MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Unstable speedometer

My speedo needle has started swinging around. (1971 mgb roadster). At around 60 mph, it swings over a ten mph range. My feeling is that the lowest reading is right, and it swings up above that, so that at 60 it reads between 60 and 70. Is it likely to be cable or instrument? How can I tell? Anyone know?

Mike
Mike Howlett

mike,

I recently had a very similiar problem with my speedo. It started out swinging in a small arch of about 10 mph and later it would swing in a much larger arch until it finally hit that little stop and the needle broke off. I sent the whole speedo in for repair and was told that the problem was created from grease migration. There was an excessive amount of grease on the speedo cable. You probably already have too much grease inside the speedo and you may have to have if overhauled. If that is the case, when you get it back and installed, make sure that you wipe away some of the grease on the cable. Hope this helps.

Cheers - Dennis - Sacramento
Dennis Rainey

I had similar problem with my 71b, i change the cable and solve the problem. It was dry rust, no lubrication.
Alf
alfredo

The easiest thing to do is to remove the inner cable and lightly lubricate it. Replace and see if that works.
If not the cheapest thing to replace is the cable.
If that does not work then it is the speedo.
Cecil Kimber

If it swings once a second or faster then it is probably a dry cable or one with a broken strand. If it is only as fast as the odometer then in my case it was a dry input shaft on the speedo, a drop of light oil cured it.
Paul Hunt

I had the same issue after replacing the cable, turned out it was the speedo. Took the speedo out and apart. There are two magnetic counter weights that spin inside a disk with 1/8 inch walls. The counter weights had some crud and corrosion on the ends which would sometimes cause friction with the walls of the disk. I simply lightly sanded the counter weight ends to remove the corrosion and crud and cleaned the walls of the disk with brake cleaner. Reassembled and voila, fix the problem. What was happening was the counter weights would grab the disk and cause it to move it more than the magnetic force would thus moving the speedo needle up. When the disk spring had too much tension, the counter weight ends would release and the spring would cause the needle to go down, past the actual speed limit. Therefore, for me, the actual speed was the middle (or average) of the high and low readings.

Don't be afraid of taking the speedo apart. It's like changing a watch battery, lots of little pieces but it's pretty straight forward.
D Gesse

Mike ,
This is one of those things with a lot of possible causes, virtually all of wich are listed above, in my case the culprit was a binding cable housing, but take care of it soon. Traffic violation tickets are never cheap,or fun, and as dennis will attest I,m sure, neither are speedo, overhaul jobs.
Jim Kelly

This thread was discussed between 13/01/2005 and 20/01/2005

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.