Speedometer question

["Cadillac Kid" Greg Surfas 15364]

Just when you think you have seen most everything a car can throw at you something new comes along. 1976 CDV with cruise control.  The FIRST start up in the day the speedometer and the odometer are dead in the water, at 0 and not moving.  After about a mile or so the thing wakes up and performs flawlessly with no shudder and is accurate (per GPS app).  All the cable connections are tight. Once the speedo wakes up regardless of the stops and starts it stays working.
Any ideas out there?
Greg Surfas

[Big Fins]

Sure Greg. Just like you and I, we are all taking a while longer to wake up and get moving! 

[Jeff Rosansky CLC #28373]

Sure Greg. Just like you and I, we are all taking a while longer to wake up and get moving! 

Well said.
Jeff

[Cadillac Fleetwood]

I suspect that the transducer (which is positioned between the two segments of the speedometer cable) has worn gears inside it.  The cable from the transmission drives a gear at the input to the transducer, which in turn drives a gear to turn the output (i.e. the cable from the transducer to the speedometer).

-Charles Fares

["Cadillac Kid" Greg Surfas 15364]

Charles
The gears are in constant mesh. This “lazy ness” is consistently the first thing in the AM. The slowdown works perfectly once awake regardless of the number of stops and restarts during the day.
Greg Surfas

[wrench]

Don’t know specifically about  your vehicle’s type of speedometer, but they used to use a magnetic coupling between the cable gearbox and the indicator needle. The indicator side has a hairspring that dampens the movement of the needle and you could have a need for lubrication of the indicator mechanism or there could be a magnetic hysteresis issue with the actual magnetic coupling.

Someone who actually deals with these can probably assist with it, there may be topics here about speedo repair/lube. You may be able to fix/lube it yourself.

My opinion about speedo repairs is that is a specialized service and a 50 year old unit would probably benefit from a full service, sorta like a clock does.

[chrisntam]

Do like I do and just start hangin' parts!



Ok, maybe not.  I'd pull the speedo cable at the trans to be sure the driven gear is ok and maybe look at the drive gear.  Cables are likely ok, that leaves the transducer or speedo head. 

If your transducer is the same as on my '70, I'm pretty sure I have an extra I can send you as a loaner to see if that helps.  Just let me know.  The extra one I have seemed to "hunt" a bit once set, but the speedo reading has always been consistent.

My guess is the speedo head.

chris.

[Bob Schuman]

The square end of the cable at the transmission fits inside the mating square hole in the gear driven by the transmission. If that square hole wears enough, it does not reliably drive the cable. Gave me fits on my 41 years ago, may be your problem, too.

[TJ Hopland]

I'm betting its in the head.   I don't see any of the other possibilities brought up fitting his description of only being a problem first drive of the day and ones it starts working its perfectly steady.   Gear and cable problems are not going to be that consistent and would likely quickly degrade. 

I don't know the inner workings of the head but I could see some 50 year old grease on the needle side of things being sticky so it takes some tugging to break free from its resting place.  I can also see it taking some time for it to stick again so that is why it works all day.    Gotta be someone here that has been into these and knows how big a job it is to clean and lube them up. 

["Cadillac Kid" Greg Surfas 15364]

Please note that the odometer does not "wake up" until the speedo does. I was of the mind that the odometer was directly driven. Oh the mysteries of life.
Greg Surfas

[TJ Hopland]

Ya you would think the odo would just be a gear reduction sort of thing.   I wonder if maybe its got something to do with the one way action that I assume a 76 would have?    The thing where you can't just put the car in reverse and take miles off?   Maybe its that clutch sort of thing that is causing all the issues?   Does the speedo work in reverse on a 76?  If so that would be more complexity and things to not age well. 

Hmm...  makes me want to go take one apart and see what is going on in there. 

["Cadillac Kid" Greg Surfas 15364]

Please do and let me know.

[The Tassie Devil(le)]

Please note that the odometer does not "wake up" until the speedo does. I was of the mind that the odometer was directly driven. Oh the mysteries of life. Greg Surfas 

To answer that question, yes.   The Odometer and Trip Meter are directly driven by the speedo cable.

Notice that the main driven gear shaft is at the back of the speedo frame, and is driven directly by the cable.   The Magnetic Ring that actuates the needle is way ahead of the ODO drive.

Bruce.

["Cadillac Kid" Greg Surfas 15364]

Well,
I did/didn't do it.  I just pulled the three ends of the speedometer cables loose (transmission input and output at the cruise transducer), checked the ends checked to see the cables and the transducer were free and rotating, and then put it back together. Seems like the gremlin was chased away when it saw me coming, everything works as it should. Another victory for the dis/re (disassemble, re assemble) school of mechanics.
Greg Surfas

[chrisntam]

Good to hear.  The disassemble/reassemble worked for me on the wipers.  Wipers didn't work, pulled the electrical connector on the motor, plugged it back and magically, they work!