Nnbs Drivetrain Hesitation

[DanMan_S]

I accidentally posted this in the tech how to forum but nothing came of that so here we go again:

 

I just picked up a 2007 Vortecmax Silverado 4x4 last week and am noticing a significant hesitation/metallic bang when you hit the gas in tow/haul mode. Anyone else have something like this?

 

 

If you're in tow/haul mode, get off the gas and let it coast for a few seconds (so that it shifts into OD and goes into V4 mode), then hit the gas pedal again there is a significant pause before the truck actually starts to move and when it does it feels like something kicked you in the back of the seat. It usually happens hard enough to result in a metallic bang from under the truck (I assume the drivetrain slack).

 

What the heck is causing this?

[asilverblazer]

I've noticed I can catch my truck by surprise... If I suddenly press the accelerator to the floor, there is occasionally a 1-2 second delay, so that instead of being thrust back into the seat you actually fall forward as when you let off the gas. Then when the truck realizes you mean buisness and quits playing with itself and opens the throttle you get a huge burst of power. I chock (or is it chaulk) it up to torque management.

[grimmysnr]

I've noticed I can catch my truck by surprise... If I suddenly press the accelerator to the floor, there is occasionally a 1-2 second delay, so that instead of being thrust back into the seat you actually fall forward as when you let off the gas. Then when the truck realizes you mean buisness and quits playing with itself and opens the throttle you get a huge burst of power. I chock (or is it chaulk) it up to torque management.

 

 

Same here. The PCM learns though. When i first bought the truck it did it at every stop light and then went away. I did some maintenance the other day that made me pull the negative batt cable (which resets the PCM) and then it came back. ITs been about a 2 weeks since then and now i dont notice it anymore. I think the PCM just needs to learn your driving style.

[DanMan_S]

In Tow/Haul, how often does the torque converter lock?

[redvett]

TCC stays locked most of the time but transmission downshifts a gear or two in hills.

[mudcruiserman]

 

this may be related to the drive by wire system for the gas pedal

 

[07Sierra07]

I accidentally posted this in the tech how to forum but nothing came of that so here we go again:

 

I just picked up a 2007 Vortecmax Silverado 4x4 last week and am noticing a significant hesitation/metallic bang when you hit the gas in tow/haul mode. Anyone else have something like this?

 

 

If you're in tow/haul mode, get off the gas and let it coast for a few seconds (so that it shifts into OD and goes into V4 mode), then hit the gas pedal again there is a significant pause before the truck actually starts to move and when it does it feels like something kicked you in the back of the seat. It usually happens hard enough to result in a metallic bang from under the truck (I assume the drivetrain slack).

 

What the heck is causing this?

 

Are you talking about a driveline clunk similar to with the older style had?

Basically when rolling slower let off the gas and coast and then press the gas again it 'clunks'?

[DanMan_S]

 

this may be related to the drive by wire system for the gas pedal

 

 

Maybe but my 05 Silverado would never do it.

 

From observations and using my dashhawk, it appears that in tow/haul mode the transmission won't upshift when you take your foot off the gas, instead it unlocks the torque convertor and the engine drops to an idle. Then when you hit the gas again the engine revs up and the torque convertor relocks, suddenly taking up the slack in the drivetrain.

[07Sierra07]

I've noticed I can catch my truck by surprise... If I suddenly press the accelerator to the floor, there is occasionally a 1-2 second delay, so that instead of being thrust back into the seat you actually fall forward as when you let off the gas. Then when the truck realizes you mean buisness and quits playing with itself and opens the throttle you get a huge burst of power. I chock (or is it chaulk) it up to torque management.

 

Hrm, so I'm not theonly one with the delay then.... shortly after getting the truck I almost had a couple of accidents with it. I would hit the throttle to the floor to change lanes to get around someone to find that the truck would pretty much fall flat on it's face for about 2 seconds before going anywhere..... Now I don't rely on the "367" HP under the hood as it's only available to me when the truck decides it should be. Truck is about 3 months old... I'll have to 'test' 'er out again to see if she's learned how to behave!

[DanMan_S]

Are you talking about a driveline clunk similar to with the older style had?

Basically when rolling slower let off the gas and coast and then press the gas again it 'clunks'?

 

I'm not too familar with the older clunk as my GMT800 never displayed any of this behavior. I'm only experiencing it in tow/haul mode and it hits hard enough that you think something in the drivetrain is going to break. I'm scared of what would happen if I was coasting and then had to pin the throttle to the floor...at partial throttle it hits really hard already.

.

[07Sierra07]

Are you talking about a driveline clunk similar to with the older style had?

Basically when rolling slower let off the gas and coast and then press the gas again it 'clunks'?

 

I'm not too familar with the older clunk as my GMT800 never displayed any of this behavior. I'm only experiencing it in tow/haul mode and it hits hard enough that you think something in the drivetrain is going to break. I'm scared of what would happen if I was coasting and then had to pin the throttle to the floor...at partial throttle it hits really hard already.

.

 

 

Yours never did it? My 04 Sie did it from day 01!

I'll try to describe the driveline clunk,,,

Basically if your coasting with or without tow/haul on (mine was worse with tow/haul on) and you press the gas even just a little bit their seemed to be a severe clunk when the torque conv. would lock up.... I would like to have heard it outside the truck........ After the torque locked up though it could not be reproduced...

[DanMan_S]

Yours never did it? My 04 Sie did it from day 01!

I'll try to describe the driveline clunk,,,

Basically if your coasting with or without tow/haul on (mine was worse with tow/haul on) and you press the gas even just a little bit their seemed to be a severe clunk when the torque conv. would lock up.... I would like to have heard it outside the truck........ After the torque locked up though it could not be reproduced...

 

Yeah, my 05 never did but the 07 is doing it like crazy in tow/haul. With tow/haul off it has no problems whatsoever but I like the more immediate downshifts in tow/haul.

[asilverblazer]

I've noticed I can catch my truck by surprise... If I suddenly press the accelerator to the floor, there is occasionally a 1-2 second delay, so that instead of being thrust back into the seat you actually fall forward as when you let off the gas. Then when the truck realizes you mean buisness and quits playing with itself and opens the throttle you get a huge burst of power. I chock (or is it chaulk) it up to torque management.

 

Hrm, so I'm not theonly one with the delay then.... shortly after getting the truck I almost had a couple of accidents with it. I would hit the throttle to the floor to change lanes to get around someone to find that the truck would pretty much fall flat on it's face for about 2 seconds before going anywhere..... Now I don't rely on the "367" HP under the hood as it's only available to me when the truck decides it should be. Truck is about 3 months old... I'll have to 'test' 'er out again to see if she's learned how to behave!

 

 

I haven't noticed mine doing it lately. but I've been driving more conservatively to try a squeeze some more mpg's out of it.

[DanMan_S]

From playing around with my dashhawk I'm willing to put money on it being the torque convertor. When you get off the gas in tow/haul the engine doesn't upshift, it merely unlocks the torque convertor as you coast. When you hit the gas again it pauses and then relocks the torque convertor leading to the sudden clunk.

[ChrisNJ]

Hrm, so I'm not theonly one with the delay then.... shortly after getting the truck I almost had a couple of accidents with it. I would hit the throttle to the floor to change lanes to get around someone to find that the truck would pretty much fall flat on it's face for about 2 seconds before going anywhere..... Now I don't rely on the "367" HP under the hood as it's only available to me when the truck decides it should be. Truck is about 3 months old... I'll have to 'test' 'er out again to see if she's learned how to behave!

 

 

Welcome to the new world of torque management through electronics. very bogus. hoping mack or freightliner come out with a good truck for us soon to beat this CAFE government crap. when i was test driving the nbs's, the same thing happened to me, and i wouldn't buy it, then i drove a 6.2 in a denali and it was gone, just gotta wait a little for the trans to shift now, but much, much better, ohhh, and a lot more $. others here have said some of the hesitation will go away with time, hopefully it will.