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TR2/3/3A Speedometer is off by 10 mph??

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Yes, but it's not easy. Different approaches, depending on what is actually happening:

1) If the odometer and trip meter are also off by the same amount, then you'll need to either get a "ratio adapter" or a different speedo head that matches your gear ratios (and tire diameter).

2) If the reading is always 10 mph high (ie it also reads 30 mph when you are only doing 20); you can disassemble the speedo head and adjust the position of the needle on the shaft.

3) But if the offset is a ratio (ie it always reads 7/6 high or only 23 when you are actually doing 20) and the odo/trip meters are correct; then you'll need to adjust the strength of the flying magnet inside.
 
I should mention that speedometers of cars of that era always read high, although usually by less than 10 MPH at 60. But 5-8 was not unusual. Cars today still read at least a little high, even though with digital speedometers, they could be made virtually exact (as long as you're careful about tire pressures, anyway). The idea is that it's better to err on the high side--if you get a ticket for doing 72 in a 65 zone, because the speedometer reads 10% low, you're not going to have fond feelings toward the manufacturer. Also, with changes in tire type and size, over the years, plus drivers' carelessness in keeping the pressures right, making the speedo read a little high gives some room for all that.
 
Are there different speedos as well depending on what rear axle ratio you are running? I seem to recall that there is and that there are different numbers on the speedo face to indicate same.

Cheers
Tush
 
M_Pied_Lourd said:
Are there different speedos as well depending on what rear axle ratio you are running? I seem to recall that there is and that there are different numbers on the speedo face to indicate same.
Click to expand...
Right. There were also different speedo heads for different size tires, at least for awhile. I believe there were at least 8 different speedometers used (2 axle ratios times 2 tire sizes times kph or mph), and may have been more (when the 165 radials were introduced)

I'm not certain all this info is accurate or even complete. But here's a start anyway.

Code: 
   Axle     Original    Triumph     Jaeger      Revs/km    Revs/mi
   ratio     tires        part       part
    3.7    5.50/5.90   108192      SN6319/00     -           1180
    3.7    5.50/5.90   108193            /01    740           -
    4.1    5.90        113632            /02    820           -
    4.1    5.90        113631            /03     -           1312
    4.1    155X        119046            /04     -           1344
    4.1    155X        120206            /05    820           -
    3.7    155X        119047            /06     -           1216
    3.7    155X        120205            /07    740           -

PS, another source (TSOA newsletter 8/60) gives a slightly different calibration number for /00, which may possibly reflect a specification change made without changing the Jaeger or TR part numbers:

3.7 Dunlop(bias) 108192 SN6319/00 1184

It also seems to indicate that the 113631 and 113632 numbers were interchanged in the above list.
 
Thanks Randall,

I have the 4.1 in mine...will check to see If I have the correct speedo....I suspect not as I had a parts car with a 3.7 and I think I used the best of the 2 speedos. That would account for some of my speedo error.

Cheers
Tush
 
I put a TR6 A type overdrive in my TR3A and on the test drive I had my wife follow me and she was way back there. When we got home she asked me why I was driving so fast. My speedo said 55 and she said hers said 55 too. What could be going on here?
 
Got_All_4 said:
I put a TR6 A type overdrive in my TR3A and on the test drive I had my wife follow me and she was way back there. When we got home she asked me why I was driving so fast. My speedo said 55 and she said hers said 55 too. What could be going on here?
Click to expand...
See post #2 above.

The speedo takeoff is after the overdrive, and a TR6 A-type should have the same drive ratio (5:2) as a TR3A non-overdrive. So normally, you shouldn't have a problem. But it's possible the driven gear for the speedo takeoff was changed at some point or even that the OD wasn't originally from a TR6 (fairly common to find Volvo ODs sold as being Triumph units). Or maybe your speedo head just reads low.

Or maybe the speedo in your wife's car reads high. I know my wife's Accord does. (Operator error is always a possibility, too.)
 
Highly unlikely that it's a Volvo overdrive. It came out a 1969 TR6 car that was stored in a body shop since 1982 and it was not original to that car because it had that yellow marker from a bone yard inside the bell housing with 1971 TR6.
Operator error is possible (wives won't go there now) she was in her 740 Volvo. I think at this point I'll go for a ride and track myself with a GPS to eliminate any operator error. Did Volvos use an A type?
 
Got_All_4 said:
Did Volvos use an A type?
Click to expand...
Well, I thought so, but the Wikipedia article only says "including Jaguar, Aston Martin, Ferrari, Austin-Healey, Jensen, Bristol, AC, Armstrong Siddeley". Of course, it also says that TR6 quit using them at the end of 69, which isn't correct.

But apparently the early Volvos only got D-types, later followed by LH, J and P. Sorry about that.
 
In that case you have the most easily solved issue, as described in Randall's reply:

TR3driver said:
...2) If the reading is always 10 mph high (ie it also reads 30 mph when you are only doing 20); you can disassemble the speedo head and adjust the position of the needle on the shaft...
Click to expand...

Pretty much a matter of holding the drag cup in position (say 40 mph) and moving the needle to indicate 30 mph.

This site gives a lot of detail on assembly and adjustment:

https://triumph.daveola.com/NOTES/Speedo_Repair.pdf
 
I would suggest moving the needle by marking the current location, removing the needle by carefully prying on both sides at the same time, then reinstalling in the new position. The shaft that carries the needle is very small and breaks easily; so just trying to twist the needle is apt to break it and effectively ruin the instrument.
 
Been around for quite awhile. I guess you don't really need to know how fast you're going in areas without decent GPS coverage, like tunnels, parking garages and narrow alleys. But it would make me crazy, just wondering every time I looked at it whether it was being affected by multipath or poor DOPs. (I used to help write GPS receivers, so I'm rather uncomfortably aware of how many different ways they can go wrong, and how poorly written most cheap receivers are.)
 
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