The ratio between the transmission top gear and the rear end is only an
intermediate number which affects drive-shaft speed and individual
component stress loading. Example: If you run a 4.10 rear end and a .85
overdrive, you end up with a 3.485 overall drive ratio, which is the same
as running a 1:1 top tranny gear with a 3.45 rear end. The difference here
is once again the transmissions input-to-output first gear torque
capabitily...if you want the same 1st gear overall drive ratio between the
two transmissions, you will have to make the non-overdrive transmisssion a
lot bigger internally to cope with the added internal stresses of the
greater torque throughput in its 1st gear, which will be higher than the
overdrive tranny's 1st gear, all things being equal, at a ratio equivalent
to the product of the gear-spread*overdrive-ratio. Then you get into the
driveshaft speed...when driving along at highway speed, the driveshaft in
the overdrive tranny vehicle will be unnecessarily overspeeding when
compared to the non-od tranny vehicle. As well, when a tranny is at a drive
ratio of 1:1, the input is locked to the output, which eliminates
high-stress loading on the counter shaft assembly. This would be top gear
in the non-od unit, but the od tranny will be passing all of the load
through the counter shaft assy, unnecessarily wearing everything out. As
well, as an added side benefit, the lower numerical ratio rear end used
with the non overdrive vehicle will always have more gear tooth area in
contact, reducing ring & pinion gear pressure stresses, also allowing
higher strength and longer service life.
Whats my point? In the real world, it makes little difference, but under
high-load conditions like...who cares! :P
RF
>Ummm....this is all good except for the part about Detroit including
>overdrive as a warrantee program cost reducer. I'm pretty sure that this
>feature was included on a fuel saving basis due to the lowering of
>engine RPM on the highway. Also, I'll bet their warrantee costs went up
>when the first OD's exploded whe guys were towing trailers, or cops
>leaving the trans in OD when chasing people. I KNOW lots of cops' OD
>blew up. Just my $0.02 - the rest of your points are right on the
>money.
>Cale
>
>
>Robert France wrote:
>>
>> RE: BURNOUTS
>>
>> The clutch is a sort of sacrifical component in the vehicle which is
>> designed to wear, the transmission is not really designed to wear:
>>
>> #1 "Burn-outs" are extremely hard on driveleine components
>>
>> #2 First gear provides the highest torque multiplication
>>
>> #3 The higher the torque multiplication, the higher the stresses on the
>> internal individual components (this is why Detroit went with overdrive
>> trannys; they tend to overspeed the driveshaft but pass the load to the
>> rear axle, which is a less expensive part to warranty)
>>
>> #4 Static coefficients of friction are always higher than dynamic
>> coefficients of friction for any material; once the tire is spinning, the
>> load is much lower than when it is stationary
>>
>> So in the end, you are much more likely to fry the clutch if you try to
>> burn-out in 2nd gear, but if you have enough torque to overcome the static
>> load of the tires, this would be better than using 1st gear, therby asking
>> the transmission to try to multiply your initial lack of torque to a high
>> enough value to break the tires free, damaging the transmission while
>> trying...its your clutch, and its your transmission, and, in the end, its
>> your wallet.
>>
>> >OUCH!!!!! I thought 1st gear was bad enough on your clutch wont doing
it in
>> >second really pound the hell out of it or is there no difference?????
>>
>> > Yeah use second gear for burn outs
>
>
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:19:11 EDT