RE: [Chrysler300] Astrodome-Speedometer

There is little hair spring that returns it, and if stuck , chances are needle is bent and touching or somehow it jumped out of tiny journals it (needle)turns in. I do not think anything can go wrong inside, drive wise, as the part that spins magnet to move needle is directly driven by and mounted on cable inlet ---and odometer drives off that ,so it is spinning, if odometer moves, but needle is stuck. Might be easy, might be a bear. I have gotten into these and if you bend or mess around with bending either the spinning part or magnet, or the spring, it ends up 10-15 mph off after all that effort . Bending is related to fixing obvious problem of the parts hitting or scraping .

It works by “eddy current” which is spinning magnet induces a current into the aluminum cup , makes a torque proportional to speed, which then fights the multiturn hairspring harder and harder as you speed up; the exact gap --supposed to be between them ---impacts the torque ; bending wrecks all that.

Most common problem seems to be wear in bearing right at end of cable..often no lube there , for years dried out (a few drops of oil are good—there is felt thing on some of them to hold oil)--- when that wear happens what is supposed to spin and run true does not do that; cup like thing starts wobbling a little and one spinning cup - like part touches the other needle cup part ,so needle jumps up and then falls back, or wiggles at steady speeds; if violent enough or piece of dirt, can hurt needle,--- And its bearing/mount ..might have happened. Usually shiny place and history of needle jumping around, or flying up to 150. .

Wish I could say ‘do this” but best way , after many wasted hours, is another one, or send to specialist. Bob’s speedometer comes to mind, think I used that once , in Hemmings, but it was healthy bucks to rebuild it, and very hard to do yourself, if not impossible due to specialized parts, riveted/die cast swaged together. If you bend that super fragile hair spring you are done for, as far as accuracy—that is what sets reading per RPM . So find a used one, hopefully with low miles? On the other hand it might have fallen out of bearing and with tweezers you get it back..but not easy. Nothing to lose by looking. Tang you see on hair spring mount is to set zero, and calibration should fall out of that. It may literally be just touching dial /stuck. Ok to bend needle slightly to fix that .

A drop of oil on odo gear drive places is good too, while in there ..it can jam and then strip nylon drive teeth. (other issue in there) ; you hear faint click, click click and odo does not move, very soon no teeth left. Cannot be fixed, without speedo parts, although I put a washer under one end moved it over to engage remains of teeth, got one going, after freeing number drum .

I have 60 Dodge with stuck needle..that Speedo needle is about 6” long runs in a narrow slot and scrapes it, one side or other --went through two of them--- still does not work and cannot find good used one , must have 15 hours of in it, no cigar...looseness in needle mounts makes it not stay centered in slot . Plus hours to get these in and out .

I believe , in trying to fix this a while back , I found out somewhere there is a standard RPM for MPH, want to say 60MPH is 1000 RPM on cable , but do not take that to bank—got the impression all car speedos use that. I used speed on ½’ drill rated 950 RPM to set it close, but all in all came out poorly/erratic –but it does go up. . I used wood like a toothpick in drill to drive it held in vise. Could compare to good one that way too.

All in all a cheaply made, really crappy thing; 100k miles and ? 5 years it is hurting/worn out; just $0 .50 more could have beefed up input bearing length a lot, would last forever, never wobble. Depends if yours got oiled at assembly , too.

Good luck,

john

From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On Behalf Of GERALD OLSON olson77@xxxxxxxxxxxxx [Chrysler300]
Sent: Thursday, July 31, 2014 3:38 PM
To: Chrysler300@xxxxxxxxxxxxxxx
Subject: [Chrysler300] Astrodome-Speedometer

Anyone out there have any suggestions when the odometer works fine and the speedometer is stuck at 50 MPH weather we're doing 100 MPH or 0 MPH. No wiggle, no dance, no movement what so ever! Thanks for any input and or cure, Jerry