| |
Click on image for the lowdown. 
====
| | | Forums66 Topics128,155 Posts1,056,868 Members48,456 | | Most Online14,466
Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
| | THANKS!
For helping keep this great
old truck web site
on the Internet for over 30 years! and not clogged down
with Ads!  Again, thanks!
| | | | Joined: Jan 2011 Posts: 159 Wrench Fetcher | | Wrench Fetcher Joined: Jan 2011 Posts: 159 | I have an adaptor from JC. I put tall tires on my 1954 3100, and went to 16" rims from 15". The speedo was 10 mph slow vs. actual GPS speed. Thus, when speedo said 40, I was actually going 50.
Now here is the strange thing - With the new adaptor, I am spot on at 40 and below, but then I start to have a difference:
40 speedo = 40 actual
50 speedo = 48 actual
55 speedo = 51 actual
60 speedo = 55 actual
70 speedo = 62 actual
I thought the correction would be linear. What am I missing here? Thanks.
Harry
Last edited by harryr; 07/28/2013 9:36 PM.
| | | | | Joined: Jan 2011 Posts: 159 Wrench Fetcher | | Wrench Fetcher Joined: Jan 2011 Posts: 159 | Hasn't anyone bought one of these from JC? | | | | | Joined: Mar 2011 Posts: 277 'Bolter | | 'Bolter Joined: Mar 2011 Posts: 277 | Maybe its the speedometer not keeping up at higher speeds. I believe its a magnetic couple that connect the needle to the driven gears.
1955 First Series 3100
| | | | | Joined: Sep 2001 Posts: 29,270 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,270 | This topic is being discussed in another thread. Double-posting the same topic makes it difficult to keep track of what is being discussed in both threads. Bill mentioned the magnetism involved. I could not find a simple/clear explanation on-line, but I recall someone posting information on "waning" magnetism and/or erratic magnetism (as speed increased) due to wear/dirt in a pivot-point and/or weakening magnetism? Maybe Bill will see this post and comment/explain. | | | | | Joined: Feb 2002 Posts: 12,029 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Feb 2002 Posts: 12,029 | I think Harry got the answer to his specific question in that other post, the adapters don't cause the speedo to be more accurate than they are without adapting how our speedos work - yes, permanent magnets do weaken over time [although that'd likely affect the full range], and the hair-springs that create the "balance" with the spinning magnet can also weaken - in addition the mechanisms wear, and collect airborne contaminants that will affect the movement - but I think the main thing is that these cheap mass produced instruments aren't likely to be totally accurate over their full range even when new Bill | | | | | Joined: Jan 2011 Posts: 159 Wrench Fetcher | | Wrench Fetcher Joined: Jan 2011 Posts: 159 | I did the get the answer, and this thread should be deleted. The other thread, which was pretty much the same topic, apparently got much more attention. Thanks. | | |
|
|
| |
