8.75 question

[m99roadster]

I just had a 8.75 rear installed in my 68 Dart 4 door, when I get above 50mph there's a strong vibration and drone. When it was installed the shop reused the same spring perches I had for the 7.25. Could this be causing the pinion angle to be incorrect causing my problem? Dose anybody have any other suggestions on what to look at? Thanks

 

[Bad Sport]

Well, first of all if they used the same spring perches I really don't know what to think. The axle tubes are bigger on the 8 3/4.

I guess some more detailed info and maybe a couple of pics would help.

 

[SGBARRACUDA]

Sounds like a balance issue. Did the u-joint fit the rear 8 3/4 yoke snug? They make a couple of different size yokes. Did you have a drivetrain shop shorten and balance the drive shaft?