Last week I had a set of 4.10 FRPP gears installed into my mustang. Since delivery I've had a momentary vibration at around 23-25mph that's pretty harsh. At the time of pick up, that was it however. Now vibration is starting to occur from 45-to about 60, then again past 70+

Figuring this was likely just a tolerance stacking issue I set about indexing my driveshaft (stock, never removed or indexed previous).

Unfortunately, that didn't do a darn thing to cure the issue. Started at 180* which was far worse. Then tried every orientation possible between that. In the end the stock orientation gave the best result at keeping vibrations to a minimum.

It does however seem to be getting worse.

Does anybody have any additional ideas to try before I go back to the install shop? I'm primarily worried about messing up bearings and the like at this point.

With the car on jack stands I had a buddy run the car through a series of speeds and you can see a very defined wobble in the driveshaft at the mid coupling. It clears itself back up after about 25 mph but it's never completely wobble free.

Prior to the gear install I had zero vibration issues.

Installer said the pattern on the gears was perfect and backlash was set between 8-11 thousands. I have no gear whine whatsoever which would certainly be indicative of a gear install issue.

Any advise on the matter would be great. I don't necessarily want to shell out close to 700 for a driveshaft at this point which probably won't fix the issue.

Thanks in advance.

 

i had a vibration after i had my 1 piece driveshaft installed and it turned out my pinion bearing was worn out and if you were to get under there and right where the driveshaft bolts to the rear, if you push up on the driveshaft it had loads of play in it. try to see if you have any movement there and if so out comes the carrier to replace the bearing.

 

Did your installer use a new Pinion Bearing? The old one can get damaged when the old pinion is removed.

 

There's absolutely zero play in the driveshaft at either end, including the mid coupling.

Install included all new bearings.

 

and you absolutly sure with out a doubt that the preload and backlash are set properly? if so i would take that thing out to see if its bent or have it brought somewhere to check if its out of balance

 

My first thought after reading this thread was also the preload on the pinion bearings. It takes very specfic amount of torque on the crush collar provided in the rebuild kit to provide the proper preload. That is my only thought at this point.