Originally Posted by Dan Fletcher (Post 448831)

I wish I had already figured it out! This is really starting to be frustrating! As JC said, I've changed most everything but the roof at this point, and nothing seems to change anything.

This all started at Charlotte, TT#1. I felt a vibration in the water and in the shutdown. Car was fine the previous race (Indy). Prior to Charlotte, I changed center sections, shocks, and rear calipers. Obviously, one thinks center right away. I had removed my 5.83 and installed a 6.20 at Indy. All I did was put it back in.The second the car vibrated in the water at Charlotte, I thought how did I mess up putting the driveshaft back in? It seemed like driveshaft for sure.

Since that run, its been a full bore effort to find the issue. At Charlotte, I had rear tire balance checked (OK), sent shaft out to a Fleet Pride to get inspected (said it had a slight bow/straightened/rebalanced), changed trans and converter, replaced perfectly good u-joints, broke tires down/shifted/re-balanced. No change.

At Columbus, made TT#1 to verify baseline. TT#2 replaced shaft with PERFECT MW unit from '69 stocker. No change.

Tested at a local 1/8 mile track the following Tuesday. It was like an episode of Street Outlaws. All over the track every run, but all I need is the burnout and up to speed. Baseline, then changed tires and wheels for run #2, still vibrates. Run #3, changed pinion angle. Now this can be a whole separate discussion, but I measured it how chassis builder Gary Wisecarver told me to, and we decided it might have a little too much. I didn't measure at the track, I just lengthened the top bars one full turn. No change. In retrospect, I wish I then went the other way a full turn, but I didn't. Put pinion angle back and changed rear shocks back to "original" ones. No Change. 4 runs in an hour and a half. Out.

Before MG, I pulled the center back out and took it to my local guy, Bernie O, who has done our rears since I was a little kid. I had him inspect and replace every bearing in the rear, even though no one felt anything was wrong. We also replaced one axle bearing that felt less than perfect.

First run at MG, no change. TT#2, replaced all the front wheel bearings, no change. TT#3, removed steering stabilizer shock, no change. Well, there was a change, the front tires went goofy when the car landed, lol. I had a single 2nd round of eliminations. I'm not saying we physically removed the rear calipers, but lets just say I'm 100% confident that the new rear calipers aren't involved in the issue after that run. Rd#3, changed right front tire/wheel, rd#4 changed left front tire/wheel. No change. Finished event as is.

So, the car is in the garage and what to do next. I'm going to remove every 4 link bar and carefully inspect the rod ends, but there's no way that's the source either. After that, I can only say ring and pinion, even though nothing appears wrong. So I probably have to put the 6.20 center back in, make a run, and go from there. If that doesn't fix it, I seriously have no idea what I'm going to do.

The car was perfect, and then its like you threw a switch...

Originally Posted by Rich Biebel (Post 448848)

"sent shaft out to a Fleet Pride to get inspected (said it had a slight bow/straightened/rebalanced), "

This right here gets my attention...

said it had a slight bow......and they straightened it and rebalanced it....

A driveshaft loves to get into a harmonic vibration so I would try another shaft......just to eliminate that possibility.

We had a brand new F-450 service truck that had a ridiculous vibration starting from a dead stop. It went back to the dealer and they shimmed the rear's pinion angle.......It did lesson the vibration but did not eliminate it.....I think they tried numerous other things before the pinion angle change....

Driveshaft is where I think your issue is......just from past experiences....

Originally Posted by Rich Biebel (Post 448848)

"sent shaft out to a Fleet Pride to get inspected (said it had a slight bow/straightened/rebalanced), "

This right here gets my attention...

said it had a slight bow......and they straightened it and rebalanced it....

A driveshaft loves to get into a harmonic vibration so I would try another shaft......just to eliminate that possibility.

We had a brand new F-450 service truck that had a ridiculous vibration starting from a dead stop. It went back to the dealer and they shimmed the rear's pinion angle.......It did lesson the vibration but did not eliminate it.....I think they tried numerous other things before the pinion angle change....

Driveshaft is where I think your issue is......just from past experiences....