When i had the 10 bolt, my driveshaft (or something) would vibrate at speeds in excess of 90 mph. Now with the moser 9 inch in (4.11's, 31 splines, truetrack) i get a similar vibration but at 75 mph+. Is it something to do with the ujoint? Also, when i turn left, i hear a screech that sounds something like the metalic indicator. Should I get an LS1 driveshaft (or other aluminum DS) Or can i pull it and get it balanced? What do you guys think about this as well as the screech noise. P.S. The moser 9 inch was an easy install and a very well made unit. Bolted right it, got it doine in a couple hours.

 

it's the driveshaft, have it rebalanced, also does the rear end sit even in the car or is a tire rubbing possibly causing the screeching noise?

 

I believe it is sitting in straight, but i will have to take a look later tonight. Im thinking if something is out of position it could cause it to vibrate, but im not sure...ill keep u posted

 

Are you still using the stock DS? What were your gears before the 9-inch install? If they were 3.23's before the swap, that would correspond with the DS vibration appearing at 75mph rather than 90mph.

Did you check the length of the DS to make sure its correct for the 9-inch?

Are you still using the stock torque arm? The 9-inch lowers the pinion shaft centerline, and that drops the end of the DS, messing up the pinion angle. The DS now makes sharper angles through the u-joints, to worn u-joints will become more apparent.

Were any shims required to space the axle hub correctly with reference to the brake mounting plates? A mismatch might explain a metallic sound when making a turn in a particular direction.

 

What Fred said. Your pinion angle is bound to be out now and I would imagine your driveshaft length is incorrect. Measure for a driveshaft before you buy. Check on Denny's Driveshafts web site. I believe there is something on there that tells you how to measure and you can probably pick up a DS from them too. There pretty good. Same goes for what Fred said about the shims. If you were supposed to shim and didn't then that could be causing it. Sounds like the caliper is rubbing the rotor on turns.

Ken R.

 

sounds like a prob that the car had and not the rear end making the vibration... start simple tire balance... make sure your trans mount is not torn if stock i would replace with energy suspension about $25... and pust on a adjustable torque arm I went with the edelbrock about half the price of slp I think $159. and make sure your pinion angle is set. to check you need an angle gauge you can get from sears or home depot under $10 the adjustable torque bar will come close to factory settings so its a good start point dont play with the adjusters when you pull it out of the box.... with the car jacked up try to load all four corners of the suspension being a unibody jacking up only the rear will change your angle and you will be setting it wrong if you can jack up car and place on wheel ramps and jounce the suspension returning it to road ride heigth then install the tq arm and remove the drive line check u joints you may need to replace then not a bad idea any way..... place the angle gauge on the end of the pinion nut to find the pinion angle make the adjustments as needed

 

yes i am using the stock DS and you are right about the gears changing the speed at which the vibration occurs. As far as the DS is concerned, it was a perfect fit with the moser 9 inch. The shims are 1/8th inch shims on both sides, so i may have to adjust the caliper with some washers. I am using the stock torque arm as well.

 

What is "perfect fit" with regard to the driveshaft?

 

when i put my 9" in the stock length denny's drive shaft worked but it didnt have much of the yoke going into the trans, so i found that ford makes a longer yoke for the pinion,(1" longer than the usuall ford 9" yoke) i used this longer yoke and all is perfect with the stock length driveshaft
and stock size u-joints, i actually found 2 of these longer yokes at a swap meet so i picked both of them up just to have