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MG TD TF 1500 - Speedometer Calibration

My speedometer is not the one that came with the car when I bought it, the one in the car was froze up. I sourced another unit from a fellow in Alabama, which is in the car now. However, with a 4.8 rear, it reads exactly 10 MPH fast. I'm wondering if it came out of a TF with a final drive with taller gears, such as a 4.3 or 4.1. I'm considering a final drive gear change and thinking of not calibrating the speedometer yet until the change over. Any of you math geniuses know how a 10 MPH speedometer increase relates to a 4.8/4.3/4.1 rear? PJ
Paul161

Paul, what's the turns/mile number on the face of the speedometer just below the total miles odometer. For a TD with the standard 5.125 rear end the value is 1600 as seen on the image below. Bud

Bud Krueger

You can get an app for your smart phone, and use that.

Jim B.
JA Benjamin

My 53 TD (UK model) was exported to Japan in 1981 (returned UK 2008) & the speedo 'adjusted' to kph. I assume some gearing was changed because it didn't accurately show either mph or kph, just mph + 10 as yours.
I sent off to UK specialist who changed it back to pretty accurate mph.
Mike TD29330
M Lees

I checked the speed we were going with the GPS system and the speedometer was indicating 65 mph and GPS read back 55 mph.
Bud I'll check the numbers on the bottom and get back. Thanks. PJ
Paul161

Bud, Here's how the numbers read on a TF instrument;

On the top, below the odometer, the numbers read as follows,
51 117 515 00
SC 76 ??.
Cant read the numbers following the 76 as their behind the large end of the hand.

On the bottom below the trip meter the numbers read as follows,
1525
British
Jaeger
Paul161

The 1525 would be expected for a 4.875 rear end, normal for a TF. If you have the standard 4.875 and you're showing 10% fast, it says that the speedometer thinks that you have 4.39:1 rear end. Is your odometer also 10% optimistic? If so, you're all set for a 4.3 rear end. Time to call Dave Clark. Bud
Bud Krueger

Bud, Thanks for the read of Dave Clark. Very interesting, including the favorable reports from others. I am thinking of a 4.1 ratio to my rebuilt XPEG engine, not living in a mountainous area. I was figuring on doing this in the Winter, but now, might be sooner. I also like the heaver axles available. I know about breaking axles in British vehicles, as I broke 3 in my Land Rover before it was 3 years old. Oh yeah, the speedometer needs rebuilding also, so a calibration is no problem. PJ
Paul161

Paul
I have a Dave Clark 4.3 rear end. Very happy with it.
I sent my speedo off to Nisonger to recalibrate. They did that and cleaned it for a very reasonable fee. $150 maybe. I have checked it against the iphone speed app. Right on.
I like having an accurate speedo.

Tom
'54 TF
T Norby

To complement Bud's picture here is one for a TD that came from the factory with 4.875 gears (MK 2). The turns per mile is indicated as 1525.
Paul - let me know if you are looking for a set of MGA 4.1 gears.
Cheers, Hugh

H.D. Pite

Sent a note off to Dave Clark. Looking for some numbers, $$$. Not written in stone, Do I want to go this route or go with a 5 speed. With a 5 speed, the car won't be original. Decisions, decisions. PJ
Paul161

Hugh, if I decide on a Dave Clark rear and he doesn't have a set of 4.1 gears, I'll contact you. Thanks for chiming in! PJ
Paul161

Contacted Dave Clark to build me a 4.1 rear. Waiting for conformation. He only had one set, I hope I'm not too late. PJ
Paul161

You can also use a Garmin nav device to get a reading on actual speed. Use it on its battery power if your car is positive ground or reverse wire it if using a cigarette lighter plug.
John Quilter (TD8986)

This thread was discussed between 18/09/2015 and 21/09/2015

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