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Old 12-25-2003, 03:28 PM
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Angry drivetrain vibration

Hello, I am Sean 35 years of age and live in canton ohio. I am a very seasoned, but backyard mechanic. Done a little of everything except rebuilding trannies and rear ends. I own a 1986 s10 automatic 77r4 tranny 2wd long bed with a 2.8L engine(new) that I put in from trak auto(before it went bankrupt!) go figure! I have looked for quite some time to find a mechanic in my area that can solve my vibration problem and no luck. I have also done searches on the net to find similiar problems, and once again no luck. Did these things just vibrate back then unfixable like I have been told or is this thing solvable? Ok heres the problem. engine has less than 20,000 miles on it(fyi)(and yes it runs real good......for a 2.8). I have a drivetrain vibration from 35 on up. the worst is about 40mph. I have had the driveshaft balanced(changed vibration at 50 on up to a more soft one....I.E. not as pronounced. Oh yes, the drive shaft is a split one with a carrier bearing(new replaced). Ujoints are good as was told to me by the shop that did the balancing. As far as isolating the vibration, it vibrates when there is slight load on the drive train. In order to "piss it off and make it vibrate real good you should "get on the gas full throttle" a couple of times. When you do get on the throttle, there is no vibration all the way up to free way speed. Accelerating normally up to freeway speed vibration is there also. As you let off the gas, slowing down to 50 and slower the vibration comes back. even if you put transmission in neutral, vibration is still there. I have even shut off the engine to isolate it too while slowing down from 50 mph.........vibration still there. Tranny mount is new along with passenger side engine mount(just replaced)........drivers side engine mount is said to be good by the mechanics I work with. I have been trying to understand driveline geometry 101 document that classictrucks.com has and I am not sure I know what I am doing there as to how to check my driveline angles. I would love to be able to isolate this to the component that is guilty, but dont know any other methods or tests to run.

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Old 12-25-2003, 04:27 PM
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triple check to make sure the correct u joints are in place, had that problem once, autozones part numbers aren't always right.

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and merry Christmas!!!
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Old 12-25-2003, 04:51 PM
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hello, just went out for a drive to see if motor mount changed viration. I think it did a little but not sure. When the truck is put in neutral decelerating down to 40. the vibration gets softer after a second so basically it needs to be in drive light load to vibrate the most at 40 or so. Also, the engine does have a slight vibration, like a cylinder miss or something when you bring it to about 1600 rpm in park. this vibration goes in and out about every second, like someone is turning off and on the perverbial vibration switch every second. Not sure if this has something to do with my driveline/drivetrain vibration
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Old 12-25-2003, 07:24 PM
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wow. that would drive me real nuts. i am of same age, and I might do something radical - sell it.

Here is what I suggest; driveline alignment is not hard.

1) put a angle meter ($15 from home depot) on the pinion when the cup is on the bottom. Measure the horizontal angle, should be 1-3 deg. negative. (pointed down)

2) do the same to your trans yoke, it should be pointed UP THE SAME number of degrees, on the horizontal plane. If you are off by as much as 1 deg. difference, it will vibrate.

HOWEVER, sounds like you can make it go away. THAT sounds like carrier bearing misalignment to me. when you "load " the drive train hard, something torques in the direction of favor.

HMMMM. Check them pinion angles to start....

good luck.

CJ
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Old 12-25-2003, 08:15 PM
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yea sounds good, headed off to home depot tomorrow. By the way, the mechanic I work with says maybe I should slide the trans to carrier bearing part of the drive shaft out of the tranny a little to see if that helps(it is a two piece drive shaft that has the regular load sliding capability behind the carrier bearing so the trans to carrier bearing part does not slide at all with suspension ride or load changes. Right now I have the shaft slid all the way in the tranny, which I though was or is right. Of course on a one piece drive shaft, that is a no no since I know the tranny could be damaged do to shaft bottoming out inside tranny when the rear end axle gets closer to frame due to bumps/load. Wondering if I should go out and get a later style driveshaft and throw it in to see if that helps. I was told by a mechanic I took it too that sometimes guys would drill a hole in the shaft and fill it with spray foam....lol........dont reall want to try that one..........P.S.....................when I floor the truck, there is no vibration all the way up to freeway speed.(this just helps piss it off)
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Old 12-25-2003, 09:01 PM
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You might try loosening the motor mounts and start and load engine. They might be in a slight bind. Being a two piece drive shaft see if the slip yoke can be greased. May be drive and that can cause vibration. Have you tried disconnecting the belts and seeing if the vibration is better in neutral. May have a water pump with a slight problem. Just a few ideas.
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Old 12-26-2003, 06:58 AM
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I had to sleep on this and think about it.

sounds like its a more violent vibration than a water pump or belts, but maybe++ you can have soemone tow the truck with the shafts disconnected and isolate which shaft it is with the engine off. Just a thought. Since it is such a weird one, your going to have to pull different tricks out of the hat.
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Old 12-27-2003, 02:48 PM
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Hello, I noticed that the passenger motor mount "U" bracket that bolts to the engine block doesn't really line up. It is about an inch off towards the front of the truck! Maybe it is bent, or it is the wrong one?......So, I decided to go and inspect another at the local junk yard and low and behold, it looks fine and not bent. When I tried to install the new motor mount, it appeared to be about an inch(as stated earlier) behind the u bracket, hmmmm so I bent the crap out of the bracket to get it to line up. Question is, did it get bent do to the fact that future wife hit a tree right where the passenger frame rail is in front at 20 or so miles an hour or is this a bent bracket from before, or the wrong bracket, or(lol), is frame on that side pushed back a little. Not sure how to check to see if frame is messed up, but I would think I will find out tomorrow when I try to put the correct u bracket in. Question of the day is,,.....bent non fitting properly mount bracket possible cause of vibration due to misaligned engine/trans to driveshaft? I did look at the water pump pulley and it appears that the passenger side of the pulley is farther back than the drivers side is. You would think engine pulleys would be perfectly flat and parallel to sway bar(not sure if this is a good measurement judgement ). I do know one thing, I WILL figure out this dam vibration one way or another. It wont beat me!!
P.S. and yes I greased the crap out of the center section or yoke behind the carrier to see if that would cause vibration..........belt removal is also next to isolate components.
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Old 12-27-2003, 03:43 PM
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Take it to a local shop and pay them to put it up on a lift. If its misaligned driveline, It should be apparent by looking up from the floor. Oscillating vibration I've only ever seen from motor rotating mass (most likely a thrown flywheel weight, or a spun balancer on a externally balanced motor)

I would break down the ujoints just on GPs. I've seen good- appearing ujoint be bad and cause vibration. plus, its cheaper than randomly replacing other things....
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