|Inspection and Re-conditioning of Speedometer Cables|
article mainly addresses one major problem of bouncing speedometer gauge
needles on early Datsun/Nissan Z cars. Other causes can reside in the gauge
itself and/or be due to wear and grit in the nylon worm located where the
speedometer cable hooks into the transmission. Troubleshooting wear in the
gauge is beyond my skills. Inspection of the nylon worm gear is as easy
as undoing a 10mm bolt and pulling the tight fitting gear assemble out with
some vise grips. What follows only addresses problems with the speedometer
If your early Z car's speedometer guage needle regularly or occassionally jumps or bounces at low speeds or flutters at modest to high speeds, the possible causes of your problem could be grit, a broken wire strand or kink in your speedometer cable. I see the problem all the time, especially in the early style 240Z cables that did not have the transmission tunnel protector like the later type.
Inspecting the outer casing of the cable, especially in the engine compartment and fire wall areas, may reveal that some areas of the plastic weather protection tubing has cracked open or is missing. If so, it is a good chance that you have rust and grit entering at that point. If a car sits for a long time and then is used after major rust has formed on the inner wound wire, that a wire strand can break causing the broken wire end to cause the problem you describe.
Many times the problem can be cured by removing the cable from the car, gently removing the inner wound wire flex cable from it's outer casing with a turning action as you pull. Careful, if too much resistance is encountered, do not keep pulling or you could stretch the cable and damage it.
Once removed, you can clean out the inner and outer friction surfaces by flushing both with gasoline or solvent. Careful, do not soak cable ends that have the old rubber oil seals on them or could destroy the rubber. Blow out the outer casing interior with air and wipe dry and inspect the inner cable for any breaks in the wound wire surface or modest kinks. If all looks good, first spray WD-40 on it to lube internal areas, then coat with a clean motor oil. I also prefer to coat the whole cable with a light weight grease using a rag or my fingers to press it into the wound wire section. If you use heavy axle grease you risk creating too much resistance to the rotation of the cable when the car is cold which could overstrain an old cable and lead to more problems. Use great care to not get any grit or cleaning cloth debris on the lubricated cable before reinserting it back into the outer casing. Laying the lubricated cable on a work bench prior to re-assemble can screw up all your efforts real quick. Be sure you insert the correct into the correct end of the outer cable as well or you'll not be able to hook the cable up properly.
If you have severe kinks in either section or broken wire strands you may have a problem you can not repair to your satisfaction. Buying a used or new cable is wise in this case. I just finished inventorying my collection of used speedometer cables yesterday after a 71 240Z owner stopped by to pick up one of my best. I was surprised to find that I had a virtually new one of the older type. He was ecstatic that I had an original type for his restoration in "like new" condition because that type is no longer available from Nissan. However, the later type will work just as well and they also have the improved transmission tunnel protector. I have quite a few of both types in stock. For an additional charge I disassemble and clean up all cables I sell before shipping. Of course, you being in Australia, it will probably be most cost efficient for you to source them locally if it turns out you will need a replacement.
After re-assembly, hold up both ends in a loop and gently turn the inner cable to see if it turns full circle smoothly without any detectable grinding before reinstalling into your car.
One more preventive maintenance that is wise to do before re-installing your cable is to do a tight weather seal of all broken and missing plastic protective areas that you find on your used cable. One of the quickest and most practical methods is to use tightly wrapped and well overlapped black electrician's tape on all concerned areas of the outer cable.
TREATMENT OF CHOKE & HOOD RELEASE CABLES: A similar preventive maintenance procedure can be performed on your choke cables and wire stranded hood release cables, except that you can not easily remove the inner solid or braided wires. For these you can hang up one end with a piece of string and first drip WD-40 and then "chase" it with a light oil into the opening of the outer cable and let the different weights of lubricant "chase" themselves down into the cable, adding a few more drops every few minutes until it all starts to leak out of the bottom. Sometimes, inverting the cable half way through the process and working from the other end speeds up the oiling procedure. Be sure to pull the cable back and forth a few times as you go along to make sure that the oiling is complete.
btw, be sure to check the hood latch end of the hood release cable for wear in the stranded wire where it meets the connector stub. The aged metal strands often start to break at this point. If the cable ever breaks at this point you'll be screwed when it comes to trying to open your hood the next time, especially if your hood already is difficult to release at present. Many pay the painful price on a day when they can least afford for it to happen. Very wise to replace your hood release cable with a solid one ahead of time.
NOTE: Most early 240Z owners never realize that this damage is occurring on their cars because this area is virtually impossible to see visually without first removing the hood end of the cable from the hood female receiver mechanism. To do this you first have to unbolt and remove the female hood latch receiver from the body support in order to inspect it.
If you are in need of any used speedometer, hood, choke or hand brake cables you can find a list of what I have in stock by checking my online inventory pages link at http://www.zparts.com/selectzp.html They will be found in the Engine, Fuel-Ignition, Body and Driveline tabbed sections at the bottom of the master inventory page that I will be updating by Monday.
Good luck with your repairs,
Eric Neyerlin - Owner of Z PARTS