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Overdrive ratio from 22% to 28%

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saniloc

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Hi,

I read that some of you have change the overdrive ratio from 22% to 28%.
I have a BJ8 and i thought to do this change after changing the ring and pinion for a 3.54 to cruise on highway.
I searched on internet and I have not seen a tutorial on this modification. If you have a link, i will be very interested.

Can you explain me what parts (maybe with moss reference for parts) should be changed and how to do it?


Regards.
Nicolas
 
Cottontop

Cottontop

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saniloc

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Thansk, my post was misleading, I'm not looking for information on mounting the ring and pinion but about changing the overdrive from 22% to 28%.

Regards, Nicolas
 
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57_BN4

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Sounds like a fairly involved project as you'd have to find most of the gears out of a 28% OD which pretty much means buying a whole unit off a Jag or whatever car used that ratio. You'll get a cruising speed reduction of less than 200rpm for all that work.
 
steveg

steveg

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FWIW --
I have a 3.54 with a 5 speed Toyota W58 which I think is 22% (.783 5th). 3000rpm is about 73-74mph. My buddy Peter Roses has a 3.54 with the 28% OD on his BN6 - he's seeing about 80-81mph at 3000rpm. Both speeds are on the GPS.
 
Bob_Spidell

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The RPM reduction going from a 3.91 rear end to a 3.54 is about 11%, or 275RPM around 2,500RPM. The reduction in NVH is significant, esp. over 8hrs of driving.
 
BoyRacer

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Nicolas, If you want a 28% overdrive then you must find a 100-6 overdrive unit. The overdrive units are interchangeable.
 
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saniloc

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BoyRacer said:
Nicolas, If you want a 28% overdrive then you must find a 100-6 overdrive unit. The overdrive units are interchangeable.
Click to expand...
Thanks Richard, i see on moss that 100-6 had 28% overdrive.
Do you think it is easier to completely change the overdrive unit rather than the corresponding parts?
I will give a look if overdrive units for 100-6 are selling, but i think with the price + shipping (i am living in france), it will be a very expensive upgrade. Maybe change the parts if i have to repair the overdrive one day...
 
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harroun

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I did this in the 1980's by putting in a 100-4 sun gear into the overdrive of my BJ8. Healey Surgeons told me about it and sold me the part. Worked great.
Doug
 
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