i just increased my front castor to about 6 degrees. the jk goes down the road great but theres a ruff vibration now. its bad around 50 to 55 and 68 to 72 or so, its not all the time. my question is , is that to much angle on the stock drive shaft? if not any other suggestions. 4 door rubicon 3.5 inch lift.

 

Bump it to 7, see how it rides.

 

I'd probably go half that to start, moving to 6.5 degrees. Too much and you start plowing the front tires making your vehicle a chore to drive.

Any other symptoms? If you go into a turn a little too quickly does it feel like the front or back wheels are going to bust loose?

 

What size tires are you running? The stock driveshaft is very lenient, as is the front shaft in general. If it was a DS problem I would expect it to be from the rear. Are you sure that it is 6*? How did you measure it?

 

With your lift, 5.5 degres is safer.
How do you read the castor?

 

What kind of vibration?
Do you think it's the shaft, if so back off to 5.5 degrees. Then see what happens.

 

it handles great thats not the problem. its the vibration at certain speeds. rrrr rrrr rrrr rrrr pulsing like through the gas pedal, you can also feel it a little through the floorboard. it was done at an alignment shop, and i have an angle finder the reads exactly the same.

 

Turn the adjustable control arms 1/2 turn shorter on each side. This will be your minimal decrease and see if it does any good. At 6 degrees I'd go down, not up, at my first attempt at tuning out the vibes.
I get the same kind of vibration at around 62mph under certain road conditions, not at all under others. You can barely feel it in my case, and it wasn't there when I was at 5 degrees.

 

I have a tera 3" (more like 4" lift) and I run 5* caster. It drives great with no wandering, but no heavy steering or driveline vibes. As others suggested, I would lower the caster a bit.

 

Sounds more like too steep a drive shaft angle rather than the amount of castor. A 3.5" lift is pushing the limit with stock drive shafts.