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2-3 clunk update...

biochemist

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biochemist Enthusiast

biochemist

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OK, so I had a few extra minutes today, figured I would call a few dealers to see what they had to say...few meaning 23 actually from MA, IN, VA, NE, FL and CT. Well, needless to say 21/23 knew exactly what I was talking about (2 had no idea) and said they have never seen a problem resulting from the noise during the shift. Some were quite helpful stating they notice it most while shifting 2-3 from 15-25 mph...also some say they drive different trucks (F#%D) and those do this also. Basically, the driveshaft is hollow and aluminum...this is the main issue. Apparently OBS trucks mostly had steel shafts...less noise, then in 99 they made the Al shafts...this is when people started to notice. Some guys were quite up on the issue and stated that they have see '99's in the shop with 150k..no issues at all even though they have clunked since day 1. One guy said if you move the gas pedal, even slightly during acceleration, it can make the noise appear...which I agree with...seems when I hold the pedal constant it is less common than when I move around while accelerating...seems to be the case. He said it shoud be most noticable during normal driving conditions...really slow, you may not notice, medium pace it will show...getting on it, you will not hear it...which, again, seems to be consistant with what I observe. Anyway, just thought I would post the info for those who notice this. The poll is interesting thus far...seems most have it although a fair percentage say the never notice this...possibly a 2WD or they listen to the radio loudly? On guy said if someone tells you their truck does not do it he can drive it and get it to do it...even the 2005 model years, he see is all the time and customers call the department quite often, he prints the tsb goes grabs a new truck from the lot etc. etc...customs then just ignore it from that point forward. I asked if GM will fix it in the future....he said while customes may not like it, there is no need to fix it cause there is nothing wrong, just a noise...2 guys said they could drive any truck on the lot and it would exhibit this, now they probably meant 4x4 autos, but you get the point because 2x4 trucks (and manuals obviously) are thought not to do this as much although the TSB covers those as well...Anyway, seems that most trucks do this have it and no issues result from it other than the noise itself...which is annoying. So, for me, I am getting re-tuned (which removes most of it anyway as I stated in my review on westers) and will ignore the noise from now on, if I can :eek:...comments, questions? Later, :P:cool::)

heavy4x4 Enthusiast

heavy4x4

Posted
Posted

I get an odd clunk sound from my drivetrain when pulling away from a complete stop. It doesn't need to be hard acceleration per say, just normal application of the throttle. I feel a clunk through my truck and hear a noise similar to a low tire chirp (it's not the tires though). I did notice that if I get under my truck, I can push up on the tailshaft of my transfer case and get the whole assembly to move up 1/2" or so...complete with a clunk at the end of the travel. I'm not sure if this is what is being duplicated when driving. Any ideas? Anyone else heard of something similar to this? I was also thinking it might be wheel-hop or something, but it's not just during hard acceleration, and it's right off of the stop line.

 

Also, I don't get clunks driving at any other speeds/gears/shifts...just the initial start.

 

Thanks,

-Steve

biochemist Enthusiast

biochemist

Posted
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I get an odd clunk sound from my drivetrain when pulling away from a complete stop.  It doesn't need to be hard acceleration per say, just normal application of the throttle.  I feel a clunk through my truck and hear a noise similar to a low tire chirp (it's not the tires though).  I did notice that if I get under my truck, I can push up on the tailshaft of my transfer case and get the whole assembly to move up 1/2" or so...complete with a clunk at the end of the travel.  I'm not sure if this is what is being duplicated when driving.  Any ideas?  Anyone else heard of something similar to this?  I was also thinking it might be wheel-hop or something, but it's not just during hard acceleration, and it's right off of the stop line.

 

Also, I don't get clunks driving at any other speeds/gears/shifts...just the initial start.

 

Thanks,

-Steve

 

 

 

Hi, I think that is the slip yoke needing replacement...I am not sure about moving the tcase...do you mean push up or twist? I am thinking your clunk has to do with the slip-stick condition that a lot of people notice...the 2-3 clunk is even more common. With that said, what year is your truck? Let us know, later, :eek::cool::)

heavy4x4 Enthusiast

heavy4x4

Posted
Posted

It's a 2000 Chevy Silverado 1500 4x4 Extended Cab Short box.

 

The 1/2" of movement is pushing the tailhousing up and watching the whole transfercase & transmission move up.

 

Would someone else be willing to crawl under their truck and try the same thing...see if you get similar results?

 

-Steve

biochemist Enthusiast

biochemist

Posted
  • Author
Posted
Anyone?

 

 

 

Hey Heavy...I assume you are pushing up on the tcase where the driveshaft enters (or exits to the rear depending on how you look at it)...in that case I went out and pulled my truck up on a curb so I could crawl underneath and pushed up on the shaft and tcase with both arms (I am 6-7 ~300 lbs...not ALL fat :flag: ) and mine does not move...it is solid in place. I also checked a couple new trucks at the local chevy place...they are solid in place too...I think I know the problem with yours though...the assembly does sit on rubber mounts that will flex (you can notice this slightly when you watch them while pushing up on the tcase and this is the only movement at all I could detect on my truck or the new ones on the lot...(maybe ~64th of an inch of "flex", not really measurable though, very, very slight flex...think shock absorber) The cab and motor sit on these also BTW. I would check the rubber mounts on your truck, maybe one has gone bad and is causing the movement and noise when you take of because of the torque makes it move up and down quickly? Just a suggestion. Bottom line, the assembly does not move, at least mine and a couple on the Chevy lot down the street do not...Hope this helps, later, :D:cheers::cheers:

heavy4x4 Enthusiast

heavy4x4

Posted
Posted

Awesome...thanks for doing some dirty work crawling under trucks at the lot.

 

I'll take a look at my rubber mount.

 

-Steve

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