# 1999 gmc sierra 2500 bad vibration!



## clc2007 (Sep 26, 2011)

It only does it once in a while but becoming more cmmon. Someimes when the truck shifts into another forward gear i get a realyx bad vibration that feels lke it is coming from the rear end, the vibration feels like your going overrumble strips with the rearend! But only lasts about a second or two and clears right up, no loss of power or trans slipage while it happens, ihave flushhed the trans and replaed the filter, changed all rear u joints it has new wheels and tires! Not sture where to go from here so im thinking spider gears orbad ring and pinion? But that makes no sence why it would be those as it only happens while shifting and on acceleration any


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## clc2007 (Sep 26, 2011)

Any help would be great.


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## cartec01 (Jul 4, 2008)

clc2007,
Do you have a one or two piece driveshaft in the rear?


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## clc2007 (Sep 26, 2011)

It is a one piece.


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## cartec01 (Jul 4, 2008)

It is not ring and pinion those would howl especially if they were that bad. I managed a driveline shop for a few years, been there done that. If you replaced the u-joints, and there is no center support bearing (i.e. two piece shaft) Then it maybe be your trans... I have seen that more then once where the trans will cause a short vibration under load. Let me ask a few more questions.

I assume it has a 4L80e
How many miles on the truck, engine, trans.
Is it 4x4
Have you ever flushed the trans before this started
Does the truck have a limited slip rear differential.
have you noticed if it does it predominatly while going straight or turning
Also, since you say it does it while shifting gear I assume it does it when the truck is in motion. Has it done if from a stop?


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## clc2007 (Sep 26, 2011)

Yes it is a 4l80 e, truck has 120,000 on engine and trans, trans has ben flushed evry 25000 miles, i has limited slip. It seems to be worse after turning or going arround a curve, it hasnt done it from a dead stop, only after turning a corner or going arround a curve. Im really lost on this one.


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## clc2007 (Sep 26, 2011)

And yes it is a 4x4


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## cartec01 (Jul 4, 2008)

Ok, I believe what you are feeling is a "slip and grab" vibration not an "out of balance" vibration. I drive shaft with bad u-joints or a bad center support will cause a drive line vibration however you have replace both u-joints on the rear shaft. If it were the shaft it's self it would be constant so we can rule that out. In the rear dif you have the ring and pinion, the spider gears, the clutch disks for the posi, and the axles. So, lets do this through deductive reasoning since you are two states away and I can't look at the truck:
the drive shaft is connect to the pinion yoke which is splined, if there was a slip there it would instantly cause a total failure. The pinion shaft is set in the housing with two tapered bearings and races. If those bearing were worn it would cause the pinion gear and ring gear to mesh wrong and would surely howl, if the bearings were bad enough to cause an occasional vibration your rear end would be constantly yelling you you. The pinion rotates the ring gear with teeth, if they were to slip it would instantly cause complete failure. The ring gear is bolted to the carrier, inside the carrier are the spider gears and clutches. The spider gears could be worn, chip, or broken however if that was the case it would not occasionally vibrate it would grind, clunk, or the truck wouldn't move and it would be constant. The clutches could slip and cause a chatter and vibration, however that would only happen at the time one rear tire was going a different speed then the other rear tire and it might not do it all the time. It would not do anything while going in a straight line unless a tire lost traction.(unless it is a locker or AAM's newer helical design posi) (both of your rear tires are the same size from the same manufacturer with the same air pressure right?) The axles go into the spiders gears and that is splined, again a slip there would be fatal. An axle bearing could be bad however that would cause a noise which would be almost constant and increase and lessen while you swayed side to side.
Sorry about my thinking out loud, just cover the bases. At that mileage I would highly recommend a dif service anyway, Not an oil change place special but a trans or driveline shop where they will take the cover of, clean everything and inspect it. A good driveline tech will be able to tell at that point if there is cause for concern in the dif, like to much backlash. I think that would be good maintenance but you won't find your problem there. I would say there is about an 18% chance it is your clutches in the rear dif. Take to cover off, clean it out, refill, and add a quality friction modifier from Ford. I know, it's a GM but Ford friction mod. is the best out there IMO. See if that solves your problem. There is a 77% chance is is your trans slipping and chattering a little bit. That action in the trans will carry all the way to the rear of the truck which is where it would feel like a vibration in the rear end when it happens. There is also a 5% chance that your transfer case chain is stretched so much it is causing havoc, and has enough slack that going from no load to high load (i.e. shifting gears) it will "bounce" which would also be felt in the rear as that is where the power is being applied.
I would sure like to know the outcome of your truck. I have had many 90's GM trucks and still have 2 k3500's. Love those trucks.


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## White Gardens (Oct 29, 2008)

I rode in a truck with a guy who had the same problem. I'll call him tomorrow to see if he ever figured out the issue.

I was just as you described, felt like the rear-end and it would almost bounce or vibrate for maybe a 1/4 of a second each time it did it.

....


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## clc2007 (Sep 26, 2011)

Ya all 4 tires are the same, i really appreciate all you help as i am clueless as to what this thing has going on. I will get the rear diff done first thing in the morning, from there ill probably go to the trans shop and see what they can figure out. I agree with the trans probably being the issue as it is the only logical answer. But it is odd how it only will do it once in a while and other than that it is as solid as a rock, shifts great no slip lots of power. I hope its something simple and dont require a total rebuild, but it does have 120k on it.


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## clc2007 (Sep 26, 2011)

White Gardens;1353939 said:


> I rode in a truck with a guy who had the same problem. I'll call him tomorrow to see if he ever figured out the issue.
> 
> I was just as you described, felt like the rear-end and it would almost bounce or vibrate for maybe a 1/4 of a second each time it did it.
> 
> ....


That would be great! Dont wanna pay these top dollar shops if i dont have to lol.


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## clc2007 (Sep 26, 2011)

Updade, had the rear end looked at today and it is in great shape. So that is not the problem.


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## cartec01 (Jul 4, 2008)

Is the condition something you can replicate in anyway, or is it always "out of the blue."


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## clc2007 (Sep 26, 2011)

It is allways out of the blue, i drove it 20 miles today. And it did it 3 times. While going down the road i would let off the gas and lightly tap the brake pedal to take it out of lock up and re apply the thorotle and still couldent get it to do it, the owner of the shop drove it for about 15 min and said he thinks im crazy that it drives great and that there is nothing wrong with my truck, go figure take it to a mechanic and it wont do it for him. Ive done evrything i can think of to get it to act up on demand and no luck.


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## clc2007 (Sep 26, 2011)

He serviced the rear end and ran the computer on it checking the trans and all checks out good.


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## gmcdan (Nov 4, 2011)

just throwing it out there but possibly a broken leaf spring or two ? maybe your axle is twisting/ rotating to much on acceleration and is causing a bad ujoint angle for a few seonds . ive seen a few broken leafs in those trucks. not sure just a guess and something to look at .


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## clc2007 (Sep 26, 2011)

That does make sence i will take a peak at them, thanks for the idea


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## clc2007 (Sep 26, 2011)

Ok so i looked at the leaf springs top bottom and sides no cracks or sign of weakness, the u bolts and shackels all look good as well.


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## all ferris (Jan 6, 2005)

it sounds like a bad limited slip. I would almost bet. You say it only does it after going around a turn? The clutches in a limited slip will start to slip when they wear out and cause the exact symptoms you are describing.


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## clc2007 (Sep 26, 2011)

Ok so i took it to a dealer today they drove it and found a bad left rear caliper, and that the emergency brakes were draging verry bad, so it got a new caliper and all new rear brakes, they tor into the rear end and said the clutches and all gears are in good condition. They think the vibration has something to do with the torque convertor.does this ake any sence?


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## clc2007 (Sep 26, 2011)

Well its off to the transmission shop. Called them tonight and it goes in monday at 8 am. They said. They will find it and have it fixed by no later than thursday. So lets hope its not a huge poblem! I will keep you all posted, thankhs to all for the advise but it is geting to close to plowing season to be chasing this problem.


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## clc2007 (Sep 26, 2011)

Talked to the transmission guy this morning he said to get a tube of lube guard instant shutter fix. I put it in my truck and problem solved. So after all that the solution was an 8 dollar bottle of lube!


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## White Gardens (Oct 29, 2008)

clc2007;1357854 said:


> Talked to the transmission guy this morning he said to get a tube of lube guard instant shutter fix. I put it in my truck and problem solved. So after all that the solution was an 8 dollar bottle of lube!


Ummmmm, usually that's just a band aide on top of a potentially bad problem. What was his logic behind the Lube Guard?


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## OrionLS (Nov 7, 2011)

I'm waiting to hear how this works out. I have a 2000 silverado with the EXACT same symptoms, its frustrating.


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