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Old 10-13-2012, 05:14 PM
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Vibration

Hello everyone.

I have been hearing and feeling a bit of a sound that I am trying to pin point.

heres the setup.
chevy 454
th-400
ford 9" rear end.
4 link rear suspension.
Heres whats happening.

I will be cruising along(80-90kph) and get to a hill or a stretch before a reduced speed so I will coast a bit and that's when I hear a grinding-ish vibration and I can feel it too. Press on the gas and it goes away, let off and its back. Get below 70kph and its goes away. From trying to read things out form other posts and searching on the net I think it may be the u joints or a u joint starting to complain a little. . . has this happened to anyone and what was the fix for you?

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Old 10-13-2012, 05:20 PM
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Sounds a lot like a U joint failing. Most likely the rear one in the shaft.
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Old 10-13-2012, 05:29 PM
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Your thoughts are the same as mine then on the diagnosis. hopefully someone will chime in who has had the same issue and can post their cure.

I just took the car out for its last drive for the season today. so over the winter I have a few projects I want to tackle. I think I will replace them both for good measure.
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Old 10-13-2012, 06:16 PM
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Cure: simply replace the u joint. I have installed a freight car full of u joints in 30 years of wrenchin.
The front one usually wont be bad,but move it both directions when you have the shaft out. If it feels notchy or stiff , replace it.
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Old 10-13-2012, 06:21 PM
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Pinion angle changes cause that. Nose of the rearend drops enough to cause the u-joint to bind a bit. Goes away when you hit the gas cause pinion rises enough to stop the vibration.
What's your pinion angle now?
Try moving it up a couple degrees!
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Old 10-13-2012, 06:33 PM
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Quote:
Originally Posted by RWENUTS View Post
Pinion angle changes cause that. Nose of the rearend drops enough to cause the u-joint to bind a bit. Goes away when you hit the gas cause pinion rises enough to stop the vibration.
What's your pinion angle now?
Try moving it up a couple degrees!
Agreed. definitely check pinion angle while you are under it..... John L
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Old 10-13-2012, 06:34 PM
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I am inclined to think RWENUTS has it nailed. The U joint is most likely just a symptom for an underlying problem .
The 4 link should maintain the angle pretty well, but if the pinion angle isnt correct to begin with, the U joint would suffer first. Ulimately the pinion bearing will fail.
I totally agree with checking the pinion angle. Kudos RWE.
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Old 10-13-2012, 06:36 PM
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loose 9 ?

9 in rears that used the old crush sleeve to set pinion preload can continue to crush under hard usage and you end up with too much clearance, but I have had noise-vibration that was hard to feel anything at the U joint but were bad when i inspected during replacement,
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Old 10-13-2012, 07:01 PM
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Ok thanks guys that is a good place to start. I will check the angle and see what its like.

Also it could just be from a lack of regular maintenance. I don't know how long they have been there or if they have ever been greased. I just recently purchased the car (about a month ago) and have only had it out a hand full of times. It has been doing that since the get go but seems to have been a bit worse today.

I attached a file that I took from another post. It looks like the second image where the transmission and rear axle are parallel but at different levels.
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Name:	1280driveshaft_angles.jpg
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ID:	68397  
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Old 10-13-2012, 07:45 PM
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Go to your local hardware store for an angle finder like in the link. Easy to use. Check it with the vehicle sitting on a flat surface normally loaded.
Swanson - Building Customer Trust For Over 80 Years!
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Old 10-13-2012, 08:01 PM
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I used my fatmax extreme level and I read that the angle was at 10* I attached a pic so you could see the lvl I was talking about
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Old 10-13-2012, 08:34 PM
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Which angle was 10*?
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Old 10-13-2012, 10:37 PM
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The drive shaft was 10*
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Old 10-14-2012, 10:35 AM
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With all this said. . .what is going to be the best route to finding out which u-joints I would need to buy to replace the ones I have? Seeing as I am not 100% sure on the age of rear differential or what it came out of. With the transmission I am more positive that it is a 74 th-400 as I figure it was mated with the engine.

Do the u-joints have information stamped on them I could use to match up to a new one?

Also, I know they make different kinds of u-joints but I want to choose the right ones for my application. The car is a street/strip car. I take it to cruise nights, shows, to the local hangouts and to the strip. So in my application is it better to get the ones with the grease fittings or a sealed unit?

Some of the part stores are awful here where I live. They cant search anything if its not a stock item.
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Old 10-14-2012, 12:59 PM
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Get some Spicer U joints. lifetime warranty.
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