Trasmission Bump On Nbs

neto1978 · April 14, 2008

I've noticed when I stop at a light for a few, the transmission "bumps" a little. Almost as if someone barely tapped the rear bumper with their car. It doesn't do it all the time and it's usually after waiting at a light in Drive with my foot on the brake for at least 5 seconds.

I read a lot about it ,but no clues at all.

Questio: Is there any TSB or resolution for it ,or is it normal?

tks

jscan · April 14, 2008

I have an 08' Sierra 2500hd with about 1k miles, I am having the same problem, just a slight thump at a stop. Hope u get an answer, let me know.

dannyg2006 · April 14, 2008

I have had the same problem now for 25,000 miles. Just haven't had time to take it in yet. Mine also shifts hard into second every now and then.

jackus · April 14, 2008

I have had the same problem now for 25,000 miles. Just haven't had time to take it in yet. Mine also shifts hard into second every now and then.

Does it do those hard shifts when the tranny is cold that may be why. I have noticed those bumps too i always believed it was a late down shift from second to first and it causes that bump because nothing is spinning in there, i have never worried much about it

Huntervh · April 16, 2008

Same issue with my NBS, took it to the dealer and they said they could not replicate the problem. It happens cold, hot, towing not towing.

It seems to happen most when slowing down quickly.

cdmm151 · April 16, 2008

Same issue with my NBS, took it to the dealer and they said they could not replicate the problem. It happens cold, hot, towing not towing.

It seems to happen most when slowing down quickly.

Sounds like the same issue that plagued the trucks in the mid 1990s. It is possibly the drive shaft moving on the yoke of the tranny. the fix is to apply prop grease to the splines. If you talk to a GM mechanic that was around during that time he know what you are talking about.

neto1978 · April 16, 2008

Same issue with my NBS, took it to the dealer and they said they could not replicate the problem. It happens cold, hot, towing not towing.

It seems to happen most when slowing down quickly.

Sounds like the same issue that plagued the trucks in the mid 1990s. It is possibly the drive shaft moving on the yoke of the tranny. the fix is to apply prop grease to the splines. If you talk to a GM mechanic that was around during that time he know what you are talking about.

With all due respect ,I had a 1995 turbo diesel 1500 silverado 4L80E ,drove 160.000 miles and never had an issue like that ,it's not a grease issue ,it's more like a software that GM could't fix YET.it happened at the first 100 miles in my brand new NBS .

2007 HD · October 1, 2008

I have the same issue. Bumps when at a stop and the 2nd to 3rd shift is almost always twice as firm as any other shift. I have 2007 2500HD NBS. Any resolution on this? I haven't had time to take it in yet.

C6Racer · October 3, 2008

Well, it's normal to feel the transmission downshifting as you're coming to a stop. It almost feels as if the brake rotors were warped. This is how it is on all my family's GM trucks and vans, anyway. Doing this while it is stopped, on a new truck, does seem like it would be PCM related. My trans has gotten stuck in 2nd when coming to a stop a few times, but I think that's because I beat the crap out of it daily. I would step on the throttle to start going and all it does is rev up the engine a bit and barely moves, then BAM, it shifts into first. It even chirps the tires when it does that. If I were you guys I'd keep bugging the dealer, maybe even try a few different locations. Somebody has to feel it sooner or later.

Ranger · October 4, 2008

Dumb question, how much gas has everyone had when this occurs? I've heard from a while ago that sometimes it's just the gas sloshing back and forth, but I don't seem to get this effect even at a 3/4 tank and hard stop.

Chris's 07 · October 5, 2008

My nbs does the same thing more when i am doing city driving going a block stopping and then going a block stopping etc,dealer said it was normal just trans downshifting but i dont know about that

Darkanion · October 5, 2008

You guys might want to check out this thread :

http://www.gm-trucks.com/forums/index.php?showtopic=72456

irengineer · October 8, 2008

There have been quite a few posts over time for the 2007 HD NBS 6.0L/6Spd Truck regarding bumps after coming to a stop with your foot on the brake, often at a stop light.

While discussion of these posts have ventured into areas like prop shafts sticking and late transmission shifting, the description above points to a very specific issue that is covered by the PIP below.

Please be aware that if you have a 2007 HD NBS 6.0L/6Spd Truck there is a specific issue and solution regarding this problem. As the PIP below describes, this bump is the result of an Engine Diagnostic Test that is running. A new ECM calibration exists that will minimize the effect of this test.

Keep in mind that this PIP covers 07 HD trucks only and not 08 HD trucks as the cal change was included in 08 production cals.

Please read the PIP and present it to your dealer and make his job a little easier. Better for you the customer to be equipped with the facts.

Service Information

Document ID: 2084039

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#PIP4370: Surge Or Bump Feeling At Stops - keywords 6.0L 6spd 6L90 brake cal calibration clunk idle L90 LY6 MYD prop propshaft sag shift shaft stop stumble yolk - (Mar 19, 2008)

Subject: Surge or Bump Feeling at Stops

Models: 2007 Chevrolet Silverado

2007 GMC Sierra

Equipped with the 6.0L engine (RPO code LY6) and the 6 speed 6L90 transmission (RPO code MYD).

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The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:

A customer may describe a surge or bump feeling when the vehicle is at idle, in gear, and brake applied. The surge/bump feeling can be intermittent.

The surge or bump felt at idle may be induced by a catalyst monitoring diagnostic event. During the event the system calibration will drive the fuel system lean then rich. The test is done to monitor catalyst efficiency. This test can cause a noticeable bump or surge when the vehicle comes to a stop (at idle), transmission in gear, and the brake applied.

Recommendation/Instructions:

There is a new ECM calibration for the surge/bump feeling. The calibration is included in the latest TIS2000 calibration. If the customer concern is an idle surge/bump at stops (as described in this PI), install the latest calibration and evaluate the customer concern.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION

winkman · October 9, 2008

Hi every one . I have a 2007 NBS 1500 silverado with a 4.8l v8 and automatic trans . The truck just hit a Whopping 4000 miles tonight and i have had this bump after Stopped since the day i drove it home. Sometimes after i have been stopped for lets say about 3 secs at a red light i get a bump feeling just as if someone tapped my rear bumper. It feels as if the trans just decided to change into first gear after i been stopped. The trans shifts fine all the time and i have no other complaints. Im also a 22 year seasoned Master Technician 12 years automotive and the rest Heavy Equipment/ Diesel Tech. I too have not had the time to bring the truck back to the dealer. My gut feeling is internal Trans issue thats most likely gonna be fixed with a pcm update . I seen this post and had to respond , I was surprised at how many owners are having the exact same problem . I have checked Alldata And Mitchell on Demand and have found no TSBs on this . I dont have access to GM Tsbs . Hopefully theres a tsb released soon to adress this issue . It Really doesnt bother me that much but the suspense is killing me.

bigdogxx · October 9, 2008

I have had this problem in my 05 5.3 1500 as well and needs to be expanded to more then just the 07 hd trucks, have had the issue since new and does it every so often. I also have a issue were it feels like it happens on start up as well, most of the time when it has been sitting for a few hours, would love to get some kind of direction to look in because todays vistit to the dealer seems like it's going to be another wasted one as they tried to sell me on a 70 dollar throttle body cleaning rather then looking for the real cause.