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Triumph TR3 - Non-overdrive speedometer?

My non-overdrive TR3 speedometer tells me I'm going 45mph when I'm actually going closer to 35mph. Can anyone tell me if this would be the result of having a speedometer from an overdrive vehicle? thanks!
Chet

Just for clarification...

My TR3 is not an overdrive car. When my speedometer says 45mph, I'm actually going only about 35-38mph. I wonder if a PO installed a speedometer from an overdrive car. Would anybody know if these are the results I should expect?

Thanks again.
Chet

Chet-I might be wrong, but I don't think the speedos are different for an OD car. The speedos tend to get more optimistic with time because the spring tend to weaken. Your speedo probably needs to be recalibrated. If you want to tackle it, check out this site for smith-jaeger speedos&tachs: http://ourworld.compuserve.com/homepages/arhodes/
Berry

Chet was partially correct, but not quite. There were two different Speedo’s StanPart # 108192 (Mile) and 108193 (Kilo). They are the same Overdrive or standard transmission.

Thanks
Russ Austin

58 Comm# 401804L
Russ Austin

Chet,

A Speedo even if properly calibrated will only be as accurate as your tires. If you are driving on oversized or undersized tires, overinflated or underinflated tires, the amount of revolutions of the tire will differ greatly. It may not seem obvious but tires make a huge difference in the accuracy of your speedo readings.

Barry Shefner
59 TR3A 0TS57675L
Barry Shefner

Hi:Maybe I am wrong but I always thought there was another speedo for the cars fitted with a high ratio rear end(4.1/1).These cars usually had overdrive but the different speedo was because of the rear end ratio not the overdrive.
Chuck

Chuck-You are right, there was a speedo change with the 4.11 diff. In fact, I think the change to 165 Micheiln tires also required a change. I don't know if the numbers on the speedo face indicates the "turns per mile".
Berry

Hi Guys:
I am running a 3.75/1 diff,165x15, Cooper tires and a no O/D and at an indicated 60 mph I am turning 3000 rpm which is the spec in the workshop manual issued when the cars were on 15" bias ply tires.So it looks as though the 165 tires don't make a difference.
Chuck

Chuck - Your numbers are right. They also support what I get in 4th at 60 mph. When I click into overdrive, the tach in my TR3A drops from 3000 to 2400 rpm. I saw a slight change when I switched from bias ply to Michelin 165 RS tires but nothing to worry about, at least till a patrol car or sheriff pulls you over.

Don Elliott, Original Owner, 1958 TR3A - 8TS27489LO

BTW Chuck does your 3A have a numeral stamped onto your Comm. No. plate just before your TS number? Like the "8" in mine above. If your TR3A is a 1959, you should have a 9 pre-fix if it is a Canadian import. If you have 1961 which was first registered in Canada in 1961, the pre-fix would be a "1". If a '61 but first registered in 1962 (in Canada) the pre-fix might be a "1" or a "2".

Let us know.

Don
Don Elliott

Hi Don:The commission number on my car is TS41444 there is no number in front of the "TS".To prove your point my car was brought into Canada in 1990 from the States by a guy who intended to restore it.The customs papers state only that it is a Triumph TR3A and suggest that the year could be anything from 1959 to 1961.I registered it in Ontario as a 1958 having checked the comm.number against the mfg records and found out that it was built late in 1958.
While I was restoring it I got a parts car from a friend of mine who had bought his car years ago in toronto.It was a 1960 and the comm.number is 0TS74947 I checked the number and it was indeed built in 1960.
Sooner or later the truth will out.
Chuck

Several factors at work here. A TR's speedo drive is turned by a gear driven off the output shaft of the transmission. It's after the gears (and OD geartrain) which is why the speed is accurate in any gear. Well, as accurate as a spinning bar magnet deflecting a needle against a coil spring, each over 40 years old.
What changes the equation is the rear axle ratio. 3.7/1 is standard, and uses a speedo with 1180 turns/mile (a little '1180' will be below the odometer) Different tires (radials) need different turns/mile; I think radials have 1214 or so. A 4.1/1 rear end will have something around 1300. The 4.1 rear end was an option, sometimes fitted with OD cars.
I agree with btp44, try recalibration. A common scenario is most TRs now use 165R15 radials, but have a speedo for the taller bias-ply tires most originally came with. A car with smaller radials will not go as far (or fast) as the speedo expects for the same # of turns. Its not much difference, but magnets and sprrings age and will make a big difference. I hope that website helps - I usually lose parts whenever I take a guage apart...
Jeff

This thread was discussed between 16/07/2002 and 20/09/2002

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