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Speedo adjustment

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Radford

Radford

Jedi Knight
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I had aN O/D transmission istalled in my B and did not have the speedo adjusted at the time. Now I'm reading about 1/10th of a mile /mile high on the odometer. Is there a simple way to make this adjustment, or is it better to have a shop do it for me?

Thanks in advance for all your help.
 
If the speedometer was correct for your axle ratio & the axle has not changed, the transmission itself should not change the speedo calibration. The speedo is driven from the transmission output shaft. It's possible that the new transmission has the wrong speedo drive gear for your axle ratio. This would be fairly easy to change.

Odometer adjustment requires gear changes in the speedo. It can possibly be corrected by a speedo repair shop, or an inline ratio correction box could be installed.
D
 
MKark and Dave thanks for you answers. I look through the .pdf on speedos and I'll check the speedo drive.

I don't know what car the tranny actually came out of so I'm betting (hoping) its a drive problem
 
Try this! I had my TD speedo re-calibrated bt Nisonger after I put in a 5 speed, the speedo is now spot on.
UNIVERSITY MOTORS PRESS
SPEEDOMETER CALIBRATION



The speedometer and odometer are calibrated by the number of turns per mile that the speedo cable makes. MG TD speedometers are calibrated at about 1500 turns per mile; MGAs at about 1400; Midgets about 1300; MGBs about 1200. Finally, in 1974, all MG speedometers were calibrated at 1000 turns per mile.

Whenever the tires, wheels, differential, or gearbox is changed, a complementary change must be made in the calibration of the speedometer to assure accuracy.

The odometer is gear driven; it either works or it does not. The speedometer is driven by springs and magnets and loses its accuracy over a period of time.

To calibrate the speedometer it is necessary to determine the speedo cable’s turns per mile. In practice, it is not necessary to traverse one mile; 1/100 of a mile will do just fine.

This is a three person job – one pushes, one steers, and the third counts turns of the cable.

Measure off 1/100 of a mile – that’s 52.80 feet, or 52 feet, 9 and 5/8 inches. Mark the beginning and end with a line.

Fix a wire to the back bumper, allowing it to drop vertically and just skim the ground.

Disconnect the speedo cable from the back of the speedo and pull it as far as possible from under the dash.

Fit the cable through the center of a timing wheel – a holed disc used to set up camshaft timing – showing 360 degrees in single degree increments.

Wrap a piece of masking tape around the inner cable, allowing a “flag” or extension of several inches.

Push the car to the start line (if you overrun the line, back up the car 10 feet and come at the line again, or the cable will have slack).

Rotate the timing disc until the flag points at zero degrees.

Push the car to the finish line.

Now the person counting will have counted the turns (for instance 13) plus a partial turn, say 194 degrees. Calculate the decimal equivalent of the partial turn:

194
---- = 0.538 = 0.54
360

Therefore the cable has turned 13.54 turns for 1/100 of a mile, or 1354 turns for a mile.

Make this measurement three times and average the trials!

Send your speedometer to Bob at Nisonger Instruments, Mamaroneck, New York with the turns per mile you have measured with your gearbox, your differential, your wheels, and your tires, and Bob will return to you a speedometer that will accurately indicate the mph with a working, accurate odometer.

Nisonger Instruments
570 Mamaroneck Ave.
Mamaroneck, New York
10543 U.S.A.
914-381-1786 fax
email info@nisonger.com
www.nisonger.com
 
SilentUnicorn... You're Anthony Rhodes? It's a pleasure to meet you!

I have a printed copy of your speedo document in my tech files and refer to it frequently. I'm not sure how old my copy is so I'll have to check out your link above.

I have a question for you regarding Smiths gauges. I've noticed on several speedos and tachos that I've worked on that there is substantial axial play between the odometer worm gear and the retaining plate securing the rotating magnet assembly to the diecast frame. Do you know what this play/gap is supposed to be? I've seen some where this play has been as much as 1/32".

Thanks for any information you can share.
 
[ QUOTE ]

194
---- = 0.538 = 0.54
360

Therefore the cable has turned 13.54 turns for 1/100 of a mile, or 1354 turns for a mile.

[/ QUOTE ]

MG - you're just like talking to my old man. No surprise, you seem to have matriculated from the same type of institution. Thanks, it's like leaning over my Dad's MGA with him and solving some issue he had.
 
[ QUOTE ]
SilentUnicorn... You're Anthony Rhodes? It's a pleasure to meet you!

I have a printed copy of your speedo document in my tech files and refer to it frequently. I'm not sure how old my copy is so I'll have to check out your link above.

I have a question for you regarding Smiths gauges. I've noticed on several speedos and tachos that I've worked on that there is substantial axial play between the odometer worm gear and the retaining plate securing the rotating magnet assembly to the diecast frame. Do you know what this play/gap is supposed to be? I've seen some where this play has been as much as 1/32".

Thanks for any information you can share.

[/ QUOTE ]

i assume you throwing sand at me. Since my name is Mark and is displayed on 99.9 % of my posts.
You have obviously worked on many mor of these units than i have. Do the ones with the large amount of play still indicate correctly?
This link that i posted i found in the A/H forum. and since i just happened to be trying to fix one at the time i found it extremely helpful. This document can easily be found by googling "smiths speedometer"

Sorry if i offended anyone

Mark
 
OK here's the answer. A true 1975 will have a 1000 tpm speedo. Look on the face of the speedo below the od and there should be a serial number and 1000 tpm number. The overdrives made between 1968 and 1974 had 1,280 tpm speedo output and can be identified by the top fill on the tranny or dip stick. All of the 1000 tpm tranny's were side fill transmissions and do not have a dip stick on the top. Your error of 1/10 of a mile is most likely no caused by a difference in speedo drives. It may have been there all along and you just noticed it after you put in the new tranny. If you do have a tranny with a 1,280 output drive you can just change speedo's to a 68 to 74 one as they are the same size as what you have.
 
[ QUOTE ]
...I've noticed on several speedos and tachos that I've worked on that there is substantial axial play between the odometer worm gear and the retaining plate securing the rotating magnet assembly to the diecast frame. Do you know what this play/gap is supposed to be? I've seen some where this play has been as much as 1/32".

[/ QUOTE ]

Mark and I have something in common, we're both not Tony Rhodes.

Assuming your question was serious... I too have encountered this 'play' but have not found a way to eliminate or change it. They seem to work okay with some slop there (certainly has no effect on accuracy) though it seems that the ones with the greatest slop are prone to binding if that little needle bearing isn't lubricated.

There is a tendency I think to not lube inside a speedo as this is one place where too much lube is much worse than too little.

BTW - I have used Tony's site many times and with it as my only reference have taken a Speedo completely to bits and reassembled successfully (though there were some trying moments).
 
Geo i thought the speedometer was pretty ez....that darn odometer was a PITA to re-zero.

mark
 
The mileage was easy to set once I had all the number dials on the table in front of me. They were actually the reason for the tear-down. I tried to clean them up a bit... who knew that Triumph had painted them with water-colors?

I repainted mine using acrylic artists' paint, white & mixed to match the shade of orange that was on the tenths dial before I washed it off.

BTW - There used to be a place in Long Beach that featured Used Cars and Speedometer Repair under on roof. I always supposed they had a lot off low-mileage one-owners for sale.
 
Thanks Geo. Sorry, I thought from the other documents at the site that "Mark" was Anthony Rhodes. Sorry Mark.

Yes, my question was serious. The worm gear is a press fit on the shaft and I have been able to reposition it to close the gap to about 0.005". Why? I'm one of the people who doesn't lube those needle bearings. I'm always concerned that if there is a lot of axial play the worm gear and needle bearing will be free to "bump" up and down in response to the cable turning and start to bind on the needle bearing. By controlling the gap and the use of shims (only when necessary) I can insure that the needle bearing never binds.

I have found the later odometers much harder to clean and repair than the early ones. Those little plastic gears between each number wheel give me fits. I have always used plastic model paint for the touchups I've done to number wheels and gauge faces.
 
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