Quick question on downshifting...

KARNUT · November 1, 2019

downshifting and downshifting to slow down similar to using the brakes are 2 very different things. Every auto obviously downshifts. If you use manual mode and down shift into a high rpm to slow the truck, then that is bad for the trans. Your still putting force on the trans and internals.

Everything wears out eventually. I never wore out a transmission downshifting. I did it when I felt spunky. Pretty much always with a stick. Having fun with your ride in moderation, nothing wrong with that. My stroked blown 383 is going on 9 years now no failures. And I downshift among other things. Even burn rubber.

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fatwhiteboy · November 1, 2019

GM Powertrain experts say to not use your transmission as an engine brake because it builds up unwanted internal pressure. I am guilty, I do use all of my vehicles transmissions to slow down. My Jeep brakes are like Fred Flintstone putting his feet down to stop, downshifting has saved me from some bad crashes. The pros say don’t do it with ours torque converter trans but pretty much everyone I know that drives a bit more aggressive does. We do not have paddle shift or a manual stick like Ford but look at all of the GM cars that do. When in manual mode you are constantly up and down shifting using the paddles. I am not a powertrain expert but I have had many vehicles and broke a ton of stuff but never a trans from downshifting.

Grumpy Bear · November 1, 2019

You guys do know your transmission is equipped with Grade Logic Control, right? It downshifts automatically IF in cruise control. I don't know about your T1's but the K2's have a button on the end of the shift lever to disengage this feature. When in manual and off cruise the up and down button has a purpose. Pretty sure KARNUT mentioned this a few pages back.

MaverickZ71 · November 1, 2019

1 hour ago, mistaare said:

Just picked up a GMC 1500 last week, coming from 11 years in a 6spd Tacoma.

Two questions:

1. when in/after the break-in period can I start downshifting to help the brakes, we have some short steep hills here in the north east.
2. does downshifting and coasting use more or less gas when the RPM’s are 3g’s and you are just coasting?

thanks for any input!

The GM 1500 brakes ain't that whippy. Not towing and unloaded, I find myself stepping on the brakes 1/2 block sooner than I ever did with any other vehicle I've driven. I've blown through red lights that changed right in front of me where I see it's safe, just because I know I'll be in the middle of the intersection before it finally gets stopped. And putting the transmission into manual mode just makes your RPM's go up, it doesn't really slow you down much, as these new engines with their light flywheels and loose piston rings aren't much on compression braking.

Donstar · November 1, 2019

I downshift with manual transmissions and on very rare occasions will use an automatic to slow me down. I shift with an automatic for entertainment and do not fool myself into thinking there are any net benefits from my labor!

Wiggums · November 1, 2019

There's a hill that drops about 350 feet within half a mile. The worst part is that the speed limit drops from 50 to 35 in the middle and at the end is a stop light that is ALWAYS red.

I am going to try the cruise control. I don't want it to brake.

mistaare · November 1, 2019

Wow, these are great responses.

Maybe I should have been more clear (I didn’t expect this discussion). I am not driving around using my automatic transmission as a standard. I am slowing down at the top of steep hills, down shifting (with or without a trailer), then coasting downhill where I have to either a) stop halfway down or at the bottom or b) have to maintain a MUCH slower speed than coasting and don’t want to ride the brakes.

I do appreciate all the responses but the original question was asking if it saves fuel (Says 99 mpg on the screen) or uses more since the RPM’s are running 3-4g. And when I can start, since I am still in the break in period.

I would much rather only get (hypothetically) 200,000 miles out of the drivetrain instead of 300,000 if that means not burning up my brakes, warping my rotors, having to use an emergency run off ramps, losing my brakes completely etc aka not putting my families life in danger. I am talking about hills where these incidents happen.

Not to start a big argument, but why would manufacturers give you that option if it was so damaging and/or useless? When I was first learning how to drive back in the late 80’s I almost killed my self riding the brakes of my ‘79 ford club wagon. Had not brakes FLYING down this hill, rotor were so warped it would shake the steering wheel violently. Afterwards my dad, our mechanic and several others said nonchalantly “dipsh$t, your supposed to down shift down big hills!!!!” I have been driving a stick ever since!

thanks again for the feed back

Cpl_Punishment · November 2, 2019

From what I've read elsewhere on this forum, any time you're coasting while in gear, the torque converter drives the transmission, allowing the fuel injectors to close. So you shouldn't be burning any fuel, regardless of rpm.

RaisedByWolves · November 2, 2019

On 11/1/2019 at 4:46 PM, ct_corey said:

downshifting and downshifting to slow down similar to using the brakes are 2 very different things. Every auto obviously downshifts. If you use manual mode and down shift into a high rpm to slow the truck, then that is bad for the trans. Your still putting force on the trans and internals.

My first post on this board.

You have no idea what you're talking about.

I have routinely beat the hell out of GM trucks for 30+ odd years and have done things that would probably make you cry and look for a safe space.

My last truck is sitting in the yard with a rusted out frame and only 190K on the ODO and it still runs and drives like a champ. Im pretty sure the drive train would go 300K is it hadn't rotted out.

The article you linked was advice for old ladies and low information drivers and is not vehicle specific.

ct_corey · November 3, 2019

1 hour ago, RaisedByWolves said:

My first post on this board.

You have no idea what you're talking about.

I have routinely beat the hell out of GM trucks for 30+ odd years and have done things that would probably make you cry and look for a safe space.

My last truck is sitting in the yard with a rusted out frame and only 190K on the ODO and it still runs and drives like a champ. Im pretty sure the drive train would go 300K is it hadn't rotted out.

The article you linked was advice for old ladies and low information drivers and is not vehicle specific.

Haha you are funny! Do you have a new t1 series truck? Not sure where you get your drugs but these new trucks are NOT 300k trucks. Neither was the last 2 generations.

RaisedByWolves · November 3, 2019

16 hours ago, ct_corey said:

Haha you are funny! Do you have a new t1 series truck? Not sure where you get your drugs but these new trucks are NOT 300k trucks. Neither was the last 2 generations.

So whether I have "XXX" matters in this discussion?

Why are you deflecting from the topic of downshifting?

Wiggums · November 3, 2019

24 minutes ago, RaisedByWolves said:

So whether I have "XXX" matters in this discussion?

Why are you deflecting from the topic of downshifting?

It's a debating tactic.. a very cheap one, if you ask me. I have never heard of people being told, "It needs to be replaced because you downshifted a lot." When you downshift, you're actually going the other way with the transmission teeth, the parts that very rarely get used. You're FAR more likely to be using the opposite side of the teeth that gets worn out anyway. He thought that engines wear out a lot if you downshift too, it doesn't. Shows how much he knows.

RaisedByWolves · November 3, 2019

28 minutes ago, Wiggums said:

It's a debating tactic.. a very cheap one, if you ask me. I have never heard of people being told, "It needs to be replaced because you downshifted a lot." When you downshift, you're actually going the other way with the transmission teeth, the parts that very rarely get used. You're FAR more likely to be using the opposite side of the teeth that gets worn out anyway. He thought that engines wear out a lot if you downshift too, it doesn't. Shows how much he knows.

Fun fact, trans clutch packs dont know the difference between slipping CCW or CW, all they know is they have a job to do.. You are correct about the gears.

With my 01 Silverado I loved downshifting to hear the exhaust burble. @ 70mph into 3rd down to 50mph and into 2nd it sounded great.

Hell, when I was into wheeling every weekend I would run a sand course the quad guys set up in 2nd gear and 4low. This would allow me to rip around the track using the gas pedal as both gas and brake for a shit ton of control over vehicle speed and direction.

I had the motor out at 120K for an oil pan leak and found the flex plate shattered in the center form doing the above (Most likely) and the trans never gave me one bit of trouble.

I even kept that one as a souvenir.

And just to satisfy your curiosity as to what I own. That is the rotted out and still running stronk 01 in the background.

Edited November 3, 2019 by RaisedByWolves

anthony2558 · November 3, 2019

Just use your brakes, and tow mode. This is such a stupid question....

Edited November 4, 2019 by anthony2558

oldmann · November 11, 2019

Feel free to use the trans to slow down on hills. You will not hurt a thing. These people have no idea what it is like to drive in mountains or hills. The brakes will fail if you don't use the trans to slow down. As far as gas mileage, who cares. Safety first.