Re: [A/S] increasing gear ratio in tow vehicle

["Harvey Barlow" <harveybarlow@xxxxxxxxxxxxx>]

Susan,

Yes, you can purchase a new ring and pinion set and a qualified mechanic can
install them in your differential.  Cost will vary but the complete job
should run in the range of $500-$600.  It is important to get a quality gear
set.  I would recommend buying the gear set from the same guy who installs
it.  Otherwise, you could end up with a mechanic who says, "I'm not
responsible for the howling differential or early failure, I only installed
it."  "You bought an inferior quality gear set."

Changing from a 3 series to a 4 series is not always possible because of
physical size issues.  The pinion gear will be smaller which creates a wider
space between pinion and ring gear.  This requires either a thicker ring
gear or a spacer, which is a risky compromise.  The differential in your
Chevy van may be able to accommodate the change.  Ask a Chevy dealer with an
excellent service department or other skilled and reputable shop.

Make sure of the skill of the installer.  A skilled mechanic is required to
properly set the depth of the pinion gear into the teeth of the ring gear.
This is referred to as backlash I think.  A mistake results in a
differential that howls loudly and may self-destruct.

Changing from a 3.42 gear set to a 4.1:1 gear set will result in increased
torque or pulling power to the rear wheels, but at a cost.  Engine speed
will be higher at any given speed, you will hear slightly more engine noise
in the van, and engine wear will increase slightly.

Since the conversion van is already loaded heavily and is pushing a
considerable amount of wind because of its frontal area, it may not see a
decrease in fuel economy, fuel usage could actually decline.

Don't expect a dramatic increase in towing performance with a different gear
set.  You might take your van with a full tank of fuel and whatever
passenger and cargo load will normally reside in the van when you are towing
to a public scale and have it weighed.  You will be very surprised how heavy
it already is without the trailer.  Or, even better, weigh the van and
trailer fully loaded for travel.  You can then compare that figure to
Chevrolet's gross combined weight rating figure for a 350 cubic inch powered
van.  You will most likely discover that you have already met or exceeded
GCWR.  Towing at or near GCWR is frustrating to many drivers because the
truck/van is straining and unresponsive as you reported.  The greater the
excess towing capacity remaining at full load, the better performance will
be.

You should also consider this since you mentioned the Rockies:  a normally
aspirated gasoline engine loses approximately 3% of its power output for
every 1000 feet of elevation gain above sea level.  At 10,000 feet, a common
elevation crossing CO mountain passes, your heavily loaded van, towing a
trailer, will be trying to do so with 30% less power than at sea level.

Conversion vans with 350 cubic inch motors do not make ideal trailer
pullers.  And we have not yet addressed reserve braking or handling
characteristics.

I'm sorry to be a bearer of bad news, but if you plan to do a lot of travel,
in all terrain and all weather conditions, you may be happier in the long
run with a better puller.  If, on the other hand, you will tow only
occasionally, lightly loaded on mostly flat terrain and you are a patient
person who does not mind struggling up the grades with a long line of angry
drivers behind you, you may be satisfied with your van.

Harvey Barlow