A general transmission question applying to all vehicles

[DZink24]

On an automatic transmission, what is the purpose of gear selections 1,2, ect. I have seen some vehicles with a "3", and some of our trucks at work even have a "4" gear, as well as the typical "D". I have seen some owner manuals say that they can be used for city driving, but as any of you with a 48RE and 4:10 gears know, our motors are screaming pretty good as low as 30 mph with the selector in "2". And not for nothing, thats why they call it an "automatic". Put it in "D", and go!



It's most likely a simple explanation as to why they are designed this way, let's hear it!

 

[fox]

It's the easiest way! Manual gear selection is sometimes needed, engine braking is one need.

 

[JoeBioDiesel]

There are times when I'm rolling along off road, or in a traffic jam and I don't want it to upshift, or like fox said, for engine braking. Most drivers, however, don't use anything other than the OD range... which is OK too.

Joe

 

[PToombs]

If it's slippery out, you can put it in 2nd and it will start there. Less torque to the wheels to cause a spin. I've had to do this in a blizzard with a service truck.

 

[fox]

No, they still start in 1st!!! Just can't get past the gear you select.

 

[Allnew2Me]

My old Ford C6 would start in second gear and stay there when the selector was placed in 2, but ours (mine at least) just stop in 2.

 

[PToombs]

The one I was referring to was a '95 chevy 3500. It started in 2nd. Sorry I wasn't clear. My CTD is a stick. I'll have to try my '95 gasser, never did it on that.

 

[jwgary]

If I remember correctly from the description in my service manual, there is a difference in 1st gear selected by the transmission and 1st gear selected on the tree. Something in the valvebody is different even though you are in the same gear. Other than that it's just as Fox said, you start in 1st and go up to whatever gear you have limited as your top gear. Of course if your pressure sensor or governor have failed you will start out in 3rd gear.

 

[TWilkening]

There is some band that will apply if you manually put it in 1st. I know Dave Goerend recommended manually doing it when towing heavy on a stock transmission.

 

[JoeBioDiesel]

The rear band comes on in Low1, but only to stop the rear roller clutch from overrunning. This provides engine braking when needed. The reason some builders recommend starting on Low1 for heavy towing is that the rear band will help share some of the load that would normally be on just the rear roller clutch. Now you have 2 components holding the rear planetary gear stationary instead of just 1.

Hope that makes sense... but probably doesn't unless you've been inside an automatic trans.

Joe