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MG MGB Technical - Speedo problem

I had a problem with the speedo in my '71 B, in that it would not register speed at first, then jump up to indicate speed. This went on for a few weeks until at about 65 mph, the needle dropped to zero and that was it.

I pulled the cable at the tranny, OD without angle drive, and found the cable had broken. So, after detaching the dash and replacing the cable I took a drive. Now I get no speed indicated but the trip and full odometer both are working. What could be the issue here? The speedometer worked before the cable broke. Any ideas?

Mike
M.A. Barrera

If the odo is working but the speedo isn't then the problem is obviously inside the speedo unit. Could be something as simple as a sticking needle (which sounds like the cause of the original symptom anyway), have you tried rapping it with a knuckle when travelling? It's then a case of aopeining it up and examining the mechanism, which is nothing more than a 'keeper' disc attached to the needle, restrained by a spring, with the shaft between the two running in bearings. A magnet on the end of the cable spins inside the keeper disc, the magnetic attraction pulling the keeper round against spring pressure. I suppose the magnet or keeper could have fallen off.
Paul Hunt 2

Thanks Paul. Update is that I took her out for another drive. The speedo started indicating speed again, but, when stopped, needle would not go back to zero. Went back to about 17 mph. When I got home, I grabbed the cable under the dash and lifted it up slightly, the needle immediately went to zero! I'm going to secure the cable in this higher position with zip ties and see if that cures the problem.

I noted a post on an Austin Healey site that talked about after market cable ends being too long and damaging speedos. Do we have that issue with our MGB's?

Mike
M.A. Barrera

If your bushing in the head is worn you may have parts binding as you wiggle the cable. Maybe the magnetic part is contacting the keeper disk. I think there's a site called mgaguru.com who has some info on MGA speedos. They're all essentially the same so maybe you'll find some hints there.

I think Nosinger www.nisonger.com rebuilds Smith's sppedos and tacs. How much may be another issue.
Robert McCoy

http://home.comcast.net/~rhodes/speedo.html
Derek Nicholson

Hi Mike,

Foreign Speedo on University Avenue can work on your speedo. They did a fabulous job on mine (71 BGT), in fact almost too good. They cleaned it up so well, they other gauges look a bit shabby in comparison. There's an ad in our newsletter with the contact info.

Paul K

This thread was discussed between 02/03/2008 and 07/03/2008

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