BAD VIBES — DRIVESHAFT AN­GLES RE­SOLVED

DRIVELINE VI­BRA­TIONS ARE DAMN AN­NOY­ING, AND CAN SE­RI­OUSLY WRECK STUFF, TOO. HERE’S A WAY TO CHECK YOUR UNI JOINT AN­GLES, AND EN­SURE EV­ERY­THING IS SWEET

NZV8 - - CONTENTS - WORDS: CON­NAL GRACE PHO­TOS: ADAM CROY

e love a good fac­tory restora­tion, but you’re prob­a­bly read­ing this magazine for the same rea­sons that we’re pro­duc­ing it — the love of mod­i­fy­ing cars. Most of the cars we fea­ture have been mod­i­fied to an ex­tent, some more than oth­ers, and the ma­jor­ity ended up re­ceiv­ing an en­gine and driv­e­train up­grade along the way. But, as fun as it is to get car­ried away with choos­ing go-fast parts and play­ing the num­bers game, there’s a prac­ti­cal as­pect to driveline swaps that is of­ten over­looked — one that can poorly af­fect the way that your fin­ished build drives.

It’s to do with your driveshaft, but we’re not just talk­ing bal­anc­ing. Get the uni­ver­sal-joint an­gles wrong, and you could be run­ning in cir­cles try­ing to cor­rect the driveline vi­bra­tion that just won’t go away. Who would have thought that those science and maths lessons in school would come in handy …? Yes, we’re talk­ing about physics and ge­om­e­try, but don’t worry if you weren’t pay­ing at­ten­tion in school, be­cause it doesn’t have to be hard. Maybe a bit con­fus­ing, but not all too dif­fi­cult.

Spin some­thing, and you’ll sub­ject it to the prin­ci­ple of in­er­tia, de­fined in Isaac New­ton’s first law. Don’t worry, we’re not go­ing to get all com­plex here — ‘in­er­tia’ de­scribes the re­sis­tance of an ob­ject to a change in its state of mo­tion. Huh? The quicker an in­ert ob­ject moves, the greater the forces on it. Slowly ro­tate your driveshaft while crawl­ing along at 20kph, and ev­ery­thing will be hunky-dory. Whip it up to 4500rpm while do­ing a big old burnout, and the forces act­ing on it are go­ing to be a bit more in­clined to try to break it free, espe­cially if there is some­thing out of whack — bal­ance, or the uni­ver­sal-joint op­er­at­ing-an­gles tol­er­ance. Of course, those are two ex­tremes. In the real world, which is where your car will spend 99-per-cent of the time, any way­ward forces are most likely to man­i­fest them­selves as a driveline vi­bra­tion. This is where things can get con­fus­ing, be­cause the first sus­pect is al­most al­ways a poorly bal­anced driveshaft — even when it might not be the case.

It’s gen­er­ally ac­cepted that in a front-en­gine rear-wheel-drive ve­hi­cle, the diff-pin­ion an­gle should be pretty close to the an­gle of the en­gine and trans­mis­sion. But, when it comes to ve­hi­cles with a two-piece shaft, things get a whole lot more con­fus­ing.

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