Speedometer Troubleshooting: Common Issues

This article covers various speedometer related issues.
Common Issues
Speedometer “bouncing”
Sometimes the speedometer will appear to “bounce” when driving at a constant speed. “Bounce” in this context means that although the car is moving at a constant speed, the speedometer’s needle seems to jump around at +/- 5 MPH or so of the current speed, never resting at any particular value.
Common causes for this problem are a binding speedometer cable, a failing angle drive, or a slipping dust cap. Often it is a gear or cable binding in the system, which in turn causes extra stress on the components and will likely result in failure of the angle drive[1].
A dust cap slipping against the wheel is the simplest to fix, in that it can simply be taped or stuck onto the hub with a mild adhesive. If the squared hole in the dust cap has become rounded, then the dust cap may be slipping against the angle drive’s spindle. It may be possible to use glue or tape to make the dust cap hold the spindle better, or you can replace the dust cap with a new one from a DeLorean vendor. Note that a rounded hole may be indicative of some kind of binding elsewhere in the system.
A bad cable can be tested as per the instructions in the Speedometer Cables article. Usually the cable simply needs to be lubricated, but cables can also sometimes develop kinks or binds that limit their ability to turn smoothly. Both of these issues can put undue strain on the angle drive, eventually causing it to fail. A damaged cable should be replaced with a new one from a DeLorean vendor.
A failing angle drive implies that the entire unit is soon going to fail and will need to be rebuilt or replaced. Lubricating the angle drive may help lengthen its life and fix the bouncing problem. It is rare that an angle drive will contribute to bounce, but it common for it to fail first.
A completely failed angle drive will result in no speedometer movement at all, and the angle drive will need to be rebuilt or replaced. Usually the gearing on the drive has simply bound or failed completely, resulting in destroyed gearing and/or a snapped spindle.
Speedometer Is “Dead”
A “dead” speedometer is one that doesn’t seem to work at all, always staying at 0 MPH no matter how fast the car is moving. Often the speedometer itself is fine, and the problem lies with the angle drive. Sometimes the issue is the a slipping dust cap or a poorly lubricated cable, and rarely it may be the Lambda counter, but the vast majority of the time it is the angle drive.
(tip: you can buy a digital speed display)