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MG MGB Technical - Wacky Speedo

Have a 69 mgb roadster. When the speedometer registers above 50mph it jumps about 15-20 mph and swings back and forth +/- 20mph. Drop below 50 and it is steady. Replaced the right angle gear at the transmission and the the cable has less than 200 miles on it. Is it the head?
James Drisko

I've posted this before, but this is a new twist that I did not cover. The speedo drive is only driven by friction, no key. So, if the nut on the gearbox output flange is loose, odd things happen. Usually it gets worse as the car heats up, reading slower and slower, but it could do as you say too. You have to pull the front of the driveshaft to tighten. It is also another source of the dreaded "clunk", and frequently causes the shift lever to move back and forth as you get on/off the gas - and it could kill the gearbox eventually.

FR Millmore

Can you explain what you mean by pull the front of the driveshaft to tighten? I sometimes get the clunk when I hit the gas peddle after shifting. My speedo is all over the place. Dosn't really bother me that much
GG Ginty

Remove the four nuts holding the driveshaft to the gearbox, Pull the shaft out of the way. There is a big nut holding the flange to the gbx mainshaft, Must be TIGHT.

FR Millmore

GG Ginty

This thread was discussed between 15/07/2012 and 17/07/2012

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