PRNDM_1

[ttopcamaro86]

New to the Duramax/Allison, but long time gm driver. My ? is: What is the 1 just past the M which I know is the manual top gear limiter, and is it different than M1? I did do a search here and the internet but didn't have any luck finding anything. Also not in my manuals, or either I missed it. Thanks for any help.

[RyanbabZ71]

Check your manual, usually good reading material.

 

Start at page 307

 

https://www.chevrolet.com/content/dam/Chevrolet/northamerica/usa/nscwebsite/en/Home/Ownership/Manuals_and_Videos/02_pdf/2015-silverado-2500hd-3500hd-owners-manual.pdf

[ttopcamaro86]

Thank you Mr Ryan for the reply. I did re-read my manual at your reference point. Still doesn't mention the 1. Maybe I missed it again.

[ttopcamaro86]

And as stated in the original post I found the manual a wealth of knowledge, just doesn't explain the 1.

[SMiller]

1 is simply 1st gear, will not upshift, using M1 does the same thing, no reason to have a 1st gear slot since M1 is the same but whatever.

[ttopcamaro86]

That's it! Thank you

[ttopcamaro86]

Side note: if that is the case the 1 is useless (as you said). Was hoping it was "granny low" of long ago.

[aminga]

The last position is manual only mode. Transmission will be locked in that gear and will not upshift or downshift.

[SMiller]

The last position is manual only mode. Transmission will be locked in that gear and will not upshift or downshift.

Yes but having said that using M1 also will lock it into 1st gear and not allow a upshift or downshift...

[ttopcamaro86]

Just a mysterious little 1 that has no use.

[[email protected]]

I read somewhere, I cant recall where, that if youre driving along and need to get max transmission grade braking you can just drop in straight into the 1 and it will max out the downshifts. I've tried it on a few GM/Chev trucks from work with the 6.0 and thats exactly what it does.

[ttopcamaro86]

Whew that sounds violent, lol. Too scared to try that. Afraid it will go into first at let's just say 60 mph and cause the dmax to rev to 100,000 rpm, not good.

[Cowpie]

Yeah, that may be true, but I am not going to try it any time soon.

[SMiller]

I read somewhere, I cant recall where, that if youre driving along and need to get max transmission grade braking you can just drop in straight into the 1 and it will max out the downshifts. I've tried it on a few GM/Chev trucks from work with the 6.0 and thats exactly what it does.

While that is true, once again you can drop to M1 and it will also downshift as much as it can without going into the rev limiter.

 

For those that are to scared it is nothing different then what the engine grade braking feature does, it will not over rev or harm the motor, simply downshifts as much as it safely can.

[[email protected]]

Exactly. I haven't figured out the purpose of it either. Other than maybe saving a couple steps of one shift then a bunch of taps vs dropping shifter all the way down in a hurry maybe.

 

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