Horn Repair

The pair of original equipment horns on mt TR4 had never worked properly and despite adjustments of the tone screws, along with liberal doses of WD40, they refused to behave. The Haynes manual maintains that they are not user-serviceable and a quick inspection reveals that this woudl appear true; the halves that comprise the horn body are riveted together. However, with the aid of an electric drill, the rivet heads can be removed to allow access to the innards.

First, remove the leads while making a note as to which way round they go, and unbolt the horns. With a horn securely clamped down in a drill press, carefully drill through the rivet heads with a 1/4″ drill. Make a start for the drill by punching a point in the center of each of the rivets to ensure the bit will be correctly aligned. With a punch, tap out the rivet bodies and separate the horn body halves. Be careful not to damage the fragile seals or the diaphragm.

The horn is now in a state for inspection and repair. It is highly likely that once the cobwebs, dust and grime have been cleaned out, the components are in reasonable shape: a horn isn’t really an item that is likely to wear out with normal use, even after several decades! The make-and-break mechanism is “on”, i.e.: there should be a good conducting path through them which allows the coil to be energized, the diaphragm to move, and the path to be then broken. The rapid repeating of this sequence causes the horn to sound. The contacts in a perpetually silent horn are probably separated by a layer of muck and must be cleaned. I restored my contacts using cotton balls drenched in rubbing alcohol, and emery boards-the alcohol was also useful for generally cleaning up the horn both internally and externally. The horn can be tested with a voltmeter set to the lowest resistance range. When you can get the contacts to reliably make and break, your horn is mended, and you can begin on the other one! The halves can be rejoined using 6-32 by 3/4″ bolts, and reattached to the car. Reconnect the wires and you should be rewarded by two distinct tones. Adjust each horn for maximum volume by means of the small screw on top of the body. If you’re not into DIY, then take it an auto repair shop and let the auto repair professionals handle it. Taking your vehicle to an auto repair shop is a better option if you want to be sure that you don’t break your car.