[A/S] Ford diesels & trannys

["Harvey Barlow" <harveybarlow@xxxxxxxxxxxxx>]

John,

The transmission Ford was using behind big blocks and diesel engines before
introduction of the E4OD was known as the C-6.  They are bullet proof.

The truck you are considering must have a 3.55:1 differential.  It will have
more than adequate low rpm torque for pulling and will be pretty economical
at highway speeds.  I think my 460 gas truck with E4OD (overdrive) and 4.10:
1 gears turns about 1800 -1900 rpm @ 60mph.

You should be able to determine the rear end ratio by looking at the code
which is stamped on a tag on the frame of the driver's door and calling a
Ford dealer or consulting a Chilton's or similar manual.  The code for the
optional 4.10 gear (in 1994 but probably the same) was X25.  With traction
lock differential the code was XB5 or XC5, I've seen both used.  I don't
know what the code for the standard 3.55 gear was.  The overdrive
transmission provides a 30% ratio reduction with other factors of tire
diameter and gear ratio held constant.  So, if you know that your gear ratio
is 3.55 you multiply that number by 70% to learn the final drive ratio when
in overdrive.  I think the 30% gear reduction would translate roughly to a
30% engine rpm reduction.

Fuel consumption is reduced significantly with OD measured by a percentage
but in real terms of mpg and fuel costs, it is not a huge number until you
extrapolate out to 200,000 miles.  Stated another way, if you were using a
4.10 gear ratio going to overdrive would probably improve fuel usage by 2-3
mpg.  Using OD with a 3.55 gear ratio might not improve mileage very much
because at such low rpm, the engine might be lugging slightly and might not
run as efficiently.  It would depend on the engine, towed weight, and wind.

I'm not aware of any inherent problems with the engine and I can confidently
tell you that the old C-6 transmission was bullet proof unless it has never
been serviced and has been badly abused.  Odometer reading, service records,
color and smell of the transmission fluid would be indicators.

However, it takes the patience of a saint to drive one of those
non-turbocharged diesel powered trucks.  When you drive one with a load
there is no way possible to maintain speed up a grade.  The diesel engine
will simply ignore your throttle input.  I once drove a rented U-Haul truck
with that engine from VA to TX to transport my daughter's possessions.  The
engines will produce excellent fuel economy on flat land and will pull
awesome loads up steep grades but only at their own pace.  The driver is not
going to hurry it along.  I have encountered non-turbodiesel powered Fords
pulling trailers of similar size and weight to my own in the mountains of
Colorado and have passed them, slowly to be sure, but outpulled them with my
gas 460 on the grades.

Hope this helps.
Harvey