acceleration thump, deceleration bump

SoCalSilvo · April 11, 2018

2016 Silvo Crew Cab 5.3 - every now and then will get a bump (after stopping) like someone just tapped the bumper (I see the tach 'downshift').... Dealer says it's the gas tank, has to do with the amount of gas in the tank. But, i'm not hard stopping all the time... also why would 26 or less gallons of gas cause even a light duty truck to feel like a car just shifted the truck much less make the tach needle move. Kind of concerning, bought it to tow a 26 foot travel trailer and now I have to worry about the gas tank shifting?

Recently started getting a thump when accelerating from a dead stop... imagine a 2 liter soda bottle in the bed, hits the tail gate after you get going.... almost every single time, even a slow acceleration. Dealer says it's normal to keep the diff from ceasing/getting frozen... What? had an s-10 back in the day, followed by a 2003 silverado which didn't do either even after 10 years of abuse... warranty is almost up, I've driven other new cars that don't do this, why is this 'normal' for these brand new trucks? (sorry, I tried to search and look through the posts, didn't come across something similar... dealer did admit I'm not the only one complaining about these 2 issues)

Sierra706 · April 11, 2018

2016 Silvo Crew Cab 5.3 - every now and then will get a bump (after stopping) like someone just tapped the bumper (I see the tach 'downshift').... Dealer says it's the gas tank, has to do with the amount of gas in the tank. But, i'm not hard stopping all the time... also why would 26 or less gallons of gas cause even a light duty truck to feel like a car just shifted the truck much less make the tach needle move. Kind of concerning, bought it to tow a 26 foot travel trailer and now I have to worry about the gas tank shifting?
Recently started getting a thump when accelerating from a dead stop... imagine a 2 liter soda bottle in the bed, hits the tail gate after you get going.... almost every single time, even a slow acceleration. Dealer says it's normal to keep the diff from ceasing/getting frozen... What? had an s-10 back in the day, followed by a 2003 silverado which didn't do either even after 10 years of abuse... warranty is almost up, I've driven other new cars that don't do this, why is this 'normal' for these brand new trucks? (sorry, I tried to search and look through the posts, didn't come across something similar... dealer did admit I'm not the only one complaining about these 2 issues)

Check to see if your spare tire is properly fastened.

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Squirrely · April 11, 2018

I've had this issue on my old 95. Always felt like something bumped me when I stopped. If I threw weigh in the back, it would stop. I'm convinced it was the leaf springs.

wforrest08 · April 11, 2018

43 minutes ago, SoCalSilvo said:

I've driven other new cars that don't do this, why is this 'normal' for these brand new trucks? (sorry, I tried to search and look through the posts, didn't come across something similar...

It’s not normal. Sounds like to me you need a new dealer, one that can diagnose problems...

If your going to continue to do business with this dealership I would strongly recommend getting written documentation from them about your complaints before your warranty is up so you’ll have proof that you should have had it fixed inside your warranty period.

If it’ “normal” find a 16 or 17 on their lot equipped the same as yours same motor same tranny same driveline 2wd/4wd. Ask to/tell them you want/are going to drive it. When it doesn’t make the same noise/bump as yours ask them if that one is not operating normally like yours why they haven’t fixed it. Ask the nice guy who claims this is all normal to ride with you in both trucks to compare differences.

You didn’t mention which transmission you have the 6 or 8 speed. But if I were you I’d read though some of the threads on them especially the 8 if that’s what you have and see if anybody else’s complaints sound like your describing at least as far as the bump. I haven’t read though a lot of them and there are A LOT to know since my 15 has the 6 and has been relatively well behaved. I’ve yet to hear gas sloshing in any K2 I’ve been in yet.

Also there is a long thread about the rear springs on these trucks making noise and see if anybody’s complaints match yours as far as the thump. My 15 does have the spring noise but I seldom hear it’s definitely not all the time. On mine I can duplicate the noise by shaking either box side back and forth side to side.

SoCalSilvo · April 11, 2018

dealer stated it checked suspension, I'll make sure spare is nice and tight when i get it back tomorrow. the thing that concerns me is that it's not just noise, you can feel it. don't get me wrong, it's a truck, not looking for a smooth cadi ride.... but these two things are not happening after a bump, hard stop or fast take off....

SoCalSilvo · April 11, 2018

thank you for the replies gentlemen and thank you wforrest08 for the advise and links, I have the 6, LT trim, with I believe the 3.73 gears... the horrible 'downshift' after the truck has stopped is one thing (even though the gas tank excuse doesn't fly with me), but for it to start to have that thump after take off about 2 years later and it's the differential trying to save itself... not cool.

blue_bullet · April 11, 2018

Toyota 4Runners need to have the drive shaft slip joint lubed to prevent "loading/unloading" of the shaft when stopping at a traffic light. Don't know if GM drive shaft has that grease fitting on the drive shaft.

Just a thought.