[VAC] Re: Towing in Overdrive

["Carol and Oliver Filippi" <ofilippi@xxxxxxxxxxxxx>]

I think the real issue is the overall strength (or capacity) of the
transmission.

When I bought my '89 3/4 ton Chevy pickup, it had a 3 speed automatic {not
the 4 speed overdrive which was also available}.

The salesman, who was very knowledgeable on trucks, said that the three
speed transmission was a lot stronger and more durable than the four speed
(overdrive model), and this was marginal in a 3/4 ton, though OK for a 1/2
ton..

This information has since been confirmed by a former Chevrolet service
manager friend who is now a service manager at a Mercedes dealership.

As has been pointed out, the higher gearing of the overdrive will put a
heavier load on the input end of the transmission, especially the torque
converter. This can generate a lot of heat if under heavy load, and heat is
the major cause of failure in an automatic.

Since automakers are trying so hard to improve fuel economy - one way is
thru higher gearing in the transmission via overdrive - it is probably a lot
faster and easier for them to add an extra gear than redesign and put into
production a new torque converter (and perhaps a new housing). Thus, there
is a good possibility that these "fuel economy oriented" transmissions are
marginal in durability, which of course will show up when towing a sizeable
load repeatedly.

The bottom line: Be very cautious using overdrive while towing, unless the
transmission is specifically built for it, such as the new Allison in the
Chevy/GMC HD pickups.

Oliver Filippi