Thursday, 15 November 2018


A few years ago, I agreed to a man-wing position for a trip to the Collector's Car Show in Carlisle, Pennsylvania, and a swap meeting. A friend picked me up in his special edition of the Dodge Charger from 1970 and we started this journey. Unfortunately, twenty minutes after the 4-hour ride, I began to hear the irritating sound of a squeak behind a set of indicators. The faster we travel, the louder we write.

I leaned over and looked at the speedometer, and the needle shook rhythmically with this horrifying, high sound. I knew right away that this car has a problem with the speedometer and it will be a very long ride. Fortunately, problems with mechanically controlled speedometers can often be solved with little effort. Here we will talk about how they work and about typical problems with antique cars.

Operation of a speedometer with a toothed drive

Whether you have a Chevrolet Nova Super Sport from 1969, an oldsmobile Rocket Eight-Eight from the 1950s or even a British sports car, such as the Jaguar E-Type, speedometers work just the same. The signal comes from a driven gear that meshes with the rear transmission shaft. This setting rotates the flexible metal core inside the speedometer cable, which in turn connects to the back of the speedometer head mounted in the instrument cluster.

The faster the PTO shaft, the higher
the reading on the dashboard. This type of implementation provides car manufacturers with some flexibility in changing the calibration by changing the size of the tool that is mounted in the gearbox. For this reason, there is often a color speedometer gearbox for different tire sizes and rear differential coefficients. In fact, counting the number of teeth on the transmission and knowledge of its color are helpful in diagnosing problems with the calibration of the speedometer.

Speedometer Problem Type

In my opinion, one of the speed problems is working. High volume is made to produce an inner string. The runner can also create a noise, which runs in the same speed. If you are pulling the cord from the head and it is still raging, then you can remove the problem as a thread itself.

However, if the sound goes off if it is discontinued, the head has the subject. As noted above, the common problem is the coordination of reading. Sometimes homeowners do not notice how fast they are when they move on the road to 55 MPH and receive fast tickets for a 10-hour MPH trip.
Changing the ratio of the differential gear ratio or the size of the wheel and tire are two reasons why the speedometer gives incorrect readings. However, other improvements, such as replacing a three-speed automatic transmission with a four-speed automatic or switching a three-speed manual transmission to a modern five-speed overdrive unit will also result in erroneous readings.

Repairing speedometer problems

When they pre-assembled the speedometer cable, they filled the cable with bearing grease and then sealed both ends. This lubricant may leak, deteriorate or dry out for a long time. Without lubrication, the work becomes loud, but this is not the only problem. As the cable runs from the outside of the car to the top under the dashboard, it makes several turns along the way. This can cause a binding situation that slows down the cable.

This causes a wobbly needle that can make it difficult to read miles per hour or at least drive you crazy. The change of the speedometer's cable is one of the options, but before I do this I have a recommendation. There are two methods for lubricating the old cable that you should try. First, they produce a special grease for the speedometer cable, which is installed in the place where the cable is attached to the speedometer's head. This specially developed penetrating oil uses gravity to pass through the cable.

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