Speedometer cable

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Yote

Yote

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Re. 72 Demon - still having trouble with speedometer bouncing. At 65-70 mph it settles down, but bounces before. Some time back a member suggested to trim some off the end of the cable. I trimmed about 1/8th inch off near transmission (4 speed 833) with no improvement. Have been searching for that post with no luck. Cannot remember which end was suggested to trim. If anyone knows let me know. New cable and housing and lubed well. ANY other suggestions would be very welcome.
Yote
 
Yote said:
Re. 72 Demon - still having trouble with speedometer bouncing. At 65-70 mph it settles down, but bounces before. Some time back a member suggested to trim some off the end of the cable. I trimmed about 1/8th inch off near transmission (4 speed 833) with no improvement. Have been searching for that post with no luck. Cannot remember which end was suggested to trim. If anyone knows let me know. New cable and housing and lubed well. ANY other suggestions would be very welcome.
Yote
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There are only four things that cause that and they are:
1.The speedo head itself
2.A kinked drive cable
3.A cable binding inside the housing.
4.A damaged drive gear on the trans end

Disconnecting the cable from the speedo and running the car with the rear wheels off the ground could possibly show a jumpy cable and that can be traced back to the trans and drive gear.
Pinching the cable with your fingers while it's turning can sometimes actually let you feel the cable for varying speed that could cause a needle to jump.
Also you can take the drive cable out of the housing to make sure there are no kinks in it.
 
All I can suggest is to clean the square drive port at the back of the instrument. That square port would get packed full of crud ( contaminated grease ). I suppose that's why someone would suggest trimming the cable length there. The cable has a stop collar that sets its depth in the port so if the hole is clear the cable should fit without applying forces on the instrument.
I've handled a number of worn out speedometers and every failure was due to forces applied by the cable. Most were the earlier type. The mating/aligning collar for 68 and later is about a inch long and served a lot better than the earlier type with a collector nut ( same as transmission end ). In any case, The cable really should attach as straight as possible. No angular or linear force on the instruments spindle.
There was a recent post where a member stated a bad universal joint was causing speedo needle bounce. Head scratcher there. I can only guess the entire vehicle was vibrating.
 
I cased the same problems as you. NAPA had a replacement cable assembly. Fixed!
 
In my experience, the NAPA cable was too long.

Correct length replacements are available from Mopar though, here is the part number;

A-body speedo cable.JPG
 
As previously stated, new cable, new housing and well lubed. Cable is good with no kinks or sharp bends in housing. When gear was removed teeth appeared good and is indexed properly. I will try to see if input on instrument needs cleaned ,but doubt it , as it appeared very clean on end of old cable when removed. Is it possible that stop collar is not placed properly and end of cable at instrument needs shortened? Under dash, housing seems to have some side force applied to it but can see no other way to get it better aligned. Can any lubricant be applied at input to instrument or could that be detrimental. Bounce in speedometer quits completely at about 60 mph and above. This has me completely confused but will try your suggestions that have not already been applied. More ideas welcome. THANK YOU.
Yote
 
I have made many new cables to replace bad ones. This is the main reason needles wobble. Yes, check cable routing, but the main reason is speedo cable or head. You say you have a new cable. Humor me, remove the cable to see if it good. Put the trans end in a vise using the square driven end. Stretch out the cable and grab the square speedo end. Note this "neutral" position. With your fingers try to rotate the cable to the left and to the right. If the cable will rotate either way, 1/4 turn or more- you have a bad cable. Replace it. In the old days we used to grind a bit off the speedo end to be sure it wasn't binding the head.
 
It has been a while since I have driven the car but the speedometer is not a wobble. It is more of a bounce of 5-15 mph , until 65 to 70 mph when it quits completely.
Yote
 
I wish I still had pictures of worn out speedometer parts to share. There is a magnetic propeller turning inside a drum or bell. When the tiny bronze bushing wear enough the magnet part starts touching/kissing the edge of the bell. That scaring and the egg shaped bushings is what I had pics of. Anyway... the slightest touch/kiss at very very low speed will toss the needle from 0 to 10 or 15 mph or more.
Its theoretically possible that at a high enough speed the needle reaction disappears. Not that it isn't still happening, only that the effect isn't visible. Needle return spring tension over rides the effect. Some theory and speculation on my part. I have seen examples of the kiss became a grab and hold. The needle ends up laying at the bottom of the screen.
If you can't cure it at the cable, take the instrument to the workbench and look for its fault. Then replace it, or have it rebuilt.
 
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