Speedometer Headache

[1969Mach1_428CJ 11]

Hello,

 

I own a 1969 Mach 1 “R†Code with an automatic and air conditioning.  I’m having issues with my speedometer.  I recently had to replace my aging cluster circuit board.  The repair shop broke the clip holding the speedometer cable to the back of the speedometer gauge and installed a new cable.  Prior to the new speedo cable being installed the speedometer gauge functioned properly.  My first series of issues with the new speedo cable were as follows comparing my GPS speed to the gauge:

 

1.      The speedo gauge needle would not move until I reached a speed around 15 – 20 mph.  It would then jump up and gradually match actual speed. 

2.      If I maintained a steady speed around 50 mph the needle would slowly increase to 90 mph.

3.      When I stop the needle would not return to zero but remain at around 15 mph.

4.      When I jiggled the cable from inside the engine compartment the needle would drop to zero.

 

I suspected a bad cable and returned to the repair shop.  They replaced the cable with a new one.  My second series of issues were:

 

1.      The speedo gauge would not move until I reached 20 mph.  Then it would begin to move upwards but never reaching or matching actual speed.  Under 40 mph (gauge speed) the needle would always be lower than actual speed; e.g. gauge reads 20 mph and actual speed is 35 mph.

2.      Maintaining a steady speed of 50 mph or more the needle would increase quickly to around 90 mph.

3.      If I go over road bumps or railroad tracks the needle would bounce higher and lower and then steady itself after a few passes but never matching actual speed.  This occurs more frequently at higher speeds. This was a new issue.

4.      When I stopped the needle returns to zero.

 

The repair shop performed the following troubleshooting steps:

1.      Replace the speedo head gauge – no improvement.

2.      Removed the inner cable and greased it - no improvement.

3.      Replace the plastic speedo gear at the transmission – no improvement.

4.      Inspected the transmission out gear – appears to functioning properly.

 

I had no problems until the speedometer cable was replaced.

 

Anybody have any ideas how to fix this?

 

Thanks,

 

Larry

 

[SA69mach 39]

Just an idea, but it looks like speedo cables (twice).

Did you see what brand or manufacturer on the cables. if they got two from the same supplier, it is a clue, I guess.

Try for a Ford or Motorcraft part. Nothing to lose.

 

I actually had the same problem with my 70 when I first got it. New cable after a T5 swap and it fixed it right up. Sorry, I did not get the cable, but I think it was an aftermarket part from the markings on the bag IIRC. I think I was just lucky.

 

Find out from the shop about the supplier and maker, and maybe try a different, hopefully better part. NPD usually has quality parts, same with Rock Auto.

It sounds like you have done all the things I would think to do...

[magician 13]

Hook a drill to the cable and watch Speedo.

[1969_Mach1 333]

You can try a different brand speedo cable.  Some aftermarket cables don't work very well.  Does the odometer work okay?  There is no mechanical connection between the speedo pointer and the cable.  The odometer is mechanically connected to the cable.  If I recall, the cable rotates a hub with magnets on it.  The magnetic field interacts with a drum attached to back side of the pointer assembly.  The rotating magnetic field causes pointer movement.  I have seen where the parts got jarred and the drum intermittently touched the magnets causing all sorts of erratic pointer movement and pointer sticking.  Or the air gap between the drum and magnets is too close and the pointer reads much higher than it should.  That air gap is critical and will get too close if the speedo is worn or damaged where the cable attaches to it.  Hopefully the shop was careful when removing and installing the instrument cluster then the speedo should be okay.  But stranger things have happened.

 

It could be a combination of the aftermarket cable being slightly different and a worn out speedometer. 

 

To isolate the issue attach a drill to the cable at the trans like magician mentioned.  If the pointer movement is okay something is wrong with the speedo gear on the end of the cable at the transmission.  If it is still not correct you need to remove the instrument cluster.  Then take your original cable, cut off a short piece of the end that goes into the speedo, attach it to a drill and again watch the movement.  If it is okay, the issue is the speedo cable in the car, if it is not okay, something is wrong with the speedo.  Hopefully its a cable issue but a worn out speedometer wouldn't surprise me. 

 

It shouldn't be a headache to diagnose there are only a few components in the system.  But you may have to do it yourself and not rely on the shop.  That's the approach I would take.

[danno 128]

If you cannot figure this out, I might have a spare original cable I could let you try.

[1969Mach1_428CJ 11]

I apologize for the late response to my original speedometer problem.  I solved the issue!!!   I was directed by a transmission shop to a local speedometer cable manufacturer and who knew exactly what the issue was.  Any speedometer cable coiled, wrapped up and sitting on the shelf after a period of time develops a 'memory'.  This memory does not go away even when the cable is straightened out and installed as the inner cable will still rub against the inside of the cable housing causing the erradic behavior.  Fortunately I had kept the OEM speedo head.  The cable manufacturer tested it for free just to verify it was working properly and found it to be in perfect working order.   They made me a brand new speedometer cable for under $30 in about 20 minutes.  Gave the explanation of the after-market cable issue to the repair shop.  They told me that if they installed it and if it didn't solve the issue they would have to charge me additional labor.  Guess what??  My speedometer gauge worked as it should.  I  got a refund for the the new speedo head and their after-market cable along with a partial refund for the original labor.

The story ends with a funny anecdote.  A few months after resolving my issue a car club member was describing his speedometer headaches with the exact same issues I had experienced.  He had purchased his speedometer cable from the same retailer/repair shop as I did.  After explaining to him how I resolved it he returned the part and gave an explanation why he was returning it.  The club member told me the retailer/repair shop gave him the exact same explanation I had given to him as if they knew the issue all along.  They told him sometimes these after-market cables worked and sometime not.  They recommended he go to the speedometer cable manufacturer which he did.  Fixed his problem too.

[aslanefe 333]

2 hours ago, 1969Mach1_428CJ said:

I apologize for the late response to my original speedometer problem.  I solved the issue!!!   I was directed by a transmission shop to a local speedometer cable manufacturer and who knew exactly what the issue was.  Any speedometer cable coiled, wrapped up and sitting on the shelf after a period of time develops a 'memory'.  This memory does not go away even when the cable is straightened out and installed as the inner cable will still rub against the inside of the cable housing causing the erradic behavior.  Fortunately I had kept the OEM speedo head.  The cable manufacturer tested it for free just to verify it was working properly and found it to be in perfect working order.   They made me a brand new speedometer cable for under $30 in about 20 minutes.  Gave the explanation of the after-market cable issue to the repair shop.  They told me that if they installed it and if it didn't solve the issue they would have to charge me additional labor.  Guess what??  My speedometer gauge worked as it should.  I  got a refund for the the new speedo head and their after-market cable along with a partial refund for the original labor.

The story ends with a funny anecdote.  A few months after resolving my issue a car club member was describing his speedometer headaches with the exact same issues I had experienced.  He had purchased his speedometer cable from the same retailer/repair shop as I did.  After explaining to him how I resolved it he returned the part and gave an explanation why he was returning it.  The club member told me the retailer/repair shop gave him the exact same explanation I had given to him as if they knew the issue all along.  They told him sometimes these after-market cables worked and sometime not.  They recommended he go to the speedometer cable manufacturer which he did.  Fixed his problem too.

Can you post the contact info for the speedometer cable manufacturer you used? It may be useful for folks who needs a new cable.