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Problem Solved: Speedometer Problem

Posted by Denny B. 
Denny B. Avatar
Denny Brodbeck
Miami, FL, USA   usa
1971 MG MGB

Hello All,

Ever since I got this car (The Money Pit) I've realized that the speedometer must be incorrect. Today I took a GPS with me just to check out the speedo.

I am 7 to 8 miles off at all speeds.

When the speedometer say "40" I am actually doing "32".

When it reads "50" I am actually doing "42/43".

It is pretty much consistent all the way up the scale. When it read "80" I was actually going "73".

My speedometer is a 1280 TPM. What driven gear should I have?

Thanks.



Edited 1 time(s). Last edit at 09/03/2012 10:30AM by Denny B..
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Jim Gevay Avatar
Circle Pines, MN, USA   usa
1974 MG MGB

Denny, do you mean this red gear in my 1280TPM Speedo? I assume it's a 32 by the the label.



Early 1974 MGB with OD, SU HIF's, 72 spoke chrome WW's, Schlemmer Pertronix, DuBois fuel pump, Limey's relays, Gerry's column kit.

Attachments:
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Denny B. Avatar
Denny Brodbeck
Miami, FL, USA   usa
1971 MG MGB

In reply to # 2160180 by Jim Gevay Denny, do you mean this red gear in my 1280TPM Speedo? I assume it's a 32 by the the label.

Okay...yes...maybe.

I forgot that they are color coded.

So, you have a 1280 speedometer and a red driven gear.

So, I would have to "assume" that my driven gear should be red.

Tomorrow I will pull the driven gear and see what color it is.

I hope this is something I can do without major disassembly. I can see the angle drive on the side of the transmission. I hope it simply comes out with a couple of screws.

Thanks.

Edit: I didn't see your photo when I read your reply. Actually, I'm thinking the driven gear that the cable slides into on the transmission. I remember that they are color coded. Hopefully the colored gear in the speedo and the driven gear are supposed to be the same color.



Edited 1 time(s). Last edit at 09/02/2012 04:54PM by Denny B..
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Denny B. Avatar
Denny Brodbeck
Miami, FL, USA   usa
1971 MG MGB

Problem solved.

I contacted a gentleman by the name of Barrie Jones on a site call AllExperts.com and he sent me the following solution:


Hi Denny. You have the correct speedo for your MGB, but the zero setting needs adjustment. This requires the removal of the instrument from the car:

At your workbench, rotate the chrome bezel until the lugs at the back line up with slots in the casing. The bezel should then come off, possibly with the glass still attached to it. If not, remove the glass separately.

With the instrument face upwards, notice that the needle is resting against a wire stop. Gently press the stop inwards (it should be spring loaded) and pop the needle over it so that the needle is on the wrong side of the stop.

Look carefully at the face of the instrument. There will be a tiny white dot, and the needle should line up with it. This is the zero setting. My guess is the speedo will read about 8mph.

Carefully pull the needle off its spindle. It is a taper fit. Line the needle up with the spot, then push it back on again. Make sure it now rests on the spot, or else do it again.

Pop the needle over to its normal resting place and the instrument can now be re-assembled.

Job Done!


Thanks Barrie!
JPMilton Avatar
John Plaskett
Canfield, Ohio, USA   usa
1966 MG MGB

I have a 1966 MGB with the same speedo problem. Do you think this adjustment will work on mine?
Thanks,
John
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MG Unlimited Avatar
Lou Medeiros
Londonderry, NH, USA   usa
1980 MG MGB Limited Edition (LE) "Black Betty"

I just thought they came from the factory that way to make you think your 0-60 times are faster.smoking smiley
Denny B. Avatar
Denny Brodbeck
Miami, FL, USA   usa
1971 MG MGB

In reply to # 2161893 by JPMilton I have a 1966 MGB with the same speedo problem. Do you think this adjustment will work on mine?
Thanks,
John


According to Barrie since the error remains the same at all speeds, all that is needed is to move the pointer to the last white dot on the scale which I assume would be "zero".
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