Speedo recalibration

[tim wood]

I’m changing the diff on my car from 3.54 to 3.07 as such I need to recalibrate the speedo.
I know I can send the unit off and have this done but has anyone tried to do it themselves using maybe an internal speedo gearset from another model.

Just a thought - it can’t be that difficult to work on these?

[johnetype]

The speedometer and odometer are separate. The speedo has fixed gears as such and you recalibrate the speedo by moving the pointer to the correct reading - which you've previously determined by using a GPS derived speed readout on the road.

The odometer does need its gearset changing. This article is one of several "on the web" which explains what to do.

http://www.mgb-stuff.org.uk/Smith-jaege ... repair.pdf

For my change from 3.54 to 3.07 I bought an ex Mk 2 Jaguar speedo that had very close to the correct calibration for the odometer to use the gears from that.

[mgcjag]

Hi Tim.....the speedo has no mechanical connection between the drive cable and the indicator needle..a spinning magnet via the cable drive draws around a cup operating the needle.....the magnets become weak and depending where you take you speedo for re calibration the magnets are re energised to give a more precise (not acurate) speed reading across the speed range......as Tom says the odometer is geared.....moveing the actual indicator needle is possible but lots of trial and error but as far as im aware only one speed will be correct where you move the needle to .........Steve

[Andyp_67E]

I would get in touch with Speedy Cables, They recalibrated and reconditioned a few of my previous MGB Speedos when I converted them to V8 spec using a higher ratio back axle. From memory you provide them with the number of turns of the speedo cable for one turn of the back wheel and the radius of the rear tyres. I poked the speedo cable through a piece of paper with a circle drawn on it divided up into 15 Deg sectors, stuck some tape on the inner for a pointer to count the turns, while an assistant looked at the rear wheel and told me to stop after one turn. Repeated a few times on the drive to get a consistent figure.
I sent the Speedo off and it came back correctly calibrated (Speedo and Odometer) and looked like new.

Andy

[abowie]

Just a thought - it can’t be that difficult to work on these?

It really is.

As Steve says the speedo works using a magnet. The faster it spins the more deflection you get. It is possible to alter the strength of the magnet, and by trial and error arrive at the correct needle deflection for a given cable RPM. But this is not an easy process.

To correct the odometer you need to replace the gearset, and they are NLA anywhere that I could find. You could cannibalize an odometer for a 3.07 diff I suppose but if you had one to start with you'de be more sensible just to use it.

Bottom line. Send it to Speedograph Richfield in Notts.

[mgman]

I had my speedometer recalibrated at Richfields in Nottingham. They trade as Speedograph Richfield a very prompt and good service costing £55 Plus vat and postage. I changed the ratio to 2.88 from 3.54 which has improved the touring RPM, although living in Cornwall there is a bit more gear changing on local work.

[christopher storey]

I have nothing but praise for Richfields : When my speedo gobbled itself up , making spectacular noises as it did so, they quoted me £70 for a complete repair. I paid, and when I got it back, the damage had not been as bad as first thought and they refunded me c.£20

[Mich7920]

My 2 speedometer have been recalibrated at Richfields. Change mph for kmh and change also ratio 3.07 on the both.
Great job, communication and price.
Mich

[tim wood]

Just got my speedometer back from Richfields . Quick service, great communication and very fair price.
Tim