The question is, where are you using that long lever? With the "Power
Drive", the long lever (and accompanying torque) is before the
transmission. A higher final drive ratio puts the "long lever" after the
transmission. But, the TH425 is such a robust unit that the little 10% or
so additional torque applied with chain multiplication probably isn't
significant. I ran power drive for several years after I first got the
GMC (and my son now runs the same unit in his 26'). I liked it because it
seemed quieter than any high ratio final drive I've experienced, including
the 3.55 I now run.
Ken H.
On Tue, Jul 14, 2020 at 11:25 AM James Hupy via Gmclist <
> The engines in our coaches are designed to produce lots of torque at a very
> low rpm. That is why the GMC gets away with a 3:07 final drive ratio. That
> parameter worked, up until the 403 came along. It is an over square engine
> design. The bore is bigger than the stroke is long. It develops peak
> horsepower and torque at a higher rpm range than the 455. It really
> benefits from shorter final drive gearing. Very happy at 3400 rpm. The 455,
> not so much.
> But as it turns out, a long lever makes it much easier to lift a heavy
> load, than a short lever does. Short lever is faster than a long lever. But
> you cannot fool gravity. When you lift that same load 2 feet, makes no
> difference whether the lever is long, or short. The same amount of work is
> being done. That old formula F x D = W still applies. Do the math.
> But, with transmissions, load and heating are reduced by using shorter
> gearing.
> Looks to me like your reasoning is sound, Johnny.
> Jim Hupy
> Salem, Oregon
>
> On Tue, Jul 14, 2020, 7:58 AM Johnny Bridges via Gmclist <
>
> > Well, the input shaft to the transmission turns the same for a given road
> > speed in a given gear regardless how it gets turned that amount. Thus
> the
> > load on the clutches and hard parts is unchanged, is it not? Unless it
> > were sentient, it has no knowledge of what's turning the input shaft, the
> > internal load will be based solely on coach weight and speed, no?
> > Once the torque converter achieves stall speed, its load is determined by
> > the coach speed and weight (load) plus slippage, is it not? Slippage at
> a
> > given rate might be a bit higher at an increased speed, but I suggest the
> > difference is negligible.
> > We have, however, increased engine speed for an identical load, which
> > should reduce the torque requirement to the engine for that load should
> it
> > not?
> > Would one of the gurus go through this and sustain or refute parts of it?
> >
> > --johnny
> > --
> > Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
> > Braselton, Ga.
> > I forgive them all, save those who hurt the dogs. They must answer to me
> > in hell
> >
> >
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