Vibration at 60+ mph in driveline

[ImportSlayer347]

I have a '93 fox and recently it started having this issue.

When I hit around 60-70 mph and let off the throttle it vibrates terribly. Soon as I touch the gas again it almost goes away completely. So I know it isn't a wheel balance issue. I had them checked to be sure. I have a FRPP aluminum driveshaft. I have a FRPP super duty T-5 (rebuilt around 3,000 miles ago). New differential carrier, new axles, bearings and seals. I haven't changed gear ratios. I am currently at 3.55.

I am wondering if anyone else had this same issue and what they did about it. I'm thinking it is a worn part somewhere because it started well after rear end was done.

 

[f8tlfiveo]

Check the bolts on the driveshaft. I just had I similar problem and the bolts were loose.. Check the u joints also

 

[Tanus]

Ive had that happen twice, once it was loose drive shaft bolts, other time it was a bad tranny mount

 

[Cobra1741]

i hear the aluminum driveshafts go out of balance or check the u-joints.

 

[RatStang]

+1 for u-joints

 

[f8tlfiveo]

The problem with the driveshaft bolts is they are 12 point I think 13mm. I don't have any 12 point sockets so I end up using a little ass box wrench and giving it a couple of smacks with a hammer.. If you don't do that they will come loose over time..

 

[ImportSlayer347]

Sure enough...DRIVE SHAFT BOLTS!! My buddy who helped me change the clutch last season didn't lock-tite the bolts and they were really loose. One fell out when I grabbed the driveshaft and shook it. the other three came out by hand. My U-joints were kinda cheesy so I upgraded anyways. Either way, problem fixed!!

 

[stykthyn]

drive shaft bolts are 12pt 1/2 inch

 

[ImportSlayer347]

Actually they are 12pt 12mm. 1/2 inch is a little sloppy.