I just installed a 72 f100 9" and now I have a vibration at 15 to 25 MPH.

I replaced the brakes, wheel bearings, installed a new drive shaft, reversed eye springs, short stacked the springs and installed new shocks.
That about covers how I messed it up, now how do I fix it.
BTW it now has a choppy ride - before it has just hard.

any help will cause great admiration.

 

Do you know the condition of the 9” rear or was it from a recycler? Are you sure you didn't drop a bearing in one of the U-joints?

 

u-joints came with new shaft - should be OK. Trusted driveline shop. The 3rd member checked out OK.

 

Did you change the pinion angle on the new rearend compared to where it was set on the original rearend?

 

No not that I know of. the 72 spring mounts were not touched. Could the lowering have changed it.

PS. the front mount is flipped but in the stock location.

 

The angle of the driveshaft to the transmission output shaft must be the same as the angle of the driveshaft to the pinion gear shaft of the differential. If they are not the same angle, it will vibrate.

I'll give odds that they're different, and that's what's causing the vibration.

 

Start here:
http://www.clubfte.com/users/jniolon...nephasing.html

 

Wheels and tires are known to be good I assume? After you read the article on Niolon's site and verify pinion angle, I would have the driveline shop have a quick look at the driveshaft. I believe you that they are reputable but mistakes can be made of course. I've had a slightly different experience than Paul regarding pinion angles. I accidently installed my 4* spacers in backwards briefly and can't really say I noticed a vibration. I think you can get by with a few degrees sometimes. But you certainly must be pretty close to correct.

 

Thanks guys. I'll work through the pinion angle thing and get back to you on the results.

 

Gentlemen

your technical knowlege is surpassed only by your willinness to share.
it now runs as smooth as a baby's butt.
thank you

 

What did ya find? Inquiring minds want to know.

 

I found the transmission shaft sitting at 0 degrees. (90 degrees from level)The differential, however, was setting at 8 degrees. (98 degrees from level) I got a set of 8 degree shims from a 4x4 shop and brought the diff to 0 degrees.
There is about a 3" rise in the drive shaft and that seems to be OK.
Again thanks a bunch.

 

56extcab, Your follow-up is all the thanks we need. Just let us know about your experiences and we all learn the lesson. Thank you.