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73 Eldo, Bouncing speedometer needle below 20 mph

Started by TJ Hopland, May 01, 2020, 01:43:21 PM

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TJ Hopland

I think as long as I have had the car which has been over 20 years now the speedo has always had a little bounce when you first start rolling.  I have only been through a half a tank of gas so far this season but noticed yesterday that the needle bounces maybe 0-10 when presumably I'm going below 10 then 0-20 when I assume I am 10-20.   Over 20 its smooth and steady.  No chirping noises. Odometer and cruise works fine.  Doesn't seem to be ambient or drive length sensitive. 

Last night a pulled the cable off the trans and turned it with my fingers and it didn't feel like it was binding at all.   I was thinking next I would remove then clean and lubricate the cruise control box since I don't think I have ever had the current one apart and now know how to do it without damaging them. 

If the cruse thing doesn't change anything and I can't feel anything does that mean its something in the head?  Is that a common symptom of wear or dried lubricant?   I assume its like the cruise unit where its a magnetic coupling sort of thing?  And maybe its like the cruise where they didn't use the greatest materials and you get wear that creates contact between the two sections till the speed comes up and they kinda fall back into place?
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

MaR

Hook up the speedo without going though the cruise control actuator and see what you get.

chrisntam

It appears you’ve reached the end of your to do list and are now looking for things to do. 

:D

My ‘70 does the same thing.
1970 Deville Convertible 
Dallas, Texas

gmurph

I ended up having to replace the cruise transducer on my 72 Coupe. it had 'crashed' internally and caused the erratic problems. My father had replaced the speedo cable and of course it didn't fix it. He didn't use the car enough to care, so it was an issue when I got it.
Greg Murphy CLC#24416

1941 60S
1952 Dodge B3F
1972 Coupe de Ville

TJ Hopland

The rather sudden change in the behavior has me concerned so this got put fairly high on the list.  I don't want to end up damaging something or ending up with a non working speedo and cruise.    I'm also planning a trip to my parts cars soon so if I know where the problem is I can plan on grabbing parts for that along with the climate control stuff.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

The Tassie Devil(le)

I too would be worried about the "sudden change" as it could simply be a lack of lubricant, or a failing drive.

This type of job is good on an Eldorado (FWD) in that it is easy to access the first cable without having to get under the car.

Now, with the cable undone from the transmission, connect the inner up to a Battery Drill, and with someone inside the car, observing the speedo, run the drill and see what the needle does.   Running the drill from slow to fast will replicate the vehicles' speed.

If the needle is still playing up, you have cleared the transmission drive unit from the fault.

Now, remove the Drive Cable from the CC to the Speedo, and with the Battery Drill, operate that inner cable, and observe the needle.

If the needle is still playing up, then it is not the first cable or the CC internals, but could be the top cable or the speedo head itself.

If the needle operates smoothly, then the fault could be within the first cable, or the CC itself.

Inspecting the inner cables for kinks or broken strands is a matter of observation and feel, but the CC is mechanical when it comes to cross shaft interaction, as the drive goes in one end, transfers to a gear and out the other end.

Within the speedo head itself, the transfer of rotating action of the speedo cable to the speedo needle is via a magnetic field, and the needle runs in two "bearings".

Having access to a spare cable of known condition and attaching that to the Speedo and operating that with said battery drill will isolate all the other components and rule in or out, the speedo.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

chrisntam

1970 Deville Convertible 
Dallas, Texas

The Tassie Devil(le)

I am pretty sure it is in reverse, but it won't matter if you initially go the wrong way as it would be like going into reverse gear and travelling backwards.

The speedo needle will just stay on the stop, and not travel forward, as the magnetic coupling within the speedo head will simply spin backwards.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

billmorrow

just FWIW and from my memory of "that time" when i owned 40's '50's cars with a similar issue cleaning the speedo cable and a little grease did the trick..
IMO check the easiest thing first.. :)
Bill Morrow
Admin/owner:
forum.thinkpads.com
thinkpads.com
billmorrow.com

the stable:
'06 SL55 AMG
'59 Cadillac 62 Convertible
'70 ElDorado, 98k miles, all original
'96 Fleetwood Broughm, Red, 37k miles
2 - '95 & 1 '92 Buick Roadmaster Wagons

She was not what you would call refined,
She was not what you would call unrefined,
She was the type of person who kept a parrot.
~~~Mark Twain~~

TJ Hopland

Looks like it was the cruise.  Pulled it out and while walking to the bench gave it a spin and it seemed to be smooth.  Stared at it for a bit and thought about just trying to squirt some lube in but then I figured as long as I was this far I should open it up. 

I did take photos but somehow lost them between the phone and computer.  I got the gear cover off then pulled what I'm gonna call the clutch disc off to get a good look and feel for how the gears and shafts were.  Little gummy but not terrible.  I cleaned them up then the plastic one got some teflon silicone and the metal one motor oil.

There were signs of what I call the clutch disc rubbing on what I will call the flywheel   The flywheel is a magnet attached to the cable driven gears.  What I'm calling the clutch disc is what is more like the speedometer needle that actually does the vacuum regulating. Its a magnetic coupling so its not supposed to actually touch.  What is supposed to keep the gap is what I would call a pilot bearing.  Most of them I have taken apart that has been pretty trashed.  This one looked pretty decent so I just went with cleaning and lubrication and fingers crossed. 

Before I put it all back I gave it a quick test drive with just the gear part installed and the needle was smooth.   Got it all back together and the cruise still works and the needle isn't bouncing anymore.  What I called the pilot shaft and bearing is pretty tiny maybe even smaller than 1/16" so I'm not sure how you would go about repairing or replacing one to get the proper gap back.  Glad just clean and lube worked for now so I didn't have to buy a bunch of jeweler tools.  If that didn't fix it I have a aftermarket rostra cruise system I pulled off another car as well as I think a new one in a box.   

The innards of these aren't the most precision and heavy duty so a little cleaning and lube likely goes a long way.  There isn't any ball bearings.  If there are bearings which there isn't in every position they are sleeves.  To get the gear cover off remove the screws and rotate the cover counter clockwise about 45 degrees when viewed from where the speedo cables hook up.   That takes tension off the low speed cutout switch so you don't damage anything pulling it straight up.

The slots in the cover adjust the low speed cut off so its not the end of the world if you don't get it back exactly the same position but it would not be a bad idea to mark the position.   The shaft with the drum on it comes off the gear part by just removing the tiny screw anchoring the spring.  After that is off that assembly will lift off.  The flywheel part is held in with a pressed on collar.  You just need a punch the right size to smack the end of the shaft where the cable normally goes in.  Once that is off the plastic gear will just slide out.  If the collar won't grip when you put it back together I was able to more or less crimp it back on using a drill chuck.         
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason