RE: IML: 62 Speedometer off by 10 mph

[Ken Lang <imperialken@xxxxxxxxx>]

Something else to consider when looking at speedometer accuracy is the fact that our speedometers work off a couple of rotating magnets inside the head.  Over time these can get weak causing the speedometer to read slow.  They can also transfer some of that magnetism to the non-magnetic part and cause a faster reading.

 

An old speedometer repair guy once told me that the default for most American auto makers was 1000 revolutions of the speedometer cable for every mile traveled.  Over time that should never change unless someone has changed something in the transmission gears that feed the speedometer cable.

 

My local shop tells me they can unhook the cable from the transmission and plug it into their unit and verify the accuracy of the actual speedometer.   This would be my first step before trying to change gear ratios in the transmission.

 

Just my .02

 

Ken

67 Crown 4 Dr Ht

68 LeBaron 4 Dr Ht

 

 

 

From: mailing-list-owner@xxxxxxxxxxxxxxxx [mailto:mailing-list-owner@xxxxxxxxxxxxxxxx] On Behalf Of sosmi@xxxxxxxxxxx
Sent: Tuesday, June 12, 2007 9:08 AM
To: mailing-list@xxxxxxxxxxxxxxxx
Subject: Re: IML: 62 Speedometer off by 10 mph

 

Graham, it would seem a significant reduction in tire diameter, would be necessary to be 10 mph off at 70 mph. thats assuming it was correct before tire replacement.I would check actual gear ratio, then compare tire diameters, from original and the present.The FSM has a chart in the trans section, that gives specs for speedo pinions according to gear ratio, and tire size.Ya'll have a nice day, Dave.

 

-------------- Original message --------------
From: "Graham Quimby" <ghquimby@xxxxxxx>

> Fellow Imperialists,
>
> The speedometer on my 62 Crown seems to be off by 10 mph at all speeds
> (except 0). I have tested it at highway speeds (between 50 to 70 mph)
> and it is consistently 10 mph faster than the actual speed I’m
> traveling. The transmission and real axle are original. I have
> P235/75R15 radials. I’ve heard that a different tooth speedometer pinion
> may fix the problem since I have radial tires. I wanted to double check
> with the experts on the list what size pinion I should order.
>
> Thanks,
> Graham Quimby
> 1962 Caramel Crown 2 door Hardtop
>
>
>
>
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