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Balancing wire wheels

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TR3driver Randall Y
Confusion, Los Angeles, USA   USA
What's the calibration number on the speedo face? Those numbers would make more sense (tho still not quite right), if you have a speedo for a 4.1 axle.



Randall
56 TR3 TS13571L daily driver
71 Stag LE1473L awaiting engine rebuild
7? Stag awaiting gearbox rebuild

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parkerg1 Avatar
parkerg1 Gary Parker
Grand Island, Ne., USA   USA
1951 MG TD
1961 Triumph TR3A
1998 BMW Z3
In reply to # 1482936 by TR3driver What's the calibration number on the speedo face? Those numbers would make more sense (tho still not quite right), if you have a speedo for a 4.1 axle.

Randall, I am not familiar with what the calibration numbers are, the only thing I can see is above the odometer SN 6219/06, and below it is 1216. Are these what you are referring to? I took a little ride yesterday, and at 2500 rpm, the speedometer was reading between 42 and 43. With a 370 it should be 50, correct? I am charging the battery on my old GPS, and will check it with that when I have a chance.
Gary

TR3driver Randall Y
Confusion, Los Angeles, USA   USA
The SN number is the Smiths model number, the other 4 digit number is the number of turns the speedo cable makes per mile (aka calibration number). The drive ratio in the gearbox (assuming you have a stock gearbox) is 5:2, so at 2500 rpm, the cable should be turning 1000 rpm (2500/2.5) and the speedo should be indicating 49 mph (1000/1216 * 60).

That is independent of true ground speed (so actual final drive ratio and tire size is not a factor).

So, either your tach reads a bit high, or the speedo reads a bit low (either of which is quite possible). Or you don't have the original gears in the gearbox.

15% is actually pretty good for these old instruments, IMO. Mine was much worse.

Calibrating the speedo head is not for the faint of heart, most people elect to send them off to be repaired. Cost used to typically be around $120, probably a bit more today. Unfortunately my TR contact info didn't get copied to this laptop, but some names of places that can do it are:
MO-MA
West Valley Instruments
North Hollywood Clock
Nisonger



Randall
56 TR3 TS13571L daily driver
71 Stag LE1473L awaiting engine rebuild
7? Stag awaiting gearbox rebuild

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kirks-auto Platinum Member Robert Kirk
Davenport, Iowa, USA   USA
Morris at W. Valley is who I've used for 30 years fwiw.



Regards,
Robert Kirk

kirkbrit@yahoo.com

Business phone 563 323 1017
Orders only please 800 547 5747
cell, if you must, and I know where it is 563 940 1864

http://kirks-auto.com

Moss distributor UK importer
Beat or match any retail/delivered quote

parkerg1 Avatar
parkerg1 Gary Parker
Grand Island, Ne., USA   USA
1951 MG TD
1961 Triumph TR3A
1998 BMW Z3
Well today I had a chance to get back to it. I hooked up an electric tach, and it reads right with the tach in the car. I got my GPS charged, and it runs right with the speedometer. Not good. At 3750 rpm, I am reading right at 65. Looks to me like I must have a 411 rear end. Any other thoughts? The tires are new 165 15 radials.

Gary

TR3driver Randall Y
Confusion, Los Angeles, USA   USA
My calculations say it's closer to 4.3, assuming your tires are the same rolling diameter as the original 165-15 bias ply.
(I forget offhand which car they are from, but there were 4.3 gears available from the factory that would fit the TR3 housing.)

And evidently, whoever did it also recalibrated the speedometer.

I ran for awhile with a 4.1 and no OD; if you plan to do any freeway driving at all, I would definitely recommend finding a 3.7 axle (or gearset). They are usually pretty trouble-free, so it shouldn't be too hard to find a used one. I've got several myself, but shipping from CA to NE might be expensive.

Gearsets are also available new, but you probably should be sitting down when you check the price. If you do go with new, consider importing a 3.45 set from the UK (used in TR5 and several other cars with PI).



Randall
56 TR3 TS13571L daily driver
71 Stag LE1473L awaiting engine rebuild
7? Stag awaiting gearbox rebuild

parkerg1 Avatar
parkerg1 Gary Parker
Grand Island, Ne., USA   USA
1951 MG TD
1961 Triumph TR3A
1998 BMW Z3
Thanks Randall. I guess 411 or 430, I need to live with it. I would much prefer the 370, but as I don't intend to do any fast driving, I will just need to go a little slower on the hiway. I looked up the price of the gear sets from Rimmer Bros, and they are not priced to bad, but I don't think I am up to changing them out. 10 or fifteen years ago I may have attempted it, but at 77 no way. I still need to get it on my lift, and check the ratio by turning the drive shaft, but what ever it is, it is.
Thanks Again
Gary

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parkerg1 Avatar
parkerg1 Gary Parker
Grand Island, Ne., USA   USA
1951 MG TD
1961 Triumph TR3A
1998 BMW Z3
Well it only took me a month, but today I got the TR on my lift, and checked the rotation on the rear end. I jacked up one wheel, and marked the drive shaft. Turning the free wheel 2 full turns, my mark on the shaft showed 3.7 turns. In my thinking, that would mean I have a 3.7 rear end. Now I am totally confused. I guess I better go back and check the speedometer, and tach, to be sure that I got it all correct last time. Any other thoughts?

Gary

TR3driver Randall Y
Confusion, Los Angeles, USA   USA
Well, you've already said that whatever it is, it is; and that you don't mind going slower than everyone else. I'd say that means time to quit worrying about it, and just drive the car!

I've driven for so many years without an accurate speedometer (for various reasons), that I don't even look at it any more. With my current setup, I double the rpm in 100's and add 10% (both of which are pretty easy to do in my head), which gets me very close to actual speed in 4th OD. (For 4th direct, subtract 10% instead of add.) So, 3500 rpm is close to 77 mph (35 times two is 70, 10% of 70 is 7.) Of course, that's with tires that are substantially shorter than stock (205/55-15)



Randall
56 TR3 TS13571L daily driver
71 Stag LE1473L awaiting engine rebuild
7? Stag awaiting gearbox rebuild

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CJD john durant
Southlake, Texas, USA   USA
I am assuming the speedo is correct, since you said you checked that with GPS? It sounds to me that the tach is off. It's in a conservative direction (i.e. you won't over rev if it reads higher than actual), so you may want to live with it. If you want it right on, you can send it off...or I can show you how to calibrate it with no more than a decent rare earth magnet.



John
Southlake, TX

'55 TR2

parkerg1 Avatar
parkerg1 Gary Parker
Grand Island, Ne., USA   USA
1951 MG TD
1961 Triumph TR3A
1998 BMW Z3
Thanks Randall and John. I guess I just want to find out for sure where the differential is. I will try to check the speedometer, and tach again this weekend. John, I may ask you for your directions on recalibrating the tach, if I find that is the problem, and I suspect it is.
Thanks Again
Gary

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