Rover SD1 Forum - Snippet #1a - Repair LT77 Speed Transducer

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Tracing Rover SD1 Speed Transducer Faults

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The L/H image shows the result of a Rover SD1 LT77 Manual Gearbox Speed Transducer cable exposed to 18 years of excess heat radiated by a close proximity twin after-market stainless steel exhaust pipe (plus any local flexing). The cable insulations having shrunk significantly, allowed one of the soldered joints inside the epoxy filler to become seriously compromised, intermittantly affecting three major instrumentation functions, Speedometer, Trip Computer and Cruise Control.

The original single exhaust pipe would be less likely to cause such a problem. In addition, when correctly assembled the connector end of the transducer cable is neatly tucked under a small clamp which holds the 'loose' end to the body of the gearbox. Thus secured, the Speed Transducer cable and gearbox all move around in unison with no flexing.

If the cable is not correctly secured after maintenance is performed on, say, gearbox, clutch, speed transducer, reverse switch or the adjacent exhaust pipes then flexing is inevitable. Its also an inaccessible location, not easy to find finger room to tuck the cable into it clamp.

A more common LT77 Speed Transducer failure mode is where one of the wires simply breaks, in which case the fault becomes permanent as opposed to intermittent. Such failure is usually easier to see and to diagnose. The R/H image shows the repaired Rover SD1 Speed Transducer.

Whether arrival at this page is from previous discussions regarding tracing Rover SD1 Gearbox LT77 Speed Transducer faults or directly from Google link on the subject, the reader may be well pleased with the prospect of solving an expensive problem for a small amount of cost. However, the process described does require access to a few tools not found in the average workshop.

The techniques used are applicable to either intermittent or broken transducer connections.

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Tracing Rover SD1 Speed Transducer Faults

Ramon Alban


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