Moss Motors, Ltd

I've noticed that the speedometer needle on my 66 MGB tends to bounce so that my reading is really pretty variable.  The other day, driving at a steady speed it was bouncing between 35 and 50MPH.  Is there an adjustment that I can make to correct this? I've also noticed that my trip mileage meter doesn't change at all (which may be a different problem all together).   Thanks for any help or suggestions.

RobMGB66

Excerpt from:    http://home.comcast.net/~rhodes/speedo.pdf

Repairing Jaeger & Smiths Speedometers

By:  Anthony Rhodes

THE MALFUNCTIONING SPEEDOMETER

You have almost nothing to fear except fear itself. You CAN fix your own speedometer.

Here is some information that may help you. The first issue is to decide whether the

speedometer itself is actually the cause of the problem. Some faults that are thought to be

due to a malfunctioning speedometer are actually due to a problem with the cable running

to the speedometer, or with the drive gear in the transmission.

Frequently the cable itself is the cause of a wavering speedometer pointer. It is unfortunately

somewhat difficult to service the cable. You must be prepared to get under the car

and remove the cable from the transmission. However, it is sometimes possible to service

the cable simply from the speedometer end. You need to remove the speedometer, then

pull up some slack in the cable so the end of the cable is protruding slightly from the dash.

Then you may pull out the wire cable from the outer sheath. Lubricate the cable with white

lithium grease or gear oil and then slide the cable back into the sheath. As you get to the

last couple of inches you need to slowly spin the cable as you insert it. This will allow the

square end of the cable to seat in the square orifice in the transmission drive gear (hopefully).

If, after multiple attempts, you can not get the cable to seat, then you will have to get

under the car, and unscrew the cable from the transmission. Then press the cable fully in

the sheath, and attach the speedometer. Then, back under the car, you must gently seat

the cable into the drive on the transmission and screw it down securely. Test the speedometer

with the newly lubricated cable. Test this before fully re-installing the speedometer in

the dash.

Other causes of a wavering speedometer needle lie inside the speedometer itself. I

have seen binding of the input shaft cause wavering as it slows down, then breaks free and

turns faster briefly. Binding can also occur between the shaft and the retaining flange. I

have also seen binding in the odometer wheels (particularly the “old” style) cause cyclic

resistance against turning, resulting in wavering. There can also be a dirt or lack of lubrication

in the needle bushing between the magnet wheel and the pointer spindle. Binding

odometer wheels and needle bearings often will cause speedometer wavering that is proportional

to road speed.

(MUCH MORE CAN BE READ AT THE LINKED WEB PAGE)

spriggs' advice and the link are exactly what you need. Its very detailed, clearly written and well illustrated. This is the resource that I used to clean & reset a speedometer & odometer found on ebay to replace the one originally fitted to my car.

Ed