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Speedometer calibration

Posted by john lundberg 
Engine, Cooling, Brake and More Sale at Moss Motors
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I found a pretty good write up on how to repair/calibrate a Smiths speedometer.

http://www.tidentenn.com/cars/Speedometer%20Repairs.pdf

Are there any supplier's which will have the replacement gears for the odometer? (e.g. I need a 40 tooth instead of a 32 tooth to calibrate for my overdrive)

Tom Rynne Avatar
Tom Rynne
Milwaukee, USA   usa
I just sent my speedo to Nissonger because the odo gears weren't working. i am not sure if they supply parts but it would be the first place I'd ask. 888-781-6968





Tom
1965 Midget
18 K orig miles
All orig but new wheels

Paul Noble
Bay Village, Ohio, USA   usa
Why don't you simply try to locate a speedometer that is already calibrated correctly for your OD? There is a brisk trade in speedometers on eBay. You could by the one you need, then sell the one you have, reducing your investment.

The drawback is that, when buying from an eBay seller, you may be buying a speedo that is badly worn and won't give an accurate reading.

Nissonger is the best bet, but they're not cheap.

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I guess I figure that the part required should cost around $10.00 and that calibrating the speedo seems strait forward.

My local MG repair guy has had problems with Nossonger, so I have a trust issue with sending both my only 79 speedo and $110.

As for the correct speedo for my transmission, I believe that MG only installed one type of speedo in 79 and the info in the speedo section of the mgexperience is not correct.

I do not need to change ANY parts in my speedo to recalibrate for the OD and only need to change one gear to correct the odometer.

I should talk to Nissonger about parts availability, I have only asked about a complete repair.

John D. Weimer Avatar
Cape Girardeau, MO, USA   usa
I put an OD in my '78 and didn't have to change the speedo, works just like it always did, it still wiggles.





My Motto: Clean Body, Clean Mind...................... Take Your Pick.

chris roop Avatar
Chris Roop
Pendleton, OR, USA   usa
I think 78s only had one speedo. Well, two; wiggle and not wiggle.


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Problem Solved?!?

I believe that I can change to the late model OD pinion and that will correct the speedometer.

Has anyone done this? How hard is it to change?

Best of all, I think I have one in my parts box! smiling smiley

Rob Edwards Avatar
Rob Edwards
Raleigh, North Carolina, USA   usa
1951 MG TD MkII "TDC6000"
1969 MG MGB "182608"
1969 MG MGC GT "8806"
1969 MG MGC GT "Rcedward"
1970 MG MGB GT "Donor"   → more
Has anyone figured out the difference between o/d and non-o/d speedos where the TPM is the same?

I've got a non-o/d '69 roadster, and the speedo is 1280 TPM. I've put in an o/d gearbox from a '72 roadster, and it's speedo was 1280 TPM. Looking at catalogs, it seems that in '69 the o/d cars and non-o/d cars took different part numbers for speedos, but both were 1280 TPM. Ditto 1972.

Is 1280 _really_ 1280? Or could 1280 be, say 1278 for o/d and 1282 for non-o/d?

Cheers!





--
Rob Edwards
Raleigh, NC
http://www.mgcarz.com

If you're in NC, check out the North Carolina MG Car Club!
http://ncmgcc.org

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Rob, try checking out the link I posted at the top. TPM is TPM.

In addition, the speedometer uses a magnetic pickup which is independent of the gears. The article talks about fine tuning your speedometer for your car's final drive ratio (including the wheels).

Rob Edwards Avatar
Rob Edwards
Raleigh, North Carolina, USA   usa
1951 MG TD MkII "TDC6000"
1969 MG MGB "182608"
1969 MG MGC GT "8806"
1969 MG MGC GT "Rcedward"
1970 MG MGB GT "Donor"   → more
John, cheers! I've looked at the link and bookmarked it. Looks like interesting stuff.

My speedo seems to be calibrated fine. I'm just curious as to why different part numbers for o/d vs non-o/d for the same year car, when the TPM is the same. The part number on the face of the gauge (which is not the Unipart part number) will be the same, but the suffix is different: 5226/03 for non-o/d vs 5226/08 for o/d. As cheap as automakers are, they'll commonise as many parts as they possibly can. That tells me if there's a different number, there's some difference between the two instruments, despite that in practice they seem perfectly interchangeable....

Perplexed,





--
Rob Edwards
Raleigh, NC
http://www.mgcarz.com

If you're in NC, check out the North Carolina MG Car Club!
http://ncmgcc.org

MGB777 Avatar
Tim Smith
Oregon, Illinois, USA   usa
1975 MG Midget 1500 "Little Bro'"
1977 MG MGB "Big Brother"
1980 Triumph Spitfire 1500 "Tweedee"
I took my 77" B for a shakedown ride today for the first time. Bought the car end of January. I replaced the speedometer cable to a one piece cable and got rid of the service counter. My Tach reads 3000 rpm but my speedo reads 70-75 mph, ,, that can't be right?

What is the correct RPM for 60 mph ?? Or should I say what is the correct speedo reading for 3000 RPM ??

The link in the above messages for this topic no longer works. ?

Otherwise, my 50 mile ride was a pleasant one cool smiley

ohlord Avatar
Rob C
North of Seattle, N.W., USA   usa
1971 MG MGB "Bedouin 2"
1971 MG MGB
54 MPH in 4th standard Gear at 3000rpm
assuming you don't have an overdrive

In reply to # 2944803 by MGB777 I took my 77" B for a shakedown ride today for the first time. Bought the car end of January. I replaced the speedometer cable to a one piece cable and got rid of the service counter. My Tach reads 3000 rpm but my speedo reads 70-75 mph, ,, that can't be right?

What is the correct RPM for 60 mph ?? Or should I say what is the correct speedo reading for 3000 RPM ??

The link in the above messages for this topic no longer works. ?

Otherwise, my 50 mile ride was a pleasant one cool smiley



"You take off the roof and the top is the height of the nearest Star"

RD2/Electronic Warfare Technician Vietnam 1969-1972

ingoldsb Avatar
Terry Ingoldsby
Calgary, Alberta, Canada   can
1971 MG MGB
If you are talking about changing the plastic gear in the gearbox itself, I think you are out of luck. I went down this road a considerable way and had no success.

For some reason the factory changed the size (not number of teeth, the actual diameter) of the plastic gear when they went from 1280 TPM to 1000 TPM. You can get plastic gears with different number of teeth (for both the large and small gear), but I never found the right combo to do the swap.

Outfits like Nisonger can convert the speedo. There are also boxes that go in speedo cables that will match the gearbox and speedo.

I don't understand why Moss hasn't made a custom gear for this application (or maybe a set of gears, large and small). Hardly a week goes by without someone asking a question about speedo recalibration.



Terry Ingoldsby
terry.ingoldsby@DCExperts.com

MGB777 Avatar
Tim Smith
Oregon, Illinois, USA   usa
1975 MG Midget 1500 "Little Bro'"
1977 MG MGB "Big Brother"
1980 Triumph Spitfire 1500 "Tweedee"
NO,,,,,,,,, I don't want to change anything in the gear box. Nor do I need a ratio gizmo........

My car has stock gearing,,, No OD,,,,, and all I want is to have my stock speedometer read accurately. At 3000 RPM the speedo now reads 70 mph in 4th gear.

Thanks Rob C. ....... confused smiley you read my post accurately .......

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