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MG Car Repair/MGB speedo problem

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Question
hi Howard
noticed lately my 74 MGB speedometer needle is jumping around once I get to cruising speed. What causes this and what is the cure?
as always- thanks in advance for your great answers.
Paul W

Answer
Hi Paul,

If the needle is pulsing in a regular pulse most likely it is a dry or bent inner cable. You should remove the cable housing from the speedometer and pull the inner cable all the way out and examine it for any kinks. If you find a kink in the cable measure where the kink is in the cable and you may find a sharp bend in the outre housing at that distance which needs to be straightened or replaced. Lube the whole inner cable before installing it back into the outer housing.

If the needle jumping is not steady check the tightness of the housing nut on the speedometer and on the transmission. Some speedometers had a 90 degree drive on the back of the speedometer and you should remove it and lube with oil and check to see that it is tight.

Other things can be wrong like the speedometer head itself could be at fault duel to a worn drive. The needle is raised by a spinning magnet and that can make contact with a metal drum that the needle is attached to. This will make the needle jump at times.

Howard

MG Car Repair

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Howard M. Fitzcharles III

Expertise

MG from 1956 (USA versions only) up and Engine theory.

Experience

Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

Organizations
Associate member SAE EAA member

Publications
Import Car magazine

Education/Credentials
ASE Master Auto with L-1 certification up to 2000

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