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Still having issues with speedometer on '62 Cadillac

Started by Matt Innocenzi, June 23, 2013, 10:09:57 PM

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Matt Innocenzi

Hello all,

A month or so ago, I posted a topic on an issue I was having with the speedometer in my '62 Fleetwood.  When the engine got to operating temperature, the speedometer simply quit.  Let the engine cool down, it worked beautifully again until it got to operating temperature, and then the process started all over again.

With some help from my fellow CLC members, I tried greasing the cables - both the one from the transmission output shaft to the cruise control servo and the the one from the servo to the instrument cluster.  No luck.

I then took the advice and replaced the nylon gear in the output shaft with a spare one I had.  This time, it worked great with the engine hot or cold, but it read completely wrong - when cruising about 60 on the highway, it would only read 20 mph and going 35 or less it would not register at all.

I pulled that nylon gear out of the output shaft and noted the splines on the gear were all worn out and chewed up.  I wasn't sure if they were like that or something inside my transmission did it.  I rolled the dice and tried yet another gear in the output shaft.  This third unit works (hot or cold) but the dial on the cluster jumps all over the place - going about 40 mph it jumps from 30 to 50.  Crawling down the driveway, it bounces from 0 to 10.

What the HECK is going on? 

I attached some pics of the two nylon gears I put in - the one with the damaged splines and the one that causes the bouncy needle.  One thing I did notice is that they are at different positions on the metal shaft.  Any thoughts?

Matt
Matt I
CLC #21633
1958 Cadillac Sedan DeVille
1962 Cadillac Fleetwood

Dave Shepherd

The one im the backround is worn of course, but these different color gears are for different rear end ratios and may not match your combination, they are color coded for application. Get your diff ratio and try and track down the right gear, then you have a known starting point.

Matt Innocenzi

Dave,

Thank you very much!  I suppose that explains why the speedometer seemed off.  I did not realize they were color coded from the factory based on the rear.  They looked identical and without going cross-eyed seemed to have the same number of teeth.  The one with the blue-ish tint is actually from a '58 Cadillac transmission, but I have another '62 gear I will try out.

When I pull the gear from the output shaft, I noticed there is some surface fluid on the gear, but not much.  Should the speedometer gear be greased or does transmission fluid lubricate it?

Matt
Matt I
CLC #21633
1958 Cadillac Sedan DeVille
1962 Cadillac Fleetwood

Dave Shepherd

Matt, no grease just dab a little trans fluid on the gear before installing.

Dave J

Matt,
I fixed the speedometer on my 58 coupe and most recently on my 1956 Coupe de Ville.  Maybe I can help.  The first thing you should do is determine if the problem is in the transmission gear, the cable, or the speedo head itself.

Start by troubleshooting by isolation:

1) Disconnect the cable from the transmission and route the cable housing out on the floor where you can get at it (the inner cable won't fall out of the housing). Leave the other end of the cable attached to the instrument cluster.  Attach an electric drill to the end of the cable on the floor and slowly bring increase the speed watching the speedo head.  Do it as long as necessary to simulate the problem.  If the symptom shows up, it's not in the transmission.

2)  By a new cable or fix the old one as follows. Disconnect the cable from the instrument cluster and and remove the entire cable from the car.  Turn the cable in the housing by hand and feel for binding.  It should turn smoothly whether the housing is straight or curled.  Pull the inner cable out of the housing.  It should not have grease on it.  If the cable is dry or sticky,  flush the housing and the cable with WD40 or similar.  Drain and dry both pieces and re-install the cable in the housing while lightly lubing it with thin  black graphite oil cable lube (available at Auto Zone or Rock Auto.com). Re-install and test.  If the symptom is still there, the problem is in the cluster.

3)  In both of my cars the problem ended up being in the speedometer head.  In the 58 the symptom was a loud whining noise and a bouncing needle.  In the 56 it was a regular swing of the needle from 0 to 30 MPH at a beat of about 1 per second.  Obviously, this requires removing the instrument cluster.

With me, the irony is that I got paperwork with the 56 Coupe when I bought it showing that the speedo head had already been replaced. And indeed it had been.  Naturally, the replacement was either used or new old stock.  However, the installer failed to notice that included in the head assembly is a plastic worm gear that turns the odometer which is turned by the same cable.  That plastic gear was lubricated at the factory with grease, which had hardened after 50 plus years and should have been cleaned and re-greased.  But it was overlooked and caused the gear to bind and jump teeth, thus the bouncing needle.

Dave Johnson

 
Dave Johnson
56 CDV

Matt Innocenzi

Hi Dave,

Thank you very much for the detailed advice and logic.  I was thinking on the same lines and did many of the recommendations you proposed. 

Just to recap what I did, when I first start having this problem, I disconnected the cable that goes from the transmission to the cruise control motor.  When I turned the input spline of the cruise control motor by hand, I got normal behavior on the speedometer.  That suggested the problem had to be between the transmission and the input of the cruise control.

I removed the cable between the transmission and input of the cruise control motor, removed the inner cable, and soaked the entire thing in WD-40.  I put the inner cable back in and spun it without any binding.

The last thing I did was the transmission gear.  I figured I nailed the problem, as I solved the problem when it got hot, but introduced a new one of inaccurate readings and a bouncing needle. 

I am now thinking that I possibly have multiple problems and I am just unveiling them one at a time.

I am still stumped what physically was happening to make the speedometer quit when the engine got to operating temperature.  Obviously, steel expands when hot, but any suggestions on what was mechanically expanding to result in a disengagement?

Thank you!
Matt

Matt I
CLC #21633
1958 Cadillac Sedan DeVille
1962 Cadillac Fleetwood

Dave J

I've never dealt with cruise control.  I guess that complicates things.  It may be the link from engine temp to speedometer.

Dave
Dave Johnson
56 CDV

Matt Innocenzi

What I may do is run a bypass cable from the transmission to the instrument cluster, just to rule out the cruise control motor.  If that does not solve the problem, we are back to the logic to pinpoint bad cable, cluster, or transmission gear. 

I will keep you all posted and thanks again for the advice.
Matt I
CLC #21633
1958 Cadillac Sedan DeVille
1962 Cadillac Fleetwood

bcroe

Bypassing the cruise control is an excellent test.  They wear out at relatively low mileage and cause speedo problems; there are no cruise controls left on my cars.  Bruce Roe

Matt Innocenzi

Bruce,

I have not done it yet, but plan to try that approach tonight or tomorrow.  Would a standard speedometer cable work between the transmission and the instrument cluster? 

In your experience, when the cruise control wears out, does it cause the problems I was describing, i.e. falling needle, bouncing needle, etc.?

Matt
Matt I
CLC #21633
1958 Cadillac Sedan DeVille
1962 Cadillac Fleetwood

Dave Shepherd

Back in the day when I worked for Cadillac we did some cruise bypasses, worn gear components in the cruise can cause this heat related issue  mounted just above the manifold as you know, a regular replacement cable will work trans to speedo.

Matt Innocenzi

A big thank you to all the help and input from my fellow CLC members - I fixed it!

After learning about how the cruise control motors were bypassed by the dealer, I figured I would start with that.  I had an NOS cruise control motor on the shelf and I figured it would be much easier to swap that out than break my back trying to switch out cables on the cluster.  So, I swapped out cruise control motors, re-attached everything, and took the Fleetwood out for a cruise night tonight.  After running the car for 45 minutes at operating temperature, the speedometer worked flawlessly.  No fluttering, no bottoming out, just steady, smooth operation.

Thank you again for making this a success!

Now, to push my luck...being an engineer, we can't rest knowing something is broken and not knowing why.  Anyone have any thoughts as to exactly what is going on inside these old cruise control motors when they get hot to make the speedometer stop working?!
Matt I
CLC #21633
1958 Cadillac Sedan DeVille
1962 Cadillac Fleetwood

Dave Shepherd

I have fixed a couple over the years, take the cover off, check for hardened lube on all the components, look carefully at the drive gears.

Dave J

Dave,
I have found hardened lube to problematic on both my 56 and 58 Caddies.  Not only was it an issue in my speedometer, but also in brake light, power window and other switches, some of them NOS right off the shelf.  New Old Stock includes old grease.  Fortunately, the mechanical switches in those days can be carefully disassembled, cleaned and re-lubed with fresh dielectric grease.

Dave Johnson
Dave Johnson
56 CDV