2059
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- May 4, 2012
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I know there are several discussions about this topic, here's my story. Maybe it will help some one else with the problem.
Related to the "Twisted Yoke" thread. After installing the fresh engine, I had a bad vibration in the driveline. Why it didn't show up with the old install, I have no idea. After doing some investigation I discovered I had about 8* UP at the pinion and ~3* down at the trans output shaft. Exactly what you don't want. So I took the rearend back down to Mosher Eng. and had them reposition the perches to give me 4*-6* DOWN at the pinion. Along with the reinstall I used a new Drive shaft, since the orig one had a twisted yoke and under duty U-Joints. Get everything back together and still have a vibration. It was different, but still there.
After talking to several people, "Supershafts" and "HEMI-ITIS" were very helpful. I quickly realized I needed to COMPLETELY understand my set-up and what was going on. I figured i would need to shim/wedge the rear-end and possibly the trans/engine too.
I ordered the gage and wedged from Summit. after about 10 minutes of checking. I figured I had about 5* DOWN at the pinion 1* to 2* UP at the Trans. I thought that looked about right but what I discovered was that the clearances were very tight at the pinion nut to the DS U-joint straps and they were hitting. Which made sense because the vibration would stop when under hard acceleration. The rear-end would pivot up a couple degrees and I have less of an angle at the pinion/DS U-joint. I should mention I'm running new factory Super-stock leaf springs and Caltrak lower links.
"Supershafts" summed it up when he said. "basically you want 0* when your under load" Meaning; get as "straight as you can" with your driveline geometry when under load.
So; I figured If I shimmed the rear end/pinion 4* UP to give me about 1* DOWN at the pinion (remember I started with ~5* Down at the pinion); AND I should be at about ~1* to 2* UP at the transmission output shaft.
BINGO!! It worked out perfectly!! No vibration at cruse or under acceleration / deceleration. And no signs of contact.
Moral of the story; Ask allot of questions but realize, when it comes to driveline geometry every car is slightly different. Especially these older cars with resto/mod work.
Related to the "Twisted Yoke" thread. After installing the fresh engine, I had a bad vibration in the driveline. Why it didn't show up with the old install, I have no idea. After doing some investigation I discovered I had about 8* UP at the pinion and ~3* down at the trans output shaft. Exactly what you don't want. So I took the rearend back down to Mosher Eng. and had them reposition the perches to give me 4*-6* DOWN at the pinion. Along with the reinstall I used a new Drive shaft, since the orig one had a twisted yoke and under duty U-Joints. Get everything back together and still have a vibration. It was different, but still there.
After talking to several people, "Supershafts" and "HEMI-ITIS" were very helpful. I quickly realized I needed to COMPLETELY understand my set-up and what was going on. I figured i would need to shim/wedge the rear-end and possibly the trans/engine too.
I ordered the gage and wedged from Summit. after about 10 minutes of checking. I figured I had about 5* DOWN at the pinion 1* to 2* UP at the Trans. I thought that looked about right but what I discovered was that the clearances were very tight at the pinion nut to the DS U-joint straps and they were hitting. Which made sense because the vibration would stop when under hard acceleration. The rear-end would pivot up a couple degrees and I have less of an angle at the pinion/DS U-joint. I should mention I'm running new factory Super-stock leaf springs and Caltrak lower links.
"Supershafts" summed it up when he said. "basically you want 0* when your under load" Meaning; get as "straight as you can" with your driveline geometry when under load.
So; I figured If I shimmed the rear end/pinion 4* UP to give me about 1* DOWN at the pinion (remember I started with ~5* Down at the pinion); AND I should be at about ~1* to 2* UP at the transmission output shaft.
BINGO!! It worked out perfectly!! No vibration at cruse or under acceleration / deceleration. And no signs of contact.
Moral of the story; Ask allot of questions but realize, when it comes to driveline geometry every car is slightly different. Especially these older cars with resto/mod work.
