Shudder when towing at highway speed

When I tow my boat (small 16' runabout) with my 2001 Explorer Limited (V8, AWD) there is a shudder at highway speed. It starts to happen around 50 MPH and is periodic. I would say that the shudders occur at intervals of about 1 second. I am not exactly sure where the shudders originate, but you can feel it in the whole car. My passengers notice it too. This only happens when I am towing the boat. otherwise it drives beautifully at highway speed. Anyone else experienced this?

Unfortunately I do not have another trailer to tow to test if it is the boat trailer itself. However, I used to tow the boat with an F150 and never noticed it. But the trailer did sit for a year in between.

 

[MountaineerGreen]

Do you tow in OD?

When was your last fluid change?

 

[rmadsen]

I believe that last trans fluid change was about 8,000 miles ago. oil I do about every 5000 miles. I usually tow with OD override on. But I have tried it both ways and it made no difference.

 

[MountaineerGreen]

Well, in general, its a bad idea to tow in OD unless you are on straight level ground. The OD is a band only, it can quickly slip and cause problems.

It sounds to me like you have torque shudder. It is an incomplete lockup of the TC because of worn fluid. If you have been towing with OD on, it could have cooked the fluid prematurely.

When you did your fluid change, did you drop the pan and drain the TC? Or did you just drop the pan? Dropping the pan only gets ~1/2 the fluid, the TC holds a large portion of the fluid.

It wouldn't be that expensive to drop the pan, drain the TC, refill with meron V with a fresh filter. I'll bet that will stop the torque shudder. Do you know what fluid was used when it was last changed?