gmc truck noise want help - Page 2

BernieB · 10-21-2009, 05:18 AM

Thinking about it some more what I come up with is that in a typical rear wheel drive truck the driveshaft angles slightly downward from the transmission to the differential. As the vehicle starts to accelerate the differential tries to rotate opposite of the wheel rotation, which means the front of the differential is trying to rotate upward. It's prevented from doing this by the way it is attached to the leaf springs, but the springs themselves do flex a bit (spring wrap as I mentioned earlier) so there is still some upward movement. This in turn makes the line of the angle to the transmission slightly shorter, and the yoke then slides forward on the splines. It's not that the entire driveline is compressing, because the actual distance between the components doesn't really change, it's just the angles changing which changes the distance, but we do agree that if the yoke splines are not properly lubricated it can cause a temporary resistance to that motion, then a "thunk" when it finally does release and move.

(This is what happens when you're bored at 5:30 in the morning, can't sleep, and have an engineering degree.)

99-GMCSierraZ71 · 10-21-2009, 12:58 PM

I guarentee you that if you grease the spline on the yoke, it'll cure your problem, I have the same problem, I have to grease mine about every 10000k, you'll notice a difference right away
I enquired about this problem to GM a few years back, there was TSB on it and if you got the truck in there before your warrenty expries, they would have replaced it, but mine was already expired, what GM says is that it needs to be replaced with a nickel plated yoke at the tidy sum of 600 bucks, I said, yeah, I'll save the money and grease it

Brian

bmun · 10-31-2009, 11:54 AM

kennyray the advice with the grease fixed it appreciate the help

Kennyray · 10-31-2009, 06:40 PM

thanks for lettin us know how it came out, glad ya found the problem.

10-21-2009, 05:18 AM	#11
BernieB Senior Member Join Date: Jul 2009 Location: Fredericksburg, VA Posts: 1,906	Thinking about it some more what I come up with is that in a typical rear wheel drive truck the driveshaft angles slightly downward from the transmission to the differential. As the vehicle starts to accelerate the differential tries to rotate opposite of the wheel rotation, which means the front of the differential is trying to rotate upward. It's prevented from doing this by the way it is attached to the leaf springs, but the springs themselves do flex a bit (spring wrap as I mentioned earlier) so there is still some upward movement. This in turn makes the line of the angle to the transmission slightly shorter, and the yoke then slides forward on the splines. It's not that the entire driveline is compressing, because the actual distance between the components doesn't really change, it's just the angles changing which changes the distance, but we do agree that if the yoke splines are not properly lubricated it can cause a temporary resistance to that motion, then a "thunk" when it finally does release and move. (This is what happens when you're bored at 5:30 in the morning, can't sleep, and have an engineering degree.) __________________ If the guys who design 'em had to take one home, use it every day for 2 years, and do all the maint and repairs themselves, cars would have a button on the dash to change the oil, filters & plugs.

10-31-2009, 11:54 AM	#13
bmun Junior Member Join Date: Oct 2009 Posts: 4	gmc noise kennyray the advice with the grease fixed it appreciate the help

10-31-2009, 06:40 PM	#14
Kennyray Senior Member Join Date: Oct 2005 Location: Birmingham, AL Posts: 648	thanks for lettin us know how it came out, glad ya found the problem. __________________ On a quiet night you can hear a Ford rust

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10-21-2009, 12:58 PM	#12
99-GMCSierraZ71 Junior Member Join Date: Oct 2009 Location: Nanaimo BC Canada Posts: 8	I guarentee you that if you grease the spline on the yoke, it'll cure your problem, I have the same problem, I have to grease mine about every 10000k, you'll notice a difference right away I enquired about this problem to GM a few years back, there was TSB on it and if you got the truck in there before your warrenty expries, they would have replaced it, but mine was already expired, what GM says is that it needs to be replaced with a nickel plated yoke at the tidy sum of 600 bucks, I said, yeah, I'll save the money and grease it Brian