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Two concerns

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newguy

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First issue..... Did Jaeger make a amp guage for the TR3 and if so, any idea where I might get a decent working one.
Second issue.... My odometer and speedometer both show approx. 10% higher than actual. When I drive 10 miles the odometer says 11 miles. When I am driving 50MPH the speedometer shows about 55MPH. The owner before me installed a TR4 4dpeed syncro trans. and 205-15 tires. I would like to keep both modifications. ASKING FOR IDEAS? Thanks in advance to the sharpest LBC guys around.
 
The speedo error is most likely because of the larger size tires. Originals were 165-15 with an aspect ratio of 70-80%.

I've never seen a Jaeger amp gauge in a TR3. All the ones I've seen are Lucas. You can find them on e-bay. I've gotten good working gauges from that source for reasonable money.
 
The transmission should have no effect on the speedometer reading so I would agree with Art that the tires are probably the issue. What is the aspect ratio of the new tires as there are a number of calculators on the Internet that will show you what the effect would be?

One possibility to get closer assuming you have a 3.7:1 differential would be to find a TR3 speedometer for cars that came with 4.1:1 differentials. I think that would show 53.5-54 mph when you are travelling 55mph.

What's the part number on your current speedometer as we should be able to tell if it's for a 3.7 or a 4.1 differential?

Scott
 
Here's a tire size calculator. Funny thing, when I restored the TR3, I put in the Toyota transmission, and 185/70-15 tires. I thought for sure that I'd be way off on the speedo, so I checked it against the GPS. Darned if it wasn't dead on at all speeds. Sometimes you luck out! :driving:
 
If the tach is accurate, a 3.7 will give 20 mph per 1,000 rpm.
 
martx-5 said:
The speedo error is most likely because of the larger size tires. Originals were 165-15 with an aspect ratio of 70-80%.
Click to expand...

Larger size tyres would cause a speedometer/odometer error in the other direction than newguy reports, wouldn't it?

Or am I backwards?
 
based on the tire size calculator, there is something else off on the speedo. I am wondering if there is anything else that can be done. Have the speedo and odo recalibrated or something else.
 
The first thing I would look at is the accuracy of the speedometer. When I got my car it was about 10 MPH off on the low side. It had the orginal biass tires on it back then. The new tires I put on it were two sizes larger. It is still showing MPH on the low side. With a mechanical speedometer, a weak spring or any number of things will affect the accuracy of the meter. Knowing how far off it is, I just run a little faster to make up the difference.
 
I am not so concerned about the speedo. I really don't like the odo showing more miles than actual. But, would it do any good to send the speedo out to be overhauled?
 
Well, I sent my temp gauge out and had it rebuilt. It looks like new, and works like new. I was very pleased with the end product. Its a matter of whether you want to spend the money or not. Its not a cheap option.
 
205/60/15 should give you the same speed reading as the original 165/15 tires which as Jim indicated is 20mph per 1000rpm in 4th gear (without overdrive) so at 3000rpm you should be doing 60mph.

So it could just be the speedometer needs recalibration or if it's been replaced there is the possibility that it could be a speedometer for a 4.1 differential. The part number for the speedometer should be right above the odometer and below the center hub of the needle. Later speedometers will have a number similar to SN6307/04. Earlier models will have a much longer number similar to S.628. 51 118 504 04.

Regarding the ammeters, TR3's did use Lucas ammeters. I believe there was a thread on here recently about someone using a Jaeger one that was very similar except for the needle color but I think we found that those had been used in Austin Healeys originally.

Scott
 
numder on speedo is sn6319/00 How would I know if iot is a speedo for the4.1 diff. Any recomendations on a good place to have the speedo recalibrated? Again, the real concern is the odo showing more miles than reality.
As far as the amp gauge is concerned, it sounds like the Lucas gauge I have is probably the correct one.
 
The easy fix, once you determine fairly exact offset, is a correction gearbox in the speedo line.

If both are off, either speedo head is wrong (and if off the same amount, the in-line fixes both), and springs in the speedo itself will NOT affect the odo.

https://www.speedograph-richfield.com/html/minature_gearbox.html

https://www.westnet.com/~mfrank/Speedometer/Smiths.html

You order them by male/female ends where you want it, and by ration (to lower both, I think it's a 1:.9, 10% lower outut than input, but it's been a while.

Dave
 
That speedometer should be for a 3.7 differential, I believe with bias ply tires. The /04 and /06 models are supposed to be for 4.1 differentials.

It is interesting that both the odometer and speedometer are off by the same amount but I can't imagine the bias ply/radial difference would be that great.

Is it possible that you have a 4.1 differential installed? At 3000rpm with a 4.1 differential in 4th, you would be going 54mph compared to 60mph with a 3.7 differential. Sorry getting a headache here trying to figure which way it would go if you had a mismatch between speedo and diff!

Assuming your tach is accurate (big assumption), what does the speedometer show at 3000rpm in 4th and how fast are you really going?

Scott
 
Here's a little history regarding the ammeters in sidescreen Triumphs: An exert from britishcarcouncil.com/history/smiths.html
QUOTE
"Smiths' development as a supplier of components to the motor vehicle industry reached a turning point in 1930. In that year the company sold all the assets of its Lighting, Starting and Ignition Department and the whole of the share capital of M.L. Magneto Syndicate Ltd. to Joseph Lucas Ltd., and the two companies made a trading agreement under which each party undertook not to make certain products which were regarded as within the other's field of interest. The goods reserved to Lucas which Smiths undertook not to manufacture included starting, lighting and ignition equipment (but not sparking plugs), AMMETERS, batteries, electric windscreen-wipers, lamps and electric horns. The goods reserved to Smiths which Lucas undertook not to manufacture included sparking plugs, clocks and watches, speedometers and mileage recorders, petrol meters, pressure and oil gauges, dashboard thermometers and mechanical windscreen-wipers."
ENQUOTE
Frank C.
 
Borrow a GPS from someone and take a driove to confirm OD error.

If it's the same as speedo error, either wrong rear end (and if you like it, don't change it), and just get the gearbox to suit.
 
Scott: I think you may have hit the nail on the head. At 2000 RPM the speedo is indicating 45MPH. I was just out with a friend in a second car. The actual speed I was going was closer to 37MPH. At 3000RPM, indicated speed is 65MPH actual speed is 56-57 MPH. Is there a number or indicator of some type on the diff. which would tell me which ring and pinion are in it?
 
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