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Speedometer wrong

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Bruce Bowker

Bruce Bowker

Obi Wan
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I am sure you checked this but - is the speedometer or whatever you checked yours against correct?

Is it off 10 mph across tne entire range? My Mini speedometer was way off but I was bale to reset the needle and now it is perfect.
 
What I learned is that my TR3 speedo is off starting around 40mph, and about 10-12MPH around 60mph. Not a big deal, since in 4th gear, you simply double the tach reading to get speed (500RPM per 10mph...so 30 (3000RPMS) = 60MPH and 2500=50mph etc.
 
Hi all, I noticed that my speedometer is about 10 miles per hour off. I have the correct size tires(Michlin Red Lines). Any ideas on what could be causing it? The speedometer bad maybe??

Thanks
 
I have found that my speedo is off the same amout. It shows 60 at 3000 RPM's you are realy doing 50 and is 10 miles slower the it shows. I have followed my wifes Honda and used a GPS to check this. At least you wont get any tickets.

Don
 
Well here's a poser...

Speedos (on TRs anyway) seem to suffer much with waver, binding & inaccuracy. Yet the tachs seem to do just fine.

The basic mechanism is identical but with the speedo also having the gearing for the 2 odos.

Is it the longer cable run? More needle movement as you drive? Sudden zeroing out on quick stops?

I've never had a TR speedo that I could say worked perfectly... yet never had problem with the tachs.
 
Hey guys,
I recently added a J-type overdrive to my TR6 that was only a standard four speed and with the new speedo connection (dog leg) on the right of the tranny instead of the original outlet on the left and a new longer cable, my readings are now off by at least ten mph. Bummer. Any ideas on this one?

Bill
 
Yes It seems to me low by 10mph across the spectrum. Looks like its time for a rebuild since the odometer part doesn't work either.

Nice tip Sammy, I'll to remember that while my speedo is in the shop and I am driving. Thanks all
 
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Dr. Bill:
Hey guys,
I recently added a J-type overdrive to my TR6 that was only a standard four speed and my readings are now off by at least ten mph. Bummer. Any ideas on this one?
Bill<hr></blockquote>
First, I believe the four speed car had an axle ratio of 3.7/1. The OD car had an axle ratio of 4.1/1.

Since you now have the speedometer drive gear from a 4.1/1 axle (original speedometer drive on the back of the OD transmission) installed in a car with a 3.7/1 axle ratio, it will read low by about 10%.

You would need to install a speedo drive gear from a non OD equipped car, if it will fit, or recalibrate the speedometer.
D
 
If you look in the shop manual/driver's handbook, you can get RPMS per 10MPH for every gear (1000 RPMs in 2nd and 500RPMs in 4th are easy to remember) for TR3s...but each TR has a calculation. My TR-250 never had a working speedo, I just made a chart for each gear when I was just learning the car.

Remember, race drivers never have speedos. Tachs are good tools!
 
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