How to Measure Tape Recorder and Walkman Drive Belt Size

Cassette drive belts usually become stretched and hard and sometimes turn into a gooey tar-like mess, making it very difficult to determine their size. I usually use the "string method" which involves using a piece of string to thread around the pulleys the belt path would take. The length of the measured string will then give you the circumference of the belt required; however, it is first necessary to reduce the measured length by 6 % so that it stretches adequately around the pulleys.

Square-cut drive belts are usually required in these applications, and whilst high-end stereo cassette players and walkmans tend to require 0.7 mm thick belts, the old shoebox style tape recorders tend to use 1.2 mm thick belts. The thickness of belts can vary considerably depending upon the design and here is a table showing some of the values I have come across.

If the thickness is in inches, this conversion chart for the popular thicknesses might help for the conversion.

6 % Reduction Using String Method

How to use: This calculator gives you the length reduced by 6 %

Measuring Diameter and Circumference of Broken or Intact Belt

If you have a broken belt that is not stretched, then just measure its total length, which will be the value C. This is the circumference. If your belt is intact, then fold it neatly and measure its length L, then multiply that value by two to give the circumference, as shown by the formula below.

C = 2 × L

It is better to calculate the diameter of the belt once you have the circumference C. You will get a more accurate value than by measuring it. Simply divide the circumference value by PI, which is 3.1415, to give the diameter, as shown by the formula below.

Diameter = C / 3.1415

Calculating Diameter

How to use: You have to input only the circumference value in millimetres, and the calculator will find all the other values for you. It provides the values in inches and millimetres for both circumference and diameter.

Walkman Drive Belt

Walkmans usually require much thinner belts in the range of 0.7 mm, and consequently they are much more difficult to find than the standard 1.2 mm thick ones.

At one time, it was very difficult to find 0.7 mm thick belts for Walkmans. For this model, 1.2 mm thick belt does not work at all so that was out of the question. However, I managed to find 1 mm thick belts that were worth trying.

I managed to squeeze the belt between the pulley wheel and plastic pillar guide by slight stretching it. However, once in place, it all fitted fine as you can see!

As you can see, with a 1 mm thick belt there is just enough clearance between the belt and the motor surface.

As you can see the capstan pulleys are able to hold the thicker belt without any problems, and there is just enough clearance.

Walkman Drive Belt Suppliers

Fix Your Audio (fixyouraudio.com) usually has drive belts and parts for a wide range Walkmans. Run by Marian Mihok in Slovakia, I found it to be a very useful resource for spare parts.

eBay is also a very good platform for finding cassette drive belts, their postage costs are very fair and you get a fast service. Sometimes it is much more economical to buy a bag of assorted sized belts for a few pounds and looking for one with sufficient tension.