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-   -   Harmonic Vibration (http://www.hotrodders.com/forum/harmonic-vibration-203418.html)

RoadSide Dan 08-09-2011 04:46 AM

Harmonic Vibration
 
What's the correct pinion angle for a 9" Ford rearend?

My '53 Chevy 3600 had a 9" Ford offset rear end and a two piece driveshaft. It ran pretty smooth at that time.

While doing a frame-off restoration, I decided to convert to a single piece driveshaft and set the rearend angle more in line with the driveshaft. Converting to a single piece driveshaft and resetting the pinion angle to 3 degrees has resulted in a bad harmonic that starts about 35 mph and increases with speed.

Help.

S10xGN 08-09-2011 09:50 AM

U-joints are designed to handle some amount of misalignment. Do you trust whoever built the driveshaft? I'd start by verifying the phase angles, both sets of "ears" should be in exactly the same plane...

Russ

KMatch 08-09-2011 12:23 PM

There is no 1 size fits all. You need to measure the angle at the rear of the transmission of engine tilt. If it's 3 degrees, the pinion must be tilted up 3 degrees. 2 for 2, and so on and some will be good with a degree or so of difference and others, not so much. Another thing, never run a driveshaft at zero degrees at either end (driveshaft straight) - this will kill u-joints as the needles will pound grooves in everything.

RoadSide Dan 08-20-2011 01:56 AM

harmonic vibration
 
Well, it looks like the pinion ange is 3/3, but 3 down and another 3 down--ugh. :( :mad: The front u-joint is slinging grease and is fighting back. I've only been able to drive it at 20-30 mph thus far. The body work looks good, but...

S10xGN 08-20-2011 09:55 AM

Quote:

Originally Posted by RoadSide Dan
Well, it looks like the pinion ange is 3/3, but 3 down and another 3 down--ugh. :( :mad: The front u-joint is slinging grease and is fighting back. I've only been able to drive it at 20-30 mph thus far. The body work looks good, but...

That could be your problem. When I built my Maverick, my "cohorts" told me to weld the spring perches with the nose at 6 down because of the leaf springs. Obviously, they are racers and not street drivers. :mwink: After realizing that my Caltrac bars don't allow any pinion rise, I ordered a set of 8 shims (from an offroad place) to counteract my negative pinion angle. I now have my trans at 4 down and the pinion at 2 up, and all is good!

Russ


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