[Healeys] Help with BT7 (new thread - I got bounced again!!!!!)

[Bob Spidell]

OK, I'm confused. I always figured the car's speed was determined by final drive output speed, whether that speed was produced with or without O/D. IOW, if the final drive is producing 2,000RPM in straight 4th--about 45MPH, roughly--or producing 2,000RPM (final drive--at the driveshaft) in top-O/D you'd still indicate 45MPH. The only difference would be engine RPM. I don't think you need a different speedometer, as both O/D and non-O/D speedo adapters pick up the speed at final drive (in front of the front driveshaft yoke and behind the transmission and O/D if fitted). Only if you change the final drive--e.g. by changing the diff gears, wheel size, etc.--would you need a different/recalibrated speedo. 

Also, I think the speedos are calibrated in 'turns per mile;' i.e. the number of turns of the cable (or adapter output) as the car travels one mile. This is important for the odometer and tripmeter, which are fixed gearing, but the speedo's indicator needle can be moved around. 

Or am I full of pan sludge? 

Bob 


-------------------------------- 
Bob Spidell - San Jose, CA 

----- Original Message -----


Hi 
With the risk of sticking my chin out now I think I will change the 
statement to say that only BN4:s had the information about overdrive/non 
overdrive in the VIN. And a rule is not a rule if there are no 
deviations to it, so in line with that sometimes this letter is omitted. 
As a matter of fact, yesterday I looked at a 100/6 that didn't have an 
overdrive. I even drove it around the block. That's true. 
Have never encountered a big Healey without overdrive, although I have 
seen several 100/6:es that were born without it, but have later been 
equipped with it. 
This car had an unusual speedometer, normally these cars have SN6105/06 
with tpi value of 1525. This car had SN6155/19 with tpi value of 1020. 
Graded in Miles Per Hour, of course. That belongs to a 3000 without 
overdrive. So there is the proof that 3000 could come without overdrive, 
although I have never seen any. 
I am sure that this car must be the ONLY big Healey in Sweden without an 
overdrive. 

Per