Hi Tony,
I can't help you with all of your questions but I can answer one or two of
them.
> I am checking out my new 4A. I see that the speedo is pretty far off. I
> am not sure what differential unit is in the car. I am running 185/70
> tires. I did not do a measured mile yet, but I am trying to get info to
> use when I have the measured mile data. The speedo says 1184 as its
> ratio.
The 1184 means the number of turns of the cable to equal one mile on the
speedo.
This speedo will probably have the part # 209182 just below the right most
digit of the trip indicator. According to the book this speedo is for a car
that has a 3.7 differential installed and using tires that are 550/590 x 15".
Two things can affect the speedo calibration. The diff ratio and the tire
size. Although I suppose that if the tranny was a non standard unit that
put out different values than stock then that could also affect things.
> When the speedo says _approximately_ 65MPH (you know the up & down
> waver of those speedos) I seem to be going noticably under 60, probably
> 55mph. This is in overdrive! My tach is non-functional right now, so I
> can't tell the rpms except it seemed around 3000 or somewhat under.
Sounds like you need a new speedo cable or to drastically clean this one
for sure. If its wavering a lot then it can very easily break the speedo head.
That one I know from experience!! There should be very little if any waver.
It would see that with the size of tires you're running should give you just
the opposite affect than what you're seeing.
I would suspect that y our diff might have a ratio of something like 4.55 or
so. Thats the only think I can think of that would cause you to be going so
slow for the estimted engine RPM.
> I am interested in info that I can use to calculate my overall ratio and
> supposing normal transmission ratios, the differential ratio.
Normal tranny ratios should be, 1st=3.14, 2nd=2.01, 3rd=1.65, 4th=1.0,
OD=0.82 and reverse = 3.22. The OD should be the "A" type.
The ratios that were available for the IRS rear end are 3.45 (TR6), 3.70, 4.1,
4.3 (TR6), 4.55 (TR6), and 4.875.
> Is there a way to tell the diff ratio by looking at it?
Hopefully someone else can explain how to determine diff ratio.
> I know this was discussed before, but please bear with me. Maybe this is
> a topic for the FAQs!!
Good idea for the FAQ (Malcom you listening!).
Brad (Lincoln Nebraska 402-464-1502)
My 1st attempt at a web site. Http://www.141.com/triumphs
1964 Spitfire4 BFC25720L
1973 Spitfire Mk IV (for sale or trade?)
1962 TR4 CT288L (To Maine or bust)
1959 TR3A TS41311L (someday)
1951 Dodge Truck 82217766 B-3-B-108
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