Smiths Tachometer Servicing

Common faults, part numbers, calibration and negative ground conversion.

Written by Glenn Wallace – 2006-04-02
How-To Library > Electrical and Instruments Section

MGB Smiths Tachometer Wiring Schematic and Parts Diagram,
Calibration and Negative Ground Conversion

— Smiths Tachometer Servicing —

Written by Glenn Wallace – Created 2006-04-02 Published 2006-04-02
Contents © Copyrighted and published under the following terms:
Copyright © the author and published by permission or fair use.

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Member Comments on Smiths Tachometer Servicing ↵

Rated 3 out of 10 based on 2 ratings

2009-01-19 16:10:07 # 1261

Comment by Andrew Bird

I thought I would add some pictures of the tach out of my 70 GT.

http://www.andrewbirdonline.com/pictures1/Tach/Tach.JPG

http://www.andrewbirdonline.com/pictures1/Tach/Tach2.JPG

http://www.andrewbirdonline.com/pictures1/Tach/Tach3.JPG

http://www.andrewbirdonline.com/pictures1/Tach/Tach4.JPG

The first and last picture show the capacitor that usually fails. I replaced
mine with this capacitor from RadioShack:

http://www.radioshack.com/product/index.jsp?
productId=2102479&cp=2032058.2032230.2032267&pg=1&allCount=100&fbn=Type/Electrol
ytic+Capacitors&f=PAD/Product+Type/Electrolytic+Capacitors&fbc=1&numProdsPerPage
=100&parentPage=family

2012-03-05 16:23:20 # 5081

Comment by Ingo Berger

1974 1/2 BGT, After 3 years tacho failed, al connection look ok & clean, added earth wire to stub on back, no result. Am hopeless with wiring diagrams.

2012-04-13 22:14:35 # 5617

Comment by Robbie P

where can i find this info on a 65 midget positive ground where the system has been upgrades to an electronic ignition,new coil, and new generator? Tach now runs at +2,000 to + 2,00rpm's. Is there an internal adjustment in the tach or is there a way to put a resistor in line to correct for what appears to be either an increased voltage or amperage or both ovet the old points system when the tach worked fine. it is an ome replacement which worked with the old ignition system. Any fix it ideas?

2013-08-19 08:36:46 # 11442

Comment by Michael Little

The tach in my 71 B, is not working, any ideas on where I should start to trouble shoot ?

2014-02-12 21:59:55 # 14103

Comment by Skye Nott

Please ask your questions in the MG Experience Forums: http://www.mgexp.com/phorum/

2015-11-28 07:47:52 # 30621

Comment by Richard U

Rating: 2/10

The article doesn't appear to be there: only a single wiring diagram.

2015-12-04 13:18:12 # 30739

Comment by david abbott

Rating: 4/10

No info on tacho servicing, just a wiring diagram.

2021-10-04 15:23:22 # 76915

Comment by Stuart Kindell

I found the schematic diagram very helpful....but have any of you managed to calibrate your tach using a square wave generator as described in the article?I couldn't make it work. I managed to make the needle move, but it tracked signal amplitude as much as, or more than frequency, and increasing the frequency lowered the reading, and it only moved through about a third of the scale. Has anyone here had better results?

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