Can someone with IRS help me?

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Dcsport

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Okay my buddy has a 2003 XLT with the 9.75" rear. He has some slight vibration around 40-50 mph and asked me to help him figure it out. I did the usual research beforehand and noticed the many TSBs surrounding the rear axle. I suspected a rear end rebuild was his fate, but we poked around anyway to see if anything jumped out. U-joints looked good though we went ahead and replaced them anyway as preventative maintenance.

Anyway we were checking to see if the ring and pinion had any obvious play in it and noticed that the cv axles seemed to have significant play in them when rotating the driveshaft by hand with wheels locked up, but since it seems the same on both sides I figured it was normal, but want to make sure. I've never dealt with IRS before so I searched the internet and came up with nothing! Can I get someone who has known good cv axles in their rear IRS to crawl under and try and spin the driveshaft by hand to see if the inner part of the cv axle has significant play? A video would be awesome! :) You probably don't need to even jack it up!
 

dougmcp

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I trust you have already rotated the tires to eliminate the wheel/tire combination.
Is the vibration while the throttle is being applied?
 
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Dcsport

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I trust you have already rotated the tires to eliminate the wheel/tire combination.
Is the vibration while the throttle is being applied?

He did get a new set of Michelin tires last year that barely have any miles on them. I told him to go ahead and have them balanced and rotated anyway since its free where he bought them.

It is more noticeable when the throttle is applied, I believe. I'll double check with him tomorrow.
 
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Dcsport

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Here's what he said: Most noticable at a constant speed but letting off the gas quickly makes it almost dissapear.
 

dougmcp

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I have a Gen1 Expy with a solid rear axle but like any vehicle with CV joints, if you have vibration with throttle applied the joints are the first area of suspect.
To further diagnose it I would try the same speeds in a different gear to eliminate the motor and transmission from the mix.
 
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