My father just called (I am on the other side of the county at the moment..) and gave the following description:

99 4Runner 2WD auto V6

Starting yesterday, while accelerating there is a noticeable/visible front end shake. You can see the gear shift vibrating heavily. If you put the truck in neutral, it does not reproduce. If you let off throttle and coast when in D, the vibration goes away -- only under load.

My initial thought was U-joints, but it doesn't seem to follow that pattern. All initial fluid checks were good - nice red atf, no smell of burnt fluid or signs of wear.

Ideas? My father will attempt to continue troubleshooting today and feed me the info, I can get dirty working on it in a few weeks if required.

Cheers!

 

tire inflation pressures check first-simple and cost free.

Driveshaft inspection/has it been lubed lately?- check second.

Front end alignment get done and pump the tech with questions. How are those tie rod inners and outers-too much play in the steering rack? Ball joints can and do fail catastrophically, get the entire front end inspected by someone who sees a lot of Runners.

Front sway bar also springs to mind, but seems like a longshot to me.

 

Tire pressures are good. One wouldn't typically expect the front end alignement to show issue on acceleration on RWD models, no torque steer influence to worry with. Last time I did a cursory check of the truck everything was in good condition... I will give it a full checkup when I get back.

Unsure on the condition of lube on the driveshaft.

 

Sounds like the u-joints to me, especially since it goes away in "N" and only happens under load.