Lurching while reversing uphill

Nanotech Environmental · August 7, 2017

When I go to reverse uphill, I find it a bit tough to properly modulate slow speeds with the pedal. When the pedal is pressed, it's like there is nothing, nothing, nothing, then waaay too much and the truck lurches backwards. Not a big deal when there is open space behind, but it a bit of an issue when trying to hook up to a trailer or back into a tight spot.

I find I have to use the brakes and gas at the same time to maintain some semblance of control.

Anyone else have this issue?

I have done the gas pedal mod, so not much to improve there. Is there something in the software that can be changed to address this?

jono20 · August 7, 2017

I noticed the same thing when I was at my dad's house a few weeks ago. Was trying to park behind another vehicle on his driveway and found it really difficult to control while backing up, just as you described.

slopra · August 7, 2017

I'll add a tally to the count of people who have noticed this.

I plan to have the 3x flush, and any updates applied to the transmission in the next month or so when I have time to address shifting issues. I'll report back if that ends up possibly improving it. I back into an uphill driveway as close to my garage as possible so I notice it daily.

Mackdriver · August 8, 2017

Do you have hill assist? I've found my 17 slt does pretty much what you describe, and I was worried a bit until I saw the "hill assist active" while it was happening a couple times. It's only when I'm reversing uphill that I felt it do that, and when I saw the message on screen it all made sense.

Nanotech Environmental · August 8, 2017

I don't believe I have hill assist on mine....

TheBlackPearl · August 8, 2017

I've only "booped" the garage door once while backing up to it...

It didn't leave a mark, thankfully.

dorkweed · August 8, 2017

http://www.gm-trucks.com/forums/topic/167606-gas-pedal-flex-solution/page-1

silveradosid · August 8, 2017

3beejaay3 said he did the pedal mod and no change

Thomcat · August 8, 2017

My Silverado does it too! But so does my Malibu, my Impala and the AWD Traverse. And so does about every other of the dozens of vehicles with auto transmissions. Think it's hard with an auto tranny; try it with a newer manual with hill assist like my old '15 Camaro! Forward is no problem because you have hill assist, but in reverse you have to simultaneously release the clutch, handbrake and feed gas precisely or you'll either stall and roll forward or chirp tires and lurch in reverse.

Anyone ever try driving in San Francisco with an older model auto tranny without the hill hold feature; you have the same situation both in reverse and forward? It's harder to modulate speed in reverse because the engine is fighting against both gravity and fluid slippage in the torque convertor and the driver is attempting to compensate using only the gas. This is very hard to modulate with only the gas because if not fed quick enough the vehicle will roll forward, too fast and you get a lurch as the torque convertor locks - doesn't happen on a hill facing forward because the newer trannys have the hill hold feature which prevents rollback if the gas is fed too slow and release when the correct threshold is reached.

Solution when backing up in reverse is the same as it was in the older trannys without rollback prevention when starting from forward or reverse on a hill - Power Braking - drive with two feet working and balancing the brake and gas at the same time. Takes a little bit of practice and skill - that's why it is now standard on most vehicles - to dumb down the skill level needed to control a vehicle. Guess it's time for another dumb down feature and add a hill hold feature for driving in reverse!

Nanotech Environmental · August 8, 2017

My Silverado does it too! But so does my Malibu, my Impala and the AWD Traverse. And so does about every other of the dozens of vehicles with auto transmissions. Think it's hard with an auto tranny; try it with a newer manual with hill assist like my old '15 Camaro! Forward is no problem because you have hill assist, but in reverse you have to simultaneously release the clutch, handbrake and feed gas precisely or you'll either stall and roll forward or chirp tires and lurch in reverse.

Anyone ever try driving in San Francisco with an older model auto tranny without the hill hold feature; you have the same situation both in reverse and forward? It's harder to modulate speed in reverse because the engine is fighting against both gravity and fluid slippage in the torque convertor and the driver is attempting to compensate using only the gas. This is very hard to modulate with only the gas because if not fed quick enough the vehicle will roll forward, too fast and you get a lurch as the torque convertor locks - doesn't happen on a hill facing forward because the newer trannys have the hill hold feature which prevents rollback if the gas is fed too slow and release when the correct threshold is reached.

Solution when backing up in reverse is the same as it was in the older trannys without rollback prevention when starting from forward or reverse on a hill - Power Braking - drive with two feet working and balancing the brake and gas at the same time. Takes a little bit of practice and skill - that's why it is now standard on most vehicles - to dumb down the skill level needed to control a vehicle. Guess it's time for another dumb down feature and add a hill hold feature for driving in reverse!

My 06 Sierra 1500 was never lurchy like this one is. Nor was any other vehicle I've driven(both automatics and manuals). I'm talking about in the same exact conditions(my driveway) Yes, I did have to do a bit more throttle manipulation than when on flat ground, but nothing like how it is on my 17. I do use the 2 pedal method to compensate, but it's not a solution. I suspect it may have something to do with drive by wire, as opposed to the old school throttle cable connecting the pedal to the throttle body on the 06.

It could be the calibration on the gas pedal assembly........because when I push the pedal down a bit in reverse, going uphill, nothing happens. Then when I push it a bit more, nothing happens, Then still a bit more and suddenly the engine speed 'catches up' to where it should be, and the vehicle lurches. I'd suggest that the torque converter is only a secondary potential contributing issue. The main factor appears to be that the engine doesn't gain speed properly in a linear manner, in relation to the pedal being pushed small amounts in those specific circumstances.

Thomcat · August 8, 2017

My 06 Sierra 1500 was never lurchy like this one is. Nor was any other vehicle I've driven(both automatics and manuals). I'm talking about in the same exact conditions(my driveway) Yes, I did have to do a bit more throttle manipulation than when on flat ground, but nothing like how it is on my 17. I do use the 2 pedal method to compensate, but it's not a solution. I suspect it may have something to do with drive by wire, as opposed to the old school throttle cable connecting the pedal to the throttle body on the 06.

It could be the calibration on the gas pedal assembly........because when I push the pedal down a bit in reverse, going uphill, nothing happens. Then when I push it a bit more, nothing happens, Then still a bit more and suddenly the engine speed 'catches up' to where it should be, and the vehicle lurches. I'd suggest that the torque converter is only a secondary potential contributing issue. The main factor appears to be that the engine doesn't gain speed properly in a linear manner, in relation to the pedal being pushed small amounts in those specific circumstances.

.02 Just had to try it to see what's up and I was wrong about one thing Hill Start Assist is active when going uphill in both Forward and in Reverse. Never noticed that the hill start assist message also lights up in the DIC when in reverse, probably too busy turning around or looking at the backup camera screen.

Either way it can be easily modulated with gas only without having to resort to power braking. Going uphill in reverse the truck remains stopped once the foot is removed from the gas and brake while the engine is idling. Slow even increase of the gas from idle to the point where the brakes release the wheel and it slowly moves rearward - works evenly both on the shallow and steep parts of the driveway. A little stiffer on the gas gave a quicker release but no lurching because the brakes (hill assist braking) release between about 800-1000 rpm. Release is a slight bit more noticeable in reverse than forward - figure that could be due to a different gear ratio in R than 1st. Once released I can crawl as slow as I want or easing on the gas until stopped in reverse without using the brake pedal, when the engine rpm balances the slippage in the torque convertor. HSA won't re-engage until the brake is cycled.

No dead spot at all in the gas feed - nice even climb of rpm and that is likely the problem if it does lurch - a flat spot in the pedal will cause the HSA to release abruptly at a higher rpm - but then shouldn't the same condition be noticeable going forward from a stop on a hill???? Truck has grade decent control, but that switch was unlit/inactive. also has motorized pedals which might account for a more stable, less flexible mount of the gas pedal assembly making it easier to modulate. If the gas pedal mount is stable a flat spot or sudden rpm jump could be a faulty gas pedal servo or if HSA is active the controlling software for the release of the HSA braking may be set at too high an rpm..

Nanotech Environmental · August 8, 2017

I don't believe that mine has hill start assist. If I let of the gas backing up a hill, it will roll forward.

Thomcat · August 10, 2017

Seems without a hill start assist, the only solution is to power brake on a steep hill otherwise the engine is fighting both gravity and the torque convertor.Try it with a single foot and as soon as you're off the brake a load is placed trying to slow the engine from idle - could be the newer more efficient turbines aggravate the situation in newer models.