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

[Bob Spidell]

Yeah, looks like the speedometer drive pinion assembly is different between earlier and later cars (according the Moss 
catalog, anyway).

Also, IIRC the non-O/D cars had a taller rearend; between the two differences a different speedo would be required (or 
speedos can be fitted with different internal gearing--that's what I did when I installed a 3.54 rearend).

Bob


On 8/29/2012 4:55 PM, Per Schoerner wrote:
> Bob
> Yes, you are correct, the speed of the driveshaft is what determines the speed. But the different boxes have different 
> speedometer drive gearing. So,for a 3000 overdrive the driveshaft turns 3,2 revolutions to turn the speedo 1 turn. A 
> 100/6 overdrive does the same in 2,5 turns. A 100/6 gearbox without overdrive does the same in 2 turns. I have yet to 
> figure out what a 3000 non overdrive box does.
> Hence the different speedometers.
> BTW. sorry about the confusion, I meant tpm of course, not tpi.
> Per
>
> Bob Spidell skrev 2012-08-30 01:37:
>> 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
>


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Bob Spidell           San Jose, CA            bspidell at comcast.net

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