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Fed up with 9" vibrations

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Old 08-04-2012, 03:13 PM   #1
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Default Fed up with 9" vibrations

01' Hawk with T56. I upgraded to MWC 9" with 3.70 gears and PST metal shaft. Car has Hotchkis LCA and Panhard bar. MWC set up has short arm.

Coasting at lower speeds (like downhill) vibrates but stops when I let out the clutch in gear. Drones bad at 75+ and vibrates but always worse when I let off.

I have -3.7 degrees on the balancer, -4.4 on the tranny output flange. I have been up and down the spectrum with the adjustable arm and when I incease negative pinion angle the coast vibe is less but drone is worse, opposite for increasing angle. I have been as high as 6.5 on the + and 3.5 on the-. I usually got 2 flats on the nut and I have over a 100 hours in this tuning and no luck.

Today I replaced the tailshaft bushing, no change, I have also changed the u-joints. I have a pit and today I had the rear just off the ground and had the wife run the car at 80+ and just vibrates everywhere so you can pinpoint it.

I can't take it anymore and am ready to rebuild the 10 bolt and go back. Wife won't even drive the car anymore it is so bad. I plan on having the drive shaft checked this week.

Any ideas?
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Old 08-05-2012, 11:56 PM   #2
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Could be the harmonic balancer, the driveshaft, or could be in the transmission. A lot of folks will say transmissions dont vibrate, but when bearings and gears wear and develop slack between them and the shafts they're on, vibrations show up.
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Old 08-06-2012, 10:32 AM   #3
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As camd01silv stated problem could be one/combo many things, but I do not think it would be just the 9" I do not think just going back to the 10 will correct your problems
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Old 08-06-2012, 11:30 AM   #4
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Find someone who can spin up the driveline and check it dynamically. You might have your problem right there.
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Old 08-06-2012, 06:50 PM   #5
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how far in is the tranny yoke ?drive shaft mite be too short.maybe have the shaft rebalanced .
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Old 08-06-2012, 10:28 PM   #6
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"how far in is the tranny yoke ?drive shaft mite be too short."
GOOD point ,garygnu

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Old 08-07-2012, 05:19 AM   #7
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I chased a vibe for years and adjusted and replaced drive shafts to no avail. Did the tailshaft bushings too. Loads of wasted time and frustration.

One day I noticed that my vibes were only in 5th and 6th gears and decided to blame the T56 since there was nothing else that could be casuing the vibe. I was correct and the tranny needed a rebuild and ever since it has been smooth as silk.

First make sure the DS is balanced, then reach the speed at which it vibes in 4th, 5th and 6th and determine if it is only vibrating in 5th or 6th. If so, go here Project "fix that damn 5th/6th gear high speed vibration".

FTR, the PST DS I received was not properly balanced. When I got it, it had no added weights. When they checked it and returned it, there was a newly added large washer on one end so clearly it was out of whack. The vibe this gave off was around 50MPH.
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Old 08-07-2012, 10:00 AM   #8
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Originally Posted by wrd1972 View Post
I chased a vibe for years and adjusted and replaced drive shafts to no avail. Did the tailshaft bushings too. Loads of wasted time and frustration.

One day I noticed that my vibes were only in 5th and 6th gears and decided to blame the T56 since there was nothing else that could be casuing the vibe. I was correct and the tranny needed a rebuild and ever since it has been smooth as silk.

First make sure the DS is balanced, then reach the speed at which it vibes in 4th, 5th and 6th and determine if it is only vibrating in 5th or 6th. If so, go here Project "fix that damn 5th/6th gear high speed vibration".

FTR, the PST DS I received was not properly balanced. When I got it, it had no added weights. When they checked it and returned it, there was a newly added large washer on one end so clearly it was out of whack. The vibe this gave off was around 50MPH.
Good response ^^

Frequently these type of problems existed prior to up-grading a rearend but the vibrationswere partially absorbed with the flimsy stock drivetrain. Adding a sturdy driveshaft and rearend makes it seem they are the problem but in reality they are simply revealing prior issues.

I'm confused with the measurements You gave with Your balancer. Hopefully You are not using these to set Your pinion angle?

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Old 08-08-2012, 02:55 PM   #9
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I am currently setting the pinion angle based upon the drive shaft angle. It is -1 so I have the pinion set +.5 right now. I have to wait two weeks to get the DS checked as the only shop around that can do it is closing for vacation. I know the owner real good so he will not BS me.

Low speed vibrations are on coast, high speed is both under load and coast. Vibration/drone in 4th at 85 is less pronounced than in 6th.

I'll check the tranny yoke depth this weekend when I get time.
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Old 08-11-2012, 07:03 AM   #10
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I have a vibration in my setup as well. I complained about it as soon as I got back home after the swap. Long story short my issue is from the Strange axels not having enough flange on them to properly center the rims.
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Old 08-11-2012, 10:58 AM   #11
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...Long story short my issue is from the Strange axels not having enough flange on them to properly center the rims.
Who's rims if I may ask? It's usually rims that are wrong instead of axles. They try and market the rim to different applications. I had a set I got rid of for just that reason. Higher quality rim fit perfect. Strange is such a high quality company...but I guess it's possible they let something out the door they shouldn't have.
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Old 08-11-2012, 04:27 PM   #12
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Agree with above, it's not the 9".
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Old 08-11-2012, 06:22 PM   #13
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I had a vibration that turned out to be a worn/improperly torqued pinion gear. Apparently the yoke had been taken off to replace a seal, and then corners cut on properly setting it back up.
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Old 08-11-2012, 09:37 PM   #14
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Who's rims if I may ask? It's usually rims that are wrong instead of axles. They try and market the rim to different applications. I had a set I got rid of for just that reason. Higher quality rim fit perfect. Strange is such a high quality company...but I guess it's possible they let something out the door they shouldn't have.
Stock rims. This was also confirmed by a well repudiated shop in Orlando who only handles driveline issues. In fact his first question if I had Strange axels (before even looking at my car). Its the axels in my car, the rims are 100% fine.
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Old 08-12-2012, 02:12 AM   #15
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Stock rims. This was also confirmed by a well repudiated shop in Orlando who only handles driveline issues. In fact his first question if I had Strange axels (before even looking at my car). Its the axels in my car, the rims are 100% fine.
Repudiated= To reject emphatically as unfounded, untrue, or unjust.

Did you mean reputable?
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Old 08-13-2012, 04:48 AM   #16
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Repudiated= To reject emphatically as unfounded, untrue, or unjust.

Did you mean reputable?
Lol yeah. Autocorrect and not proofreading ftl :-(
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Old 08-13-2012, 02:27 PM   #17
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I have a vibration in my setup as well. I complained about it as soon as I got back home after the swap. Long story short my issue is from the Strange axels not having enough flange on them to properly center the rims.
The wheels on our cars are lug centric, they don't use the axle hub to center on.
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Old 08-13-2012, 05:31 PM   #18
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The wheels on our cars are lug centric, they don't use the axle hub to center on.
Not correct, The wheels are hub centric and use the hub to center on.
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Old 08-13-2012, 07:41 PM   #19
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Well my AR TTMs are lug centric and they work fine on my 4th gen. The center bore on these wheels is larger in dia than the axle hub.
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Old 08-17-2012, 02:26 PM   #20
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The wheels on our cars are lug centric, they don't use the axle hub to center on.
Yes they do. My stock wheels center up on the the stock axles. The centric on the stock axles stick out almost 2 inches. My Moser axles have only about 1/8 to a 1/4 inch centric on them and do not engage the wheels. With the car jacked up and running with the 9 inch in it the wheels wobble up and down and do not run true. Put the 10 bolt back in and the wheels run true and my vibes are gone...to the op...I had same problem, ended up putting the 10 bolt back in. Vibes are gone, when I get around to it I am going to weld up the centric on the Mosers then turn them down in a lathe.

The bolt in style studs are not as straight as the pressed in type, and should net be used to center the wheel up. If you look close in this video you can see my passenger side wheel moving up and down. I messed with this 9 inch for over a year before figuring it out.

http://s105.photobucket.com/albums/m...=VIDEO0009.mp4
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Old 08-17-2012, 02:26 PM
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