j30 vibration at 40mph

[Eswift]

My j30 has always vibrated at 40mph. its not horrible, but annyoing enough that i avoid 40mph. Is the driveshaft in need of balancing? should i have it checked out?> any recommendations?

[VimyJ]

Does your J shudder in other gears at 40 mph?

[Eswift]

i have only noticed it in 4th gear, cruising at 40 mph. i have not noticed it shuddering at any other time. when i manually select gear 3 when it is shuddering, and then go 40mph, its fine. If i slow down in 3rd gear to the rpm that was causing the vibration in 4th gear, there is no vibration there either.

[VimyJ]

Does the shudder stop if you shift from drive to 3rd at 40 mph? This would disengage the torque converter. Looks like the TC could be your problem. It will be interesting to hear from Prof. Mike.

[Eswift]

yeah, the vibration stops if you manually select 3 when its going 40mph, and then the vibration is gone as you continue at 40mph. why the torque converter? isnt that above procedure just shifting from 4th gear overdrive into 3rd gear?

[Q45tech]

Sounds like the engine is running rough and not producing enough torque [below speced amount] to move the car at 40 mph [in 4th == lugging] 1600 rpm vs 2100 in 3rd gear at 40.Especially in light of the other posted problems.

[Mayhem_J30]

Sounds like the engine is running rough and not producing enough torque [below speced amount] to move the car at 40 mph [in 4th == lugging] 1600 rpm vs 2100 in 3rd gear at 40.Especially in light of the other posted problems.

probably that FI thing again. get that fixed!

[Eswift]

ive been through injectors before, this vibration problem has been there without the injector problem.

[pitaq]

Could it be you have a cylinder misfiring in that range?

A miss in my J always felt like a little shudder.

[Professor_Mike]

You might check the EGR tubes for plugging at the plenum connection, usually one side will plug and effect the mixture. Becoming more common as Js get older.