the Pacific Highway, a pinion bearing that had been humming happily through the night at around 75mph let go suddenly. In a big way…

Eventually an NRMA towtruck unloaded us beside an old garage in Maclean. While the mechanic had gone for the weekend, my spirits lifted when the bloke on duty said he knew a cane-farmer nearby who was a backyard Holden wrecker. Not only was the farmer happy to bring me a good diff-centre, he offered a choice of ratios. With the deal done – using borrowed tools, jack and axle stands, and a sheet of gasket paper I found behind the garage workbench – I got stuck in.

With the wedding in mind (and my planned pre-wedding snooze abandoned) there was a touch of LeylandBrothers pressure on my progress: “Will Mal get the sump back on before the tide comes in?”

While I can’t remember whether Mal Leyland did beat the tide, I do remember that we didn’t quite get to Surfers Paradise in time for the wedding. All wasn’t lost though; after thoroughly degreasing myself, and taking a brief kip, I was in top form for the reception. And the cane-farm diff worked like a charm for as long as I had the HR.