I've always heard that way-back-when, the simplest way to rewind a car's odometer was to drive backwards (at least in some models). Is this true? Did those manufacturers miss such an obvious gaming method?
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12What a classic from Ferris Bueller -- perhaps the most famous example... (LINK)– HendyCommented Jun 27, 2011 at 23:12
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1wiki says true but no refs, only way to be fully sure is to ask a mechanic that worked on those and tried it. OTOH I recall the movie Mathilda showed the father forging an odometer by turning the cable backwards with a drill (how accurate that is depends on how well hollywood researched that)– ratchet freakCommented Jun 27, 2011 at 23:28
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7It was also mentioned in the Roald Dahl book Matilda.– Golden CuyCommented Jun 28, 2011 at 11:40
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@Andrew +1, I was going to mention the same. ;-) Loved that book.– Konrad RudolphCommented Jun 28, 2011 at 11:42
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1Driving backwards a few thousand miles still does not seem like the simplest method ... ever tried this on public roads - not very practical!– DanielCommented Jun 6, 2018 at 12:53
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3 Answers
Yes, older cars used mechanical odometers, which go forward or backwards, depending on which way the gears are turned. Modern cars use electronic odometers. I couldn't find anything indicating over what time period this changed. It was well before my time behind the wheel, though.
I also found a January 1961 article from Popular Science Magazine on the prevalence of odometer rollback fraud. (Page 59, if the link doesn't jump right to it)
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9There was an intermediate period with mechanical odometers that (a) wouldn't go backwards when in reverse and (b) were tamper-evident for rollback. I can't find a good reference. Plenty of anecdote though.– Oddthinking ♦Commented Jun 28, 2011 at 0:34
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no word if any safety (like a simple one way slip lock or an adapted coaster brake) is used on the output on the gearbox to the odometer Commented Jun 28, 2011 at 0:37
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@Ratchet, I think such devices were added (in 70s and 80s) but I can't find proof.– Oddthinking ♦Commented Jun 29, 2011 at 8:44
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1Indeed, whether the odometer is mechanical or electronic has nothing to do with it; either it is built to not go backwards, or it isn't.– psusiCommented Jul 1, 2011 at 15:40
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3Not all mechanical odometers ran backwards, vintage Ferrari's never did, all odometers (USA) would not reverse starting in the 80's to prevent fraud.– MoabCommented Aug 25, 2011 at 1:38
Mechanical odometers could be tampered with in myriad ways. I have seen people literally use a screwdriver to manually move the numbers backwards, I have seen drills used and various other methods. Even now, you can have your 'mileage adjusted' digitally; it's a huge area of crime here in the UK and people are still getting jailed for it.
This link actually mentions Ferris Buellers Day off:
You can also see that mechanical odometers like this one are rewindable. When you run the car in reverse, the odometer actually can go backwards -- it's just a gear train. In the movie "Ferris Bueller's Day Off," in the scene where they have the car up on blocks with the wheels spinning in reverse -- that should've worked! In real life, the odometer would've turned back. Another trick is to hook the odometer's cable up to a drill and run it backwards to rewind the miles.
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1It was a 61 Ferrari 250 GT Californian; it would have defintely had a mechanical Odometer– HairyCommented Jun 28, 2011 at 12:20
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2@Hairy: how do we know it "definitely" would have had a mechanical, reversible odometer? You seem to have experience... but how are the rest of us to know this?– HendyCommented Jun 28, 2011 at 15:44
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1@Hairy, part of Hendy's point is that while you know you've seen it done, and you know what would be in a '61 Ferrari, we don't know that you know. If you can provide a reference, it will probably shut us up.– Oddthinking ♦Commented Jun 29, 2011 at 8:47
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1I know Veglias, of that era and up to 1979, were mechanical speedos, with mechanical odomoeters. I know there were no rachet patents applied to them, I know, and have proven, you can adjust them (mechanical odometers) by drill, screwdriver, driving backwards, etc. However, I do not know, nor can I find, the precise Veglia instrumentation model number, a 1961 Ferrari 250 Californian used. However, the car in the film, was a kit car based on an old MGB and even had Smiths instruments (one close up shows this), which were mechanical, and I have adjusted these.– HairyCommented Jun 30, 2011 at 6:47
A point which no one has yet brought up is where the odometer cable is attached. If it is attached after the gearbox, then it will go forwards or backwards. If it is attached before the gearbox, then no matter whether you travel forwards or backwards, it will always move in a positive direction.
According to this article on madehow.com, speedometers attached to the back of the transmission started to be used from 1921 (prior to this they were attached to one of the wheel axles, which would allow for reversal of the mechanism)
So Hairy's point that mechanical odometers are automatically susceptible to reversal is not the case. I can't find any definite evidence for the percentage split between wheel attachments and engine attachments, though, but as @Oddthinking pointed out, it has been made moot anyway with the introduction of digital odometers.
answered May 16, 2014 at 15:13
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11If it was attached before the gearbox, it will count revs of the motor, not of the wheel: The ODO would show same speed and distance when driving at 2000RPM in first gear as in last gear, though real speed (and distance) may differ by a factor of about 4 or more. So, it does not make sense to attach the ODO before the gearbox. It makes sense to attach it directly behind the gearbox, because distance to the dashboard is shorter, and because the gearbox doesn't move so much w.r.t. the chassis. Maybe, you confuse gearbox & differential? The input to diff. also reverses its direction...– sweberCommented Mar 10, 2016 at 9:00