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Old 10-13-2003, 01:35 PM
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Drive shaft out of balance??

Hi All~

Just wondering-

If I take a drive shaft, put a new yoke on is it a certainty that it will need rebalanced?

I needed a custom drive shaft for a '67 Mustang I just put a 9" rear end and a 429 in and managed to locate one just the right length at a bone yard. So I just slapped the yoke on it and now I have a terrible vibration that I suspect is coming from the drive shaft - but I'm not certain.

Thanks in advance.

Gary

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Old 10-13-2003, 03:35 PM
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terrible vibration kinda comes along with the 429
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Old 10-13-2003, 03:45 PM
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Well, that too...but this vibration is only noticable after - lets say 20 - 25 MPH. I don't have the speedo hooked up so I'm not certain of the exact speed. It doesn't vibrate sitting still, and even driving fairly slow it not noticable...but once you get going a little bit you can really feel it. And interestingly enough, if you go faster or slower it doesn't seem to change. Once it starts it stays about the same.

Also, I don't seem to notice it during acceloration. Could it be the rear end? I never rebuilt a rear end before, this was my first one. Had good documentation and it all seemed to go together as planned and documented.

GB
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Old 10-13-2003, 08:38 PM
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A balanced drive shaft with a properly installed different yoke should not need to be rebalanced. A vibration from a unbalanced driveshaft normally vibrates differently as the speed changes. Actually, it sounds to me like you may need to check the clearances, meaning make sure the engine, trans, exhaust, etc, are not hitting somewhere.
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Old 10-14-2003, 10:40 PM
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Make sure your drive shaft is not bottoming out in the transmission! (drive shaft too long) This will cause the vibration you are talking about.

Also, if you put another yoke on that drive shaft, did you index it just like the original? There needs to be an index offset between the front and rear yokes.
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Old 10-15-2003, 12:33 AM
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vibration

Hi! Gary, I was just thinking about your vibration. When you installed the yak, did you at lest look at the "U" joint and made sure that the needles were all still in the cup with the seal in good shape and grease was OK? And when you pressed or drove them in place, and put the lock ring back in place, did you push them back agents the lock ring? (It could be that
"U" joint is not installed correctly, to tight, cup's off center, missing needles, no grease, press to one side more then the other.
If you have a two peace drive shaft then all "U" joints must be in line with each other (where the slip joint is and because it is splined must be 90% to the joint it mates two, not 30% or 45% or what ever.)
Next! The Ring and Pennon. At low speed the rear end more then likely don't make nose unless it is really in bad shape or not put together right. At higher speed the pennon well press hard agents the ring gear and well mate further out on the ring gear. So if the back lash is to tight it well get tighter as it moves out (goo's faster) and then it well for sure make a vibration and probably nose.
A one peace drive! Well, look at the splines on the yoke, are they worn, the right size, yoke to long (bottoming out ), Tail shaft berg. OK?
next! What about a rear wheel berg.?
My guess is one or more of the above hope this helps. --Gene Neal
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Old 10-15-2003, 10:25 AM
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Okay folks...I realize now that I didn't post enough info. Sorry about that.

Before I put it all back together I rebuilt the rear end. This included all new bearings, seals, and gears. Even a new to me but used factory type Posi unit. My thinking is that the only part to be suspect in that equation would be the new posi unit as the rest of the parts were original...except for seals and bearings. Also, I believe I got the backlash set properly at .008 - .012 (I think that was the number)...I shot for .009.

The length is not an issue, in fact it might be a little short. There is about 3 - 3.5 inches between the base of the yoke and the rubber sleeve around the tail shaft of the trans. This is a one piece drive shaft.

U Joints - double checked. They went together properly and without and hint of a problem. All 6 lock rings still in place.

Smurf - As far as indexing, I have no clue what you mean by that. Do you mean that the trans yoke and the rear end yoke have to be paired up in an opposing fashion?

Gene - because I am going to pull the auto and replace with a four or five speed I didn't do jack to the trans...other than replace the filter. So I don't know if the tail shaft bearing is good or bad. Wouldn't it cause the seal to fail if the bearing were bad and cause it to leak?

Thanks for the suggestions guys. I'm going to take it for another ride tonight and see if I can finger this thing out.
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Old 10-16-2003, 12:42 AM
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vibration

Gary! The transmission tail bushing (berg). if badly worn (while the drive shaft is installed, grab the yoke by your hand and bush it up and down or from side to side, should be very little to none movement). Yes, this will cause a leak. And even if you install a double lip seal and a new wiper it wont last very long, it well later leak again. Also remove the rear "U" joint and see if the yoke slides in and out freely. Is the yoke on the rear end tight? I mean at the proper torque! And did you put a cutter pine in the nut? Or may be you used an elastic nut, that OK too just make sure that it was a NEW one not a used one.
Gary! you must think about the gear ratio in the rear end when you go from an auto to a standard trans. think of it like this: If you had an auto trans, and then R/R the rear end with one out of a Car that had a standard trans, your Car would have more power than before. And every thing would fine. But if you take the auto trans. out and put a standard trans. in its place with the same old rear end, It well terr up the trans. gears in a very short time. just a thought! ------Gene Neal
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Old 10-16-2003, 03:47 AM
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Quote:
Originally posted by '67Pony
Smurf - As far as indexing, I have no clue what you mean by that. Do you mean that the trans yoke and the rear end yoke have to be paired up in an opposing fashion?
That's it. Mine are clocked 20 degrees from each other. Just checked it. But... It's a 1100 hp blown big block car (4 rear ends and 3 drive shafts have been terminated) and there might be the possiblity that the drive shaft has twisted that much. But every time I have shortened a driveshaft, I have always witness marked where the yoke was and put it back at the same clock position and I have never had vibration problems.

But in as much as I have destroyed 3 driveshafts in this car in the past 5 years, I have ordered a new Denny's driveshaft and it should come in this week. (New cam and converter has me worried again) I'll post how the yokes are clocked when it get's here.

Anyway, just be glad all it does is vibrate. When they come apart, all hell breaks loose. Even with a driveshaft loop, it busts trannys and beats the floorboard.

Gene had a good idea on the bushing issue. I had a bushing come out of a TH400 one time and it did vibrate quite noticeably. I was told that the reason it came out was because the driveshaft was too short and it let the yoke move up and down too much! And if you think your driveshaft might be a little short... So check that transmission yoke for side play like Gene suggested.
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