OT: Commercial truck automatic transmission shifting

Hi all -

I know this is a bit off topic for metalworking (or maybe I'm trying to avoid a catastrophic failure that would require metalworking?) but this group seems to know something about everything...

We just acquired a 1997 GMC C7500 truck with Cat 32 series diesel engine and an automatic transmission. This is my first heavy truck with an automatic and I'm wondering how to shift it...

Just leave it in D and go for it, or upshift through D1, D2, D3 and D to simulate a manual tranny?

My one over the road tryout was going 15 miles to DMV this morning to get the beastie titled and registered and I just left it in D, but it shifts different than the passenger automatics I'm used to... There seem to be RPM related shift points and easing back on the throttle doesn't necessarily cause an upshift...

A web search yielded many, many ads for trucks for sale but not much on shift points or user instructions... Anyone got pointers or experience with something like this?

Thanks in advance,

Carla

As the test pilot climbs out of the experimental aircraft, having torn off the wings and tail in the crash landing, the crash truck arrives; the rescuer sees a bloodied pilot and asks, 'What happened?' The pilot's reply: 'I don't know, I just got here myself!' - Attributed to Ray Crandell (Lockheed test pilot) [/quote]

Aside from my 3/4 ton GMC Duramax/Allison, and riding a fair number of city, Greyhound, and airport shuttle buses, my only experience with a truck close to yours is the Isuzu 20,000 gvw 20' box truck at work. It's automatic and all everyone who drives it does is drop it into drive and go. No one at the used truck dealership we bought it at or the shop that maintains it for us has ever suggested anything different, and none of those bus drivers ever manually shifted either :-).

----- Regards, Carl Ijames

..> We just acquired a 1997 GMC C7500 truck with Cat 32 series diesel engine

Carla, the people in this group are great folk, but with all due respect, I'd go to a GMC truck dealer and have their mechanics look it over and explain it to you.

(and if you are short on cash to do it, get a business loan to help you out)

That's the sort of things that many dealerships will do for free, either because they're nice people or because they think it'll bring you back for repair work, or both.

Wouldn't that information be in the owner's manual, though?

Just drop it into Drive and put the pedal to the metal. On a medium/heavy deisel the shifting is a bit different because you are running the engine on a governor and there is no manifold vacuum. On a car, backing off the throttle raises the vacuum, accellerating the upshift.Even on Diesel V-Dubs the shifting is "strange" to anyone who normally drives a gas engined automatic.

For normal driving just drop it into D and go. The others are used if you want to prevent the trans from shifting up to a higher gear.

Heavy truck automatics shift different than most cars. Will feel strange till you get used to it.

I have a Ford F650, I just leave it in D. It does shift differently.