TR4/4A Speedometer off 10mph

I have a 64 TR4 w/ OD that I am restoring. I sent the speedo out to be re-conditioned and have the odometer repaired. It reads 10 fast @ 30 mph, and 20 fast @ 60. It has an 1184 speedometer in it. Are they matched to a specific rear gear? I am assuming something has been changed at some point (rear, gauge). Is there any way to "cheat" the calibration? Sorry for the newbie question, my wheelhouse is GM where you can just change the drive and driven gear inside the trans and be on your way. Thank you!

This is what's called a "slope error", as opposed to an offset error where the reading is off by a constant amount at all speeds. Wrong gearing or tire size might cause it, but it also could be the wrong instrument for the car, or bad calibration. I don't know for sure how the shops do calibration, but I messed around with the magnet strength. This isn't for the timid restorer.

About 3/4 down this page: https://bullfire.net/TR6/TR6-40/TR6-40.html

Ed

Yes, Triumph's practice at the time was to adjust for final drive ratio and tire size by changing the calibration of the speedo head. 1184 should be right for a 3.7 final drive and 165 tires IIRC. If someone has changed to 4.1 gears, that would explain the 10%. I'm not sure offhand, you might be able to go that far with low profile tires, but they would be pretty short.

Any speedo shop should be able to make up a "ratio converter", which is just a small gearbox that goes in the speedo cable. My local shop quoted $100 for the box and initial set of gears, and $40 for additional sets (if I needed to change the ratio later). But that was a few years back, so prices might be higher today.

The problem with changing calibration on your own is that the magnet only changes the speedometer reading. The odometer and trip meter will still be off, unless you also change the gears that drive them. Not impossible, but a significant problem to solve.

Thank you! It has 4.10s in it. I believe they were changed at some point. A ratio converter looks like the way to go.

Can a shop like Nisonger recalibrate the speedo without using a ratio converter?

I didn't ask Nisonger, but several local shops told me 'no'. They would only restore it to original, not modify it to a different calibration.

I just received an email from Nisonger offering to recalibrate my Jaeger without using a ratio converter:
[COLOR=rgba(0, 0, 0, 0.85098)][FONT=&quot] [/FONT][/COLOR][COLOR=rgba(0, 0, 0, 0.85098)][FONT=&quot][/FONT][/COLOR]
Attached you will find the instructions covering the determination of thecorrect calibration for your Speedo based upon the current configuration of
the drive train in your car. Should a "Custom Calibration" be required, ,because of the additional parts and labor required there will be anadditional $25 (minimum)charge over and above our standard $185 (plusshipping) rebuilding charge.

The instructions detail a procedure of pushing the car over a measured 52' 9 1/2" and counting the turns of the cable disconnected from the speedometer. I plan on sending them my Jaeger.