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  #1 (permalink)  
Old 08-18-2003, 01:24 PM
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Bad vibrations

I recently replaced my 2:73 10 bolt with a 3:73 12 bolt. The problem I am having is with a driveline vibration. It used to vibrate at around 85 mph with the 2:73's. Now with the lower gears the driveline is vibrating around 65. I replaced both u-joints and it was better but not gone. I also noticed that there were 2degree shims between the springs and pads.( Is that a GM deal or did someone else put them in?) Other than balancing the drive shaft, hard to do here in the small town I live in, does anyone have any suggestions. Does the pinion( spell?) angle have to be at the same angle as the transfer case output shaft? Would taking out the shims help? I dont seem to have the time I used to to try everything so I thought I would ask first. Any help would be appreciated.

Also to correct the speedo what do I need to do? Can I get away with just changing the cable gear?

Oh yeah in case your not psychic the vehicle is a 84 Blazer 4x, 700tranny with a new process transfer, I think.

Thanks again.

John

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Last edited by propaniac; 08-18-2003 at 07:27 PM.
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Old 08-18-2003, 06:24 PM
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have you checked your tires? different sizes, broken belt or maybe a wheel weight fell off one of them
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Old 08-18-2003, 07:25 PM
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I dont think its a tire. I can feel the vibration change as I give it gas. When accelerating it is almost gone. It gets real noticable as I lift the throttle and gets better when I am coasting with no gas. I dont know what to do, maybe the driveline is off balance. Its just strange that when I grease the u-joints it seems to quit for a little while.

Did chevy put cv joints in the short trucks like ford?
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Old 08-18-2003, 08:16 PM
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Cool

it sure sounds like a problem with the drive shaft.

Out of balance shaft, bent, bad angles of the U joints. A bad bushing at the rear of the transfer case, worn out drive shaft yoke?

It is common to shim a diff to the springs to help a drive shaft angle in a lifted or lower vehicle.
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Old 08-18-2003, 11:51 PM
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i deal with this these types of problems daily. they can be very frustrating, and some times hard to find!
due to my current condition, i'll not offer my opinion today, but will return to this post later.
big help i am !
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Old 08-21-2003, 10:39 AM
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Thanks everyone. Crosley the the truck is bone stock on the suspension. The reason I mentioned the shims was that I remember reading somewhere that the pinion and the output shaft have to be at the same angle if they are not it will vibrate. I guess I will try getting a new slip yoke and see what happens. I will also try replacing the bushing in the tail shaft. Axle bastard. I look forward to your advise.

Thanks,

John
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Old 08-21-2003, 11:43 AM
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Did you check the joints after you changed them? Do they move freely? Did you press um or beat um out?

Also, did you check the frt axle joints?
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Old 08-21-2003, 06:33 PM
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found this searching for pinion angle info might help www.diferentials.com/diagnosing.shtml
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Old 08-21-2003, 08:32 PM
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Thanks zonk that was exactly what I was looking for. Looks like if I take out the shims it should help. I was real carefull taking out the old u-joints. Pressed em out and new ones back in. So I dont think I bent anything. Who knows I will let ya know if I get it fixed.
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Old 08-21-2003, 08:36 PM
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i guess what i would do is check the drive shaft for dents and missing weights
first. check the tranny mount for excessive play and check for broken springs.
does the pinion yoke have tabs to keep the u-joint centered? if not, are there snap rings or c-clips on the caps to center the joint. if there aren't tabs on the yoke there must be c-clips. (sounds dumb, but i have seen it many times, and done it a few my self, leaving the snap rings off .)
when you changed the ratio, the speed when the vibrations come in lowered?
do any of the u-joint caps turn in the yoke?
i wish i had a good answer for you. hope this helps.
i can balance drive shafts by the way, if there isn't some where closer to you, maybe i can help with that.
sorry i took so long, i was a bit boozy and sleepy the other night, i always get my self into some kind of trouble like that.
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Old 08-21-2003, 08:55 PM
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Hey no problem axle, I been guilty of that myself a few times. (few too many actually)
I checked the driveline when I had it out and it looked ok. No dents or missing weights, well actually no weights, drive line is painted black and there is no missing paint where a weight would have been. The vibration has stayed at the same driveline speed. With the 2.72's I didnt notice it because I didnt drive 80 mph too often. With the 3.73's I notice it around 60-65sih. The gear change moved the vibration to a speed where I tend to drive more often. If I drive 55 it dosent vibrate or if I decelerate when I am going 65 it quits vibrating. I am going to try taking out the shims ( they were 2 deg, thick end to the back raising the yoke up) and see what happens. I will let you know if anything happens. m

Thanks for your help guys
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Old 08-22-2003, 11:39 AM
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If anyone is following this I took out the shims and the vibration is much better, almost gone.
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Old 08-22-2003, 07:51 PM
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Pro... I am glad that you got the vibration better. I would suggest that you still, as someone mentioned, check the u-joints. I am concerned because you said that it gets better for awhile, when you grease the joints. That indicates to me that you have excessive movement in the joints. I have seen guys beat the joints out to replace them and damage the yoke or drive shaft, by spreading them. Even with the clips in them, the joint can move and make everything out of balance.

Just my thoughts.
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Old 08-23-2003, 12:06 PM
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Sometimes the bearings get in a bind when you put them in. To free them up, just hit each shoulder of the driveshaft yokes with a hammer. Not a big hammer, and not real hard. If the shaft is out, it's easy to feel the bind, and easy to feel the difference after you hit it.
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Old 08-27-2003, 06:17 PM
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I just got back from a 320 mile trip and the vibration was gone for the first 30 min and then it showed back up. Had to slow down to keep from going insane. Plus side I did get 14 mpg. I am kinda discouraged. With the old gears the drivline turned much slower so I never noticed. I cant enjoy the power of the new gears on the highway. I being a cheapskate finally decided on having one made and shipped to me. At least I can have the guy put the matching 12 bolt yoke on the end of the tube so I dont have to have the conversion u-joint.

thanks for your suggestions everyone I think the darn thing is bent or the yokes are not alligned anymore.

john
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