ConcoursMustang Forums

Restoring - General discussions that span across many different groups of years and models => Processes, Products & Techniques => Topic started by: socalgt on July 06, 2017, 05:46:13 PM

Title: 1966 speedometer inaccurate
Post by: socalgt on July 06, 2017, 05:46:13 PM

My speedometer reads from accurate to 10 or more mph too high, never on the low side.  It does occasionally read correctly, but not for long.   It really doesn't "jump around", it's just almost always steadily indicating too high.  From what I've read, attempts to lubricate the cable don't usually fix this problem and it ends up needing a new speedometer head.  Is that the consensus from those that have tried to repair the inaccuracy by lubricating or installing a new cable?  (Factory rims w/205/70R/14) original speedometer, automatic 3.00 rear end ratio.

                                                                                                 Thanks...

                                                                                                           

Title: Re: 1966 speedometer inaccurate
Post by: rocket289k on July 16, 2017, 03:04:49 PM

Hi There,

Aside from your comment that the speedometer is "sometimes" correct this really sounds like you have the incorrect gear on your speedo cable.  The P205 is larger than the factory original tire.  A P195 75/R14 is the closest that you can to the correct size and ride height on a  65 or 66 when using P-metric sized tires.

West Coast Classic Cougar has a handy calculator on their website to help you determine the correct number of teeth you need on the speedo cable gear based on your tire dimensions.

http://www.classic-cougar.com/tools/speedocalc/speedocalc.php

To determine your tire diameter in inches use this site:  https://tiresize.com/calculator/

Based on the information that you provided you need a speedometer gear with 19 teeth.  I'd start with the speedometer cable gear to ensure that it is correctly sized and not worn and then move on to the cable and the speedo head itself in diagnosing this issue.

Regards,

Ron

Title: Re: 1966 speedometer inaccurate
Post by: socalgt on July 23, 2017, 11:50:09 AM

Thanks....I would have thought it was the gear also, except that the needle sometimes wanders from 55 all the way to 80.  I'll try to remove the cable from the speedometer and lubricate the speedometer itself where the cable enters.

Title: Re: 1966 speedometer inaccurate
Post by: jwc66k on July 23, 2017, 05:04:41 PM

Quote from: socalgt on July 23, 2017, 11:50:09 AM

Thanks....I would have thought it was the gear also, except that the needle sometimes wanders from 55 all the way to 80.  I'll try to remove the cable from the speedometer and lubricate the speedometer itself where the cable enters.

Remove, thoroughly clean the tube and cable in solvent and inspect for signs of wear. When reinstalling, be leery of oil based lubricants, they solidify over time, and attract and retain dirt. I prefer a dry type, graphite for example. 
Jim